Magnet assembly

Abstract

There is provided a method of manufacturing a magnet assembly for a transducer. The method comprises positioning the magnet assembly at least partially between a first magnetization coil and a second magnetization coil and magnetizing the magnet assembly by: (i) passing a first current through the first magnetization coil to generate a first magnetic field to magnetize a first magnetizable portion of the magnet assembly, the first magnetic field extending in a first direction, and (ii) passing a second current through the second magnetization coil to generate a second magnetic field to magnetize a second magnetizable portion of the magnet assembly, the second magnetic field extending in a second direction opposite to the first direction.

Description

MAGNET ASSEMBLYCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Patent Application No. 63 / 585,869, filed September 27, 2023, and to U.S. Patent Application No. 63 / 575,103, filed April 5, 2024, each of which is incorporated herein by reference in its entirety'FIELD OF THE DISCLOSURE

[0002] The present disclosure is related to consumer goods and, more particularly, to methods, systems, products, features, services, and other elements directed to media playback or some aspect thereof.BACKGROUND

[0003] Options for accessing and listening to digital audio in an out-loud setting were limited until in 2002. when SONOS, Inc. began development of anew type of playback system. Sonos then filed one of its first patent applications in 2003, entitled “Method for Synchronizing Audio Playback between Multiple Networked Devices,’' and began offering its first media playback systems for sale in 2005. The Sonos Wireless Home Sound System enables people to experience music from many sources via one or more networked playback devices. Through a software control application installed on a controller (e.g., smartphone, tablet, computer, voice input device), one can play what she wants in any room having a networked playback device. Media content (e.g., songs, podcasts, video sound) can be streamed to playback devices such that each room with a playback device can play back corresponding different media content. In addition, rooms can be grouped together for synchronous playback of the same media content, and / or the same media content can be heard in all rooms synchronously.BRIEF DESCRIPTION OF THE DRAWINGS

[0004] Features, examples, and advantages of the presently disclosed technology may be better understood with regard to the following description, appended claims, andaccompanying drawings, as listed below; A person skilled in the relevant art will understand that the features shown in the drawings are for purposes of illustrations, and variations, including different and / or additional features and arrangements thereof, are possible.

[0005] Figure 1A is a partial cutaway view of an environment having a media playback system configured in accordance with examples of the present technology;

[0006] Figure IB is a schematic diagram of the media playback system of Figure 1 A and one or more networks;

[0007] Figure 1C is a block diagram of a playback device;

[0008] Figure ID is a block diagram of a playback device;

[0009] Figure IE is a block diagram of a network microphone device;

[0010] Figure IF is a block diagram of a network microphone device;

[0011] Figure 1G is a block diagram of a playback device;

[0012] Figure 1H is a partially schematic diagram of a control device;

[0013] Figure 2 depicts an example magnet assembly;

[0014] Figure 3 depicts an example process for forming a magnet assembly, prior to magnetization;

[0015] Figure 4A depicts a schematic perspective view of an example magnetization device, at a first time;

[0016] Figure 4B depicts a schematic perspective view of the magnetization device of Figure 4A, at a second time;

[0017] Figure 5 A depicts a schematic side view of the example magnetization device of Figure 4 A;

[0018] Figure 5B depicts a schematic side view of the example magnetization device of Figure 4B;

[0019] Figure 6 depicts a simulation of first and second magnetic fields;

[0020] Figure 7 depicts a fixture for holding one or more magnet assemblies:

[0021] Figure 8A depicts another example magnet assembly, prior to magnetization;

[0022] Figure 8B depicts the magnet assembly of Figure 8 A, after being magnetized;

[0023] Figure 9A depicts a monolithic magnetizable element, prior to magnetization;

[0024] Figure 9B depicts the monolithic magnetizable element of Figure 9A, after being magnetized;

[0025] Figure 10 a simulation of first and second magnetic fields through the monolithic magnetizable element of Figure 9A;

[0026] Figure 11 depicts a schematic side view of a first arrangement for controlling a width of a region within a monolithic magnetizable element in a magnetization device;

[0027] Figure 12 depicts a schematic side view of a second arrangement for controlling a width of a region within a monolithic magnetizable element in a magnetization device;

[0028] Figure 13 depicts a schematic side view of a third arrangement for controlling a width of a region within a monolithic magnetizable element in a magnetization device;

[0029] Figure 14 depicts a schematic perspective view of Figure 13;

[0030] Figure 15 depicts example BL curves plotted on a graph;

[0031] Figure 16 depicts a simulation of first and second magnetic fields through a monolithic magnetizable element having a through hole or void;

[0032] Figures 17A-17D are schematic top-down views of example monolithic magnetizable elements having a through hole or void;

[0033] Figure 18A depicts another monolithic magnetizable element, prior to magnetization;

[0034] Figure 18B depicts the monolithic magnetizable element of Figure 18A, after being magnetized;

[0035] Figure 19 depicts a schematic cross-section of an example motor compnsing a magnet assembly and a voice coil;

[0036] Figure 20 depicts a schematic cross-section of an example motor comprising a monolithic magnet and first and second voice coils;

[0037] Figure 21 depicts a flow diagram of a first example method:

[0038] Figure 22 depicts a flow diagram of a second example method; and

[0039] Figure 23 depicts a flow diagram of a third example method.

[0040] The drawings are for the purpose of illustrating example examples, but those of ordinary7skill in the art will understand that the technology' disclosed herein is not limited to the arrangements and / or instrumentality' shown in the drawings.DETAILED DESCRIPTIONI. Overview

[0041] Embodiments described herein relate to the manufacture of magnets and magnet assemblies for transducers. Conventional methods of manufacture for transducers comprising a stack of two or more magnets (also referred to as a magnet assembly) typically involve magnetizing magnetizable elements individually, and then assembling the magnet stack from the magnetized elements. This process can be difficult, given that the magnetic fields of the magnetized elements can repel each other. Furthermore, the process is labor intensive and / or time intensive, often requiring several people to manufacture the magnet assembly. Aspects of the present disclosure relate to an improved process, in which the elements to be magnetized are assembled first, and then magnetized. This may reduce the labor and / or time to manufacture the magnet assembly. Other aspects relate to an improved process in which a monolithic magnetizable element is magnetized to provide a monolithic magnet that has a magnetic field that resembles tw o or more magnets stacked together.

[0042] For an example magnet assembly comprising tw o magnets (referred to herein as magnetized elements), this process can be achieved using two magnetization coils; a first magnetization coil can magnetize a first magnetizable element or portion of the magnetassembly by generating a first magnetic field, and a second magnetization coil can magnetize a second magnetizable element or portion of the magnet assembly by generating a second magnetic field. In a first example, a first magnetizable element can be affixed to one side of a spacer element, and a second magnetizable element can be affixed to the other, opposite side of the spacer element, and the first magnetization coil can magnetize the first magnetizable element, and the second magnetization coil can magnetize the second magnetizable element. In a second example, a first magnetizable element can be affixed to a second magnetizable element, and the first magnetization coil can magnetize the first magnetizable element, and the second magnetization coil can magnetize the second magnetizable element. In a third example, a first magnetizable portion of a monolithic magnetizable element can be magnetized by the first magnetization coil, and a second magnetizable portion of the monolithic magnetizable element can be magnetized by the second magnetization coil to form a monolithic magnet. In some examples, a monolithic magnet may be referred to as a magnet assembly since the magnetic field of the monolithic magnet resembles two or more magnets that have been stacked.

[0043] The use of at least two magnetization coils to magnetize at least two different magnetizable portions of a magnet assembly can result in a more uniform magnetic field distribution throughout the magnet assembly. For example, arranging the magnet assembly to be magnetized between two magnetization coils can avoid different ends of the magnet assembly having different magnetic field strengths. The use of at least two magnetization coils can reduce the time taken to manufacture the magnet assembly, since no rotation of the magnet assembly or a single magnetizing coil is required.

[0044] In example magnet assemblies comprising three or more magnets, further magnetization coils can be used to magnetize further magnetizable portions of the magnet assembly.

[0045] As such, according to a first aspect, there is provided a method of manufacturing a magnet assembly for a transducer, the method comprising: (i) positioning the magnet assembly at least partially between a first magnetization coil and a second magnetization coil, wherein the magnet assembly defines a longitudinal axis, and the longitudinal axis is arranged parallel to a winding axis of the first magnetization coil and a winding axis of the second magnetization coil, and (ii) magnetizing the magnet assembly by: (a) passing a first current through the first magnetization coil to generate a first magnetic field to magnetize a first magnetizable portion of the magnet assembly, the first magnetic field extending in a first direction, and (b) passing a second current through the second magnetization coil to generate a second magnetic field to magnetize a second magnetizable portion of the magnet assembly, the second magnetic field extending in a second direction opposite to the first direction.

[0046] In the above example method, the magnet assembly is changed from being in an unmagnetized state to being in a magnetized state, as a result of the two magnetic fields from the two magnetization coils. The term “magnet assembly” therefore encompasses an assembly comprising unmagnetized elements, as well as an assembly comprising magnetized elements. It will be appreciated however that in some examples, the magnet assembly may be in a weak magnetized state before being further magnetized by the two magnetization coils. In examples, the magnet assembly may be referred to more generally as a magnet.

[0047] In examples, positioning the magnet assembly comprises positioning the magnet assembly before being magnetized by the first and second magnetization coils.

[0048] In examples, the first and second magnetic fields have the same field strength.

[0049] In examples, the first and second magnetizable portions have substantially the same magnetic coercivity.

[0050] In examples, once magnetized, the magnet assembly comprises a stack of two or more magnets (where the magnets may be separated by one or more spacer elements). The stack may be a linear stack.

[0051] A spacer element may be known as a pole piece, in some examples.

[0052] The first magnetizable portion may be arranged closer to the first magnetization coil than to the second magnetization coil. Similarly, the second magnetizable portion may be arranged closer to the second magnetization coil than to the first magnetization coil.

[0053] In examples, the longitudinal axis extends at least partially between the first and second magnetization coils.

[0054] In some examples, magnetizing the magnet assembly may comprise magnetizing only part of the magnet assembly, such as the first and second magnetizable portions. For example, a spacer element positioned between the two magnetizable portions may not be magnetized.

[0055] In some examples, the first and second magnetization coils are substantially the same (such as having the same number of turns, the same wire thickness, the same wire material, same wire cross-sectional shape, etc.).

[0056] The first direction may point away from the first magnetization coil, such as away from a midpoint of a winding axis of the first magnetization coil. Similarly, the second direction may point away from the second magnetization coil, such as away from a midpoint of a winding axis of the second magnetization coil. It will be appreciated that the presence of other magnetic fields, such as the second magnetic field, distorts the first magnetic field. The first direction may therefore be defined in the absence of other magnetic fields, such as the second magnetic field. Similarly, the second direction may be defined in the absence of the first magnetic field.

[0057] Once magnetized, the first and second magnetizable portions may become, at least partially, first and second magnetized portions, respectively. Similarly, once magnetized, firstand second magnetizable elements may become, at least partially, first and second magnetized elements, respectively.

[0058] In examples, the first and second magnetic fields magnetize the first and second magnetizable portions so that they have an inverted or opposite polarity. For example, where the first and second magnetizable portions are arranged closest to each other, the first and second magnetizable portions will be magnetized to have the same polarity facing each other. Like poles are therefore arranged facing towards each other. Put another way, in the magnet assembly, the two magnetizable portions are magnetized with inverted polarity7. In examples, an end of the first magnetizable portion that is arranged closest to the first magnetization coil has a same polarity as an end of the second magnetizable portion that is arranged closest to the second magnetization coil.

[0059] In examples, the first magnetic field extends: (i) in the first direction along the winding axis of the first magnetization coil away from the first magnetization coil, and (ii) into or out of the magnet assembly in a direction substantially perpendicular to the longitudinal axis. Similarly, in examples, the second magnetic field extends: (i) in the second direction along the winding axis of the second magnetization coil away from the second magnetization coil, and (ii) into or out of the magnet assembly in a direction substantially perpendicular to the longitudinal axis. For example, the magnetic fields may extend into or out of the magnet assembly along a side of the magnet assembly. The magnetic fields may therefore bend away from the longitudinal axis, such as through a spacer (if present) or in another region of the magnet assembly.

[0060] In a particular example, the first and second currents are passed through the first and second magnetization coils, respectively, at substantially the same time. Applying the currents at the same time ensures the two magnetic fields interact with each other, which can provide an evenly distributed field through the magnet assembly. One magnetic field can therefore limitthe extent of the other magnetic field, effectively providing shielding, which may be useful in certain circumstances.

[0061] The first and second currents may be applied via a current source, such as a capacitor or a capacitor bank, or a voltage source. For example, a single current source may power both magnetization coils in parallel or series. In other examples, the first and second currents maybe applied via separate current sources or separate voltage sources. For example, the first current may be applied via a first current source and the second current may be applied via a second current source.

[0062] In some examples, the first and second currents are substantially the same. For example, the first and second currents have the same magnitude or are equal in terms of the amount of current they carry. The two currents may therefore have the same value in amps. Applying both currents having the same magnitude can ensure evenly distributed fields extend through the magnet assembly, such as through both the first and second magnetizable portions.

[0063] The first and second magnetizable portions or elements may be or comprise ferromagnetic material, such as iron.

[0064] Example magnet assemblies may be used in a transducer. For example, one or more voice coils may extend around a magnet assembly. In particular, a voice coil may extend around the magnet assembly7at a boundary betw een the first and second magnetized portions. When a current is applied to the voice coil, the voice coil will move along the magnet assembly in a direction parallel to the longitudinal axis.

[0065] In some examples, the method further comprises arranging the first magnetization coil relative to the second a magnetization coil, such that one of: (i) at the first magnetization coil, the first direction points towards the second magnetization coil, and at the second magnetization coil the second direction points towards the first magnetization coil, or (ii) at the first magnetization coil, the first direction points away from the second magnetization coil, andat the second magnetization coil the second direction points away from the first magnetization coil. As mentioned, generating the magnetic fields so that they point in opposite directions results in the first and second magnetizable portions having an inverted polarit .

[0066] As briefly mentioned above, the first and second magnetizable portions may be part of the same magnetizable element. As such, in some examples, the first magnetizable portion and the second magnetizable portion form a monolithic magnetizable element. The method may therefore further comprise providing the monolithic magnetizable element. Magnetizing a single magnetizable element may further reduce the number of steps required to manufacture the magnet assembly because separate elements do not need to be affixed together. This can also avoid having a magnet assembly having misaligned elements. Additionally, having two or more elements affixed to each other can mean the different elements behave differently when undergoing thermal expansion and / or contraction. Furthermore, adhesives used to affix the elements together can melt or behave unpredictably when undergoing thermal expansion and / or contraction. Use of a monolithic magnetizable element in a transducer can therefore eliminate, or at least reduce the impact of, these issues.

[0067] In an alternative example, the magnet assembly comprises a first magnetizable element and a second magnetizable element affixed to the first magnetizable element, the first magnetizable element comprising the first magnetizable portion and the second magnetizable element comprising the second magnetizable portion. The method may therefore further comprise providing the first magnetizable element, providing the second magnetizable element and affixing the first magnetizable element to the second magnetizable element. Affixing together two magnetizable elements without a spacer between them may reduce the number of steps required to manufacture the magnet assembly. This can also reduce the likelihood of the magnet assembly having misaligned elements, given fewer elements are affixed together. In some examples, the first and second magnetizable elements are, or define, the first and secondmagnetizable portions, respectively. In some cases, providing the first and second magnetizable elements comprises providing first and second magnetizable elements having substantially the same magnetic coercivity.

[0068] In either a monolithic magnetizable element or an assembly where the first and second magnetizable elements are affixed directly to each other, an intermediate “region” (referred to in some examples as a “pole piece”) may be formed along the magnet assembly where the oppositely directed first and second magnetic fields meet and repel each other. As discussed above, in this region, the magnetic field lines may bend and be substantially orientated perpendicular to the longitudinal axis. As will be discussed in more detail, as a result of these magnetic fields repelling each other, a magnetic neutral zone may exist in this region where the resultant magnetic field is approximately zero, such that there is no or minimal magnetic flux.

[0069] In an example, the first magnetizable portion may be magnetized to form a first magnetized portion of the magnet assembly and a first part of the region, and the second magnetizable portion may be magnetized to form the second magnetizable portion of the magnet assembly and a second part of the region. The region may therefore be formed from parts of the first and second magnetizable portions, and be formed between the first and second magnetized portions.

[0070] The “length” of this region, where the length is measured in a direction along the longitudinal axis, can affect the output of a transducer that incorporates the magnet assembly. It may therefore be useful to adapt the length of the region for particular requirements. For example, it has been found that changing the length of the region changes a BL curve of the transducer, where the BL curve is a graphical representation of how the BL factor (the product of magnetic flux density, B. and voice coil length. L) varies with an excursion distance of a voice coil from its rest position. Ideally, a flat BL curve is preferred for a transducer. A widerregion can result in a flatter BL curve. A flatter BL curve indicates that the magnetic field strength remains relatively constant over the excursion distance of the voice coil of the transducer, which can result in a more consistent performance across different positions of the voice coil. This consistency can lead to better linearity and predictability' in the behavior of the transducer, resulting in more accurate reproduction of audio signals. A "pointy" or steep BL curve, meaning a significant change in BL value for the coil excursion distance, can indicate non-linearity in the operation of the transducer. This non-linearity may lead to distortion, uneven frequency response, and other undesirable effects in the sound produced by the transducer. Another important consideration for BL curves is the BL factor itself. Higher BL values can be preferable in certain situations, which can result in higher efficiency and better control.

[0071] In some examples, this property of the region length may be referred to as a “magnetic aperture” because of a loose similarity to optical aperture. In the case of optics, for instance, increasing or decreasing the aperture of a camera iris can decrease and increase, respectively, the depth of field of light entering the camera lens, thereby affecting to what extent different objects are in and out of focus with relation to focal plane. Somewhat similarly, increasing or decreasing the length of the region can adjust the BL to be more or less “focused” on the excursion range of a corresponding voice coil in relation to a center point of the excursion range.

[0072] The inventors have found that the length of the region may be selectively controlled during the magnetization process by controlling the reluctance around the region and / or the magnetic flux through the region. Accordingly, in examples, magnetizing the first magnetizable portion forms a first magnetized portion of the magnet assembly, magnetizing the second magnetizable portion forms a second magnetized portion of the magnet assembly. and the magnet assembly, after being magnetized by the first and second magnetization coils.comprises: (i) a first end that has a same polarity as a second end of the magnet assembly, the first and second ends being spaced apart along the longitudinal axis, and (ii) a region between the first and second ends. The method comprises, during the magnetizing, forming the region with a particular length, the length being measured in a direction along the longitudinal axis, by controlling at least one of: a magnetic reluctance external to the magnet assembly adjacent the region and a magnetic flux through the region.

[0073] In examples, in the region, magnetic flux extends substantially perpendicular to the longitudinal axis, and in the first and second magnetized portions, the magnetic flux extends substantially parallel to the longitudinal axis and points in opposite directions.

[0074] The region is arranged between the first and second magnetized portions.

[0075] The length may be referred to as a thickness, axial width and / or a longitudinal extent of the region.

[0076] In a particular example, the magnet assembly is a monolithic magnet assembly.

[0077] In some examples (such as those having only a single region formed along the magnet assembly) the region is located centrally along a length of the magnet assembly.

[0078] The first end of the magnet assembly may be a first outer end of the magnet assembly, such as a first terminal end of the magnet assembly. The second end of the magnet assembly may be a second outer end of the magnet assembly, such as a second terminal end of the magnet assembly.

[0079] In particular examples, controlling the magnetic flux through the region comprises at least one of: (i) controlling a distance between the first and second magnetization coils along the longitudinal axis, wherein the length of the region is based on the distance, (ii) controlling magnitudes of the first and second currents, wherein the length of the region is based on the magnitudes, (iii) arranging at least a third magnetization coil between the first and second magnetization coils, the third magnetization coil having a winding axis that is substantiallyperpendicular to the winding axes of the first and second magnetization coils, wherein the length of the region is based on a cross-sectional width of the third magnetization coil, the cross-sectional width measured parallel to the longitudinal axis, or (iv) arranging a permanent magnet between the first and second magnetization coils, the permanent magnet having a magnetic axis that is substantially perpendicular to the winding axes of the first and second magnetization coils, wherein the length of the region is based on a cross-sectional width of the magnet, the cross-sectional width measured parallel to the longitudinal axis.

[0080] Using one or more of these techniques, the length of the region may be controlled, as desired. In each of these cases, the magnetic flux through the region is increased or decreased. For example, a particular distance and / or particular currents may be selected to provide the required length of the region. In another example, a “wider” or “narrower” coil or magnet dia eter / idth may be selected to provide the required length of the region. A wider width may increase the flux through a greater region along the magnet assembly, thereby increasing the length of the region. For example, controlling the magnetic flux through the region comprises distributing magnetic flux over a greater or narrower length of the magnet assembly. The magnetic field of the third magnetization coil or the permanent magnet may be aligned in the same direction as the magnetic field passing through the region (that is, perpendicular to the longitudinal axis).

[0081] In examples, one or more permanent magnets and / or one or more third magnetization coils may be arranged around the magnet assembly. A magnetic axis of each permanent magnet or third magnetization coil may be arranged perpendicular to the longitudinal axis.

[0082] In an example, controlling the magnetic reluctance external to the magnet assembly adjacent the region comprises: arranging magnetizable material between the first and second magnetization coils and at least partially around the magnet assembly, such that the first magnetic field flows through the first magnetizable portion and through the magnetizablematerial and the second magnetic field flows through the second magnetizable portion and through the magnetizable material, wherein the length of the region is based on a cross- sectional width of the magnetizable material, the cross-sectional width measured parallel to the longitudinal axis.

[0083] Arranging magnetizable material around the magnet assembly provides another simple method to control the length of the region. Magnetizable material having a particular width or thickness may be selected to provide the required length of the region.

[0084] The use of such magnetizable material draws or bends the magnetic flux out of the first and second magnetizable portions. The magnetizable material can help shape or direct the magnetic fields through the magnet assembly, and thereby act as a magnetic lens.

[0085] The magnetizable material may be arranged in a ring around the magnet assembly during magnetization.

[0086] In examples, the first magnetic field flows through the magnetizable material in a direction approximately perpendicular to the first direction (and longitudinal axis), and the second magnetic field flows through the magnetizable material in a direction approximately perpendicular to the second direction (and longitudinal axis).

[0087] In an example, the magnetizable material comprises an aperture and the magnet assembly is positioned within or through the aperture during magnetization.

[0088] In an example, the magnetizable material is a low reluctance material, for example a soft magnetic material, such as soft iron. In some examples, the magnetizable material comprises steel. In examples, the magnetizable material has a lower reluctance than air, for example, which may surround the rest of the magnet assembly.

[0089] The magnetizable material may be referred to as ancillary magnetizable material or auxiliary magnetizable material.

[0090] The magnetizable material is separate from the magnet assembly.

[0091] In some examples, a through hole or a void may be formed in the region. This may be formed in an area of the region that has a low magnetic flux density, and as such, may not overly reduce the effectiveness of the magnet assembly. Introducing a void or through hole reduces the amount of magnetic material in the magnet assembly, reducing the weight and cost. The hole / void can be introduced in a part of the magnet assembly where there is a magnetic neutral zone / point (that is, the point where the magnetic field(s) balance and therefore the resultant magnetic field is approximately zero). In some examples, the size of the hole / void can affect the width of the BL curve, and therefore the size can be selected based on the particular requirements of the transducer.

[0092] Accordingly, in some examples, the magnet assembly, after being magnetized by the first and second magnetization coils, comprises: (i) a first end that has a same polarity as a second end of the magnet assembly, the first and second ends being spaced apart along the longitudinal axis, and (ii) a region between the first and second ends. The method further comprises forming the magnet assembly such that at least one of: (i) a through hole extends through the region, or (ii) the region includes a void.

[0093] In some examples, the through hole / void has a rotational symmetry order of at least 2 about the longitudinal axis (which ensures that the magnetic forces are evenly balanced around the axis, providing consistent transducer performance).

[0094] The void may comprise a vacuum or air, or material that is different from the magnetized / magnetizable material forming the magnet assembly. In some cases, the material may be a different magnetized / magnetizable material to the magnetized / magnetizable material forming the rest of the magnetic assembly, for example, it may be cheaper or have a lower density. In some cases, the material may not be magnetized / magnetizable material.

[0095] In the above method, the step of forming the hole or void could be performed before. during or after magnetization of the first and second magnetizable portions. For example.powdered magnetizable material may be sintered or 3D printed to leave a void or through hole. As another example, after being formed (and either prior to or after magnetization), a through hole could be bored through the magnetic assembly. The through hole or void may be formed prior to magnetization (that is, before the region exists, but it may be formed in a place where the region does exist after magnetization).

[0096] In examples, the through hole may be parallel the longitudinal axis of the magnet assembly or the through hole may be perpendicular the longitudinal axis of the magnet assembly.

[0097] As briefly mentioned, the through hole or void may be formed in the region of the magnet assembly where there is a magnetic neutral zone / point. A magnetic neutral point of the region may therefore be located within the through hole or void.

[0098] In examples where a monolithic magnetizable element is magnetized, the method may further comprise: forming the monolithic magnetizable element by: (i) obtaining powdered magnetizable material, and (ii) sintering the powdered magnetizable material to form the monolithic magnetizable element. The method may further comprise before sintering the powdered magnetizable material, magnetically orientating the powered magnetizable material by subjecting the powdered magnetizable material to third and fourth magnetic fields that have one of: (i) substantially the same form as the first and second magnetic fields, or (ii) a form that differs from the first and second magnetic fields based on a degree of deformation that occurs to the during sintering. For example, the powdered magnetizable material may be arranged in a mould and in this pre-sintered state, the volume occupied by the powdered magnetizable material may be larger than the volume occupied by the monolithic magnetizable element once formed, due to deformation during sintering. For example, the powdered magnetizable material may be more compacted after sintering, and so the third and fourth magnetic fields applied to the powdered magnetizable material may have a lower magnetic fluxdensity when compared to the first and second magnetic fields applied to the monolithic magnetizable element.

[0099] In alternative examples, the magnet assembly comprises a first magnetizable element, a second magnetizable element and a spacer element affixed to and arranged between the first and second magnetizable elements, and the first magnetizable element comprises the first magnetizable portion and the second magnetizable element comprises the second magnetizable portion. The method may further comprise: (i) providing the first magnetizable element, the second magnetizable element and the spacer element, (ii) affixing the first magnetizable element to a first side of the spacer element, and (iii) affixing the second magnetizable element to a second side of the spacer element.

[0100] The first magnetizable element, the spacer element and the second magnetizable element may form a linear stack.

[0101] In some examples, the first and second magnetizable elements are, or define, the first and second magnetizable portions, respectively.

[0102] The spacer element may have a high reluctance, to stop or reduce interference between the magnetic fields generated by the magnetization coils, and the magnetizable elements themselves.

[0103] In examples, providing the spacer element comprises providing a spacer element comprising non-magnetizable material (such as plastic).

[0104] In some examples, providing the first and second magnetizable elements comprises providing first and second magnetizable elements having substantially the same magnetic coercivity. Having the same coercivity can ensure that the magnetizable elements are equally magnetized, which ensures a more uniform displacement of a voice coil that extends around the magnet assembly in an assembled transducer.

[0105] In certain examples, two or more magnet assemblies can be magnetized at the same time, using the same magnetization coils. Accordingly, in some examples, the method further comprises positioning a second magnet assembly at least partially between the first magnetization coil and the second magnetization coil, and simultaneously magnetizing the magnet assembly and the second magnet assembly. Magnetizing two or more magnet assemblies simultaneously can further reduce manufacturing time.

[0106] In some cases, the magnet assembly and the second magnet assembly can be held in place by one or more holders, such as one or more holders of a fixture. For example, a fixture may be arranged at least partially between the first magnetization coil and the second magnetization coil, and two or more magnet assemblies can be received in separate holders of the fixture. The holders can hold the magnet assemblies in place during magnetization.

[0107] In some examples, positioning the magnet assembly at least partially between the first magnetization coil and the second magnetization coil comprises holding the magnet assembly in a first holder of a fixture, the fixture arranged at least partially between the first magnetization coil and the second magnetization coil, and positioning the second magnet assembly at least partially between the first magnetization coil and the second magnetization coil comprises holding the second magnet assembly in a second holder of the fixture.

[0108] As mentioned, the fixture can hold the magnet assemblies in place, thereby ensuring even magnetization and improving uniformity between different batches.

[0109] In a particular example, holding the magnet assembly and the second magnet assembly in a first and second holder of a fixture comprises at least partially receiving the magnet assembly and the second magnet assembly in a first and second receptacle, respectively, of the fixture.

[0110] In some cases, at least one of the first and second magnetization coils are moveable.As such, in examples, the method may further comprise: after positioning the magnet assemblyat least partially between the first magnetization coil and the second magnetization coil and prior to magnetizing the magnet assembly, moving at least one of: (i) the first magnetization coil towards the second magnetization coil, or (ii) the second magnetization coil towards the first magnetization coil. Enclosing the magnet assembly between the first and second magnetization coils can help focus and direct the magnetic fields on the magnet assembly, thereby improving efficiency.

[0111] According to a second aspect, there is provided a magnetization device for magnetizing a magnet assembly having a longitudinal axis, the magnetization device comprising: (i) a first magnetization coil having a winding axis configured to be arranged parallel to the longitudinal axis and configured to generate a first magnetic field for magnetizing a first magnetizable portion of the magnet assembly, the first magnetic field extending in a first direction, (ii) a second magnetization coil having a winding axis configured to be arranged parallel to the longitudinal axis, the second magnetization coil being spaced apart from the first magnetization coil and configured to generate a second magnetic field for magnetizing a second magnetizable portion of the magnet assembly, the second magnetic field extending in a second direction opposite to the first direction, and (iii) one or more current sources configured to apply: (a) a first current to the first magnetization coil to generate the first magnetic field, and (b) a second current to the second magnetization coil to generate the second magnetic field.

[0112] In an example, the magnet assembly is a magnet assembly for a transducer.

[0113] In a particular example, the magnetization device is for magnetizing a monolithic magnetizable element.

[0114] The one or more current sources may be a single current source coupled to both the first magnetization coil and the second magnetization coil, and configured to apply: (a) the firstcurrent to the first magnetization coil to generate the first magnetic field and (b) the second current to the second magnetization coil to generate the second magnetic field.

[0115] Alternatively, the one or more current sources may include a first current source coupled to the first magnetization coil and configured to apply the first current to the first magnetization coil to generate the first magnetic field, and a second current source coupled to the second magnetization coil and configured to apply the second current to the second magnetization coil to generate the second magnetic field.

[0116] In examples, a current source may be a capacitor or a capacitor bank.

[0117] In some examples, the one or more current sources are configured to apply the first and second currents to the first and second magnetization coils, respectively, at substantially the same time.

[0118] In a particular case, the device may further comprise a controller for controlling the one or more current sources such that they apply the first and second currents at substantially the same time.

[0119] In examples, the one or more current sources are configured to apply the first and second currents to the first and second magnetization coils, respectively, such that they have substantially the same current. In other words, the first and second currents have the same magnitude or are equal in terms of the amount of current they carry. The two currents may therefore have the same value in amps.

[0120] In examples, the first magnetization coil is configured to generate the first magnetic field having a first field strength at the first magnetizable portion and the second magnetization coil is configured to generate the second magnetic field having a second field strength at the second magnetizable portion, the first and second field strengths being substantially equal. Having magnetic fields of the same magnitude may ensure an evenly distributed field extends through the magnet assembly, and may result in the two magnetizable portions being equallymagnetized. It will be understood that the magnetic field strength varies depending upon where the field strength is measured. As such, the field strengths are measured at positions that are the same distance from their respective magnetization coils.

[0121] In some examples, the device is configured to receive the magnet assembly at least partially between the first and second magnetization coils, and wherein, in use, one of: (i) at the first magnetization coil, the first direction points towards the second magnetization coil, and at the second magnetization coil the second direction points towards the first magnetization coil, or (ii) at the first magnetization coil, the first direction points away from the second magnetization coil, and at the second magnetization coil the second direction points away from the first magnetization coil.

[0122] In particular arrangements, the device further comprises at least one of: (a) at least a third magnetization coil arranged between the first and second magnetization coils, the third magnetization coil having a winding axis that is substantially perpendicular to the winding axes of the first and second magnetization coils, and (b) magnetizable material arranged between the first and second magnetization coils, the magnetizable material being configured to extend at least partially around the magnet assembly, such that in use, the first magnetic field flows through the first magnetizable portion and through the magnetizable material and the second magnetic field flows through the second magnetizable portion and through the magnetizable material.

[0123] In some examples, the device may comprise a fixture arranged at least partially between the first and second magnetization coils for receiving the magnet assembly.

[0124] In certain examples, the device further comprises a fixture arranged at least partially between the first and second magnetization coils, the fixture comprising a first holder and a second holder, the first holder being configured to hold the magnet assembly, and the secondholder being configured to hold a second magnet assembly for magnetization by the magnetization device.

[0125] In some examples, the device comprises two fixtures, each fixture configured to hold or receive opposite ends of the magnet assembly.

[0126] In examples, the or each fixture may be part of an enclosure, which houses the magnetization coil.

[0127] The fixture may be a plate, for example. The first and second holders may be first and second receptacles for at least partially receiving a magnetic assembly therein. The fixture may comprise a plurality of holders, each holder for holding a magnetic assembly therein.

[0128] In some examples, at least one of: (i) the first magnetization coil is moveable towards the second magnetization coil, or (ii) the second magnetization coil is moveable towards the first magnetization coil.

[0129] According to a third aspect, there is provided a system, comprising: (i) the magnetization device of the second aspect, and (ii) one or more workstations for assembling a magnet assembly. For example, the one or more workstations may be for affixing a first magnetizable element to a first side of a spacer element and affixing a second magnetizable element to a second side of the spacer element to provide the magnet assembly, the first magnetizable element comprising the first magnetizable portion and the second magnetizable element comprising the second magnetizable portion. As another example, the one or more workstations may be for affixing a first magnetizable element to a second magnetizable element to provide the magnet assembly, the first magnetizable element comprising the first magnetizable portion and the second magnetizable element comprising the second magnetizable portion.

[0130] According to a fourth aspect, there is provided a monolithic magnet having a longitudinal axis, the monolithic magnet comprising: (i) a first magnetized portion having afirst magnetic flux substantially orientated along the longitudinal axis, (ii) a second magnetized portion positioned along the longitudinal axis from the first magnetized portion and having a second magnetic flux substantially orientated along the longitudinal axis in the opposite direction to the first magnetic flux, and (iii) and a region positioned between the first magnetized portion and the second magnetized portion.

[0131] In an example, the first magnetic flux is orientated in the first direction and the second magnetic flux is orientated in the second direction.

[0132] As briefly mentioned above, a first magnetizable portion of a monolithic magnetizable element may be magnetized to form the first magnetized portion of the monolithic magnet and a first part of the region, and a second magnetizable portion of the monolithic magnet may be magnetized to form the second magnetizable portion and a second part of the region.

[0133] In examples, the region includes a magnetic neutral zone. The neutral zone may be located along a midpoint of the region, the midpoint measured in a direction parallel to the longitudinal axis.

[0134] In examples, the region has a third magnetic flux substantially orientated perpendicular to the longitudinal axis. In examples, the region has a first length along the longitudinal axis. The length of the region may be defined as the part of the monolithic magnetizable element where the magnetic flux is perpendicular to the longitudinal axis.

[0135] In examples, the region is located centrally between outer ends of the first and second magnetized portions. This can provide a symmetric / balanced magnetic field to the voice coil that may extend around the monolithic magnet.

[0136] In certain examples, the monolithic magnet is used to drive a single membrane, and a motor may therefore have a single voice coil coupled to the membrane. The voice coil may extend around the monolithic magnet adjacent to the region that is formed along the monolithicmagnet. Here, the voice coil may be at a rest position. In some cases, however, the monolithic magnet may be used to drive two or more membranes, such as opposing membranes. In such cases, there may be two or more voice coils arranged at different positions along the length of the monolithic magnet, and each voice coil may extend around different regions that are formed along the monolithic magnet. As such, two or more regions of the form described above maybe formed along the monolithic magnet, where each region is arranged between two magnetized portions. This allows a monolithic magnet to be created that has three (or more) “magnets” along its length, which may be useful for use with two or more voice coils.

[0137] Accordingly, in examples, the monolithic magnet may further comprise: (a) a third magnetized portion positioned along the longitudinal axis from the second portion and having a third magnetic flux substantially orientated along the longitudinal axis in the same direction to the first magnetic flux, and (b) a second region positioned between the second magnetized portion and the third magnetized portion. The second region may have the same or similar features as the region described above.

[0138] In examples, at least one of: (i) a through hole extends through at least part of a magnetic neutral zone of the region or (ii) the region defines a void that includes at least part of the magnetic neutral zone.

[0139] In some examples, the through hole or void has a rotational symmetry order of at least 2 about the longitudinal axis.

[0140] In a particular example, the through hole extends through the region in a direction perpendicular to the longitudinal axis and has a rotational symmetry order of 2. In some examples, a center of the through hole (measured along the length of the through hole, in a direction perpendicular to the longitudinal axis) passes through the longitudinal axis.

[0141] According to a fifth aspect, there is provided a motor comprising the monolithic magnet of the fourth aspect and one or more voice coils. The motor may be referred to as a transducer assembly in other examples.

[0142] According to a sixth aspect, there is provided a playback device, comprising the motor of the fifth aspect.

[0143] According to a seventh aspect, there is provided a method of manufacturing a monolithic magnet, the method comprising: (i) positioning a monolithic magnetizable element at least partially between a first magnetization coil and a second magnetization coil, wherein the monolithic magnetizable element defines a longitudinal axis, and the longitudinal axis is arranged parallel to a winding axis of the first magnetization coil and a winding axis of the second magnetization coil, (ii) magnetizing the monolithic magnetizable element to provide a monolithic magnet by: (a) passing a first current through the first magnetization coil to generate a first magnetic field to magnetize a first magnetizable portion of monolithic magnetizable element, and (b) passing a second current through the second magnetization coil to generate a second magnetic field to magnetize a second magnetizable portion of the monolithic magnetizable element, and (iii) during the magnetizing, forming a region within the monolithic magnet having a particular length, the length being measured in a direction along the longitudinal axis, by controlling at least one of: (A) a magnetic reluctance external to the monolithic magnet adjacent the region, and (B) a magnetic flux through the region.

[0144] The method may include any or all of the other method steps described in other aspects, such as the first aspect.

[0145] In examples, the method may comprise determining the length (such as determining a desired length required for the monolithic magnet) and controlling the magnetic reluctance and / or flux to achieve the desired length.

[0146] In examples, controlling the magnetic flux through the region comprises controlling a distance between the first and second magnetization coils along the longitudinal axis, wherein the length of the region is based on the distance. For example, the coils may be moved closer together or further apart to achieve the required length.

[0147] In examples, controlling the magnetic flux through the region comprises controlling magnitudes of the first and second currents, wherein the length of the region is based on the magnitudes.

[0148] In examples, controlling the magnetic flux through the region comprises arranging at least a third magnetization coil between the first and second magnetization coils, the third magnetization coil having a winding axis that is substantially perpendicular to the winding axes of the first and second magnetization coils, wherein the length of the region is based on a cross- sectional width of the third magnetization coil, the cross-sectional width measured parallel to the longitudinal axis.

[0149] In examples, controlling the magnetic flux through the region comprises arranging a permanent magnet between the first and second magnetization coils, the permanent magnet having a magnetic axis that is substantially perpendicular to the winding axes of the first and second magnetization coils, wherein the length of the region is based on a cross-sectional width of the magnet, the cross-sectional width measured parallel to the longitudinal axis.

[0150] In examples, controlling the magnetic reluctance external to the monolithic magnet adjacent the region comprises arranging magnetizable material between the first and second magnetization coils and at least partially around the monolithic magnetizable element, wherein the length of the region is based on a cross-sectional width of the magnetizable material, the cross-sectional width measured parallel to the longitudinal axis.

[0151] In examples, the method further comprises forming at least one of: (i) a through hole through the region or (ii) a void within the region.

[0152] In examples, the method further comprises: (i) positioning the monolithic magnetizable element at least partially between the first magnetization coil and a third magnetization coil, the second magnetization coil being arranged between the first and third magnetization coils and extending around the monolithic magnetizable element, wherein a winding axis of the third magnetization coil is parallel to winding axes of the first and second magnetization coils, and (ii) passing a third current through the third magnetization coil to generate a third magnetic field to magnetize a third magnetizable portion of monolithic magnetizable element, the third magnetic field extending in the same direction as the first magnetic field.

[0153] In the same way as described above, a second region within the monolithic magnet may be formed between second and third magnetized portions, and a length of the second region may be controlled to have a particular length.

[0154] According to a further aspect, there is provided a method of manufacturing a magnet assembly for a transducer, the method comprising: (i) positioning the magnet assembly at least partially between a first magnetization coil and a second magnetization coil, and (ii) magnetizing the magnet assembly by: (a) passing a first current through the first magnetization coil to generate a first magnetic field to magnetize a first magnetizable portion of the magnet assembly, and (b) passing a second current through the second magnetization coil to generate a second magnetic field to magnetize a second magnetizable portion of the magnet assembly. The method may comprise any or all of the features discussed above or herein.

[0155] In some examples, the first and second currents are supplied by a single cunent source. In other examples, the first and second currents are supplied by first and second current sources, respectively.

[0156] According to a further aspect, there is provided a magnetization device for magnetizing a magnet assembly for a transducer, the magnetization device comprising: (i) afirst magnetization coil configured to generate a first magnetic field for magnetizing a first magnetizable portion of the magnet assembly, and (ii) a second magnetization coil spaced apart from the first magnetization coil and configured to generate a second magnetic field for magnetizing a second magnetizable portion of the magnet assembly. The device may comprise any or all of the features discussed above or herein.

[0157] In some examples, the device further comprises: (iii) one or more current sources configured to apply: a first current to the first magnetization coil to generate the first magnetic field and a second current to the second magnetization coil to generate the second magnetic field.

[0158] In some examples, the one or more current sources comprises: (iii) a first current source coupled to the first magnetization coil and configured to apply a first current to the first magnetization coil to generate the first magnetic field, and (iv) a second current source coupled to the second magnetization coil and configured to apply a second current to the second magnetization coil to generate the second magnetic field.

[0159] In other examples, the one or more current sources is a single current source coupled to the first and second magnetization coils and configured to apply a current (such as first and second currents) to the first and second magnetization coils to generate the first and second magnetic fields, respectively. For example, the first magnetization coil and the second magnetization coil might be connected in series when the first and second currents are the same. Alternatively, they might be connected in parallel but each presenting a respective effective resistance or impedance so that the desired first and second currents are achieved. When the first current is the same as the second current, the first magnetization coil and the second magnetization coil may have the same resistance or impedance.II. Suitable Operating Environment

[0160] Figure 1A is a partial cutaway view of a media playback system 100 distributed in an environment 101 (e.g., a house). The media playback system 100 comprises one or more playback devices 110 (identified individually as playback devices HOa-n), one or more network microphone devices (“NMDs”), 120 (identified individually as NMDs 120a-c), and one or more control devices 130 (identified individually as control devices 130a and 130b).

[0161] As used herein the term “playback device” can generally refer to a network device configured to receive, process, and output data of a media playback system. For example, a playback device can be a network device that receives and processes audio content. In some examples, a playback device includes one or more transducers or speakers powered by one or more amplifiers. In other examples, however, a playback device includes one of (or neither ol) the speaker and the amplifier. For instance, a playback device can comprise one or more amplifiers configured to drive one or more speakers external to the playback device via a corresponding wire or cable.

[0162] As will be understood, a transducer, such as an audio transducer, may comprise a magnet assembly, a voice coil, and a diaphragm or membrane.

[0163] Moreover, as used herein the term NMD (i.e., a “network microphone device”) can generally refer to a network device that is configured for audio detection. In some examples, an NMD is a stand-alone device configured primarily for audio detection. In other examples, an NMD is incorporated into a playback device (or vice versa).

[0164] The term “control device” can generally refer to a network device configured to perform functions relevant to facilitating user access, control, and / or configuration of the media playback system 100.

[0165] Each of the playback devices 110 is configured to receive audio signals or data from one or more media sources (e.g., one or more remote servers, one or more local devices) andplay back the received audio signals or data as sound. The one or more NMDs 120 are configured to receive spoken word commands, and the one or more control devices 130 are configured to receive user input. In response to the received spoken word commands and / or user input, the media playback system 100 can play back audio via one or more of the playback devices 110. In certain examples, the playback devices 110 are configured to commence playback of media content in response to a trigger. For instance, one or more of the playback devices 110 can be configured to play back a morning playlist upon detection of an associated trigger condition (e.g., presence of a user in a kitchen, detection of a coffee machine operation). In some examples, for instance, the media playback system 100 is configured to play back audio from a first playback device (e.g., the playback device 110a) in synchrony with a second playback device (e.g., the playback device 110b). Interactions between the playback devices 110, NMDs 120, and / or control devices 130 of the media playback system 100 configured in accordance with the various examples of the disclosure are described in greater detail below.

[0166] In the illustrated example of Figure 1 A, the environment 101 comprises a household having several rooms, spaces, and / or playback zones, including (clockwise from upper left) a master bathroom 101a, a master bedroom 101b, a second bedroom 101c, a family room or den lOld, an office lOle, a living room lOlf, a dining room 101g, a kitchen lOlh, and an outdoor patio lOli. While certain examples and examples are described below in the context of a home environment, the technologies described herein may be implemented in other types of environments. In some examples, for instance, the media playback system 100 can be implemented in one or more commercial settings (e.g., a restaurant, mall, airport, hotel, a retail or other store), one or more vehicles (e.g., a sports utility vehicle, bus, car, a ship, a boat, an airplane), multiple environments (e.g., a combination of home and vehicle environments). and / or another suitable environment where multi -zone audio may be desirable.

[0167] The media playback system 100 can comprise one or more playback zones, some of which may correspond to the rooms in the environment 101. Each of the playback zones and / or the individual rooms may be referred to as a listening environment. The media playback system 100 can be established with one or more playback zones, after which additional zones may be added, or removed to form, for example, the configuration shown in Figure 1 A. Each zone maybe given a name according to a different room or space such as the office lOle, master bathroom 101a, master bedroom 101b, the second bedroom 101c, kitchen lOlh, dining room 101g, living room lOlf, and / or the balcony lOli. In some examples, a single playback zone may include multiple rooms or spaces. In certain examples, a single room or space may include multiple playback zones.

[0168] In the illustrated example of Figure 1A, the master bathroom 101a, the second bedroom 101c, the office lOle, the living room lOlf, the dining room 101g, the kitchen lOlh, and the outdoor patio lOli each include one playback device 110, and the master bedroom 101b and the den 101 d include a plurality of playback devices 110. In the master bedroom 101b, the playback devices 1101 and 110m may be configured, for example, to play back audio content in synchrony as individual ones of playback devices 110, as a bonded playback zone, as a consolidated playback device, and / or any combination thereof. Similarly, in the den 101 d, the playback devices HOh-j can be configured, for instance, to play back audio content in synchrony as individual ones of playback devices 110, as one or more bonded playback devices, and / or as one or more consolidated playback devices. Additional details regarding bonded and consolidated playback devices are described below with respect to Figures IB and IE.

[0169] In some examples, one or more of the playback zones in the environment 101 may each be playing different audio content. For instance, a user may be grilling on the patio 101 i and listening to hip hop music being played by the playback device 110c while another user ispreparing food in the kitchen lOlh and listening to classical music played by the playback device 110b. In another example, a playback zone may play the same audio content in synchrony with another playback zone. For instance, the user may be in the office lOle listening to the playback device 1 lOf playing back the same hip hop music being played back by playback device 110c on the patio lOli. In some examples, the playback devices 110c and 11 Of play back the hip hop music in synchrony such that the user perceives that the audio content is being played seamlessly (or at least substantially seamlessly) while moving between different playback zones. Additional details regarding audio playback synchronization among playback devices and / or zones can be found, for example, in U.S. Patent No. 8,234,395 entitled, “System and method for synchronizing operations among a pl urality of independently clocked digital data processing devices,” which is incorporated by reference above. a. Suitable Media Playback System

[0170] Figure IB is a schematic diagram of the media playback system 100 and a cloud network 102. For ease of illustration, certain devices of the media playback system 100 and the cloud network 102 are omitted from Figure IB. One or more communication links 103 (referred to hereinafter as “the links 103”) communicatively couple the media playback system 100 and the cloud network 102.

[0171] The links 103 can comprise, for example, one or more wired networks, one or more wireless networks, one or more wide area networks (WAN), one or more local area networks (LAN), one or more personal area networks (PAN), one or more telecommunication networks (e.g., one or more Global System for Mobiles (GSM) networks, Code Division Multiple Access (CDMA) networks, Long-Term Evolution (LTE) networks, 5G communication network networks, and / or other suitable data transmission protocol networks), etc. The cloud network 102 is configured to deliver media content (e.g., audio content, video content, photographs, social media content) to the media playback system 100 in response to a request transmittedfrom the media playback system 100 via the links 103. In some examples, the cloud network 102 is further configured to receive data (e g. voice input data) from the media playback system 100 and correspondingly transmit commands and / or media content to the media playback system 100.

[0172] The cloud network 102 comprises computing devices 106 (identified separately as a first computing device 106a, a second computing device 106b, and a third computing device 106c). The computing devices 106 can comprise individual computers or servers, such as, for example, a media streaming service server storing audio and / or other media content, a voice sendee server, a social media server, a media playback system control server, etc. In some examples, one or more of the computing devices 106 comprise modules of a single computer or server. In certain examples, one or more of the computing devices 106 comprise one or more modules, computers, and / or servers. Moreover, while the cloud network 102 is described above in the context of a single cloud network, in some examples the cloud network 102 comprises a plurality of cloud networks comprising communicatively coupled computing devices. Furthermore, while the cloud network 102 is shown in Figure IB as having three of the computing devices 106, in some examples, the cloud network 102 comprises fewer (or more than) three computing devices 106.

[0173] The media playback system 100 may be configured to receive media content from the networks 102 via the links 103. The received media content can comprise, for example, a Uniform Resource Identifier (URI) and / or a Uniform Resource Locator (URL). For instance, in some examples, the media playback system 100 can stream, download, or otherwise obtain data from a URI or a URL corresponding to the received media content. A network 104 communicatively couples the links 103 and at least a portion of the devices (e.g., one or more of the playback devices 110, NMDs 120. and / or control devices 130) of the media playback system 100. The network 104 can include, for example, a wireless network (e.g., a WiFinetwork, a Bluetooth, a Z-Wave network, a ZigBee, and / or other suitable wireless communication protocol network) and / or a wired network (e.g., a network comprising Ethernet, Universal Serial Bus (USB), and / or another suitable wired communication). As those of ordinary skill in the art will appreciate, as used herein, “WiFi” can refer to several different communication protocols including, for example, Institute of Electrical and Electronics Engineers (IEEE) 802.11a, 802.11b, 802.11g, 802.11n, 802.11ac, 802.11ac, 802.11ad, 802.11af, 802.11ah, 802.11ai, 802.1 laj, 802.11aq, 802.11ax, 802. Hay, 802.15, etc. transmitted at 2.4 Gigahertz (GHz), 5 GHz, and / or another suitable frequency.

[0174] In some examples, the network 104 comprises a dedicated communication network that the media playback system 100 uses to transmit messages between individual devices and / or to transmit media content to and from media content sources (e.g., one or more of the computing devices 106). In certain examples, the network 104 is configured to be accessible only to devices in the media playback system 100, thereby reducing interference and competition with other household devices. In other examples, however, the network 104 comprises an existing household communication network (e.g., a household WiFi network). In some examples, the links 103 and the network 104 comprise one or more of the same networks. In some examples, for instance, the links 103 and the network 104 comprise a telecommunication network (e.g., an LTE network, a 5G network). Moreover, in some examples, the media playback system 100 is implemented without the network 104, and devices comprising the media playback system 100 can communicate with each other, for example, via one or more direct connections, PANs, telecommunication networks, and / or other suitable communication links.

[0175] In some examples, audio content sources may be regularly added or removed from the media playback system 100. In some examples, for instance, the media playback system100 performs an indexing of media items when one or more media content sources are updated.added to. and / or removed from the media playback system 100. The media playback system 100 can scan identifiable media items in some or all folders and / or directories accessible to the playback devices 110, and generate or update a media content database comprising metadata (e.g., title, artist, album, track length) and other associated information (e.g., URIs. URLs) for each identifiable media item found. In some examples, for instance, the media content database is stored on one or more of the playback devices 110, network microphone devices 120, and / or control devices 130.

[0176] In the illustrated example of Figure IB, the playback devices 1101 and 110m comprise a group 107a. The playback devices 1101 and 110m can be positioned in different rooms in a household and be grouped together in the group 107a on a temporary or permanent basis based on user input received at the control device 130a and / or another control device 130 in the media playback system 100. When arranged in the group 107a, the playback devices 1101 and 110m can be configured to play back the same or similar audio content in synchrony from one or more audio content sources. In certain examples, for instance, the group 107a comprises a bonded zone in which the playback devices 1101 and 110m comprise left audio and right audio channels, respectively, of multi-channel audio content, thereby producing or enhancing a stereo effect of the audio content. In some examples, the group 107a includes additional playback devices 1 10. In other examples, however, the media playback system 100 omits the group 107a and / or other grouped arrangements of the playback devices 110.

[0177] The media playback system 100 of Figure IB includes the NMDs 120a and 120d, each comprising one or more microphones configured to receive voice utterances from a user. In the illustrated example of Figure IB, the NMD 120a is a standalone device and the NMD 120d is integrated into the playback device 1 lOn. The NMD 120a, for example, is configured to receive voice input 121 from a user 123. In some examples, the NMD 120a transmits data associated with the received voice input 121 to a voice assistant service (VAS) configured to(i) process the received voice input data and (ii) transmit a corresponding command to the media playback system 100. In some examples, for instance, the computing device 106c comprises one or more modules and / or servers of a V AS (e.g., a VAS operated by one or more of SONOS®, AMAZON®, GOOGLE® APPLE®, MICROSOFT®). The computing device 106c can receive the voice input data from the NMD 120a via the network 104 and the links 103. In response to receiving the voice input data, the computing device 106c processes the voice input data (i. e. , “Play Hey Jude by The Beatles”), and determines that the processed voice input includes a command to play a song (e.g., “Hey Jude”). The computing device 106c accordingly transmits commands to the media playback system 100 to play back “Hey Jude” by the Beatles from a suitable media service (e.g., via one or more of the computing devices 106) on one or more of the playback devices 110. Although the media playback system 100 is shown as including a plurality of playback devices 110a- 11 On, an NMD 120a, a control device 130a, and a network 104, in other examples the media playback system 100 may include one playback device incorporating an upward-firing transducer and one or more microphones, as well as a processor and memon stored at, for example, the playback device, a network microphone device, or a control device. b. Suitable Playback Devices

[0178] Figure 1C is a block diagram of the playback device 110a comprising an input / output 111. The input / output 111 can include an analog I / O I l la (e.g., one or more wares, cables, and / or other suitable communication links configured to carry analog signals) and / or a digital I / O 11 lb (e.g., one or more wires, cables, or other suitable communication links configured to carry digital signals). In some examples, the analog I / O I l la is an audio line-in input connection comprising, for example, an auto-detecting 3.5mm audio line-in connection. In some examples, the digital I / O 111b comprises a Sony / Philips Digital Interface Format (S / PDIF) communication interface and / or cable and / or a Toshiba Link (TOSLINK) cable. Insome examples, the digital I / O 111b comprises a High-Definition Multimedia Interface (HDMI) interface and / or cable. In some examples, the digital I / O 111b includes one or more wireless communication links comprising, for example, a radio frequency (RF), infrared, WiFi, Bluetooth, or another suitable communication protocol. In certain examples, the analog I / O I l la and the digital 111b comprise interfaces (e.g., ports, plugs, jacks) configured to receive connectors of cables transmitting analog and digital signals, respectively, without necessarily including cables.

[0179] The playback device 110a, for example, can receive media content (e.g., audio content comprising music and / or other sounds) from a local audio source 105 via the input / output 111 (e.g., a cable, a wire, a PAN, a Bluetooth connection, an ad hoc wired or wireless communication network, and / or another suitable communication link). The local audio source 105 can comprise, for example, a mobile device (e.g., a smartphone, a tablet, a laptop computer) or another suitable audio component (e.g., a television, a desktop computer, an amplifier, a phonograph, a Blu-ray player, a memory storing digital media files). In some examples, the local audio source 105 includes local music libraries on a smartphone, a computer, a networked-attached storage (NAS), and / or another suitable device configured to store media files. In certain examples, one or more of the playback devices 110, NMDs 120, and / or control devices 130 comprise the local audio source 105. In other examples, however, the media playback system omits the local audio source 105 altogether. In some examples, the playback device 110a does not include an input / output 111 and receives all audio content via the network 104.

[0180] The playback device 110a further comprises electronics 112, a user interface 113 (e.g., one or more buttons, knobs, dials, touch-sensitive surfaces, displays, touchscreens), and one or more transducers 114 (referred to hereinafter as “the transducers 114”). The one or more transducers may include further upward-firing transducers and / or a horizontal-firingtransducer. The electronics 112 is configured to receive audio from an audio source (e.g., the local audio source 105) via the input / output 111, one or more of the computing devices 106a- c via the network 104 (Figure IB)), amplify the received audio, and output the amplified audio for playback via one or more of the transducers 114. The playback device 110a includes one or more microphones 115 (hereinafter referred to as “the microphones 115”). The microphones 115 may comprise a plurality of microphones, and may be arranged as a microphone array. The microphone array may be an asymmetrical microphone array. In certain examples, for instance, the playback device 110a having the microphones 115 can operate as an NMD configured to receive voice input from a user and correspondingly perform one or more operations based on the received voice input.

[0181] In the illustrated example of Figure 1C, the electronics 112 comprise one or more processors 112a (referred to hereinafter as “the processors 112a”), memory 112b, software components 112c, a network interface 112d, one or more audio processing components 112g (referred to hereinafter as “the audio components 112g”), one or more audio amplifiers 112h (referred to hereinafter as “the amplifiers 112h”), and power 112i (e.g., one or more power supplies, power cables, power receptacles, batteries, induction coils. Power-over Ethernet (POE) interfaces, and / or other suitable sources of electric power). In some examples, the electronics 112 optionally include one or more other components 112j (e.g., one or more sensors, video displays, touchscreens, battery charging bases).

[0182] The processors 112a can comprise clock-driven computing component(s) configured to process data, and the memory 112b can comprise a computer-readable medium (e.g., a tangible, non-transitory computer-readable medium, data storage loaded with one or more of the software components 112c) configured to store instructions for performing various operations and / or functions. The processors 112a are configured to execute the instructions stored on the memory 112b to perform one or more of the operations. The operations caninclude, for example, causing the playback device 110a to retrieve audio data from an audio source (e.g., one or more of the computing devices 106a-c (Figure IB)), and / or another one of the playback devices 110. In some examples, the operations further include causing the playback device 110a to send audio data to another one of the playback devices 110a and / or another device (e.g., one of the NMDs 120). Certain examples include operations causing the playback device 110a to pair with another of the one or more playback devices 110 to enable a multi-channel audio environment (e.g., a stereo pair, a bonded zone).

[0183] The processors 112a can be further configured to perform operations causing the playback device 110a to synchronize playback of audio content with another of the one or more playback devices 110. As those of ordinary skill in the art will appreciate, during synchronous playback of audio content on a plurality of playback devices, a listener will preferably be unable to perceive time-delay differences between playback of the audio content by the playback device 110a and the other one or more other playback devices 110. Additional details regarding audio playback synchronization among playback devices can be found, for example, in U.S. Patent No. 8,234,395, which was incorporated by reference above.

[0184] In some examples, the memory 112b is further configured to store data associated with the playback device 110a, such as one or more zones and / or zone groups of which the playback device 1 10a is a member, audio sources accessible to the playback device 110a, and / or a playback queue that the playback device 110a (and / or another of the one or more playback devices) can be associated with. The stored data can comprise one or more state variables that are periodically updated and used to describe a state of the playback device 110a. The memory 112b can also include data associated with a state of one or more of the other devices (e.g., the playback devices 110, NMDs 120, control devices 130) of the media playback system 100. In some examples, for instance, the state data is shared during predetermined intervals of time (e.g., every 5 seconds, every 10 seconds, every 60 seconds) among at least aportion of the devices of the media playback system 100, so that one or more of the devices have the most recent data associated with the media playback system 100.

[0185] The network interface 112d is configured to facilitate a transmission of data between the playback device 110a and one or more other devices on a data network such as, for example, the links 103 and / or the network 104 (Figure IB). The network interface 112d is configured to transmit and receive data corresponding to media content (e.g., audio content, video content, text, photographs) and other signals (e.g., non-transitory signals) comprising digital packet data including an Internet Protocol (IP)-based source address and / or an IP-based destination address. The network interface 112d can parse the digital packet data such that the electronics 112 properly receives and processes the data destined for the playback device 110a.

[0186] In the illustrated example of Figure 1C, the network interface 112d comprises one or more wireless interfaces 112e (referred to hereinafter as “the wireless interface 112e”). The wireless interface 112e (e.g., a suitable interface comprising one or more antennae) can be configured to wirelessly communicate with one or more other devices (e.g., one or more of the other playback devices 110, NMDs 120, and / or control devices 130) that are communicatively coupled to the network 104 (Figure IB) in accordance with a suitable wireless communication protocol (e.g., WiFi, Bluetooth, LTE). In some examples, the netw ork interface 112d optionally includes a wired interface 112f (e g., an interface or receptacle configured to receive a network cable such as an Ethernet, a USB-A, USB-C, and / or Thunderbolt cable) configured to communicate over a wired connection with other devices in accordance with a suitable wired communication protocol. In certain examples, the network interface 1 12d includes the wired interface 112f and excludes the wireless interface 112e. In some examples, the electronics 112 excludes the network interface 112d altogether and transmits and receives media content and / or other data via another communication path (e.g., the input / output 111).

[0187] The audio components 112g are configured to process and / or filter data comprising media content received by the electronics 112 (e g., via the input / output 111 and / or the network interface 112d) to produce output audio signals. In some examples, the audio processing components 112g comprise, for example, one or more digital -to-analog converters (DAC), audio preprocessing components, audio enhancement components, a digital signal processors (DSPs), and / or other suitable audio processing components, modules, circuits, etc. In certain examples, one or more of the audio processing components 112g can comprise one or more subcomponents of the processors 112a. In some examples, the electronics 112 omits the audio processing components 112g. In some examples, for instance, the processors 112a execute instructions stored on the memory 112b to perform audio processing operations to produce the output audio signals.

[0188] The amplifiers 112h are configured to receive and amplify the audio output signals produced by the audio processing components 112g and / or the processors 112a. The amplifiers 112h can comprise electronic devices and / or components configured to amplify audio signals to levels sufficient for driving one or more of the transducers 114. In some examples, for instance, the amplifiers 112h include one or more switching or class-D power amplifiers. In other examples, however, the amplifiers include one or more other types of power amplifiers (e.g., linear gain power amplifiers, class-A amplifiers, class-B amplifiers, class-AB amplifiers, class-C amplifiers, class-D amplifiers, class-E amplifiers, class-F amplifiers, class-G and / or class H amplifiers, and / or another suitable type of power amplifier). In certain examples, the amplifiers 112h comprise a suitable combination of two or more of the foregoing types of power amplifiers. Moreover, in some examples, individual ones of the amplifiers 112h correspond to individual ones of the transducers 114. In other examples, however, the electronics 112 includes a single one of the amplifiers 112h configured to output amplifiedaudio signals to a plurality of the transducers 114. In some other examples, the electronics 112 omits the amplifiers 112h.

[0189] The transducers 114 (e.g., one or more speakers and / or speaker drivers) receive the amplified audio signals from the amplifier 112h and render or output the amplified audio signals as sound (e.g., audible sound waves having a frequency between about 20 Hertz (Hz) and 20 kilohertz (kHz)). In some examples, the transducers 114 can comprise a single transducer. In other examples, however, the transducers 114 comprise a plurality of audio transducers. In some examples, the transducers 114 comprise more than one type of transducer. For example, the transducers 114 can include one or more low frequency transducers (e.g., subwoofers, woofers), mid-range frequency transducers (e.g., mid-range transducers, midwoofers), and one or more high frequency transducers (e.g., one or more tweeters). As used herein, “low frequency” can generally refer to audible frequencies below about 500 Hz, “midrange frequency” can generally refer to audible frequencies between about 500 Hz and about 2 kHz, and “high frequency” can generally refer to audible frequencies above 2 kHz. In certain examples, however, one or more of the transducers 114 comprise transducers that do not adhere to the foregoing frequency ranges. For example, one of the transducers 114 may comprise a mid-woofer transducer configured to output sound at frequencies between about 200 Hz and about 5 kHz.

[0190] By way of illustration, SONOS, Inc. presently offers (or has offered) for sale certain playback devices including, for example, a “SONOS ONE,” “MOVE,” “PLAYA,” “BEAM,” “PLAYBAR,” “PLAYBASE,” “PORT,” “BOOST,” “AMP,” and “SUB.” Other suitable playback devices may additionally or alternatively be used to implement the playback devices of example examples disclosed herein. Additionally, one of ordinary skilled in the art will appreciate that a playback device is not limited to the examples described herein or to SONOS product offerings. In some examples, for instance, one or more playback devices 110 compriseswired or wireless headphones (e.g., over-the-ear headphones, on-ear headphones, in-ear earphones). In other examples, one or more of the playback devices 110 comprise a docking station and / or an interface configured to interact with a docking station for personal mobile media playback devices. In certain examples, a playback device may be integral to another device or component such as a television, a lighting fixture, or some other device for indoor or outdoor use. In some examples, a playback device omits a user interface and / or one or more transducers. For example, FIG. ID is a block diagram of a playback device I lOp comprising the input / output 111 and electronics 112 without the user interface 113 or transducers 114.

[0191] Figure IE is a block diagram of a bonded playback device HOq comprising the playback device 110a (Figure 1C) sonically bonded with the playback device HOi (e.g., a subwoofer) (Figure 1A). In the illustrated example, the playback devices 110a and HOi are separate ones of the playback devices 110 housed in separate enclosures. In some examples, however, the bonded playback device HOq comprises a single enclosure housing both the playback devices 110a and HOi. The bonded playback device HOq can be configured to process and reproduce sound differently than an unbonded playback device (e.g., the playback device 110a of Figure 1C) and / or paired or bonded playback devices (e.g., the playback devices 1101 and 110m of Figure IB). In some examples, for instance, the playback device 110a is fullrange playback device configured to render low frequency, mid-range frequency, and high frequency audio content, and the playback device 1 lOi is a subwoofer configured to render low frequency audio content. In some examples, the playback device 110a, when bonded with the first playback device, is configured to render only the mid-range and high frequency components of a particular audio content, while the playback device HOi renders the low frequency component of the particular audio content. In some examples, the bonded playback device 1 lOq includes additional playback devices and / or another bonded playback device.c. Suitable Network Microphone Devices (NMDs)

[0192] Figure IF is a block diagram of the NMD 120a (Figures 1A and IB). The NMD 120a includes one or more voice processing components 124 (hereinafter "‘the voice components 124") and several components described with respect to the playback device 110a (Figure 1C) including the processors 112a, the memory 112b. and the microphones 115, the software components 112c, the network interface 112d, and power 112i. The NMD 120a optionally comprises other components also included in the playback device 110a (Figure 1C), such as the user interface 113 and / or the transducers 114. as well as other components 112j. In some examples, the NMD 120a is configured as a media playback device (e.g., one or more of the playback devices 110), and further includes, for example, one or more of the audio components 112g (Figure 1C), the amplifiers 114, and / or other playback device components. In certain examples, the NMD 120a comprises an Internet of Things (loT) device such as, for example, a thermostat, alarm panel, fire and / or smoke detector, etc. In some examples, the NMD 120a comprises the microphones 115, the voice processing components 124, and only a portion of the components of the electronics 112 described above with respect to Figure IB. In some examples, for instance, the NMD 120a includes the processor 112a and the memory 112b (Figure IB), while omitting one or more other components of the electronics 112. In some examples, the NMD 120a includes additional components (e.g., one or more sensors, cameras, thermometers, barometers, hygrometers).

[0193] In some examples, an NMD can be integrated into a playback device. Figure 1G is a block diagram of a playback device 1 lOr comprising an NMD 120d. The playback device 1 lOr can comprise many or all of the components of the playback device 110a and further include the microphones 115 and voice processing components 124 (Figure IF). The playback device 11 Or optionally includes an integrated control device 130c. The control device 130c can comprise, for example, a user interface (e.g., the user interface 113 of Figure IB) configuredto receive user input (e.g., touch input, voice input) without a separate control device. In other examples, however, the playback device 1 lOr receives commands from Ir control device (e.g., the control device 130a of Figure IB).

[0194] Referring again to Figure IF, the microphones 115 are configured to acquire, capture, and / or receive sound from an environment (e.g., the environment 101 of Figure 1A) and / or a room in which the NMD 120a is positioned. The received sound can include, for example, vocal utterances, audio played back by the NMD 120a and / or another playback device, background voices, ambient sounds, etc. The microphones 115 convert the received sound into electrical signals to produce microphone data. The voice processing components 124 receive and analyzes the microphone data to determine whether a voice input is present in the microphone data. The voice input can comprise, for example, an activation word followed by an utterance including a user request. As those of ordinary' skill in the art will appreciate, an activation word is a word or other audio cue that signifying a user voice input. For instance, in query ing the AMAZON® VAS, a user might speak the activation word "Alexa." Other examples include "Ok, Google" for invoking the GOOGLE® VAS and "Hey, Siri" for invoking the APPLE® VAS.

[0195] After detecting the activation word, voice processing components 124 monitor the microphone data for an accompanying user request in the voice input. The user request may include, for example, a command to control a third-party device, such as a thermostat (e.g., NEST® thermostat), an illumination device (e.g., a PHILIPS HUE ® lighting device), or a media playback device (e.g., a Sonos® playback device). For example, a user might speak the activation word "Alexa" followed by the utterance ‘‘set the thermostat to 68 degrees” to set a temperature in ahome (e.g., the environment 101 of Figure 1 A). The user might speak the same activation word followed by the utterance “turn on the living room” to turn on illumination devices in a living room area of the home. The user may similarly speak an activation wordfollowed by a request to play a particular song, an album, or a playlist of music on a playback device in the home. d. Suitable Control Devices

[0196] Figure 1H is a partially schematic diagram of the control device 130a (Figures 1A and IB). As used herein, the term ’control device” can be used interchangeably with “controller” or “control system.” Among other features, the control device 130a is configured to receive user input related to the media playback system 100 and, in response, cause one or more devices in the media playback system 100 to perform an action(s) or operation(s) corresponding to the user input. In the illustrated example, the control device 130a comprises a smartphone (e.g., an iPhone™, an Android phone) on which media playback system controller application software is installed. In some examples, the control device 130a comprises, for example, a tablet (e.g., an iPad™), a computer (e.g., a laptop computer, a desktop computer), and / or another suitable device (e.g., a television, an automobile audio head unit, an loT device). In certain examples, the control device 130a comprises a dedicated controller for the media playback system 100. In other examples, as described above with respect to Figure 1G, the control device 130a is integrated into another device in the media playback system 100 (e.g., one more of the playback devices 110, NMDs 120, and / or other suitable devices configured to communicate over a network).

[0197] The control device 130a includes electronics 132, a user interface 133, one or more speakers 134, and one or more microphones 135. The electronics 132 comprise one or more processors 132a (referred to hereinafter as “the processors 132a”), a memory 132b, software components 132c, and a network interface 132d. The processor 132a can be configured to perform functions relevant to facilitating user access, control, and configuration of the media playback system 100. The memory 132b can comprise data storage that can be loaded with one or more of the software components executable by the processor 132a to perform thosefunctions. The software components 132c can comprise applications and / or other executable software configured to facilitate control of the media playback system 100. The memory 112b can be configured to store, for example, the software components 132c, media playback system controller application software, and / or other data associated with the media playback system 100 and the user.

[0198] The network interface 132d is configured to facilitate network communications between the control device 130a and one or more other devices in the media playback system 100, and / or one or more remote devices. In some examples, the network interface 132d is configured to operate according to one or more suitable communication industry standards (e.g., infrared, radio, wired standards including IEEE 802.3, wireless standards including IEEE 802.11a, 802.11b, 802.11g, 802.11n, 802.11ac, 802.15, 4G, LTE). The network interface 132d can be configured, for example, to transmit data to and / or receive data from the playback devices 110, the NMDs 120, other ones of the control devices 130, one of the computing devices 106 of Figure IB, devices comprising one or more other media playback systems, etc. The transmitted and / or received data can include, for example, playback device control commands, state variables, playback zone and / or zone group configurations. For instance, based on user input received at the user interface 133, the network interface 132d can transmit a playback device control command (e g., volume control, audio playback control, audio content selection) from the control device 130 to one or more of the playback devices 1 10. The network interface 132d can also transmit and / or receive configuration changes such as, for example, adding / removing one or more playback devices 110 to / from a zone, adding / removing one or more zones to / from a zone group, forming a bonded or consolidated player, separating one or more playback devices from a bonded or consolidated player, among others.

[0199] The user interface 133 is configured to receive user input and can facilitate control of the media playback system 100. The user interface 133 includes media content art 133a (e.g..album art, lyrics, videos), a playback status indicator 133b (e.g., an elapsed and / or remaining time indicator), media content information region 133c, a playback control region 133d, and a zone indicator 133e. The media content information region 133c can include a display of relevant information (e.g., title, artist, album, genre, release year) about media content currently playing and / or media content in a queue or playlist. The playback control region 133d can include selectable (e.g., via touch input and / or via a cursor or another suitable selector) icons to cause one or more playback devices in a selected playback zone or zone group to perform playback actions such as, for example, play or pause, fast forward, rewind, skip to next, skip to previous, enter / exit shuffle mode, enter / exit repeat mode, enter / exit cross fade mode, etc. The playback control region 133d may also include selectable icons to modify equalization settings, playback volume, and / or other suitable playback actions. In the illustrated example, the user interface 133 comprises a display presented on atouch screen interface of a smartphone (e.g., an iPhone™, an Android phone). In some examples, however, user interfaces of vary ing formats, styles, and interactive sequences may alternatively be implemented on one or more network devices to provide comparable control access to a media playback system.

[0200] The one or more speakers 134 (e g., one or more transducers) can be configured to output sound to the user of the control device 130a. In some examples, the one or more speakers comprise individual transducers configured to correspondingly output low frequencies, midrange frequencies, and / or high frequencies. In some examples, for instance, the control device 130a is configured as a playback device (e.g., one of the playback devices 1 10). Similarly, in some examples the control device 130a is configured as an NMD (e.g., one of the NMDs 120), receiving voice commands and other sounds via the one or more microphones 135.

[0201] The one or more microphones 135 can comprise, for example, one or more condenser microphones, electret condenser microphones, dynamic microphones, and / or other suitable types of microphones or transducers. In some examples, two or more of the microphones 135are arranged to capture location information of an audio source (e.g., voice, audible sound) and / or configured to facilitate filtering of background noise. Moreover, in certain examples, the control device 130a is configured to operate as playback device and an NMD. In other examples, however, the control device 130a omits the one or more speakers 134 and / or the one or more microphones 135. For instance, the control device 130a may comprise a device (e.g., a thermostat, an loT device, a network device) comprising a portion of the electronics 132 and the user interface 133 (e.g., a touch screen) without any speakers or microphones.III. Magnet Assembly

[0202] As previously discussed, the present disclosure relates to the manufacture of a magnet assembly that can form part of a transducer. The magnet assembly, once part of a transducer, may be incorporated into a playback device, a network microphone device or a control device such as one of those devices discussed above in relation to Figures 1 A-H.

[0203] Figure 2 depicts an example magnet assembly 200, which may also be referred to as a magnet stack. This particular magnet assembly 200 comprises two magnets - a first magnet 202 (also known as a first magnetized portion or element) and a second magnet 204 (also known as a second magnetized portion or element). The first magnetized portion 202 can be formed by magnetizing a first magnetizable portion or element of the magnet assembly 200, for example, by exposing the first magnetizable portion to a first magnetic field, such as that generated by a first magnetization coil. Similarly, the second magnetized portion 204 can be formed by magnetizing a second magnetizable portion or element of the magnet assembly 200, for example, by exposing the second magnetizable portion to a second magnetic field, such as that generated by a second magnetization coil. The magnet assembly 200 of this example further comprises a spacer element 210 arranged between the first and second magnetized portions 202, 204. Prior to magnetization, a first magnetizable element can be affixed, via an adhesive, such as glue, to one side of the spacer element 210, and a second magnetizableelement can be affixed to the other side of the spacer element 210. In this case, the first magnetizable element is the first magnetizable portion that becomes the first magnetized portion 202 once magnetized. Similarly, the second magnetizable element is the second magnetizable portion that becomes the second magnetized portion 204 once magnetized.

[0204] In this example, the first magnetized portion 202 and the second magnetized portion 204 are magnetized having an inverted polarity. For example, a north pole 202a of the first magnetized portion 202 is arranged facing a north pole 204a of the second magnetized portion 204. A south pole 202b of the first magnetized portion 202 is arranged facing away from the second magnetized portion 204, and a south pole 204b of the second magnetized portion 204 is arranged facing away from the first magnetized portion 202. The first magnetized portion 202 is therefore generally magnetized along a first magnetic axis 206 of the first magnetized portion 202 and second magnetized portion 204 is generally magnetized along a second magnetic axis 208 of the second magnetized portion 204. In this configuration, the magnet assembly 200 defines a longitudinal axis 212 that is generally parallel to the first and second magnetic axes 206, 208.

[0205] The example magnet assembly 200 may form part of a transducer by additionally including a voice coil. For example, a voice coil may extend around the magnet assembly 200 in the region where the first and second magnetized portions 202, 204 have opposing polarity, such as around the spacer element 210. As is well known, when a current is passed through the voice coil, a magnetic field is generated by the voice coil, which interacts with the magnetic fields of the first and second magnetized portions 202, 204. This interaction causes the voice coil to be displaced, such as along the longitudinal axis 212 of the magnet assembly 200. The voice coil can be connected to a diaphragm / membrane, and thereby cause displacement of the diaphragm, causing a sound wave to be generated.

[0206] Figure 3 depicts an example process for forming a magnet assembly prior to magnetization. It will be appreciated that some steps may be performed in different orders to those which are described below, and some steps may be performed simultaneously. The following steps may occur at one or more workstations, such as one or more workstations of a manufacturing facility.

[0207] In a first step 302, a spacer element 210 is received in an enclosure 304. From here, an adhesive, such as glue, is received on one side of the spacer element 210, while the spacer element 210 is within the enclosure 304.

[0208] In a second step 306, a first magnetizable element / portion 308 of the magnet assembly is received in the enclosure 304, and on top of the adhesive so that the first magnetizable element 308 can be adhered to one side of the spacer element 210. The adhesive can then bond the first magnetizable element 308 and the spacer element 210 together. The adhesive may be a contact adhesive. In some examples, step 306 may comprise curing the adhesive.

[0209] In a third step 310, the first magnetizable element 308 and the spacer element 210 are removed from the enclosure 304. As shown, the first magnetizable element 308 and the spacer element 210 are bonded together.

[0210] In a fourth step 312, a second magnetizable element / portion 314 is received in an enclosure 316.

[0211] In a fifth step 318, an adhesive, such as glue, is received on one side of the second magnetizable element 314, while the second magnetizable element 314 is within the enclosure 316.

[0212] In a sixth step 320, the spacer element 210 and first magnetizable element 308 are received within the enclosure 316, so that the second magnetizable element 314 can be adhered to the other, opposite side of the spacer element 210. The adhesive can then bond the secondmagnetizable element 314 and the spacer element 210 together. In some examples, optional step 322 may comprise curing the adhesive.

[0213] In step 324. the magnet assembly is removed from the enclosure 316, and the magnet assembly is formed. As shown, the magnet assembly comprises the first magnetizable element 308, the spacer element 210 and the second magnetizable element 314. From here, the magnet assembly may be magnetized.

[0214] Figure 4A depicts a schematic perspective view of at least part of an example magnetization device 400 for magnetizing a magnet assembly 402 at a first time. Figure 5A depicts a schematic side view of the example magnetization device 400 of Figure 4A at the first time. The magnet assembly may be the same as, or similar to, the magnet assembly prepared following the process described above in relation to Figure 3. As such, prior to being introduced into the magnetization device, 400, the magnet assembly 402 is in an assembled but unmagnetized state. As will be discussed in more detail below, the magnetization device 400 may also be used to magnetize monolithic magnetizable elements.

[0215] As shown in Figure 4A, the magnetization device 400 comprises a first magnetization coil 404 configured to generate a first magnetic field for magnetizing a first magnetizable portion / element 408 of the magnet assembly 402. The device 400 further includes a second magnetization coil 406 spaced apart from the first magnetization coil 404 and configured to generate a second magnetic field for magnetizing a second magnetizable portion / element 410 of the magnet assembly. Figure 4A further depicts a spacer element 412, affixed to and arranged between the first and second magnetizable elements 408, 410. In some examples, and as will be discussed below, the spacer element 412 may be omitted. It will be appreciated that the thicknesses / lengths, as measured along the longitudinal axis, and relative thicknesses of the spacer element 412, and the first and second magnetizable elements 408, 410 may differ to that which is illustrated in the Figures.

[0216] The first and second magnetization coils 404, 406 may be housed within separate enclosures. For example, individual turns of the coils are not depicted in Figure 4A. In some examples, one or both enclosures housing the first and second magnetization coils 404, 406 may comprise or define a fixture 422 to hold the magnet assembly 402 in place. In other examples, one or more fixtures may be located on top of the enclosures. In another example, a single fixture may be located between the first and second magnetization coils 404, 406. In an example, a receptacle or holder may be formed in the fixture to hold / locate the magnet assembly during magnetization. Figure 4A, for example, depicts the magnet assembly 402 located within a receptacle 418 of a fixture 422, the fixture 422 forming part of an enclosure housing the second magnetization coil 406. As shown, the fixture 422 is located between the first and second magnetization coils 404, 406.

[0217] The wires forming the first and second magnetization coils 404, 406 can be wound around a winding axis for the coils 404, 406. For example, the wire(s) forming the first magnetization coil 404 may be would around a first winding axis 414, and the wire(s) forming the second magnetization coil 406 may be wound around a second winding axis 416. The winding axes 404, 406 are parallel to each other, in this example, and are also parallel to a longitudinal axis 420 of the magnet assembly 402.

[0218] Figure 4A depicts the magnet assembly 402 arranged at least partially between the first and second magnetization coils. In some examples, at least one of the first magnetization coil 404 or the second magnetization coil 406 is moveable tow ards the other magnetization coil 404, 406. For example, one or both of the magnetization coils 404, 406 may be moved via one or more actuators, such as pneumatic actuators. Figure 4B depicts the magnetization device 400 of Figure 4A at a second, later, time, after one or both of the magnetization coils 404, 406 have been moved relative to each other. For example, the space between the first and second magnetization coils 404, 406 may be decreased, and in some cases, minimized. Figure 5Bdepicts a schematic side view of the example magnetization device 400 of Figure 4B at the second time. In other examples, the first and second magnetization coils 404. 406 are not moveable relative to each other.

[0219] Once the magnet assembly 402 is suitably positioned between the first and second magnetization coils 404, 406, currents may be applied to the first and second magnetization coils 404, 406 by one or more current sources.

[0220] In particular, to generate the first magnetic field, a current source 504 (shown in Figures 5A and 5B), applies a first current to the first magnetization coil 404 to generate a first magnetic field. In this particular example, and in absence of all other magnetic fields, the first current is applied such that the first magnetic field extends in a first direction, such as towards or away from the second magnetization coil 406. For example, a north pole of the first magnetic field may point towards the second magnetization coil 406. Similarly, to generate the second magnetic field, the current source 504 applies a second current to the second magnetization coil 406 to generate a second magnetic field. In other examples, the currents may be applied by different current sources, such as a first and second current source. In the present example, the first and second currents have the same magnitude and are applied at the same time. In this particular example, and in absence of all other magnetic fields, the second current is applied such that the second magnetic field extends in a second direction opposite to the first direction. For example, a north pole of the second magnetic field may point towards the first magnetization coil 404. The first and second magnetic fields therefore point in opposite directions, such as both towards the magnet assembly 402 (as in the example of Figure 5B) or both away from the magnet assembly 402 (when the direction of the currents are reversed).

[0221] As an example, Figure 5B depicts the first magnetic field generally extending in a first direction away from the first magnetization coil 404, such as towards the second magnetization coil 406. In this example, the arrow 508 points from the south pole to the northpole of the first magnetic field generated by the first magnetization coil 404. Similarly. Figure 5B depicts the second magnetic field generally extending in a second direction away from the second magnetization coil 406. such as towards the first magnetization coil 404. In this example, the arrow 510 points from the south pole to the north pole of the second magnetic field generated by the second magnetization coil 406. It will be understood that at distances further away from the magnetization coils and in directions perpendicular to the winding axes 414, 416 of the first and second magnetization coils 404, 406, the field lines will bend, and will no longer be parallel to the winding axes 414, 416. For example, within the spacer element 412, the field lines (and therefore magnetic flux), may bend and extend substantially perpendicular to the longitudinal axis 420.

[0222] Figure 6 depicts a computer simulation of the first and second magnetic fields and their interaction with each other. In this particular example, the first current is applied such that the part of the first magnetizable portion / element 408 closest to the first magnetization coil 404 is magnetized to be the south pole of the first magnetizable portion / element 408, and the part of the first magnetizable portion / element 408 furthest away from the first magnetization coil 404 is magnetized to be the north pole of the first magnetizable portion / element 408. Once magnetized, the first magnetizable portion / element may be considered a first magnetized portion / element. Similarly, the second current is applied such that the part of the second magnetizable portion / element 410 closest to the second magnetization coil 406 is magnetized to be the south pole of the second magnetizable portion / element 410, and the part of the second magnetizable portion / element 410 furthest away from the second magnetization coil 406 is magnetized to be the north pole of the second magnetizable portion / element 410. Once magnetized, the second magnetizable portion / element may be considered a second magnetized portion / element. The magnet assembly may therefore be in a magnetized state, and have the same form as that depicted in Figure 2.

[0223] As shown in Figure 6, due to the interaction of the first and second magnetic fields, as well as the presence of anon-magnetizable spacer element 412, the magnetic field lines bend out of the magnet assembly, and away from being substantially parallel to the winding axes 414, 416 to being perpendicular to the winding axes 414, 416. For example, in a generally cylindrical magnet assembly, the magnetic field lines may bend radially outwards from the magnet assembly. Thus, in some cases, the magnetized portions / elements may not be fully axially magnetized, since the magnetic field can bend with the magnetized portions / elements.

[0224] In the present case, due to the first and second currents having the same magnitude and a generally symmetrical arrangement about the centre of the magnet assembly or the spacer in this example, the first magnetic field has a first field strength at the first magnetizable portion that is substantially equal to a second field strength of the second magnetic field at the second magnetizable portion. For example, at point A within the first magnetizable portion 408, the magnetic field strength is equal to the magnetic field strength at point B within the second magnetizable portion 410, where points A and B are both the same distance from their respective magnetization coils 404, 406.

[0225] Figure 7 depicts a fixture 700 for holding one or more magnet assemblies in place during magnetization. In this example, the fixture 700 may be arranged between the two magnetization coils, and thus is separate from any enclosures housing the magnetization coils. Despite being separate from the magnetization coils, the fixture 700 may still form part of the magnetization device 400.

[0226] In some examples, a second fixture may hold or support one end of the magnet assembly while the fixture 700 holds another end of the magnet assembly. In this example, a single fixture holds the magnet assembly in place during magnetization.

[0227] Figure 7 depicts an example magnet assembly 704 arranged within a holder / receptacle 702. The fixture 700 of this example includes a plurality ofholders / receptacles 702 for holding / receiving a plurality of magnet assemblies. Accordingly, one or more magnet assemblies can be positioned between the magnetization coils and be simultaneously magnetized. In use, an actuator of the device may position the magnet assembly 704 into the holder / receptacle 702, or a human operator may manually position the magnet assembly 704 in place.

[0228] In the example magnet assembly of Figure 2, two magnetizable elements are separated by and affixed to a spacer element. In other examples, however, a spacer element may not be present. Instead, a first magnetizable element may be affixed to a second magnetizable element, and each magnetizable element may be magnetized. As in Figure 2, the two magnetizable elements are magnetized to have an inverted polarity, so that like poles are arranged adjacent each other (and opposite ends of the magnet assembly have like poles).

[0229] Figure 8A therefore depicts an example magnet assembly 800, in which a first magnetizable element 802 has been affixed to a second magnetizable element 804, via an adhesive, for example. In Figure 8A, the first magnetizable element 802 defines a first magnetizable portion of the magnet assembly 800 and the second magnetizable element 804 defines a second magnetizable portion of the magnet assembly 800. At this point in time, the magnet assembly is in an unmagnetized state.

[0230] Figure 8B depicts the magnet assembly 800 after magnetization by first and second magnetization coils. The first magnetizable element 802 is magnetized (forming a first magnetized portion 806) by a first magnetization coil, and the second magnetizable element 804 is magnetized (forming a second magnetized portion 808) by a second magnetization coil. The first and second magnetizable elements 802, 804 can be magnetized in opposite directions by first and second magnetization coils, as discussed earlier. For example, the magnetization device 400 of Figures 4A-5B can be used to magnetize the magnet assembly 800 of Figure 8A.

[0231] Accordingly, as shown, the first and second magnetized portions 806, 808 have inverted polarities. For example, a north pole 806a of the first magnetized portion 806 is arranged facing a north pole 808a of the second magnetized portion 808. A south pole 806b of the first magnetized portion 806 is arranged facing away from the second magnetized portion 808, and a south pole 808b of the second magnetized portion 808 is arranged facing away from the first magnetized portion 806. In this example, opposite ends, such as terminal ends, of the magnet assembly 900’ have the same polarity.

[0232] In general terms, a south pole may be referred to as a first pole, and a north pole may be referred to as a second pole (the first and second poles being different).

[0233] A region 810 may be formed between the first and second magnetized portions 806, 808. Within the region 810, magnetic flux, such as the magnetic flux of the first and second magnetized portions extends substantially perpendicular to a longitudinal axis 812 of the magnet assembly 800. During magnetization, the magnetic flux of the first and second magnetic fields of the first and second magnetization coils would also extend substantially perpendicular to the longitudinal axis 812. In contrast, magnetic flux within the first and second magnetized portions 806, 808 may be substantially orientated along the longitudinal axis 812. The magnetic flux within the first magnetized portion 806 may extend in the opposite direction to the magnetic flux within the second magnetized portion 808. Accordingly, the region 810 may be defined as the part of the magnet assembly 800 that has a magnetic flux orientated substantially perpendicular to the longitudinal axis 812.

[0234] The region 810 is formed from a part of the first magnetizable element 802 and part of the second magnetizable element 804. In this particular example, the region 810 is located centrally between an outer end 806c of the first magnetized portion 806 and an outer end 808c of the second magnetized portion 808. In this case, the outer ends 806c. 808c are terminal ends of the magnet assembly 800 because no further magnetizable elements are affixed to either ofthe outer ends 806c, 808c. In other examples, a third magnetizable element is affixed to one of the first or second magnetizable elements 802, 804 and a third magnetization coil may similarly magnetize the third magnetizable element to form a third magnetized portion and a second region, the second region being located between the third magnetized portion and one of the first or second magnetized portions 806, 808.

[0235] The resulting magnet assembly 800 shown in Figure 8B resembles the magnet assembly of Figure 2, but without a physical spacer element. Instead, the region 810 may resemble the spacer element.

[0236] As an alternative to the example magnet assembly 800 of Figures 8 A and 8B, a single (monolithic) magnetizable element may be magnetized by two or more magnetization coils to provide a monolithic magnet that has a similar form to the magnet assembly of Figure 8B once magnetized. In some cases, a monolithic magnet may be referred to as magnet assembly since it may effectively comprise two or more oppositely arranged “magnets” in the form of two or more magnetized portions each separated from each other by a region of lower flux.

[0237] Figure 9A therefore depicts an example monolithic magnetizable element 900. At this point in time, the monolithic magnetizable element 900 is in an unmagnetized state.

[0238] Figure 9B depicts the monolithic magnetizable element 900 after magnetization by first and second magnetization coils. The monolithic magnetizable element 900 in a magnetized state may be known as a monolithic magnet 900’ or a monolithic magnetized element 900’. To provide a monolithic magnet 900’ having the polarities shown, a first magnetizable portion 902 of the monolithic magnetizable element 900 is magnetized (forming a first magnetized portion 906) by a first magnetization coil, and a second magnetizable portion 904 of the monolithic magnetizable element 900 is magnetized (forming a second magnetized portion 908) by a second magnetization coil. The first and second magnetizable portions 902. 904 can be magnetized in opposite directions by the first and second magnetization coils, as discussedearlier. For example, the magnetization device 400 of Figures 4A-5B can be used to magnetize the monolithic magnetizable element 900 of Figure 9A.

[0239] Accordingly, as shown, the first and second magnetized portions 906, 908 have inverted polarities. For example, a north pole 906a of the first magnetized portion 906 is arranged facing a north pole 908a of the second magnetized portion 908 (or vice versa). A south pole 906b of the first magnetized portion 906 is arranged facing away from the second magnetized portion 908, and a south pole 908b of the second magnetized portion 908 is arranged facing away from the first magnetized portion 906 (or vice versa).

[0240] As discussed in the example of Figure 8B, a region 910 may be formed between the first and second magnetized portions 906, 908. Within the region 910, magnetic flux, such as the magnetic flux of the first and second magnetized portions, extends substantially perpendicular to a longitudinal axis 912 of the monolithic magnet 900’. During magnetization, the magnetic flux of the first and second magnetic fields of the first and second magnetization coils would also extend substantially perpendicular to the longitudinal axis 912. In contrast, magnetic flux within the first and second magnetized portions 906, 908 may be substantially orientated along the longitudinal axis 912. The magnetic flux within the first magnetized portion 906 may extend in the opposite direction to the magnetic flux within the second magnetized portion 908.

[0241] The region 910 is formed from a part of the first magnetizable portion 902 and part of the second magnetizable portion 904. In this particular example, the region 910 is located centrally between an outer end 906c of the first magnetized portion 906 and an outer end 908c of the second magnetized portion 908. In this case, the outer ends 906c, 908c are terminal ends of the monolithic magnet 900’. In other examples, a third magnetization coil may similarly magnetize a third magnetizable portion of the monolithic magnetizable element 900 to form a third magnetized portion and a second region, the second region being located between thethird magnetized portion and one of the first or second magnetized portions 906, 908. An example of this is depicted in Figures 18A and 18B.

[0242] The resulting monolithic magnet 900’ shown in Figure 9B resembles the magnet assembly of Figure 2, but without a physical spacer element and without any physical boundaries between separate magnetized portions.

[0243] Figure 10 depicts a cross section through a first magnetization coil 404, a second magnetization coil 406 and the monolithic magnetizable element 900 of Figure 9A during magnetization. Figure 10 also shows a computer simulation of the first and second magnetic fields of the first and second magnetization coils 404, 406 and their interaction with each other through the monolithic magnetizable element 900. In particular, Figure 10 shows the magnetic flux density at various points within monolithic magnetizable element 900 as a result of the first and second magnetic fields applied by the first and second magnetization coils 404, 406 respectively.

[0244] As shown, through a part of the monolithic magnetizable element 900 (which forms the first magnetized portion 906 after being magnetized) the magnetic flux is generally orientated along the longitudinal axis 912. Similarly, through another part of the magnetizable element 900 (which forms the second magnetized portion 908 after being magnetized) the magnetic flux is generally orientated along the longitudinal axis 912. The magnetic flux in these two parts is orientated in the opposite directions, resulting in the first and second magnetized portions 906, 908 having inverted polarities.

[0245] As a result of the oppositely arranged magnetic fields from the first and second magnetization coils 404, 406, the magnetic flux in the region 910 bends away from being orientated along the longitudinal axis 912 and is instead orientated perpendicular to the longitudinal axis 912. For example, in a generally cylindrical monolithic magnetizable element900, the magnetic field lines may bend radially outwards from the monolithic magnetizable element 900.

[0246] As is further shown in Figure 10, at a certain point 910a within the region 910, the magnetic fields balance and therefore the resultant magnetic field strength is approximately zero, such that there is no or minimal magnetic flux. This point or area may be known as a neutral zone 910a. In this particular case, the neutral zone 910a is located along a midpoint of a length 1002 of the region, the length 1002 being measured in a direction parallel to the longitudinal axis 912.

[0247] In this particular example, the first current is applied to the first magnetization coil 404 such that the part of the first magnetized portion 906 closest to the first magnetization coil 404 is magnetized to be the south pole of the first magnetized portion 906, and the part of the first magnetized portion 906 furthest away from the first magnetization coil 404 is magnetized to be the north pole of the first magnetized portion 906, as shown in Figure 9B. Similarly, the second current is applied to the second magnetization coil 406 such that the part of the second magnetized portion 908 closest to the second magnetization coil 406 is magnetized to be the south pole of the second magnetized portion 908, and the part of the second magnetized portion 908 furthest away from the second magnetization coil 406 is magnetized to be the north pole of the second magnetized portion, as shown in Figure 9B.

[0248] Although Figure 10 depicts a monolithic magnetizable element, it will be appreciated that the same principles apply to examples in which the magnet assembly 800 of Figure 8A is magnetized.

[0249] As briefly mentioned, the region 910 may have a length 1002 measured in a direction parallel to the longitudinal axis 912. For example, the length 1002 may be measured through a center of the region 910 along the longitudinal axis 912, such as between two boundaries wherethe magnetic flux becomes closer to being orientated perpendicular to the longitudinal axis 912 than it is orientated parallel to the longitudinal axis 912.

[0250] The monolithic magnet 900’ and magnetizable element 900 has a second length 1004 measured along the longitudinal axis 912 between outer ends of the first and second magnetized portions.

[0251] As mentioned, the length 1002 of the region 910 can affect the output of a transducer that incorporates the monolithic magnet. Controlling certain parameters or arrangements of the magnetization device can allow the length 1002 of the region 910 to be set, as desired. This can be achieved in general terms by controlling a magnetic reluctance external to the monolithic magnet adjacent the region 910 and / or a magnetic flux through the region 910.

[0252] A first example of establishing a desired length 1002 of the region 910 involves controlling the magnetic flux through the region 910 by controlling a distance between first and second magnetization coils 404, 406 along the longitudinal axis 912 of the monolithic magnetizable element 900. The length 1002 of the region 910 is therefore based on the distance between the magnetization coils 404, 406.

[0253] To illustrate, Figure 11 depicts a side view of an example magnetization device 400 where the first and second magnetization coils 404, 406 are separated by a distance 1102. In an example, moving the first and second magnetization coils 404, 406 closer together decreases the length 1002 of the region 910 by increasing the magnetic flux and flux density through the region 910. Conversely, moving the first and second magnetization coils 404, 406 further apart increases the length 1002 of the region 910. Setting the distance 1102 to a particular distance, can allow the region 910 to be formed with a required length 1002 once the monolithic magnetizable element 900 has been magnetized.

[0254] Figure 11 additionally shows the first magnetic field 1104 generated by the first magnetization coil 404 and the second magnetic field 1106 generated by the secondmagnetization coil 406. In the region 910, the magnetic flux of the first and second magnetic fields 1104, 1006 is substantially orientated perpendicular to the longitudinal axis 912.

[0255] A second example of establishing a desired length 1002 of the region 910 involves controlling the magnetic flux through the region 910 by controlling magnitudes of the first and second currents applied to the first and second magnetization coils 404, 406 respectively. The length 1002 of the region 910 is therefore based on the magnitudes. For example, a current source (not shown) can apply a first current to the first magnetization coil 404 and a second current to the second magnetization coil 406 to form the region 910 with a required length 1002 once the monolithic magnetizable element 900 has been magnetized.

[0256] A third example of establishing a desired length 1002 of the region 910 involves controlling the magnetic flux through the region 910 by arranging at least one further magnetization coil between the first and second magnetization coils 404, 406 to generate at least one further magnetic field that extends through the monolithic magnetizable element 900 where the region 910 is to be formed. The further magnetization coil(s) are arranged such that their winding axes are substantially perpendicular to the winding axes of the first and second magnetization coils 404, 406, and are therefore arranged substantially perpendicular to the longitudinal axis 912 of the monolithic magnetizable element 900.

[0257] To illustrate, Figure 12 depicts a side view of an example magnetization device 400 that further includes at least one additional magnetization coil arranged around the monolithic magnetizable element 900, each additional magnetization coil having a winding axis is substantially perpendicular to the winding axes 414, 416 of the first and second magnetization coils 404, 406. In this particular example, there is a third magnetization coil 1202 having a winding axis 1206, and a fourth magnetization coil 1204 having a winding axis 1208.

[0258] The third magnetization coil 1202 has a cross-sectional width 1210 (in this case a diameter) measured parallel to the longitudinal axis 912. and the fourth magnetization coil 1204has a cross-sectional width 1212 (in this case a diameter) measured parallel to the longitudinal axis 912. The length 1002 of the region 910 may be based on a cross-sectional widths 1210, 1212 (assuming current remains constant for different cross-sectional widths). For example, increasing the cross-sectional widths 1210, 1212 can increase the length 1002 of the region 910 (such as for a low reluctance material) by distributing the magnetic flux through the monolithic magnetizable element 900 over a greater length.

[0259] In this example, currents are applied to the third and fourth magnetization coils such that the magnetic field lines of the magnetic fields generated by the third and fourth magnetization coils point in the same direction as the magnetic field lines of the first and second magnetic fields passing through the region 910.

[0260] In the example of Figure 12, the third and fourth magnetization coils 1202, 1204 are arranged on opposite sides of the monolithic magnetizable element 900 to provide a symmetric distribution of magnetic flux through the region 910. In examples comprising more than one further magnetization coil, the further magnetization coils may be evenly spaced / distributed around the monolithic magnetizable element 900 to provide a symmetric distribution of magnetic flux through the region 910. In other examples, there may only be one further magnetization coil.

[0261] A fourth example of establishing a desired length 1002 of the region 910 involves controlling the magnetic flux through the region 910 by arranging at least one permanent magnet between the first and second magnetization coils 404, 406, where each permanent magnet has a magnetic field that extends through the monolithic magnetizable element 900 where the region 910 is to be formed. The permanent magnets(s) are arranged such that their magnetic axes are substantially perpendicular to the winding axes of the first and second magnetization coils 404, 406. and are therefore arranged substantially perpendicular to the longitudinal axis 912 of the monolithic magnetizable element 900.

[0262] Although not shown in a separate Figure, the arrangement involving one or more permanent magnets may resemble that of Figure 12, with the third and fourth magnetization coils replaced by one or more permanent magnets. Accordingly, the magnetization device 400 may include at least one permanent magnet arranged around the monolithic magnetizable element 900. Each permanent magnet also has a cross-sectional width measured parallel to the longitudinal axis 912 and the length 1002 of the region 910 is based on a cross-sectional width(s) of the one or more permanent magnets. For example, increasing the cross-sectional width(s) can increase the length 1002 of the region 910 by increasing the magnetic flux that extends into or out of the monolithic magnetizable element 900 over a greater length.

[0263] In examples, the one or more permanent magnets are arranged such that the magnetic field lines of the magnetic fields of the one or more permanent magnets point in the same direction as the magnetic field lines of the first and second magnetic fields passing through the region 910. In the same way discussed above for the further magnetization coils, the one or more permanent magnets may be spaced around the monolithic magnetizable element 900 to provide a symmetric distribution of magnetic flux through the region 910.

[0264] A fifth example of establishing a desired length 1002 of the region 910 involves controlling the magnetic reluctance external to the monolithic magnet adjacent the region 910 by arranging magnetizable material between the first and second magnetization coils 404, 406 and at least partially around the monolithic magnetizable element 900. The length 1002 of the region 910 is based on a cross-sectional width of the magnetizable material. The magnetizable material forms a low reluctance path for the magnetic fields from the first and second magnetization coils 404, 406.

[0265] To illustrate. Figure 13 depicts a side view of an example magnetization device 400 including magnetizable material 1302 extending at least partially around the monolithic magnetizable element 900. Figure 14 depicts a perspective view of the example magnetizationdevice 400 of Figure 13. Although the magnetizable material 1302 of this example fully extends around the monolithic magnetizable element 900 (with the monolithic magnetizable element 900 being located within or through an aperture 1402), in other examples, the magnetizable material 1302 may only partially extend around the monolithic magnetizable element 900. In some examples, the magnetizable material 1302 may be composed of separate parts of material, distributed at least partially around the monolithic magnetizable element 900. In the same way discussed above for the further magnetization coils, the magnetizable material 1302 may be spaced around the monolithic magnetizable element 900 to provide a symmetric distribution of magnetic flux through the region 910.

[0266] As shown in Figure 13, the magnetic fields 1104, 1106 from the first and second magnetization coils 404, 406, respectively, flow7through the monolithic magnetizable element 900 and through the magnetizable material 1302. In particular, the first magnetic field 1104 generated by the first magnetization coil 404 flows through the first magnetizable portion of the monolithic magnetizable element 900 and through the magnetizable material 1302 and the second magnetic field 1106 generated by the second magnetization coil 406 flow s through the second magnetizable portion of the monolithic magnetizable element 900 and through the magnetizable material 1302. The cross-sectional width 1304 of the magnetizable material 1302 (measured in a direction parallel to the first and second winding axes 1014, 1016 and the longitudinal axis 912) can control the length 1002 of the region 910 in the monolithic magnetizable element 900.

[0267] Figure 15 shows example BL curves plotted on a graph. The graph shows how the BL factor (the product of magnetic flux density, B, and voice coil length, L) varies with an excursion distance of a voice coil from its rest position. As mentioned, a voice coil may extend around the monolithic magnet 900?and around the region 910 in a rest position (such as in the absence of any current applied to the voice coil). When the current is applied, the voice maymove along a coil path by a distance, where the coil path is parallel to the longitudinal axis 912 of the monolithic magnet 900'.

[0268] Figure 15 depicts in particular how BL curves vary for different lengths 1002 of the region 910, where the lengths are controlled by having different cross-sectional widths 1304 of the magnetizable material 1302. Figure 15 shows that a wider cross-sectional width (such as the 13mm cross-sectional width) results in a flatter BL curve and that a narrower cross- sectional width (such as 5mm) results in a more “pointy” BL curve. Figure 15 therefore shows how the cross-sectional width of the magnetizable material 1302 enables the length 1002 of the region 910 to be controlled, which results in a transducer with a particular BL curve. It is noted that the curve for air is flatter than the curves for cross-sectional widths of 5mm, 10mm and 13mm, however such a curve has lower overall BL values, and higher BL values are generally preferable. A balance between these considerations is therefore required.

[0269] As discussed above, the region 910 may encompass a magnetic neutral zone 910a, and it may be useful to manufacture a monolithic magnetizable element 900 and / or monolithic magnet 900’ having a through hole or void formed in a location where the magnetic neutral zone is or will be once magnetized. The through hole or void can reduce the volume of magnetizable / magnetized material in the monolithic magnetizable element 900 and / or monolithic magnet 900’, which can reduce the weight and cost. To illustrate, Figure 16 depicts a through hole 1602 or void 1602 formed within the region 910 and the magnetic neutral zone 910a is located within the through hole / void 1602. Figure 16 corresponds to the same view as discussed in relation to Figure 10.

[0270] Figures 17A-D depict some example forms of through holes and voids. In particular. Figure 17A depicts a top-down view of the monolithic magnet 900’ along the longitudinal axis 912, which extends into the page. In this example, a through hole 1702 extends through the monolithic magnet 900’ along the longitudinal axis 912. The through hole 1702 of this exampleis symmetric about the longitudinal axis 912 to ensure that the magnetic forces are evenly balanced around the axis 912.

[0271] Figure 17B depicts an example in which a through hole 1704 extends through the region 910 in a direction perpendicular to the longitudinal axis 912. In this example, a center of the through hole 1704 (measured along the length of the through hole, in a direction perpendicular to the longitudinal axis 912) passes through the longitudinal axis 912. The through hole 1704 of this example has a rotational symmetry7order of 2 about the longitudinal axis 912.

[0272] Figure 17C depicts an example in which a through hole 1706 extends through the region 910 in a direction perpendicular to the longitudinal axis 912. The through hole 1706 of this example has a rotational symmetry order of 4 about the longitudinal axis 912.

[0273] Figure 17C depicts an example in which a void 1708 is formed within the region 910. The void 1708 of this example is symmetric about the longitudinal axis 912 to ensure that the magnetic forces are evenly balanced around the axis 912. In this example, the void 1708 is spherical.

[0274] As briefly discussed, in some examples, a monolithic magnetizable element may additionally comprise a third magnetizable portion which is magnetized by' a third magnetization coil. To illustrate. Figure 18A depicts a cross-section through another example monolithic magnetizable element 1800. At this point in time, the monolithic magnetizable element 1800 is in an unmagnetized state. Figure 18A also shows a cross section through a first magnetization coil 1804, a second magnetization coil 1806 and a third magnetization coil 1808, each having a winding axis arranged parallel to a longitudinal axis 1812 of the monolithic magnetizable element 1800. A magnetization device may comprise the first, second and third magnetization coils.

[0275] Figure 18B depicts the monolithic magnetizable element 1800 after magnetization by the first, second and third magnetization coils 1804, 1806, 1808. The monolithic magnetizable element 1800 in a magnetized state may be known as a monolithic magnet 1800’ or a monolithic magnetized element 1800’. To provide a monolithic magnet 1800’ having the polarities shown, a first magnetizable portion 1814 of the monolithic magnetizable element 1800 is magnetized (forming a first magnetized portion 1820) by the first magnetization coil 1804, a second magnetizable portion 1816 of the monolithic magnetizable element 1800 is magnetized (forming a second magnetized portion 1822) by the second magnetization coil 1816, and a third magnetizable portion 1818 of the monolithic magnetizable element 1800 is magnetized (forming a third magnetized portion 1824) by the third magnetization coil 1818. The first and second magnetizable portions 1814, 1816 can be magnetized in opposite directions by the first and second magnetization coils, as discussed earlier. Similarly, the second and third magnetizable portions 1816, 1818 can be magnetized in opposite directions by the second and third magnetization coils.

[0276] To achieve this magnetization, a first current is passed through the first magnetization coil 1804 to generate a first magnetic field to magnetize the first magnetizable portion 1814, where the first magnetic field extends in a first direction along the longitudinal axis 1812, a second current is passed through the second magnetization coil 1806 to generate a second magnetic field to magnetize the second magnetizable portion 1816, where the second magnetic field extends in a second direction opposite to the first direction, and a third current is passed through the third magnetization coil 1808 to generate a third magnetic field to magnetize the third magnetizable portion 1818, where the third magnetic field extends in the first direction.

[0277] Accordingly, as shown, the first and second magnetized portions 1820, 1822 have inverted polarities, as do the second and third magnetized portions 1822, 1824. For example, a north pole 1820a of the first magnetized portion 1820 is arranged facing a north pole 1822a ofthe second magnetized portion 1822 (or vice versa). A south pole 1820b of the first magnetized portion 1820 is arranged facing away from the second magnetized portion 1822, and a south pole 1822b of the second magnetized portion 1822 is arranged facing away from the first magnetized portion 1820 (or vice versa). Similarly, a south pole 1822b of the second magnetized portion 1822 is arranged facing a south pole 1824b of the third magnetized portion 1824 (or vice versa). A north pole 1822a of the second magnetized portion 1822 is arranged facing away from the third magnetized portion 1824, and a north pole 1824a of the third magnetized portion 1824 is arranged facing away from the second magnetized portion 1822 (or vice versa). In this example, opposite ends, such as terminal ends, of the monolithic magnet 1800’ have an opposite polarity.

[0278] As discussed in the example of Figure 9B, a first region 1826 may be formed between the first and second magnetized portions 1820, 1822. Within the first region 1826, magnetic flux, such as the magnetic flux of the first and second magnetized portions, extends substantially perpendicular to the longitudinal axis 1812 of the monolithic magnet 1800’. During magnetization, the magnetic flux of the first and second magnetic fields of the first and second magnetization coils would also extend substantially perpendicular to the longitudinal axis 1812. In contrast, magnetic flux within the first and second magnetized portions 1820, 1822 may be substantially orientated along the longitudinal axis 1812. The magnetic flux within the first magnetized portion 1820 may extend in the opposite direction to the magnetic flux within the second magnetized portion 1822.

[0279] The first region 1826 is formed from a part of the first magnetizable portion 1814 and part of the second magnetizable portion 1816. In this particular example, the first region 1826 is located centrally between a first outer end 1820c of the first magnetized portion 1820 and a first outer end 1822c of the second magnetized portion 1822. In this case, the outer end 1820c is a terminal end of the monolithic magnet 1800’.

[0280] A second region 1828 may also be formed between the third and second magnetized portions 1824, 1822. Within the second region 1828, magnetic flux, such as the magnetic flux of the third and second magnetized portions, extends substantially perpendicular to the longitudinal axis 1812 of the monolithic magnet 1800'. During magnetization, the magnetic flux of the third and second magnetic fields of the third and second magnetization coils would also extend substantially perpendicular to the longitudinal axis 1812. In contrast, magnetic flux within the third and second magnetized portions 1824, 1822 may be substantially orientated along the longitudinal axis 1812. The magnetic flux within the third magnetized portion 1824 may extend in the opposite direction to the magnetic flux within the second magnetized portion 1822.

[0281] The second region 1828 is formed from a part of the third magnetizable portion 1818 and part of the second magnetizable portion 1816. In this particular example, the second region 1828 is located centrally between a first outer end 1824c of the third magnetized portion 1824 and a second outer end 1822d of the second magnetized portion 1822. In this case, the outer end 1824c is a terminal end of the monolithic magnet 1800’.

[0282] The monolithic magnets (or any of the alternative magnet assemblies) described above may form part of a motor for a transducer. For example, one or more voice coils may extend around a monolithic magnet. Figure 19 depicts an example motor for a transducer comprising the monolithic magnet 900’ of Figure 9B and a voice coil 1902. The voice coil 1902 extends around the monolithic magnet 900’ and is shown in a rest position. The voice coil 1902 is coupled to a membrane 1904 via an actuating element 1906. Accordingly, as the voice coil 1902 is displaced, movement of the voice coil 1902 is transferred to the membrane 1904 via the actuating element 1906.

[0283] Figure 20 depicts an example of motor for a transducer comprising the monolithic magnet 1800’ of Figure 19B and a first voice coil 2002 and a second voice coil 2004. The firstand second voice coils 2002, 2004 both extend around the monolithic magnet 1800’ and are shown in rest positions. The first voice coil 2002 is coupled to a first membrane 2006 via a first actuating element 2010. Accordingly, as the first voice coil 2002 is displaced, movement of the first voice coil 2002 is transferred to the first membrane 2006 via the first actuating element 2100. The second voice coil 2004 is coupled to a second membrane 2008 via a second actuating element 2012. Accordingly, as the second voice coil 2004 is displaced, movement of the second voice coil 2004 is transferred to the second membrane 2008 via the second actuating element 2112.

[0284] Figure 21 depicts a flow diagram of an example method 2100. In particular, the method 2100 is a method of manufacturing a magnet assembly for a transducer. In block 2102, the method comprises positioning a magnet assembly at least partially between a first magnetization coil and a second magnetization coil. In block 2104, the method comprises magnetizing the magnet assembly by: (i) passing a first current through the first magnetization coil to generate a first magnetic field to magnetize a first magnetizable portion of the magnet assembly, the first magnetic field extending in a first direction, and (ii) passing a second current through the second magnetization coil to generate a second magnetic field to magnetize a second magnetizable portion of the magnet assembly, the second magnetic field extending in a second direction opposite to the first direction.

[0285] In some examples, block 2102 may further comprise positioning the magnet assembly at least partially between the first magnetization coil and a third magnetization coil, the second magnetization coil being arranged between the first and third magnetization coils and extending around the magnet assembly, wherein a winding axis of the third magnetization coil is parallel to winding axes of the first and second magnetization coils. As such, in some examples, block2104 may further comprise passing a third current through the third magnetization coil togenerate a third magnetic field to magnetize a third magnetizable portion of the magnet assembly, the third magnetic field extending in the same direction as the first magnetic field.

[0286] Figure 22 depicts a flow diagram of another example method 2200. In particular, the method 2200 is a method of manufacturing a monolithic magnet for a transducer. In block 2202, the method comprises positioning a monolithic magnetizable element at least partially between a first magnetization coil and a second magnetization coil, where the monolithic magnetizable element defines a longitudinal axis, and the longitudinal axis is arranged parallel to a winding axis of the first magnetization coil and a winding axis of the second magnetization coil. In block 2204, the method comprises magnetizing the monolithic magnetizable element to provide a monolithic magnet by: (i) passing a first current through the first magnetization coil to generate a first magnetic field to magnetize a first magnetizable portion of monolithic magnetizable element, and (ii) passing a second current through the second magnetization coil to generate a second magnetic field to magnetize a second magnetizable portion of the monolithic magnetizable element. In block 2206, the method comprises, during the magnetizing, forming a region within the monolithic magnet having a particular length by controlling at least one of: (a) a magnetic reluctance external to the monolithic magnet adjacent the region, and (b) a magnetic flux through the region.

[0287] In some examples, block 2202 may further comprise positioning the monolithic magnetizable element at least partially between the first magnetization coil and a third magnetization coil, the second magnetization coil being arranged between the first and third magnetization coils and extending around the monolithic magnetizable element, wherein a winding axis of the third magnetization coil is parallel to winding axes of the first and second magnetization coils. As such, in some examples, block 2204 may further comprise passing a third current through the third magnetization coil to generate a third magnetic field to magnetize a third magnetizable portion of the monolithic magnetizable element, the thirdmagnetic field extending in the same direction as the first magnetic field. In some examples, block 2206 may further comprise during the magnetizing, forming a second region within the monolithic magnet having a particular length by controlling at least one of: (a) a magnetic reluctance external to the monolithic magnet adjacent the second region, and (b) a magnetic flux through the region.

[0288] The monolithic magnetizable element(s) may be obtained in any suitable way. In examples, the monolithic magnetizable element(s) described above may be formed by sintering powdered magnetizable material. Figure 23 depicts a flow diagram of an example method 2300 of forming a monolithic magnetizable element.

[0289] In block 2302, the method comprises obtaining one or more materials, such as one or more magnetizable materials. For example, a pretreated Praseodymium-Neodymium alloy, pure Iron, Ferro-boron, etc., may be weighed according to a specified proportion. In block 2304, the method comprises melting the one or more materials and casting the melted material into one or more sheets. For example, the one or more materials obtained in block 2302 may be added to a vacuum melting furnace and melted under protection of argon at a high temperature and casted into thin sheets. In block 2306, the method comprises processing the one or more sheets to form a coarse powder. For example, the one or more NdFeB alloy sheets are exposed to a hydrogen gas, and the gas causes the Nd rich material to expand and burst into a coarse powder. In block 2308, the method comprises processing the coarse powder to form a fine powder. For example, the coarse powder is exposed to a high-pressure nitrogen flow, which causes the coarse powder particles to collide with each other and refine it into a micronsized powder.

[0290] In general terms, blocks 2302-2308 comprise preparing a powdered magnetizable material. It will be understood that in some examples, powdered magnetizable material may be obtained and used directly without needing to be prepared as part of the method.

[0291] In block 2310, the method comprises exposing the powder to magnetic fields to orientate the powder according to the magnetic field. For example, using first and second magnetization coils, the powder may be exposed to first and second magnetic fields of a form substantially the same as the first and second magnetic fields described earlier. This step therefore pre-orientates the powered particles before a further step of magnetizing the monolithic magnetizable element once the powdered particles have been sintered. In some cases, sintering the powdered particles causes the material to deform / change shape due to the application of heat and / or pressure. In some cases, the form of the magnetic fields applied in block 2310 may differ from the magnetic fields applied during the further step of magnetizing the monolithic magnetizable material to account for this deformation. Block 2310 further comprises applying pressure to compact the powder. The pressing of the powder may be performed at the same time the powder is exposed to the magnetic fields. A pressed powder is obtained in block 2310.

[0292] In block 2312, the method comprises sintering the pressed powder to form the monolithic magnetizable element. For example, a high temperature and / or pressure is applied to the pressed powder in a sintering furnace. In an example, a pyknotic NdFeB element is formed. In some examples, block 2312 further comprises inspecting the monolithic magnetizable element to determine magnetic properties of the monolithic magnetizable element.

[0293] In block 2314, the method comprises magnetizing the monolithic magnetizable element. For example, in block 2314, the method 2100 or 2200 may be performed.V. Conclusion

[0294] The above discussions relating to playback devices, controller devices, playback zone configurations, and media content sources provide only some examples of operating environments within which functions and methods described may be implemented. Otheroperating environments and / or configurations of media playback systems, playback devices, and network devices not explicitly described may also be applicable and suitable for implementation of the functions and methods.

[0295] The description above discloses, among other things, various example systems, methods, apparatus, and articles of manufacture including, among other components, firmware and / or software executed on hardware. It is understood that such examples are merely illustrative and should not be considered as limiting. For example, it is contemplated that any or all of the firmware, hardware, and / or software examples or components can be embodied exclusively in hardware, exclusively in software, exclusively in firmware, or in any combination of hardware, software, and / or firmware. Accordingly, the examples provided are not the only ways to implement such systems, methods, apparatus, and / or articles of manufacture.

[0296] Additionally, references to “example” means that a particular feature, structure, or characteristic described in connection with the example can be included in at least one example of an invention. The appearances of this phrase in various places in the specification are not necessarily all referring to the same example, nor are separate or alternative examples mutually exclusive of other examples. As such, the examples described, explicitly and implicitly understood by one skilled in the art, can be combined with other examples.

[0297] The specification is presented largely in terms of illustrative environments, systems, procedures, steps, logic blocks, processing, and other symbolic representations that directly or indirectly resemble the operations of data processing devices coupled to networks. These process descriptions and representations are typically used by those skilled in the art to most effectively convey the substance of their work to others skilled in the art. Numerous specific details are set forth to provide a thorough understanding of the present disclosure. However, it is understood to those skilled in the art that certain examples of the present disclosure can bepracticed without certain, specific details. In other instances, well known methods, procedures, components, and circuitry have not been described in detail to avoid unnecessarily obscuring examples of the examples. Accordingly, the scope of the present disclosure is defined by the appended claims rather than the foregoing description of examples.

[0298] When any of the appended claims are read to cover a purely software and / or firmware implementation, at least one of the elements in at least one example is hereby expressly defined to include a tangible, non-transitory medium such as a memory7, DVD, CD, Blu-ray, and so on, storing the software and / or firmware.

Claims

CLAIMS1. A method of manufacturing a magnet assembly for a transducer, the method comprising: positioning the magnet assembly at least partially between a first magnetization coil and a second magnetization coil, wherein the magnet assembly defines a longitudinal axis, and the longitudinal axis is arranged parallel to a winding axis of the first magnetization coil and a winding axis of the second magnetization coil; and magnetizing the magnet assembly by: passing a first current through the first magnetization coil to generate a first magnetic field to magnetize a first magnetizable portion of the magnet assembly, the first magnetic field extending in a first direction; and passing a second current through the second magnetization coil to generate a second magnetic field to magnetize a second magnetizable portion of the magnet assembly, the second magnetic field extending in a second direction opposite to the first direction.

2. The method of claim 1. wherein the first and second currents are passed through the first and second magnetization coils, respectively, at substantially the same time.

3. The method of claim 1 or 2, wherein the first and second currents are substantially the same.

4. The method of any preceding claim, further comprising: arranging the first magnetization coil relative to the second a magnetization coil, such that one of:(i) at the first magnetization coil, the first direction points towards the second magnetization coil, and at the second magnetization coil the second direction points towards the first magnetization coil; or(ii) at the first magnetization coil, the first direction points away from the second magnetization coil, and at the second magnetization coil the second direction points away from the first magnetization coil.

5. The method of any preceding claim, wherein one of: the first magnetizable portion and the second magnetizable portion form a monolithic magnetizable element; or the magnet assembly comprises a first magnetizable element and a second magnetizable element affixed to the first magnetizable element, the first magnetizable element comprising the first magnetizable portion and the second magnetizable element comprising the second magnetizable portion, and wherein the method further comprises: providing the first magnetizable element, providing the second magnetizable element and affixing the first magnetizable element to the second magnetizable element.

6. The method of claim 5, wherein: magnetizing the first magnetizable portion forms a first magnetized portion of the magnet assembly; magnetizing the second magnetizable portion forms a second magnetized portion of the magnet assembly; and the magnet assembly, after being magnetized by the first and second magnetization coils, comprises: a first end that has a same polarity as a second end of the magnet assembly, the first and second ends being spaced apart along the longitudinal axis; and a region between the first and second ends; and and the method comprises during the magnetizing, forming the region with a particular length, the length being measured in a direction along the longitudinal axis, by controlling at least one of: a magnetic reluctance external to the magnet assembly adjacent the region; and a magnetic flux through the region.

7. The method of claim 6, wherein controlling the magnetic flux through the region comprises at least one of: controlling a distance between the first and second magnetization coils along the longitudinal axis, wherein the length of the region is based on the distance; controlling magnitudes of the first and second currents, wherein the length of the region is based on the magnitudes;arranging at least a third magnetization coil between the first and second magnetization coils, the third magnetization coil having a winding axis that is substantially perpendicular to the winding axes of the first and second magnetization coils, wherein the length of the region is based on a cross-sectional width of the third magnetization coil, the cross-sectional width measured parallel to the longitudinal axis; and arranging a permanent magnet between the first and second magnetization coils, the permanent magnet having a magnetic axis that is substantially perpendicular to the winding axes of the first and second magnetization coils, wherein the length of the region is based on a cross-sectional width of the magnet, the cross- sectional width measured parallel to the longitudinal axis.

8. The method of claim 6 or 7, wherein controlling the magnetic reluctance external to the magnet assembly adjacent the region comprises: arranging magnetizable material between the first and second magnetization coils and at least partially around the magnet assembly, such that the first magnetic field flows through the first magnetizable portion and through the magnetizable material and the second magnetic field flows through the second magnetizable portion and through the magnetizable material, wherein the length of the region is based on a cross-sectional width of the magnetizable material, the cross- sectional width measured parallel to the longitudinal axis.

9. The method of any of claims 5 to 8, wherein: the magnet assembly, after being magnetized by the first and second magnetization coils, comprises: a first end that has a same polarity7as a second end of the magnet assembly, the first and second ends being spaced apart along the longitudinal axis; and a region between the first and second ends; and the method further comprises forming the magnet assembly such that at least one of: a through hole extends through the region; and the region includes a void.

10. The method of any of claims 1 to 4, wherein:the magnet assembly comprises a first magnetizable element, a second magnetizable element and a spacer element affixed to and arranged between the first and second magnetizable elements; and the first magnetizable element comprises the first magnetizable portion and the second magnetizable element comprises the second magnetizable portion; and the method further comprises: providing the first magnetizable element, the second magnetizable element and the spacer element; affixing the first magnetizable element to a first side of the spacer element; and affixing the second magnetizable element to a second side of the spacer element.

11. The method of claim 10, wherein providing the first and second magnetizable elements comprises providing first and second magnetizable elements having substantially the same magnetic coercivity’.

12. The method of any preceding claim, further comprising: positioning a second magnet assembly at least partially between the first magnetization coil and the second magnetization coil, and simultaneously magnetizing the magnet assembly and the second magnet assembly.

13. The method of claim 12, wherein: positioning the magnet assembly at least partially between the first magnetization coil and the second magnetization coil comprises holding the magnet assembly in a first holder of a fixture, the fixture arranged at least partially between the first magnetization coil and the second magnetization coil; and positioning the second magnet assembly at least partially between the first magnetization coil and the second magnetization coil comprises holding the second magnet assembly in a second holder of the fixture.

14. The method of any preceding claim, further comprising: after positioning the magnet assembly at least partially between the first magnetization coil and the second magnetization coil and prior to magnetizing the magnet assembly, moving at least one of:the first magnetization coil towards the second magnetization coil; or the second magnetization coil towards the first magnetization coil.

15. A magnetization device for magnetizing a magnet assembly having a longitudinal axis, the magnetization device comprising: a first magnetization coil having a winding axis configured to be arranged parallel to the longitudinal axis and configured to generate a first magnetic field for magnetizing a first magnetizable portion of the magnet assembly, the first magnetic field extending in a first direction; a second magnetization coil having a winding axis configured to be arranged parallel to the longitudinal axis, the second magnetization coil being spaced apart from the first magnetization coil and configured to generate a second magnetic field for magnetizing a second magnetizable portion of the magnet assembly, the second magnetic field extending in a second direction opposite to the first direction; and one or more current sources configured to apply: a first current to the first magnetization coil to generate the first magnetic field; and a second current to the second magnetization coil to generate the second magnetic field.

16. The magnetization device of claim 15, wherein the one or more current sources are configured to apply the first and second currents to the first and second magnetization coils, respectively, at substantially the same time.

17. The magnetization device of claim 15 or 16, wherein the one or more current sources are configured to apply the first and second currents to the first and second magnetization coils, respectively, such that they have substantially the same current.

18. The magnetization device of any of claims 15 to 17, wherein the first magnetization coil is configured to generate the first magnetic field having a first field strength at the first magnetizable portion and the second magnetization coil is configured to generatethe second magnetic field having a second field strength at the second magnetizable portion, the first and second field strengths being substantially equal.

19. The magnetization device of any of claims 15 to 18, wherein the device is configured to receive the magnet assembly at least partially between the first and second magnetization coils, and wherein, in use, one of:(i) at the first magnetization coil, the first direction points towards the second magnetization coil, and at the second magnetization coil the second direction points towards the first magnetization coil; or(ii) at the first magnetization coil, the first direction points away from the second magnetization coil, and at the second magnetization coil the second direction points away from the first magnetization coil.

20. The magnetization device of any of claims 15 to 19, wherein the device further comprises at least one of: at least a third magnetization coil arranged between the first and second magnetization coils, the third magnetization coil having a winding axis that is substantially perpendicular to the winding axes of the first and second magnetization coils; and magnetizable material arranged between the first and second magnetization coils, the magnetizable material being configured to extend at least partially around the magnet assembly, such that in use, the first magnetic field flows through the first magnetizable portion and through the magnetizable material and the second magnetic field flows through the second magnetizable portion and through the magnetizable material.

21. The magnetization device of any of claims 15 to 20, wherein the device further comprises a fixture arranged at least partially between the first and second magnetization coils, the fixture comprising a first holder and a second holder, the first holder being configured to hold the magnet assembly, and the second holder being configured to hold a second magnet assembly for magnetization by the magnetization device.

22. The magnetization device of any of claims 15 to 21, wherein at least one of:the first magnetization coil is moveable towards the second magnetization coil; or the second magnetization coil is moveable towards the first magnetization coil.

23. A system, comprising: the magnetization device of any of claims 15 to 22; and one or more workstations for assembling a magnet assembly.

24. A monolithic magnet having a longitudinal axis, the monolithic magnet comprising: a first magnetized portion having a first magnetic flux substantially orientated along the longitudinal axis; a second magnetized portion positioned along the longitudinal axis from the first magnetized portion and having a second magnetic flux substantially orientated along the longitudinal axis in the opposite direction to the first magnetic flux; and and a region positioned between the first magnetized portion and the second magnetized portion.

25. The monolithic magnet of claim 24, wherein the region includes a magnetic neutral zone.

26. The monolithic magnet of claim 24 or 25, wherein the region has a third magnetic flux substantially orientated perpendicular to the longitudinal axis.

27. The monolithic magnet of any of claims 24 to 26, wherein the region is located centrally between outer ends of the first and second magnetized portions.

28. The monolithic magnet of any of claims 24 to 27, further comprising: a third magnetized portion positioned along the longitudinal axis from the second portion and having a third magnetic flux substantially orientated along the longitudinal axis in the same direction to the first magnetic flux; and a second region positioned between the second magnetized portion and the third magnetized portion.

29. The monolithic magnet of any of claims 24 to 28, wherein at least one of: a through hole extends through at least part of a magnetic neutral zone of the region; and the region defines a void that includes at least part of the magnetic neutral zone.

30. The monolithic magnet of claim 29, wherein the through hole or void has a rotational symmetry order of at least 2 about the longitudinal axis.

31. The monolithic magnet of claim 29 or 30, wherein the through hole extends through the region in a direction perpendicular to the longitudinal axis and has a rotational symmetry order of 2.

32. A motor, comprising: the monolithic magnet of any of claims 24 to 31; and one or more voice coils.

33. A playback device, comprising the motor of claim 32.

34. A method of manufacturing a monolithic magnet, the method comprising: positioning a monolithic magnetizable element at least partially between a first magnetization coil and a second magnetization coil, wherein the monolithic magnetizable element defines a longitudinal axis, and the longitudinal axis is arranged parallel to a winding axis of the first magnetization coil and a winding axis of the second magnetization coil; magnetizing the monolithic magnetizable element to provide a monolithic magnet by: passing a first current through the first magnetization coil to generate a first magnetic field to magnetize a first magnetizable portion of monolithic magnetizable element; and passing a second current through the second magnetization coil to generate a second magnetic field to magnetize a second magnetizable portion of the monolithic magnetizable element; andduring the magnetizing, forming a region within the monolithic magnet having a particular length, the length being measured in a direction along the longitudinal axis, by controlling at least one of: a magnetic reluctance external to the monolithic magnet adjacent the region; and a magnetic flux through the region.

35. The method of claim 34, wherein controlling the magnetic flux through the region comprises controlling a distance between the first and second magnetization coils along the longitudinal axis, wherein the length of the region is based on the distance.

36. The method of claim 34 or 35, wherein controlling the magnetic flux through the region comprises controlling magnitudes of the first and second currents, wherein the length of the region is based on the magnitudes.

37. The method of any of claims 34 to 36, wherein controlling the magnetic flux through the region comprises arranging at least a third magnetization coil between the first and second magnetization coils, the third magnetization coil having a winding axis that is substantially perpendicular to the winding axes of the first and second magnetization coils, wherein the length of the region is based on a cross-sectional width of the third magnetization coil, the cross-sectional width measured parallel to the longitudinal axis.

38. The method of any of claims 34 to 37, wherein controlling the magnetic flux through the region comprises arranging a permanent magnet between the first and second magnetization coils, the permanent magnet having a magnetic axis that is substantially perpendicular to the winding axes of the first and second magnetization coils, wherein the length of the region is based on a cross-sectional width of the magnet, the cross-sectional width measured parallel to the longitudinal axis.

39. The method of any of claims 34 to 38, wherein controlling the magnetic reluctance external to the monolithic magnet adjacent the region comprises arranging magnetizable material between the first and second magnetization coils and at least partially around the monolithic magnetizable element, wherein the length of the region is based on across-sectional width of the magnetizable material, the cross-sectional width measured parallel to the longitudinal axis.

40. The method of any of claims 34 to 39, further comprising forming at least one of: a through hole through the region; or a void within the region.

41. The method of any of claims 34 to 40, further comprising: positioning the monolithic magnetizable element at least partially between the first magnetization coil and a third magnetization coil, the second magnetization coil being arranged between the first and third magnetization coils and extending around the monolithic magnetizable element, wherein a winding axis of the third magnetization coil is parallel to winding axes of the first and second magnetization coils; and passing a third current through the third magnetization coil to generate a third magnetic field to magnetize a third magnetizable portion of monolithic magnetizable element, the third magnetic field extending in the same direction as the first magnetic field.

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