Transducer assembly

Abstract

There is provided a transducer assembly, comprising: (i) a first membrane, (ii) a second membrane, (iii) a magnet assembly, (iv) a first actuating element coupled to the first membrane and comprising a first voice coil, the first voice coil extending around the magnet assembly and being arranged to generate a magnetic field for interacting with magnetic fields generated by the magnet assembly to move the first actuating element along an axis of the magnet assembly relative to the magnet assembly, and (v) a second actuating element coupled to the second membrane and comprising a second voice coil, the second voice coil extending around the magnet assembly and being arranged to generate a magnetic field for interacting with magnetic fields generated by the magnet assembly to move the second actuating element along the axis relative to the magnet assembly.

Description

TRANSDUCER ASSEMBLYCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Patent Application No. 63 / 587,343, filed October 2, 2023, and to U.S. Patent Application No. 63 / 587,353, filed October 2, 2023, 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, sendees, 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. Tn 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, and accompanying 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 is a schematic side view depicting an example first type of transducer assembly;

[0014] Figure 3 is a schematic side view depicting an example first type of transducer assembly having an extension pole piece;

[0015] Figure 4 is a schematic side view depicting another example first type of transducer assembly having an extension pole piece;

[0016] Figure 5 is a schematic side view depicting another example first t pe of transducer assembly, where the first and second membranes are flat;

[0017] Figures 6A and 6B are schematic side views depicting another example first type of transducer assembly, where the first and second membranes have apertures formed therein;

[0018] Figure 7 is a schematic side view depicting an example second type of transducer assembly;

[0019] Figure 8 depicts a transparent top-down view of the transducer assembly of Figure 7;

[0020] Figure 9 is schematic side view depicting another example second type of transducer assembly, where the first and second membranes have apertures formed therein; and

[0021] Figure 10 depicts a transparent top-down view of another example second type of transducer assembly, where a plurality of motors drive each of the first and second membranes.

[0022] The drawings are for the purpose of illustrating example examples, but those of ordinary skill 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

[0023] Embodiments described herein relate to transducer assemblies, playback devices comprising one or more transducer assemblies, and systems, such as media playback systems, comprising one or more playback devices.

[0024] A first type of transducer assembly, for example as described in Figures 2-6B, includes an arrangement of two membranes (also known as diaphragms), where eachmembrane can cause propagation of acoustic energy (i.e., sound) when driven by a single motor (that is. a single magnet assembly / stack. and one or more voice coils for each membrane). The specific types of transducer assemblies described comprise a first membrane and a second membrane, and the membranes may be arranged to propagate acoustic energy in opposite directions. By utilizing a common magnet assembly to drive the two membranes, the weight, size and cost of the transducer assembly may be reduced compared to existing systems in which each membrane may be driven using separate magnet assemblies / stacks. Lighter and more compact transducer assemblies may enable a playback device that contains such a transducer assembly to itself be lighter and more compact, which can often be desirable for consumers. Furthermore, driving both membranes along the same axis can mean the membranes do not need to be driven together.

[0025] A second type of transducer assembly, for example as described in Figures 7-10, includes an arrangement of two membranes, each driven by separate motor arrangements (each motor arrangement comprising one or more motors), where the motor arrangements each drive the respective membranes "off-center" (i.e., away from the center of the membrane). The specific types of transducer assemblies described comprise a first membrane and a second membrane, and the membranes may be arranged to propagate acoustic energy in opposite directions. Driving the two membranes off-center may reduce the size (such as volume) of the transducer assembly, while maximizing the area of the membranes, and thereby increasing the sound pressure generated by each membrane. More compact transducer assemblies may enable a playback device that contains such a transducer assembly to itself be more compact, which can often be desirable for consumers.

[0026] Examples of the first type of transducer assembly will be discussed first, followed by examples of the second type of transducer assembly. As such, according to a first aspect of the first type of transducer assembly, there is provided a transducer assembly comprising: (i) a first membrane, (ii) a second membrane, (iii) a magnet assembly, (iv) a first actuating element coupled to the first membrane and comprising a first voice coil, the first voice coil extending around the magnet assembly and being arranged to generate a magnetic field for interacting with a magnetic field of the magnet assembly to move the first actuating element along an axis of the magnet assembly relative to the magnet assembly, and (v) a second actuating element coupled to the second membrane and comprising a second voice coil, the second voice coil extending around the magnet assembly and being arranged to generate a magnetic field forinteracting with the magnetic field of the magnet assembly to move the second actuating element along the axis relative to the magnet assembly.

[0027] As mentioned, both membranes can therefore share the same magnet assembly. A membrane may be alternatively known as a diaphragm.

[0028] In examples, the magnet assembly (also known as a magnet stack) comprises a stack of three or more magnets (also known as magnetic elements). In some cases, the magnets may be separated by one or more spacer elements. A spacer element may be known as a pole piece, in some examples.

[0029] The magnetic elements within the magnet assembly may be linearly arranged, along an axis of the magnet assembly. The magnet assembly may therefore be a linear magnet assembly. The axis of the magnet assembly may be a central axis or a longitudinal axis of the magnet assembly. The voice coils may be driven parallel to the axis of the magnet assembly. The membranes may also be driven parallel to the axis of the magnet assembly.

[0030] In an example, the magnet assembly comprises axially magnetized magnetic elements, with each magnetic element being magnetized along the axis, such as the longitudinal axis of the magnet assembly (although, as will become apparent, not necessarily in the same direction along the axis).

[0031] The first membrane may be arranged at, near or towards one end of the magnet assembly, and the second membrane may be arranged at, near or towards the other, opposite end of the magnet assembly.

[0032] In examples, the first voice coil extends around the axis of the magnet assembly and the second voice coil extends around the axis.

[0033] As is well known, when an electric current is passed through a voice coil, the interaction of the magnetic field generated by the voice coil causes the moveable voice coil to be displaced relative to the static magnet assembly (or vice versa). The voice coil may be annular and extend around an axis (such as a coil axis). The magnet assembly may be received within the voice coil. The voice coil may be displaced along the axis of the magnet assembly. In some examples, the coil axis and the axis of the magnet assembly are substantially co-axial.

[0034] In its simplest form, the first actuating element may comprise only the first voice coil. For example, the first voice coil may be attached or otherwise coupled to the first membrane. Similarly, the second actuating element may comprise only the second voice coil. In other examples, however, each actuating element may comprise the voice coil and one or more other components that couple the voice coil to the respective membrane, such as a former and / orsupport elements. For example, the actuating elements may each comprise a voice coil enclosure containing the voice coil, and in some cases, each voice coil enclosure may be coupled to a suspension system, and the suspension system (also known as a spider or speaker damper) is coupled to a support assembly, where the support assembly transfers movement of the voice coils to the respective membranes. As such, the voice coils may be coupled directly and / or indirectly to the membrane, such that movement of the voice coils transfer movement to the membranes. For example, as the voice coils are displaced, the voice coil enclosures are also displaced, which in turn causes the support assemblies to be displaced. The movement of the support assemblies thus transfers movement to the respective membranes.

[0035] In some examples, a central axis of the first membrane is either coaxial with a central axis of the second membrane or approximately coaxial with the central axis of the second membrane. The axes may therefore be parallel. Both axes may also be coaxial with the axis of the magnet assembly. A central axis of a membrane may alternatively be known as (or be parallel to) a sound axis of the membrane, in some examples. A “sound axis’" as used herein is an axis defining the main direction sound radiates from the membrane. In general, the sound axis will be parallel to the direction of movement of the membrane.

[0036] In examples, the first and second membranes have a circular shape. In other examples, the first and second membranes have any other shape, such as a conical shape or a conical frustum shape. The membranes may have different shapes and / or sizes to each other. In some examples, the first and second membranes are flat, and therefore define a flat plane. In some examples, only one of the membranes is flat.

[0037] In certain arrangements, a surface area of the first membrane is equal to a surface area of the second membrane. In other examples, the first and second membranes have different surface areas.

[0038] In particular examples, the first and second membranes are substantially the same. For example, the first and second membranes may have the same size, and / or same shape, and / or same surface area. They may be configured to output audio within the same frequency range. This configuration may ensure the sound produced by the first and second membranes is well balanced.

[0039] In a particular example, the magnet assembly comprises: (a) a first magnetic element, (b) a second magnetic element, and (c) a third magnetic element. The second magnetic element is arranged between the first and third magnetic elements, and the first, second and third magnetic elements are arranged along the axis of the magnet assembly. The first voice coil isarranged relative to the first and second magnetic elements such that the magnetic field generated by the first voice coil interacts with magnetic fields of the first and second magnetic elements to move the first actuating element along the axis, and the second voice coil is arranged relative to the second and third magnetic elements such that the magnetic field generated by the second voice coil interacts with magnetic fields of the second and third magnetic elements to move the second actuating element along the axis.

[0040] Accordingly, an arrangement of three magnetic elements may allow the movement of the first and second voice coils to be controlled.

[0041] In examples, the first, second and third magnetic elements are stacked along the axis of the magnet assembly. As mentioned, the magnetic elements may therefore be linearly arranged along the axis.

[0042] The first, second and third magnetic elements are magnetized, and therefore are, or comprise, magnetized magnetic material, such as ferromagnetic material (e.g., iron). The first, second and third magnetic elements may be permanent magnets, such as a magnet formed from a hard magnetic material.

[0043] In some examples, the second magnetic element is spaced apart from the first magnetic element (such as via a spacer element). In some examples, the second magnetic element is additionally or alternatively spaced apart from the third magnetic element (such as via a spacer element).

[0044] In examples, the first and second magnetic elements have oppositely arranged magnetic poles. For example, where the first and second magnetic elements are arranged closest to each other, the first and second magnetic elements have the same polarity facing each other. Like poles are therefore arranged facing towards each other. As such, a magnetic field of the first magnetic element points in the opposite direction to a magnetic field of the second magnetic element. The first and second magnetic elements therefore have an inverted or opposite polarity. Similarly, the third and second magnetic elements have oppositely arranged magnetic poles. The first and third magnetic elements may therefore have magnetic fields pointing in the same direction. As such, a magnetic field of the first magnetic element points in the opposite direction to a magnetic field of the second magnetic element, and the same direction to a magnetic field of the third magnetic element.

[0045] In a particular example, the first magnetic element is axially magnetized in a first direction, the second magnetic element is axially magnetized in a second direction, the seconddirection being opposite to the first direction, and the third magnetic element is axially magnetized in the first direction.

[0046] Having magnetic elements magnetized and arranged in this way means that the first and second magnetic elements repel each other, and the first voice coil can be positioned in this region, which subjects the first voice coil to the maximum force at this position. Similarly, the third and second magnetic elements repel each other, and the second voice coil can be positioned in this region.

[0047] In a particular example, the first and second directions are parallel to the axis of the magnet assembly, but point in opposite directions.

[0048] In some examples, the first magnetic element is a first magnet, the second magnetic element is a second magnet, and the third magnetic element is a third magnet. The magnet assembly may therefore comprise no more than three magnets. Accordingly, only three magnets may be required to control two voice coils, thereby minimizing the weight and cost of the assembly. Having only three magnets also reduces the number of times separate parts are affixed (such as adhered / glued) to each other, thereby simplifying manufacture. Each magnet may be separate and distinct from each other (at least initially, prior to assembly).

[0049] In some examples, the transducer assembly further comprises an extension pole piece extending around the second magnetic element and between the first and second voice coils. An extension pole piece may stop (or at least reduce) the magnetic fields generated by the two voice coils from interacting with each other. The extension pole piece may extend away from the second magnetic element in a direction generally perpendicular to the axis of the magnet assembly. In an example, the extension pole piece may not pass or extend through the second magnetic element.

[0050] In an alternative example, the extension pole piece may pass or extend through the second magnetic element. The second magnetic element may therefore comprise two or more magnets separated by the extension pole piece. Passing through the second magnetic element can provide a more secure way to hold the extension pole piece in place, and may also further stop or reduce the magnetic fields from the two voice coils from interacting with each other. As such, in examples, the second magnetic element comprises at least two magnets, at least one of the two magnets being spaced apart from at least another magnet of the at least two magnets by an extension pole piece, wherein the extension pole piece extends away from the second magnetic element and between the first and second voice coils. The extension polepiece may extend away from the second magnetic element in a direction generally perpendicular to the axis of the magnet assembly.

[0051] The extension pole piece may be a single piece of material, or may include different pieces of material, such as two or more parts. The extension pole piece may or may not be formed from solid material. In one example, the extension pole piece is substantially flat, such as ‘"disc” shaped. In other examples, the extension pole piece is not flat, and may curve or bend towards one or both membranes. For example, the extension pole piece may comprise or resemble two inverted “cups”. For example, one voice coil and one side of the magnet assembly may be inside one “cup” and the other voice coil and the other side of the magnet assembly may be inside the other “cup”. The two cup-shapes may be separate or may be monolithic. The extension pole piece may be formed using a stamping manufacture process.

[0052] The extension pole piece may be or comprise a low reluctance material. A low reluctance material would allow smaller magnetic elements to be used in the magnet assembly, reducing costs. In other examples, the extension pole piece is or comprises plastic material. A high reluctance material can protect the voice coils from each other.

[0053] In some examples, the transducer assembly further comprises a first pole piece arranged between the first and second magnetic elements for concentrating the magnetic flux on the first voice coil, and a second pole piece arranged between the third and second magnetic elements for concentrating the magnetic flux on the second voice coil. As such, the second magnetic element is spaced apart from the first magnetic element by at least the first pole piece and the third magnetic element is spaced apart from the second magnetic element by at least the second pole piece. The pole pieces may be or comprise magnetic material, such as ferromagnetic material (e.g., iron). The pole pieces are unmagnetized, but it will be appreciated that the magnetic elements in the magnet assembly can weakly magnetize the pole pieces. The pole pieces having a low reluctance allows the pole pieces to act as a “magnetic lens”.

[0054] In certain examples, for at least one of the first or second pole pieces, a thickness of the pole piece can be varied during use. The thickness may be measured in a direction along the axis of the magnet assembly. The thickness (and therefore a spacing between the first and second magnetic elements and / or a spacing between the second and third magnetic elements) can be dynamically changed as the voice coil(s) move. For example, as the voice coil moves away from a rest position (where the rest position is the position of the voice coil in the absence of a current applied to the voice coil), the thickness can be reduced. This effectively reduces the excursion distance of the voice coil from the rest position, resulting in a higher BL valueon the BL curve, where a higher BL value can mean the transducer has a higher sensitivity, better efficiency and / or improved control. As such, in an example, the thickness of the pole piece can be reduced when an excursion distance of the voice coil is increased.

[0055] In examples, the thickness of one or more pole pieces may be varied in use based on a volume level of a playback device (and therefore the transducer assembly). In such a case, the thickness may be varied based on the volume slider.

[0056] In an example, the thickness of the pole piece is mechanically varied.

[0057] In one example, a motor or linear motor, may be used to vary the thickness, and therefore distance / spacing between the magnetic elements. Example linear motors include piezo motors, magnetic linear motors (transducers), etc.

[0058] In another example, the thickness, and therefore distance / spacing between the magnetic elements may be varied using a passive element, such as a loaded spring for example, which can use the motion or magnetic fields of the voice coil / magnetic elements to change size / shape.

[0059] In examples, to stop the membranes from colliding with the magnet assembly, a minimum gap / spacing between the membranes and the magnet assembly must be larger than the maximum mechanical excursion distances of the voice coils. In some examples: (i) when the first voice coil is in a rest position, the magnet assembly is spaced apart from the first membrane by a distance that is greater than a maximum mechanical excursion distance of the first voice coil, and / or (ii) when the second voice coil is in a rest position, the magnet assembly is spaced apart from the second membrane by a distance that is greater than a maximum mechanical excursion distance of the second voice coil.

[0060] Reducing the distances between the membranes and the magnet assembly, while ensuring the distances are greater than the maximum mechanical excursion distances, ensures that the transducer assembly has a lowest possible profile. For example, to ensure a low profile, the distances, dm, between each membrane and the magnet assembly at its nearest point to the membrane may be given by the following equation: de < dm < (de + v), where de is the maximum mechanical excursion distance, and v is a distance between about 10mm and 0.1mm, such as 10mm, 7.5mm, 5mm, 2.5mm, 1mm, 0.8mm, 0.6mm, 0.4mm, 0.2mm or 0.1mm.

[0061] The distance between the first membrane and the magnet assembly may be measured from one end of the magnet assembly (such as one end of the first magnetic element), and the distance between the second membrane and the magnet assembly may be measured from another, opposite end of the magnet assembly (such as one end of the third magnetic element).

[0062] The rest position of a voice coil is the position of the voice coil relative to the magnet assembly in the absence of a current applied to the voice coil.

[0063] In examples, at least one of: (i) the first membrane is substantially conical or frustoconical, and the transducer assembly further comprises a first dust cap arranged on the first membrane, and when the first voice coil in a rest position, the magnet assembly is spaced apart from the first dust cap by a distance that is greater than a maximum mechanical excursion distance of the first voice coil, and (ii) the second membrane is substantially conical or frustoconical, and the transducer assembly further comprises a second dust cap arranged on the second membrane, and when the second voice coil in a rest position, the magnet assembly is spaced apart from the second dust cap by a distance that is greater than a maximum mechanical excursion distance of the second voice coil. As such, in the same way discussed above, to stop the magnet assembly from colliding with the dust caps, a minimum gap / spacing must be larger than the maximum mechanical excursion distance.

[0064] Reducing the distances between the dust caps and the magnet assembly, while ensuring the distances are greater than the maximum mechanical excursion distances, ensures that the transducer assembly has a lowest possible profile. For example, to ensure a low profile, the distances, dm, between each dust cap and the magnet assembly at its nearest point to the dust cap may be given by the following equation: de < dm < (de + v), where de is the maximum mechanical excursion distance, and v is a distance between about 10mm and 0.1mm, such as 10mm. 7.5mm. 5mm, 2.5mm, 1mm. 0.8mm, 0.6mm, 0.4mm. 0.2mm or 0.1mm.

[0065] In some examples, the magnet assembly (such as a portion of the magnet assembly) is arranged in a space between the first (and / or second) dust cap and a narrow7end of the first (and / or second) membrane (the membrane being conical or frustoconical, and having a narrow end and a wide end). This can result in a lower profile transducer assembly.

[0066] The distance between the first dust cap and the magnet assembly may be measured from one end of the magnet assembly (such as one end of the first magnetic element), and the distance between the second dust cap and the magnet assembly may be measured from another, opposite end of the magnet assembly (such as one end of the third magnetic element).

[0067] In some examples, one or both membranes have an aperture, and the magnet assembly can pass through the aperture as the membrane moves. Therefore, rather than (or in addition to) having a spacing / gap between the magnet assembly and the membrane(s) or dust cap(s), as discussed above, the magnet assembly may at least partially extend through the aperture(s), so that the magnet assembly does not contact the membrane(s). This results in a low profileassembly. Accordingly, in examples, at least one of: (i) the first membrane delimits a first aperture, and in use, the magnet assembly extends through the first aperture, and (ii) the second membrane delimits a second aperture, and in use, the magnet assembly extends through the second aperture. In an example, one or both membranes may be “ring” shaped.

[0068] In use, means that a current is applied to the voice coil, thereby causing the membrane to move. The magnet assembly may only pass through the aperture beyond certain excursion distances, or may extend through the aperture for all excursion distances (including in the rest position). The magnet assembly may therefore extend through the aperture while the voice coil is in the rest position and / or during excursion. For example, in the rest position the magnet assembly may not extend through the aperture, but in use, when the voice coil moves, the magnet assembly may pass through the aperture.

[0069] In examples, there may be an airtight sealing between the membrane and the motor within the aperture. This may be useful for low bass applications.

[0070] As discussed, the first and second membranes may be arranged at opposite ends of the magnet assembly. As such, the first and second membranes may be said to be arranged back-to-back. This “back-to-back” configuration may allow sound to be directed in different directions into a room, filling the room and / or providing a particular sound profile. In examples, the first membrane is configured to generate a first acoustic wave, the second membrane is configured to generate a second acoustic wave, and the first and second acoustic waves are directed away from the transducer assembly in substantially opposite directions. Acoustic waves may be alternatively known as acoustic energy, in some examples.

[0071] While the discussion above relates a transducer assembly with two membranes, the disclosure is not limited to two membranes. Further examples may include more than two membranes, such as when membranes are concentric and / or one being provided inside the other.

[0072] According to a second aspect of the disclosure, there is provided a playback device comprising the transducer assembly of the first aspect, discussed above. In examples, the playback device comprises a plurality of transducer assemblies of the first aspect.

[0073] According to a third aspect of the disclosure, there is provided a system comprising: the playback device of the second aspect, and at least one further playback device. The at least one further playback device may or may not comprise a transducer assembly of the first aspect. For example, the at least one further playback device may comprise a different type of transducer assembly.

[0074] The system may further comprise a controller configured to send an instruction to the playback device to cause the playback device to play back audio.

[0075] Aspects of the second type of transducer assembly will now be described. According to a fourth aspect of the disclosure, there is provided a transducer assembly, comprising: (i) a first membrane, (ii) a second membrane, (iii) a first motor arrangement, arranged between the first and second membranes, configured to drive the first membrane along a first axis, the first motor arrangement comprising one or more motors for driving the first membrane, and (iv) a second motor arrangement, arranged between the first and second membranes, configured to drive the second membrane along a second axis, the second motor arrangement comprising one or more motors for driving the second membrane. The first axis is offset from a first central axis of the first membrane and the second axis, and the second axis is offset from a second central axis of the second membrane.

[0076] Offsetting the first and second axes from each other and from the central axes of the membranes may reduce the size (such as volume) of the transducer assembly, and / or allow the area of the speaker membranes to be increased.

[0077] In examples, the first axis is offset from the first central axis of the first membrane such that the first motor arrangement drives the first membrane off-center (such as at a point away from a midpoint or center of a longest dimension of the first membrane). Similarly, the second axis is offset from the second central axis of the second membrane, such that the second motor arrangement drives the second membrane off-center (such as at a point away from a midpoint or center of a longest dimension of the second membrane). The longest dimension of the membrane may alternatively be referred to as a length of the membrane. In examples, the first axis and the first central axis may be arranged at midpoints along the first membrane in a direction measured perpendicular to the longest dimension and the first axis. Similarly, in examples, the second axis and the second central axis may be arranged at midpoints along the second membrane in a direction measured perpendicular to the longest dimension and the second axis. In some examples, the longest dimension may also be an axis of symmetry.

[0078] In examples, each motor arrangement comprises one or more motors. In a particular case, each motor arrangement comprises a single motor to drive each respective membrane along the respective axis. For example, a magnet stack of each single motor is arranged on the respective axis.

[0079] In certain arrangements, a surface area of the first membrane is equal to a surface area of the second membrane. In other examples, the first and second membranes have different surface areas.

[0080] In examples, the first and second membranes are arranged at opposite ends of the transducer assembly. The first and second membranes are therefore arranged to be driven in opposite directions. As such, the first and second membranes may be said to be arranged back- to-back. In examples, the first membrane is configured to generate a first acoustic wave, the second membrane is configured to generate a second acoustic wave, and the first and second acoustic waves are directed away from the transducer assembly in substantially opposite directions. Other examples may use waveguides to adjust the directions of the acoustic waves.

[0081] The first and second membranes may be substantially flat.

[0082] The first and second membranes may be substantially the same. For example, the first and second membranes may have the same size, and / or the same shape and / or same surface area. They may be configured to output audio within the same frequency range. This configuration may ensure the sound produced by the first and second membranes is well balanced.

[0083] In some examples, the first membrane has a line of symmetry in a direction perpendicular to the first axis, and the first axis coincides with the line of symmetry7at a point offset from a midpoint of the line of symmetry7. The first axis therefore coincides with the first membrane at a point closer to one end of the first membrane than another, opposite end of the first membrane. Similarly, the second membrane has a line of symmetry in a direction perpendicular to the second axis, and the second axis coincides with the line of symmetry at a point offset from a midpoint of the line of symmetry. Again, the second axis coincides with the second membrane at a point closer to one end of the second membrane than another, opposite end of the second membrane. The line of symmetry of the first membrane may be parallel to the line of symmetry7of the second membrane. The first membrane and the second membrane may have a single line of symmetry.

[0084] The term “arranged between the first and second membranes” may mean at least part of the motor arrangement is arranged between the first and second membranes. For example, in some cases, a magnet assembly of a motor arrangement may' extend beyond the “footprint” of a membrane, and / or a magnet assembly of a motor arrangement may extend through an aperture in a membrane.

[0085] In some examples, at least one of: (i) the first motor arrangement comprises a first motor configured to drive the first membrane, the first motor comprising: (a) a first magnet assembly arranged along the first axis, and (b) a first actuating element coupled to the first membrane and comprising a first voice coil, the first voice coil extending around the first axis and being arranged to generate a magnetic field for interacting with one or more magnetic fields generated by the first magnet assembly to move the first actuating element along the first axis; or (ii) the second motor arrangement comprises a second motor configured to drive the second membrane, the second motor comprising: (a) a second magnet assembly arranged along the second axis, and (b) a second actuating element coupled to the second membrane and comprising a second voice coil, the second voice coil extending around the second axis and being arranged to generate a magnetic field for interacting with one or more magnetic fields generated by the second magnet assembly to move the second actuating element along the second axis.

[0086] Having motors arranged on the first and second axes may allow the membranes to be driven along the axes effectively.

[0087] In its simplest form, an actuating element (such as one, or both, of the first and second actuating elements) may comprise only a voice coil. In other examples, an actuating element may comprise one or more other components that couple the voice coil to the respective membrane, such as a former and / or support elements.

[0088] In examples, a magnet assembly (such as one or both of the first and second magnet assemblies) comprises a stack of two or more magnets, such as first and second magnets (also known as first and second magnetic elements). In some cases, the first and second magnetic elements of a magnet assembly may be separated by one or more spacer elements. A spacer element may be known as a pole piece, in some examples. In certain examples, a thickness of the pole piece can be varied during use.

[0089] The magnetic elements within a magnet assembly may be linearly arranged, along an axis (such as a longitudinal axis) of the magnet assembly. In a particular case, the magnetic elements of the first magnet assembly are linearly arranged along the first axis, and the magnetic elements of the second magnet assembly are linearly arranged along the second axis. A magnet assembly may therefore be a linear magnet assembly. The axis of a magnet assembly may be parallel to the first and second axes along which the first and second membranes are driven. The voice coils (such as one or both of the first and second voice coils), and therefore both membranes, may be driven parallel to the axes of their respective magnet assemblies. Inan example, a magnet assembly comprises axially magnetized magnetic elements, with each magnetic element being magnetized along the axis, such as the longitudinal axis of the magnet assembly. The first and second magnetic elements are magnetized, and therefore are or comprise magnetized magnetic material, such as ferromagnetic material (e.g., iron). The first and second magnetic elements may be permanent magnets, for example comprising a hard magnetic material. In examples, the first and second magnetic elements have oppositely arranged magnetic poles. For example, where the first and second magnetic elements are arranged closest to each other, the first and second magnetic elements have the same polarity facing each other. Like poles are therefore arranged facing towards each other. As such, a magnetic field of the first magnetic element points in the opposite direction to a magnetic field of the second magnetic element. In a particular example, the first magnetic element is axially magnetized in a first direction, the second magnetic element is axially magnetized in a second direction, the second direction being opposite to the first direction.

[0090] In examples, the first voice coil extends around the first magnet assembly (and therefore around the first axis) and the second voice coil extends around the second magnet assembly (and therefore around the second axis).

[0091] In an example, at least one of: (i) the first motor arrangement comprises a single motor, or (ii) the second motor arrangement comprises a single motor. The single motor of the first motor arrangement may therefore be the first motor discussed above. Similarly, the single motor of the second motor arrangement may therefore be the second motor discussed above. The first motor arrangement may therefore only comprise the first motor and the second motor arrangement may only comprise the second motor. The first and / or second magnet arrangement may therefore comprise no further motors. Having a single motor driving each membrane may reduce the complexity, weight and / or cost of the transducer assembly. Furthermore, use of a single motor driving along each axis may assist with driving the membranes uniformly.

[0092] In some examples, at least one of: (i) when the first voice coil is in a rest position, the first magnet assembly is spaced apart from the first membrane by a distance that is greater than a maximum mechanical excursion distance of the first voice coil, or (ii) when the second voice coil is in a rest position, the second magnet assembly is spaced apart from the second membrane by a distance that is greater than a maximum mechanical excursion distance of the second voice coil. This particular spacing may stop the magnet assembly from colliding with the membrane.

[0093] In addition, reducing the distances between the membranes and the magnet assemblies, while ensuring the distances are greater than the maximum mechanical excursiondistances, ensures that the transducer assembly has a lowest possible profile. For example, to ensure a low profile, the distances, dm. between each membrane and its respective magnet assembly at its nearest point to the membrane may be given by the following equation: de < dm < (de + v), where de is the maximum mechanical excursion distance, and v is a distance between about 10mm and 0.1mm. such as 10mm, 7.5mm, 5mm, 2.5mm, 1mm, 0.8mm, 0.6mm, 0.4mm, 0.2mm or 0.1mm.

[0094] The distance between the first membrane and the first magnet assembly may be measured from one end of the first magnet assembly, and the distance between the second membrane and the second magnet assembly may be measured from one end of the second magnet assembly .

[0095] In some examples, one or both membranes have an aperture, and the magnet assembly can pass through the aperture as the membrane moves. This results in the transducer assembly having a low profile. Accordingly, in examples, at least one of: (i) the first membrane delimits a first aperture, and in use, the first magnet assembly extends through the first aperture, and (ii) the second membrane delimits a second aperture, and in use. the second magnet assembly extends through the second aperture. In an example, one or both membranes may be “ring” shaped.

[0096] As discussed previously, the first and / or second magnet assembly may only pass through the aperture beyond certain excursion distances, or may extend through the aperture for all excursion distances (including in the rest position).

[0097] In some examples, rather than the motor arrangement(s) having a single motor, a plurality of motors may operate to drive the membrane along the axis. For example, multiple motors may be arranged around the axis along which the membrane is driven. Use of a plurality of motors, rather than a single motor, may distribute the forces over a wider area on the membranes and / or may provide greater stability for the membranes. Accordingly, in examples, at least one of: (i) the first motor arrangement comprises a plurality of motors arranged around the first axis and configured to collectively drive the first membrane along the first axis, or (ii) the second motor arrangement comprises a plurality of motors arranged around the second axis and configured to collectively drive the second membrane along the second axis.

[0098] The plurality of motors may be equally spaced around the first / second axis.

[0099] In some examples, the plurality of motors driving a particular membrane operate in unison, that is, the excursion distance and direction for each voice coil of each motor is thesame at any particular moment in time. In other examples, the excursion distance and direction for each voice coil of each motor may be different.

[0100] Each motor of the plurality of motors may comprise a voice coil coupled with the membrane. In some examples, the voice coils for the plurality of motors driving a particular membrane are each coupled to a single support assembly to drive the membrane. In other examples, the voice coils for the plurality of motors driving a particular membrane are separately coupled to the membrane.

[0101] In examples, at least one of: (i) the first central axis of the first membrane coincides with a midpoint of a longest dimension of the first membrane, or (ii) the second central axis of the second membrane coincides with a midpoint of a longest dimension of the second membrane. In examples, the longest dimension of the first membrane may coincide with a line of symmetry of the first membrane. Similarly, the longest dimension of the second membrane may coincide with a line of symmetry of the second membrane.

[0102] In examples, at least one of: (i) the first axis coincides with a center of mass of the first membrane, or (ii) the second axis coincides with a center of mass of the second membrane. At the center of mass of the membrane, the moments acting on the membrane are balanced, which may ensure the membrane is driven linearly, which can result in higher quality audio being generated by the membrane / transducer assembly.

[0103] In examples, the first membrane has a first surface area defined between one end of the first membrane and the first axis, and the first surface area is equal in size to a second surface area of the first membrane defined betw een an opposite end of the first membrane and the first axis. The second membrane has a third surface area defined between one end of the second membrane and the second axis, and the third surface area is equal in size to a fourth surface area of the second membrane defined between an opposite end of the second membrane and the second axis.

[0104] In certain examples, at least one of: (i) the first axis is offset from the first central axis such that the first axis coincides with the first membrane at a point closer to a first end of the first membrane than a second, opposite end of the first membrane, and the second motor arrangement is arranged between the first and second membranes in a space between the second end of the first membrane and the first axis, and (ii) the second axis is offset from the second central axis such that the second axis coincides with the second membrane at a point closer to a first end of the second membrane than a second, opposite end of the second membrane, and the first motor arrangement is arranged between the first and second membranes in a spacebetween the second end of the second membrane and the second axis. Arranging the motor arrangements in this way may reduce the overall volume occupied by the transducer assembly (by reducing the '‘width’’ of the transducer assembly for example). The first central axis may be at a midpoint between the first end of the first membrane and the second end of the first membrane. The second central axis may be at a midpoint between the first end of the second membrane and the second end of the second membrane. The first and second ends of a membrane may be ends of the membrane along its longest dimension.

[0105] The first central axis may therefore be: (i) between the first and second ends of the first membrane and (ii) between the second end of the first membrane and a point where the first axis coincides with the first membrane. Similarly, the second central axis may therefore be: (i) between the first and second ends of the second membrane and (ii) between the second end of the second membrane and a point where the second axis coincides with the second membrane. The second motor arrangement is therefore arranged under the “longer” side of the first membrane and the first motor arrangement is arranged under the “longer” side of the second membrane.

[0106] In examples, the first axis coincides with the second membrane at a point closer to the second end of the second membrane than the first end of the second membrane and the second axis coincides with the first membrane at a point closer to the second end of the first membrane than the first end of the first membrane.

[0107] In some examples, the one or more motors of the first motor arrangement at least partially overlap along the first and second central axes with the one or more motors of the second motor arrangement. Put another way, the one or more motors of the first motor arrangement at least partially overlap between the first and second membranes with the one or more motors of the second motor arrangement. This may enable the transducer assembly to have a low profile, and is possible because the one or more motors of the first motor arrangement are offset from the one or more motors of the second motor arrangement.

[0108] In examples, the first membrane has a first shape, the second membrane has a second shape and the first and second shapes are the same and are rotated by 180 degrees with respect to each other. Arranging the membranes in this way may allow the motor arrangements to be offset from each other, thereby reducing the overall volume occupied by the transducer assembly. Furthermore, having membranes with the same shape may provide the transducer assembly with a more balanced sound profile. In a particular example, the first and second membranes may also have the same shape and size. In other examples the sizes of the first andsecond membranes may be different, but they may have the same shape. In a particular example, the first and second membranes are teardrop shaped. The membranes may be rotated by 180 degrees with respect to each other about the first and second axes, respectively.

[0109] In examples, at least one of: (i) the first membrane has a first shape, the first shape having a rotational symmetry of order 1, and (ii) the second membrane has a second shape, the second shape having a rotational symmetry' of order 1. In other words the first and second membranes have a shape which does not have rotational symmetry. In examples, the first and second membranes each have a single line of symmetry. A tear drop shape, for example, has a single line of symmetry7and a rotational symmetry' of order 1 (no rotational symmetry ).

[0110] In examples, the first membrane is configured to generate a first acoustic wave, the second membrane is configured to generate a second acoustic wave, and the first and second acoustic waves are directed away from the transducer assembly in substantially opposite directions.

[0111] According to a fifth aspect of the disclosure, there is provided a playback device comprising the transducer assembly of the fourth aspect, discussed above. In examples, the playback device comprises a plurality of transducer assemblies of the fourth aspect.

[0112] According to a sixth aspect of the disclosure, there is provided a system comprising: the playback device of the fifth aspect, and at least one further playback device. The at least one further playback device may or may not comprise a transducer assembly of the fourth aspect. For example, the at least one further playback device may comprise a different type of transducer assembly. The system may further comprise a controller configured to send an instruction to the playback device to cause the playback device to play back audio.

[0113] While some examples described herein may refer to functions performed by given actors such as “users,” “listeners,” and / or other entities, it should be understood that this is for purposes of explanation only. The claims should not be interpreted to require action by any such example actor unless explicitly required by the language of the claims themselves.II. Suitable Operating Environment

[0114] 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).

[0115] 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 of) 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.

[0116] A transducer, also known as a transducer assembly, may comprise at least: a magnet assembly, at least one voice coil, and at least one diaphragm or membrane.

[0117] 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).

[0118] 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.

[0119] 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) and play 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.

[0120] 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.

[0121] 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 may be 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.

[0122] 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.

[0123] 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 lOli and listening to hip hop music being played by the playback device 110c while another user is preparing 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. PatentNo. 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

[0124] 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.

[0125] 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 transmitted from 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.

[0126] 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 serv er, 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.

[0127] 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 WiFi network, 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. l lah, 802.1 lai, 802. 1 laj, 802.11aq, 802.1 lax, 802. Hay, 802.15, etc. transmitted at 2.4 Gigahertz (GHz), 5 GHz, and / or another suitable frequency.

[0128] 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 accessibleonly 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.

[0129] 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 system 100 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.

[0130] 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 110. In other examples, however, the media playback system 100 omits the group 107a and / or other grouped arrangements of the playback devices 110.

[0131] 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 VAS (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 HOa-llOn, 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 memory stored at, for example, the playback device, a network microphone device, or a control device. b. Suitable Playback Devices

[0132] 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 wires, 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. In some examples, the digital I / O 111b comprises a High-Definition Multimedia Interface (HDMI) interface and / or cable. In some examples, the digital I / O 11 lb includes one or morewireless communication links comprising, for example, a radio frequency (RF), infrared, WiFi, Bluetooth, or another suitable communication protocol. In certain examples, the analog I / O 11 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.

[0133] 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.

[0134] 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-firing transducer. 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.

[0135] 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, battery7charging bases).

[0136] 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 can include, 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).

[0137] 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.

[0138] In some examples, the memory7112b 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 110a 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 a portion 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.

[0139] 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.

[0140] 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 network 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 112d 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).

[0141] 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 networkinterface 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.

[0142] 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 amplified audio signals to a plurality of the transducers 114. In some other examples, the electronics 112 omits the amplifiers 112h.

[0143] 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 usedherein, “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.

[0144] By way of illustration, SONOS, Inc. presently offers (or has offered) for sale certain playback devices including, for example, a “SONOS ONE,” “MOVE,” “PLAY:5,” “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 comprises wired 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 1 10 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.

[0145] 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 1 10a 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 lowfrequency 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)

[0146] 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 1 12b (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).

[0147] 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) configured to receive user input (e.g., touch input, voice input) without a separate control device. In other examples, however, the playback device 11 Or receives commands from another control device (e.g.. the control device 130a of Figure IB).

[0148] 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 querying 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.

[0149] 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 word followed 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

[0150] 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 130acomprises, 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).

[0151] 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 those functions. 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.

[0152] 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 110. Thenetwork 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.

[0153] 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 a touch screen interface of a smartphone (e.g., an iPhone™, an Android phone). In some examples, however, user interfaces of varying 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.

[0154] 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 110). 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.

[0155] 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 135 are 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.

[0156] It will be appreciated that one or more components illustrated in at least Figure 1C are optional, and may be omitted from a playback device. A playback device may comprise one or more transducer assemblies. In examples, the playback device further comprises one or more processors and memory storing instructions.III. Transducer Assembly

[0157] As previously discussed, the present disclosure relates to transducer assemblies. One or more transducer assemblies 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 1A-H. a. A First Type of Transducer Assembly with Shared Magnet Assembly

[0158] Figures 2-6B relate to a first type of transducer assembly, and Figures 7-10 relate to a second type of transducer assembly. Each will be discussed in turn.

[0159] Figure 2 is a schematic side view depicting an example first type of transducer assembly 200, comprising a first membrane 202 (or diaphragm or cone), a second membrane 204 (or diaphragm or cone), a magnet assembly 206. a first actuating element coupled to the first membrane 202 and a second actuating element coupled to the second membrane 204. In this example, the first actuating element comprises a first voice coil 208 connected (either directly or indirectly) to a first support element 212 (also known as a former), the first support element 212 being connected to the first membrane 202. Similarly, the second actuating element comprises a second voice coil 210 connected (either directly or indirectly) to a second support element 214 (also know n as a former), the second support element 214 being connected to the second membrane 204. In other cases, each actuating element may comprise few er or more components. For example, in its simplest form, each actuating element may comprise a voice coil that is directly coupled to its respective membrane.

[0160] In this example, the first and second membranes 202, 204 both have a frustum shape, with narrow^ ends of the frustums being arranged closer to the voice coils 208, 210, and wider ends of the frustums facing outwards, and away from the magnet assembly 206. In other examples, the first and second membranes 202, 204 take other forms. For example, the firstand second membranes 202, 204 may be flat. Each membrane 202, 204 optionally has a dust cap positioned thereon, to cover an aperture 232, 234 formed through the membrane 202, 204. In particular, a first dust cap 226 is arranged on the first membrane 202, and a second dust cap 218 is arranged on the second membrane 204.

[0161] As shown, the magnet assembly 206 extends through each aperture formed in each membrane 202, 204. For example, one end of the magnet assembly 206 extends through a first aperture 232 formed through the first membrane 202, and an opposite end of the magnet assembly 206 extends through a second aperture 234 formed through the second membrane 204. The magnet assembly is therefore arranged in a space between the first dust cap 226 and a narrow end of the first membrane (i.e.. the point at where the aperture 232 is formed), and in a space between the second dust cap 228 and a narrow end of the second membrane (i.e.. the point at where the aperture 234 is formed). This configuration enables the transducer assembly 200 to have a lower profile. In this example, where the first and second voice coils 208, 210 are in their rest positions, the magnet assembly 206 extends through the first aperture 232 and through the second aperture 234. In some examples, however, the first and second voice coils 208, 210 do not extend through the apertures 232, 234 in their rest positions, but only pass through the apertures 232, 234, when the voice coils 208, 210 are displaced (i.e., in use and no longer in their rest positions), such displaced inwardly, closer to the second magnetic element 218.

[0162] In this example, the magnet assembly 206 comprises three magnets - a first magnetic element 216 (in the form of a first permanent magnet 216), a second magnetic element 218 (in the form of a second permanent magnet 218), and a third magnetic element 220 (in the form of a third permanent magnet 218). As shown, the second magnetic element 218 is arranged between the first and third magnetic elements 216, 220. In some examples, the magnet assembly is formed from a monolithic element.

[0163] The magnet assembly 206 of this example further comprises a first spacer element 222 (also known as a first pole piece 222) arranged between the first and second magnetic elements 216, 218. and a second spacer element 224 (also known as a second pole piece 224) arranged between the second and third magnetic elements 218, 220. A pole piece can help focus or concentrate the magnetic flux from the magnetic elements onto the voice coil. In some examples, one or both spacer elements are omitted.

[0164] As shown in Figure 2, the first magnetic element 216 and the second magnetic element 218 are magnetized having an inverted polarity. For example, a north pole 216a of thefirst magnetic element 216 is arranged facing a north pole 218a of the second magnetic element 218. A south pole 216b of the first magnetic element 216 is arranged facing away from the second magnetic element 218, and a south pole 218b of the second magnetic element 218 is arranged facing away from the first magnetic element 216. Similarly, the third magnetic element 220 and the second magnetic element 218 are magnetized having an inverted polarity. For example, a south pole 218b of the second magnetic element 218 is arranged facing a south pole 220b of the third magnetic element 220. A north pole 218a of the second magnetic element 218 is arranged facing away from the third magnetic element 220, and a north pole 220a of the third magnetic element 220 is arranged facing away from the second magnetic element 218. Accordingly, the first and third magnetic elements 216, 218 are generally axially magnetized in the same direction (referred to as a first direction, shown with arrows A and C), and the second magnetic element 218 is generally axially magnetized in the opposite direction (referred to as a second direction, shown with arrow B). Opposite ends of the magnet assembly 206 therefore have opposite polarity (see for example, a first end of the magnet assembly 206 being a south pole 216b, and a second, opposite, end of the magnet assembly 206 being a north pole 220a).

[0165] In this particular configuration, the magnet assembly 206 defines a longitudinal axis 230 that is generally parallel to magnetization directions of the first, second and third magnetic elements 216, 218, 220. In some examples, rather than being axially magnetized along a certain direction, the magnetization direction may bend through the magnetic element.

[0166] As illustrated, the first voice coil 208 is arranged relative to the first and second magnetic elements 216, 218 (such as arranged at a midpoint between the first and second magnetic elements 216, 218), such that a magnetic field generated by the first voice coil 208 interacts with magnetic fields of the first and second magnetic elements 216. 218. This causes the first voice coil (and therefore the first actuating element and the first membrane 202) to move along the axis 230. The first voice coil 208 therefore extends around the magnet assembly 206 in the region where the first and second magnetic elements 216, 218 have opposing polarity. Figure 2 shows the first voice coil 208 in a rest position (having no displacement or excursion along the axis 230).

[0167] Similarly, the second voice coil 210 is arranged relative to the second and third magnetic elements 218, 220 (such as arranged at a midpoint between the second and third magnetic elements 218, 220), such that a magnetic field generated by the second voice coil 210 interacts with magnetic fields of the second and third magnetic elements 218. 220. This causesthe second voice coil (and therefore the second actuating element and the second membrane 204) to move along the axis 230. The second voice coil 210 therefore extends around the magnet assembly 206 in the region where the second and third magnetic elements 218, 220 have opposing polarity. Figure 2 shows the second voice coil 210 in a rest position (having no displacement or excursion along the axis 230).

[0168] As is well known, movement of a membrane causes an acoustic wave to be generated. In this case, movement of the first membrane 202 causes a first acoustic wave 236 to be generated, and movement of the second membrane 204 causes a second acoustic wave 238 to be generated, the first and second acoustic waves 236, 238 being generally directed away from the transducer assembly 200 in substantially opposite directions. For example, Figure 2 depicts the first acoustic wave 236 travelling away from the transducer assembly 200 in one direction, and the second acoustic wave 238 travelling away from the transducer assembly 200 in the opposite direction. The two directions may be generally parallel to the longitudinal axis 230, which is parallel to the excursion directions of the voice coils 208, 210. Some examples (not shown) may include waveguides positioned after the membranes, to change the direction of the acoustic wave.

[0169] As discussed, in this example, both the first and second membranes 202, 204 are frustoconical, and dust caps 226, 228 cover the apertures 232, 236 formed through the membranes 202, 204. As shown in Figure 2. where the first voice coil 208 is in a rest position, one end of the magnet assembly 206 (i.e., the first magnetic element 216) is spaced apart from the first dust cap 226 (at their closest point) by a distance Di, that is greater than a maximum mechanical excursion distance of the first voice coil 208. Similarly, when the second voice coil 210 is in a rest position, an opposite end of the magnet assembly 206 (i.e., the third magnetic element 220) is spaced apart from the second dust cap 228 (at their closest point) by a distance D2, that is greater than a maximum mechanical excursion distance of the second voice coil 210. This ensures the magnet assembly 206 does not contact the dust caps during use.

[0170] As mentioned, in some examples, one or both spacer elements 222, 224 can be varied in thickness during use, where the thickness of the spacer element 222, 224 is measured parallel to the axis 230. In one example, the spacer element 222, 224 may be formed from deformable material, that can be compressed or extended during use. In other example, the spacer elements 222, 224 may be mechanically varied in thickness. For example, one or more components or layers of the spacer element 222, 224 may be moved. In a particular example, when theexcursion distances of the voice coils 208, 210 increases, the thickness of the spacer elements 222, 224 may be decreased.

[0171] In some examples, the transducer assembly 200 further includes an extension pole piece to help shield the magnetic fields from the two voice coils 208, 210 from each other. Figure 3 therefore depicts a modification of the transducer assembly 200 of Figure 3, in which an extension pole piece 302 extends around the second magnetic element 218 and between the first and second voice coils 208, 210. Other features of the transducer assembly 200 correspond to those described in relation to Figure 2 above. Similarly, any other transducer assemblies described above or herein may incorporate an extension pole piece of the form discussed here, or any other form discussed above or herein.

[0172] In some examples, the extension pole piece 302 contacts the second magnetic element 218, In other examples, they do not contact each other. Other features of the transducer assembly may hold the pole piece 302 in place (not shown).

[0173] In a variation on the transducer assembly 200 of Figure 3, the extension pole piece may extend through the magnet assembly, between the first and second voice coils 208, 210. The second magnetic element of the magnet assembly may therefore be comprised of two or more separate magnets, the two or more magnets being magnetized in the same direction, and thereby forming the second magnetic element.

[0174] To illustrate, Figure 4 depicts a further modification of the transducer assembly of Figures 2 and 3. where an extension pole piece 402 extends through the second magnetic element 218, betw een a first magnet 404 of the second magnetic element 218 and a second magnet 406 of the second magnetic element 218. The first magnet 404 is therefore separated and spaced apart from the second magnet 406 by the extension pole piece 402. As in the example of Figure 3, the extension pole piece 402 extends away from and around the second magnetic element 218 and between the first and second voice coils 208, 210.

[0175] As mentioned, the first and second magnets 404, 406 are magnetized in the same direction as each other. Accordingly, overall, the magnetization of the first and second magnets 404, 406 means that the second magnetic element 218 is magnetized in the same direction as discussed in relation to Figure 2 (opposite to the magnetization direction of both the first and third magnetic elements 216, 218).

[0176] Although the extension pole piece 402 is shown having a variation in thickness (being thinner at parts external to the magnet assembly 206), the extension pole piece 402 may have a uniform thickness in other examples. Having a thicker section arranged ithin the magnetassembly 206 can provide an additional spacing between the two voice coils 208. 210, thereby allowing a greater excursion of the voice coils.

[0177] As discussed, in alternative examples, one or both membranes may have flat profiles, or substantially flat profiles, rather than being frustum shaped. Figure 5 therefore depicts a modification of the transducer assembly 200 of Figure 2, in which the membranes are flat. In particular, in Figure 5, the first membrane 502 and the second membrane 504, both have a flat shape. Other features of the transducer assembly 200 correspond to those described in relation to Figure 2 above. It will be appreciated that any other transducer assemblies described above or herein may include one or more flat membranes. Although not shown in the example of Figure 5. an extension pole piece may additionally be included, such as was discussed in relation to Figures 3 and 4.

[0178] In the example of Figure 5, the membranes 502, 504 do not include dust caps. However, in a similar way as discussed above in Figure 2, when the first voice coil 208 is in a rest position, one end of the magnet assembly 206 (i.e., the first magnetic element 216) is spaced apart from the first membrane 502 (at their closest point) by a distance Di, that is greater than a maximum mechanical excursion distance of the first voice coil 208. Similarly, when the second voice coil 210 is in a rest position, an opposite end of the magnet assembly 206 (i.e., the third magnetic element 220) is spaced apart from the second membrane 504 (at their closest point) by a distance D2, that is greater than a maximum mechanical excursion distance of the second voice coil 210. This ensures the magnet assembly 206 does not contact the membranes during use.

[0179] In some examples, one or both of the membranes may be ring or halo shaped. For example, one or both membranes may delimit an aperture though the membrane. Figures 6A and 6B therefore depict an example transducer assembly 200 having flat membranes, each with an aperture formed through the membrane. Other features of the transducer assembly 200 correspond to those described in relation to Figure 2 above. It will be appreciated that any other transducer assemblies described above or herein may include one or more flat membranes having apertures formed therein.

[0180] In particular. Figures 6A and 6B depict a transducer assembly 200 comprising a first membrane 602 delimiting a first aperture 606, and a second membrane 604 delimiting a second aperture 608. As discussed, by having apertures formed through the membranes, the transducer assembly 200 can have a lower profile. For example, the transducer assembly of Figure 6A has a lower profile than the transducer assembly of Figure 5, because a spacing between themembrane and the magnet assembly can be reduced to less than the maximum mechanical excursion distance of the voice coil.

[0181] In Figure 6A, the voice coils 208, 210 are in their rest positions. In Figure 6B, the voice coils 208, 210 are located at their positions of maximum mechanical excursion. As shown, the magnet assembly 206 is shown extending through the first and second apertures 606, 608. As discussed, in other examples, the magnet assembly 206 may extend through the first and second apertures 606, 608 when the voice coils 208, 210 are also in their rest positions. b. A Second Type of Transducer Assembly with Offset Magnet Assemblies

[0182] Figure 7 is a schematic side view depicting an example second type of transducer assembly 700, comprising a first membrane 702 (or diaphragm or cone) having a first end 702a and a second end 702b, and a second membrane 704 (or diaphragm or cone) having a first end 704a and a second end 704b. The transducer assembly 700 further comprises a first motor arrangement to drive the first membrane 702 along a first axis 706, and a second motor arrangement to drive the second membrane 704 along a second axis 708. As shown, the first and second axes 706. 708 are parallel to each other. The first motor arrangement of this example comprises a single motor, referred to herein as a first motor, to drive the first membrane 702 along the first axis 706. Similarly, the second motor arrangement of this example comprises a single motor, referred to herein as a second motor, to drive the second membrane 704 along the second axis 708. The first and second motors are arranged between the first and second membranes 702. 704, as shown in Figure 7.

[0183] The first motor comprises a first magnet assembly 710 arranged along the first axis 706, and a first actuating element coupled to the first membrane 702. In this example, the first actuating element comprises a first voice coil 714 connected (either directly or indirectly) to a first support element 718 (also known as a former), the first support element 718 being connected to the first membrane 702. The second motor comprises a second magnet assembly 712 arranged along the second axis 708, and a second actuating element coupled to the second membrane 704. In this example, the second actuating element comprises a second voice coil 716 connected (either directly or indirectly) to a second support element 720 (also known as a former), the second support element 720 being connected to the second membrane 704. In other examples, each actuating element may comprise fewer or greater components. For example, in its simplest form, each actuating element may comprise a voice coil that is directly coupled to its respective membrane.

[0184] As shown in Figure 7, the first motor at least partially overlaps along the first and second central axes 722, 724 with second motor. For example, the first and second magnet assemblies 710, 712 overlap between the first and second membranes 702, 704 in the region, R.

[0185] As is well known, movement of a membrane causes an acoustic wave to be generated. In this case, movement of the first membrane 702 causes a first acoustic wave 726 to be generated, and movement of the second membrane 704 causes a second acoustic wave 728 to be generated, the first and second acoustic waves 726, 728 being generally directed away from the transducer assembly 700 in substantially opposite directions. For example, Figure 7 depicts the first acoustic wave 726 travelling away from the transducer assembly 700 in one direction, and the second acoustic wave 728 travelling away from the transducer assembly 700 in the opposite direction. The two directions may be generally parallel to the first and second axes 706, 708, which are parallel to the excursion directions of the voice coils 714, 716. Other examples may include one or more waveguides (not shown) positioned after the membranes to change the direction of the acoustic waves.

[0186] In this example, the first and second membranes 702, 704 are both flat, and have the same size (and therefore surface area). In other examples, the membranes 702, 704 may not be flat and / or may not have the same size.

[0187] In the example of Figure 7. the first membrane 702 has a center of mass, and the first axis 706 coincides with the center of mass of the first membrane 702. The first motor arrangement (and in this case, the first motor) drives the first membrane 702 at its center of mass. Similarly, the second membrane 707 has a center of mass, and the second axis 708 coincides with the center of mass of the second membrane 704. The second motor arrangement (and in this case, the second motor) drives the second membrane 704 at its center of mass.

[0188] The first membrane 702 defines a first central axis 722 that coincides with a midpoint (or center) of a longest dimension of the first membrane 702. The second membrane 704 also defines a second central axis 724 that coincides with a midpoint (or center) of a longest dimension of the second membrane 704. As shown in Figure 7. the first central axis 722 is offset from the first axis 706, and the second central axis 724 is offset from the second axis 708. The first and second axes 706, 708 are also offset from each other. The first and second membranes 702, 704 are therefore driven “off-center’" by their respective motor arrangements. In this particular example, the first and second central axes 722, 724 coincide.

[0189] In the example of Figure 7, the first axis 706 is offset from the first central axis 722 such that the first axis 706 coincides with the first membrane 702 at a point A. closer to the first end 702a of the first membrane 702 than the second end 702b of the first membrane 702. Similarly, the second axis 708 is offset from the second central axis 724 such that the second axis 708 coincides with the second membrane 704 at a point B, closer to a first end 704a of the second membrane 704 than the second end 704b of the second membrane 704. In this example, point A corresponds to the center of mass of the first membrane 702, and point B corresponds to the center of mass of the second membrane 704. The first and second membranes 702, 704 are arranged relative to each other such that their center of masses are offset from each other. Figure 7 shows the second motor (that is, the second magnet assembly 712 and the second vice coil 716) positioned between the first and second membranes 702, 704 in a space between the second end 702b of the first membrane 702 and the first axis 706, and the first motor (that is, the first magnet assembly 710 and the first vice coil 714) positioned between the first and second membranes 702, 704 in a space between the second end 704b of the second membrane and the second axis 708. Accordingly, a "longer side" of the first membrane 702 (that is, the portion of the membrane between the first axis 706 and the second end 702b), allows the second motor arrangement to be arranged in the space below it). Similarly, a “longer side” of the second membrane 704 (that is, the portion of the membrane between the second axis 708 and the second end 704b), allows the first motor arrangement to be arranged in the space below it).

[0190] In this example, each magnet assembly 710. 712 comprises two magnets - a first magnetic element 730, 732 (in the form of a first permanent magnet 730, 732) and a second magnetic element 734, 736 (in the form of a second permanent magnet 734, 736). Both magnet assemblies 710, 712 of this example further comprise a spacer element 738, 740 (known as pole pieces) arranged between the first and second magnetic elements within each magnet assembly. As discussed above, a pole piece can help focus or concentrate the magnetic flux from the magnetic elements onto the voice coils 714, 716. In some examples, one or both spacer elements 738, 740 are omitted. As mentioned, in some examples, one or both spacer elements 738, 740 can be varied in thickness during use.

[0191] As shown in Figure 7 for the first magnet assembly 710, the first magnetic element 730 and the second magnetic element 734 are magnetized having an inverted polarity. For example, a north pole 730a of the first magnetic element 730 is arranged facing a north pole 734a of the second magnetic element 734. A south pole 730b of the first magnetic element 730 is arranged facing away from the second magnetic element 734, and a south pole 734b of thesecond magnetic element 734 is arranged facing away from the first magnetic element 730. Similarly, for the second magnet assembly 712, the first magnetic element 732 and the second magnetic element 736 are magnetized having an inverted polarity. For example, a north pole 732a of the first magnetic element 732 is arranged facing a north pole 736a of the second magnetic element 736. A south pole 732b of the first magnetic element 732 is arranged facing away from the second magnetic element 736, and a south pole 736b of the second magnetic element 736 is arranged facing away from the first magnetic element 732. Accordingly, the first 730, 732 and second 734, 736 magnetic elements of each magnet assembly 710, 712 are generally axially magnetized in opposite directions. Furthermore, opposite ends of each magnet assembly 710, 712 have the same polarity (see for example, a first end of the first magnet assembly 710 being a south pole, and a second, opposite, end of the first magnet assembly 710 being a south pole). Although Figure 7 shows both magnet assemblies 710, 712 having south poles at their ends, it will be appreciated that one or both magnet assemblies 710, 712 may have north poles at their ends.

[0192] In this particular configuration, each magnet assembly 710, 712 defines a longitudinal axis that is generally parallel to magnetization directions of the first and second magnetic elements 730, 732, 734, 736. In some examples, rather than being axially magnetized along a certain direction, the magnetization direction may bend through the magnetic element.

[0193] As illustrated, the first voice coil 714 is arranged relative to the first and second magnetic elements 730, 734 of the first magnet assembly 710 (such as arranged at a midpoint between the first and second magnetic elements 716, 718), such that a magnetic field generated by the first voice coil 714 interacts with magnetic fields of the first and second magnetic elements 730, 734. This causes the first voice coil 714 (and therefore the first actuating element and the first membrane 702) to move along the first axis 706. The first voice coil 714 therefore extends around the first magnet assembly 710 in the region where the first and second magnetic elements 730, 734 have opposing polarity. Figure 7 shows the first voice coil 714 in a rest position (having no displacement or excursion along the first axis 706).

[0194] Similarly, the second voice coil 716 is arranged relative to the first and second magnetic elements 732, 736 of the second magnet assembly 712 (such as arranged at a midpoint between the first and second magnetic elements 732, 736), such that a magnetic field generated by the second voice coil 716 interacts with magnetic fields of the first and second magnetic elements 732, 736. This causes the second voice coil 716 (and therefore the second actuating element and the second membrane 704) to move along the second axis 708. The second voicecoil 716 therefore extends around the second magnet assembly 712 in the region where the first and second magnetic elements 732. 736 have opposing polarity. Figure 7 shows the second voice coil 716 in a rest position (having no displacement or excursion along the second axis 708).

[0195] As shown in Figure 7, where the first voice coil 714 is in a rest position, one end of the first magnet assembly 710 (i.e., the first magnetic element 730) is spaced apart from the first membrane 702 (at their closest point) by a distance Di, that is greater than a maximum mechanical excursion distance of the first voice coil 714. Similarly, when the second voice coil 716 is in a rest position, one end of the second magnet assembly 706 (i.e., the first magnetic element 732) is spaced apart from the second membrane 704 (at their closest point) by a distance D2, that is greater than a maximum mechanical excursion distance of the second voice coil 716. As an alternative, one or both membranes 702, 704 may delimit an aperture, through which the magnet assembly 710, 712 can pass in use.

[0196] Although Figure 7 depicts each motor arrangement comprising a single motor, it will be appreciated that the same principles can be applied when either or both motor arrangements comprise a plurality of motors, such as motors distributed around the first and / or second axes 706, 708.

[0197] Figure 8 depicts a top-down view of the transducer assembly of Figure 7, showing the first membrane 702 in front of (or above) the second membrane 704, and the first and second motor arrangements between the membranes 702, 704. Figure 8 is therefore shown with transparency, to allow the arrangement of the components to be seen most clearly.

[0198] Figure 8 further depicts the first and second voice coils 714, 716 extending around the first and second axes, respectively, which extend through the membranes 702, 704 at points A and B. respectively. Furthermore, the first central axis of the first membrane 702 extends though the first membrane (and into and out of the page) at point C, and the second central axis of the second membrane 704 extends though the second membrane (and into and out of the page) at point D. Point C therefore shows the midpoint or center of the first membrane 702 along its longest dimension (which, in this example, coincides with a single axis of symmetry 802 of the first membrane 702), and point D shows the midpoint or center of the second membrane 704 along its longest dimension (which, in this example, coincides with a single axis of symmetry of the second membrane 704). As mentioned, because the first and second membranes are the same size and shape, point D is behind point C. Points A and C are both positions that are at midpoints along the first membrane 702 in a direction measuredperpendicular to the longest dimension of the first membrane 702 and the first axis (i.e., in a direction parallel to axis 804). Points B and D are both positions that are at midpoints along the second membrane 704 in a direction measured perpendicular to the longest dimension of the second membrane 704 and the second axis.

[0199] In this example, the first membrane 702 has a shape that has a rotational symmetry' of order 1 and a single axis of symmetry, and in particular, has a tear drop shape. The second membrane 704 also has a shape that has a rotational symmetry of order 1 and a single axis of symmetry, and in particular, has a tear drop shape. Figure 8 shows the shapes of the two membranes being the same, but the first membrane 702 is rotated by 180 degrees with respect to the second membrane 704 (or vice versa) about the central axis 722, 724. This allows the first and second axes 706, 708 to be offset to accommodate the motors in a side-by-side arrangement between the membranes 702, 704. Although the membranes both have tear drop shapes, in other examples, the membranes may have other shapes.

[0200] In this example, both membranes 702, 704 have the same shape and size, and each have a single line of symmetry. Point C therefore corresponds to a midpoint along a line of symmetry 802 of the first membrane 702, and point D corresponds to a midpoint along a line of symmetry7of the second membrane 704. In this example, the lines of symmetry extend between the first 702a, 704a and second 702b. 704b ends of the membranes 702, 704.

[0201] As mentioned earlier, the first membrane 702 has a first surface area defined between the first end 702a of the first membrane and the first axis (at point A), and the first surface area is equal in size to a second surface area of the first membrane 702 defined between the second, opposite, end 702b of the first membrane and the first axis. For example, in Figure 8, the first surface area is given by the area to the left of axis 804, were axis 804 is perpendicular to both the first axis and the longest dimension of the first membrane 702 (the longest dimension being measured along axis 802). The second membrane 704 is similarly configured.

[0202] Figure 8 further depicts the first axis 706 (point A) being offset from the first end 702a of the first membrane 702 by a distance D3 and being offset from the second end 702b of the first membrane 702 by a distance D4. As shown, D3 is less than D4. so the first axis 706 coincides with the first membrane 702 at a point closer to the first end 702a than the second end 702b. Similarly, the second axis 708 (point B) is offset from the first end 704a of the second membrane 704 by a distance that is less than a distance between the second end 704b of the second membrane 704. The first 702a, 704a and second 702b, 704b ends of each membrane 702, 704 are ends of the membrane along its longest dimension.

[0203] As briefly mentioned above, in some examples, the first and / or second membranes delimit an aperture through which a magnet assembly of a motor can extend during use. Figure 9 therefore depicts an example transducer assembly 700 where an aperture is formed through both membranes. Other features of the transducer assembly correspond to those described in relation to Figure 7 and 8 above. It will be appreciated that any other transducer assemblies described above or herein may include membranes having an aperture formed therein.

[0204] In particular. Figure 9 depicts a transducer assembly 700 comprising a first membrane 902 delimiting a first aperture 906, and a second membrane 904 delimiting a second aperture 908. As discussed, by having apertures formed through the membranes, the transducer assembly 700 can have a lower profile. For example, the transducer assembly of Figure 9 has a lower profile than the transducer assembly of Figure 7, because the spacings between the membranes 902, 904 and the magnet assemblies 710, 712 can be reduced to less than the maximum mechanical excursion distance of the voice coils 714, 716.

[0205] In Figure 9, the voice coils 714, 716 are in their rest positions, and the magnet assemblies 710, 712 do not extend through the respective apertures 906, 908. However, in use and for at least the maximum mechanical excursion distance for each voice coil 714, 716, the magnet assemblies 710, 712 do extend through the respective apertures 906, 908. As discussed, in other examples, the magnet assemblies 710, 712 may extend through the first and second apertures 906, 908 respectively when the voice coils 714, 716 are also in their rest positions.

[0206] As briefly mentioned above, in some examples, the first and / or second motor arrangements comprise more than one motor to collectively drive a membrane along an axis. Figure 10 therefore depicts a schematic top-down, transparent, view of an example transducer assembly 700 where the first motor arrangement comprises a plurality of motors (in this case four motors 1002a-d) arranged and equally spaced around the first axis (which coincides with the first membrane 702 at point A), where the motors are configured to collectively operate to drive the first membrane 702 along the first axis. Similarly, the second motor arrangement comprises a plurality of motors (in this case four motors 1004a-d) arranged and equally spaced around the second axis (which coincides with the second membrane 704 at point B), where the motors are configured to collectively operate to drive the second membrane 704 along the second axis. As discussed above, each motor 1002a-d, 1004a-d may comprise a magnet assembly and a voice coil coupled to the respective membrane. Other features of the transducer assembly 700 correspond to those described in relation to Figure 7 and 8 above.IV. Conclusion

[0207] The description above discloses, among other things, various example transducer assemblies. It is understood that such examples are merely illustrative and should not be considered as limiting.

[0208] 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. Other operating 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.

[0209] 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.

[0210] 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.

[0211] 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 be practiced 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.

[0212] 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 memory, DVD, CD, Blu-ray, and so on, storing the software and / or firmware.

Claims

CLAIMS1. A transducer assembly, comprising: a first membrane; a second membrane; a magnet assembly; a first actuating element coupled to the first membrane and comprising a first voice coil, the first voice coil extending around the magnet assembly and being arranged to generate a magnetic field for interacting with a magnetic field of the magnet assembly to move the first actuating element along an axis of the magnet assembly relative to the magnet assembly; and a second actuating element coupled to the second membrane and comprising a second voice coil, the second voice coil extending around the magnet assembly and being arranged to generate a magnetic field for interacting with the magnetic field of the magnet assembly to move the second actuating element along the axis relative to the magnet assembly.

2. The transducer assembly of claim 1, wherein the magnet assembly comprises: a first magnetic element; a second magnetic element; and a third magnetic element; wherein: the second magnetic element is arranged between the first and third magnetic elements; the first, second and third magnetic elements are arranged along the axis of the magnet assembly; the first voice coil is arranged relative to the first and second magnetic elements such that the magnetic field generated by the first voice coil interacts with magnetic fields of the first and second magnetic elements to move the first actuating element along the axis; and the second voice coil is arranged relative to the second and third magnetic elements such that the magnetic field generated by the second voice coil interacts with magnetic fields of the second and third magnetic elements to move the second actuating element along the axis.

3. The transducer assembly of claim 2, wherein: the first magnetic element is axially magnetized in a first direction; the second magnetic element is axially magnetized in a second direction, the second direction being opposite to the first direction; and the third magnetic element is axially magnetized in the first direction.

4. The transducer assembly of claim 3, wherein the first magnetic element is a first magnet, the second magnetic element is a second magnet, and the third magnetic element is a third magnet.

5. The transducer assembly of any of claims 2 to 4, further comprising an extension pole piece extending around the second magnetic element and between the first and second voice coils.

6. The transducer assembly of any of claims 2 to 3, wherein the second magnetic element comprises at least two magnets, at least one of the two magnets being spaced apart from at least another magnet of the at least two magnets by an extension pole piece, wherein the extension pole piece extends away from the second magnetic element and between the first and second voice coils.

7. The transducer assembly of any of claims 2 to 6, further comprising: a first pole piece arranged between first and second magnetic elements for concentrating the magnetic flux on the first voice coil; and a second pole piece arranged between third and second magnetic elements for concentrating the magnetic flux on the second voice coil.

8. The transducer assembly of claim 7, wherein for at least one of the first or second pole pieces, a thickness of the pole piece can be varied during use.

9. The transducer assembly of any preceding claim, wherein at least one of:when the first voice coil is in a rest position, the magnet assembly is spaced apart from the first membrane by a distance that is greater than a maximum mechanical excursion distance of the first voice coil; and when the second voice coil is in a rest position, the magnet assembly is spaced apart from the second membrane by a distance that is greater than a maximum mechanical excursion distance of the second voice coil.

10. The transducer assembly of any of claims 1 to 8, wherein at least one of: the first membrane is substantially conical or frustoconical, and the transducer assembly further comprises a first dust cap arranged on the first membrane, and when the first voice coil in a rest position, the magnet assembly is spaced apart from the first dust cap by a distance that is greater than a maximum mechanical excursion distance of the first voice coil; and the second membrane is substantially conical or frustoconical, and the transducer assembly further comprises a second dust cap arranged on the second membrane, and when the second voice coil in a rest position, the magnet assembly is spaced apart from the second dust cap by a distance that is greater than a maximum mechanical excursion distance of the second voice coil.

11. The transducer assembly of any of claims 1 to 8, wherein at least one of: the first membrane delimits a first aperture, and in use, the magnet assembly extends through the first aperture; and the second membrane delimits a second aperture, and in use, the magnet assembly extends through the second aperture.

12. The transducer assembly of any preceding claim, wherein: the first membrane is configured to generate a first acoustic wave, the second membrane is configured to generate a second acoustic wave; and the first and second acoustic waves are directed away from the transducer assembly in substantially opposite directions.

13. A playback device comprising the transducer assembly of any preceding claim.

14. A system comprising: the playback device of claim 13; and at least one further playback device.

15. A transducer assembly, comprising: a first membrane; a second membrane; a first motor arrangement, arranged between the first and second membranes, configured to drive the first membrane along a first axis, the first motor arrangement comprising one or more motors for driving the first membrane; and a second motor arrangement, arranged between the first and second membranes, configured to drive the second membrane along a second axis, the second motor arrangement comprising one or more motors for driving the second membrane; wherein: the first axis is offset from a first central axis of the first membrane and the second axis; and the second axis is offset from a second central axis of the second membrane.

16. The transducer assembly of claim 1 , wherein at least one of: the first motor arrangement comprises a first motor configured to drive the first membrane, the first motor comprising: a first magnet assembly arranged along the first axis; and a first actuating element coupled to the first membrane and comprising a first voice coil, the first voice coil extending around the first axis and being arranged to generate a magnetic field for interacting with one or more magnetic fields generated by the first magnet assembly to move the first actuating element along the first axis; or the second motor arrangement comprises a second motor configured to drive the second membrane, the second motor comprising: a second magnet assembly arranged along the second axis; and a second actuating element coupled to the second membrane and comprising a second voice coil, the second voice coil extending around the second axis and being arranged to generate a magnetic field for interacting with one or more magnetic fieldsgenerated by the second magnet assembly to move the second actuating element along the second axis.

17. The transducer assembly of claim 15 or 16, wherein at least one of: the first motor arrangement comprises a single motor; or the second motor arrangement comprises a single motor.

18. The transducer assembly of claim 16 or 17 when appendant to claim 16, wherein at least one of: when the first voice coil is in a rest position, the first magnet assembly is spaced apart from the first membrane by a distance that is greater than a maximum mechanical excursion distance of the first voice coil; or when the second voice coil is in a rest position, the second magnet assembly is spaced apart from the second membrane by a distance that is greater than a maximum mechanical excursion distance of the second voice coil.

19. The transducer assembly of claim 16 or 17 when appendant to claim 16, wherein at least one of: the first membrane delimits a first aperture, and in use, the first magnet assembly extends through the first aperture; or the second membrane delimits a second aperture, and in use, the second magnet assembly extends through the second aperture.

20. The transducer assembly of any of claims 15 to 19, wherein at least one of: the first motor arrangement comprises a plurality of motors arranged around the first axis and configured to collectively drive the first membrane along the first axis; or the second motor arrangement comprises a plurality of motors arranged around the second axis and configured to collectively drive the second membrane along the second axis.

21. The transducer assembly of any of claims 15 to 20, wherein at least one of: the first central axis of the first diaphragm coincides with a midpoint of a longest dimension of the first diaphragm; orthe second central axis of the second diaphragm coincides with a midpoint of a longest dimension of the second diaphragm.

22. The transducer assembly of any of claims 15 to 21, wherein at least one of: the first axis coincides with a center of mass of the first membrane; or the second axis coincides with a center of mass of the second membrane.

23. The transducer assembly of any of claims 15 to 22, wherein at least one of: the first axis is offset from the first central axis such that the first axis coincides with the first membrane at a point closer to a first end of the first membrane than a second, opposite end of the first membrane, and the second motor arrangement is arranged between the first and second membranes in a space between the second end of the first membrane and the first axis; and the second axis is offset from the second central axis such that the second axis coincides with the second membrane at a point closer to a first end of the second membrane than a second, opposite end of the second membrane, and the first motor arrangement is arranged between the first and second membranes in a space between the second end of the second membrane and the second axis.

24. The transducer assembly of any of claims 15 to 23, wherein the one or more motors of the first motor arrangement at least partially overlap along the first and second central axes with the one or more motors of the second motor arrangement.

25. The transducer assembly of any of claims 15 to 24, wherein: the first membrane has a first shape, the second membrane has a second shape and the first and second shapes are the same and are rotated by 180 degrees with respect to each other.

26. The transducer assembly of any of claims 15 to 25, wherein at least one of: the first membrane has a first shape, the first shape having a rotational symmetry of order 1; and the second membrane has a second shape, the second shape having a rotational svmmetrv of order 1.

27. The transducer assembly of any of claims 15 to 26, wherein: the first membrane is configured to generate a first acoustic wave, the second membrane is configured to generate a second acoustic wave; and the first and second acoustic waves are directed away from the transducer assembly in substantially opposite directions.

28. A playback device comprising the transducer assembly of any of claims 15 to 27.

29. A system comprising: the playback device of claim 28; and at least one further playback device.

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