Speaker

Abstract

A loudspeaker (100) is provided, which includes a frame (200), a diaphragm (300) suspended from the frame, and a drive unit (400); wherein the drive unit has a fixed part (420) fixed to the frame and a translatable part (440) fixed to the diaphragm, the translatable part of the drive unit includes a magnet unit (441) configured to generate a magnetic field in an air gap (442), and the fixed part of the drive unit includes a voice coil (422) configured to be located in the air gap when the diaphragm is stationary; and the loudspeaker is operable to excite the voice coil so that the magnet unit moves relative to the voice coil along a movement axis (102), thereby causing the diaphragm to move along the movement axis to generate sound.

Description

[0001] Cross - reference to related applications

[0002] This application claims the priority of GB2204878.9 filed on April 4, 2022. Technical field

[0003] The present invention relates to a loudspeaker including a frame, a diaphragm, and a drive unit. In some examples, the present invention relates to a subwoofer. Background art

[0004] A typical conventional loudspeaker has a frame, a diaphragm, and a drive unit for sound reproduction. In use, the drive unit moves the diaphragm, which acts as a piston, back and forth to generate a pressure wave, i.e., sound.

[0005] The drive unit generally includes a magnet unit attached to the frame and a voice coil attached to the diaphragm. By exciting the voice coil, the magnet unit and the voice coil cooperate magnetically with each other, i.e., interact magnetically, to achieve the displacement of the combination of the voice coil and the diaphragm, thereby generating sound. Summary of the invention

[0006] Compared with the conventional loudspeaker outlined in the above background art section, according to the present invention, there is provided a loudspeaker having a drive unit including a translatable magnet unit and a fixed voice coil.

[0007] According to a first aspect of the present invention, there is provided a loudspeaker including a frame, a diaphragm suspended from the frame, and a drive unit. The drive unit has a fixed part fixed to the frame and a translatable part fixed to the diaphragm. The translatable part of the drive unit includes a magnet unit configured to generate a magnetic field in an air gap. The fixed part of the drive unit includes a voice coil configured to be located in the air gap when the diaphragm is stationary. The loudspeaker is operable to excite the voice coil to move the magnet unit relative to the voice coil along a movement axis, thereby moving the diaphragm along the movement axis to generate sound.

[0008] The loudspeaker can provide an improved structure with fewer and / or simpler components, for example, eliminating the need for flexible leads and the ticking noise that may be associated with flexible leads. Moreover, the exemplary loudspeaker can be manufactured on existing production lines using existing machines, jigs, and fixtures.

[0009] The loudspeaker may include one or more suspension elements, preferably at least two suspension elements.

[0010] One or more suspension elements may include a first suspension element, such as a surround, attached to the frame at a first landing surface on the frame. The first suspension element may be attached to the diaphragm directly or indirectly. In particular, the first suspension element may be fixed to the outer edge of the diaphragm.

[0011] One or more suspension elements may include a second suspension element, such as a surround, which is attached to the frame at a second landing surface on the frame. The second suspension element may be fixed, for example, to a translatable part of the drive unit, or may be fixed to the diaphragm at a position located inwardly relative to the outer edge of the diaphragm.

[0012] The center of gravity of the translatable part of the drive unit may have a position along the movement axis between the first landing surface and the second landing surface.

[0013] By positioning the center of gravity of the magnet unit between the first landing surface and the second landing surface, wobbling can be suppressed. More particularly, the wobbling mode of the loudspeaker may be pushed outside the operating frequency range of the loudspeaker.

[0014] The second suspension element (such as a surround) may have a position along the movement axis and may be arranged to extend radially towards the magnet unit of the drive unit and fixed to the magnet unit of the drive unit. This may allow the loudspeaker to have a reduced depth compared to a conventional loudspeaker where the surround is typically above or below the magnet unit (see, for example, Figure 1 ).

[0015] The second suspension element may extend radially in a direction perpendicular to the movement axis, i.e., may extend in a direction perpendicular to the movement axis.

[0016] By arranging the second suspension element to extend perpendicular to the movement axis, a space-efficient arrangement can be achieved. This may allow for an improved shallow loudspeaker, particularly in the case where the center of gravity is located between the landing surfaces, as described above. The resulting loudspeaker can be both shallow and suppress diaphragm wobbling. This is in contrast to a shallow loudspeaker with a conventional configuration, which is particularly prone to diaphragm wobbling due to its shallow construction.

[0017] The diaphragm may have a first radiation surface facing forward (e.g., away from the frame) and a second radiation surface facing backward (e.g., towards the frame).

[0018] The translatable part of the drive unit may be located in a slot passing through the diaphragm.

[0019] The exposed part of the translatable part of the drive unit may face forward. Similarly, the interior of the translatable part may face backward.

[0020] The exposed part may dissipate heat generated in the loudspeaker to the surrounding air during use. In particular, heat generated due to the excitation of the voice coil may be dissipated in this way.

[0021] The exposed portion of the translatable part may include a structured cooling element. The structured cooling element can increase the surface area, thereby improving heat transfer to the surrounding air. The structured cooling element may include protrusions or depressions, such as cooling fins or cooling channels.

[0022] By providing a structured cooling element on the exposed portion of the translatable part, heat transfer from the translatable part to the ambient air can be improved. Especially in the case where the translatable part includes a heat conductor having a high thermal conductivity (e.g., at least 20 watts / (meter×Kelvin)), the heat generated due to operation can be removed from the speaker more efficiently.

[0023] The diaphragm may include a heat conductor having a high thermal conductivity (e.g., at least 40 watts / (meter×Kelvin)). Preferably, the heat conductor is formed of a metal or a metal alloy. More preferably, the heat conductor is formed of aluminum or an aluminum alloy.

[0024] In a conventional speaker, the spatial separation between the voice coil and the diaphragm (e.g., due to the use of a voice coil former) may impede heat transfer from the voice coil to the diaphragm. In contrast, in a speaker according to the present invention, heat transfer, for example, through the translatable part of the drive unit to the diaphragm can be improved. Additionally, in the case where the translatable part of the drive unit also has a high thermal conductivity, heat transfer from the speaker can be further improved.

[0025] The wire forming the voice coil can have any suitable cross-section. The cross-section of the wire can be circular or non-circular. Suitably, the cross-section of the wire is selected to increase the fill factor of the voice coil. The wire forming the voice coil can have a rectangular cross-section, optionally a square cross-section. Herein, a square can be understood as a subset of the rectangular shape.

[0026] Since the voice coil is included in the fixed part fixed to the frame, the weight of the voice coil is supported by the frame. In contrast, in a conventional speaker as described above, the voice coil is connected to the diaphragm, such that the increased weight of the voice coil may make the diaphragm prone to wobbling, and thus an increased fill factor may be undesirable.

[0027] In some examples, the fixed part of the drive unit includes a voice coil former (in addition to the voice coil), wherein the voice coil is mounted on the voice coil former (e.g., wound around the voice coil former).

[0028] In some examples, the translatable part of the drive unit is a magnet unit.

[0029] The magnet unit (or “magnet system”) may include at least one permanent magnet and may include at least one flux guide (e.g., two flux guides). The at least one flux guide may be configured to guide the magnetic flux provided by the at least one permanent magnet to the air gap.

[0030] The mass of at least one permanent magnet can be less than the mass of the voice coil. That is, at least one permanent magnet can have a first mass, the voice coil can have a second mass, and the first mass can be less than the second mass. The first mass can be at least two times smaller than the second mass.

[0031] Thus, compared with the above-mentioned conventional loudspeaker, the mass of the voice coil may exceed or even greatly exceed the mass of the permanent magnet. Different from the conventional loudspeaker, the increase in the mass of the voice coil does not make the diaphragm more likely to swing because the mass of the voice coil is borne by the frame rather than attached to the diaphragm.

[0032] At least one flux guide can include a yoke, optionally arranged as a U-shaped yoke, and can include a washer.

[0033] The flux guide / each flux guide can be made of a material with high thermal conductivity (e.g., at least 40 watts / (meter × Kelvin)), especially a metal or a metal alloy. This can contribute to heat dissipation (in addition to guiding the flux).

[0034] The yoke can include a base and side walls extending from the base.

[0035] The thickness of the voice coil in the radial direction perpendicular to the moving axis can be at least three times, optionally five times, greater than the thickness of the side wall of the yoke in the radial direction. The side wall can have a uniform thickness or a non-uniform thickness. In the case where the side wall has a uniform wall thickness, the thickness of the voice coil in the radial direction can be greater than the (uniform) wall thickness in the radial direction, optionally at least three times, optionally five times. In the case where the side wall has a non-uniform wall thickness, the thickness of the voice coil in the radial direction can be greater than the maximum value of the (non-uniform) wall thickness in the radial direction, optionally at least three times, optionally five times.

[0036] According to some examples, the magnet unit can include one permanent magnet and two flux guides. The two flux guides can be arranged as a washer and a yoke. The permanent magnet can be located between the washer and the yoke. The washer and the yoke can be arranged to define an air gap between the side walls of the washer and the yoke.

[0037] According to some other examples, the magnet unit can include two permanent magnets and three flux guides. The three flux guides can be arranged as a washer and two yokes. The washer can be located between the two permanent magnets, and the two permanent magnets are arranged to have the same magnetic poles facing each other. Each yoke can extend from one of the two permanent magnets to define an air gap between the corresponding yoke and the washer.

[0038] According to some other examples, the magnet unit can include one permanent magnet and three flux guides, and the flux guides are arranged as two washers and a tubular yoke, such as a cylindrical yoke. The permanent magnet can be located between the two washers. The tubular yoke can extend around the permanent magnet and the two washers to define two air gaps between the tubular yoke and the two washers.

[0039] The loudspeaker as described above can be provided as a subwoofer, which is configured to generate sound having a frequency in the low - frequency range. The low - frequency range may include 60 - 80 Hz, and more preferably includes 40 - 100 Hz. By way of example, the low - frequency range may be 20 Hz - 100 Hz.

[0040] The loudspeaker as described above can be disposed in a housing. The housing may define an internal volume of at most 1.5 liters, and the loudspeaker is mounted in the internal volume.

[0041] In a second aspect of the present invention, a loudspeaker assembly can be provided, including a plurality of loudspeakers according to the first aspect of the present invention.

[0042] For example, a first loudspeaker according to the first aspect of the present invention and a second loudspeaker according to the first aspect of the present invention can be provided, which can be arranged in a back - to - back configuration such that the first loudspeaker and the second loudspeaker (e.g., the first radiation surface thereof) face opposite directions.

[0043] In some examples, a loudspeaker assembly is provided, including:

[0044] a first loudspeaker and a second loudspeaker;

[0045] The first loudspeaker includes a first frame and a first diaphragm suspended from the first frame, and the second loudspeaker includes a second frame and a second diaphragm suspended from the second frame;

[0046] The first loudspeaker includes a first driving unit, and the second loudspeaker includes a second driving unit;

[0047] The first driving unit includes a first fixed part fixed to the first frame and a first translatable part fixed to the first diaphragm. The first translatable part includes a first magnet unit configured to generate a first magnetic field in a first air gap. The first fixed part of the first driving unit includes a first voice coil configured to be located in the first air gap when the first diaphragm is stationary; and

[0048] The second driving unit includes a second fixed part fixed to the second frame and a second translatable part fixed to the second diaphragm. The second translatable part includes a second magnet unit configured to generate a second magnetic field in a second air gap. The second fixed part of the second driving unit includes a second voice coil configured to be located in the second air gap when the second diaphragm is stationary;

[0049] wherein, when the first diaphragm and the second diaphragm are stationary, at least a part of the fixed part of the first driving unit is located in the space between the first diaphragm and the second diaphragm, and wherein, when the first diaphragm and the second diaphragm are stationary, at least a part of the fixed part of the second driving unit is located in the space between the first diaphragm and the second diaphragm;

[0050] Wherein, the speaker assembly is operable to excite the first voice coil and the second voice coil, such that the first magnet unit and the second magnet unit move in opposite directions along the moving axis, thereby moving the first diaphragm and the second diaphragm to generate sound.

[0051] The first voice coil and the second voice coil may be configured to be excited by the same signal. By using the same signal, complete cancellation of the forces due to the displacement of the first translatable part and the second translatable part can be achieved.

[0052] The first speaker and the second speaker may be provided, for example, as 5-inch (12.7 cm) subwoofers in enclosures having a net volume of approximately 1.5 liters each.

[0053] The speaker assembly may include a magnetic shielding member between the first speaker and the second speaker to magnetically shield the magnet units of the first speaker and the second speaker from each other.

[0054] By providing the magnetic shielding member, the interaction between the magnet unit of the first speaker and the magnet unit of the second speaker can be reduced. In particular, the magnetic shielding member may provide sufficient magnetic shielding to prevent the magnet units from interacting when at rest and / or when the speaker assembly is operated within the normal operating range.

[0055] The magnetic shielding member may be configured to become magnetically flux saturated when the magnet unit of the first speaker and the magnet unit of the second speaker approach the magnetic shielding member, thereby causing mutual repulsion of the magnet units.

[0056] By including magnetic shielding and allowing it to be magnetically saturated, the performance of the speaker can be improved, and at the same time, safe operation is ensured even when operating at peak power, since the additional forces experienced by the magnet units can prevent collisions of the translatable parts with the magnetic shielding member or the frame.

[0057] The magnetic shielding member may be provided as a sheet of metal or metal alloy (optionally steel).

[0058] To avoid any doubt, the first speaker and / or the second speaker may include any one or more of the features described in connection with the first aspect of the present invention.

[0059] A third aspect of the present invention may provide a vehicle, such as an automobile, including a speaker according to the first aspect or a speaker assembly according to the second aspect as described above. More particularly, the speaker or the speaker assembly may be provided in the footwell or under the seat of the automobile, or indeed at any other location suitable for encapsulating the speaker in the automobile.

[0060] The present invention includes combinations of the described aspects and preferred features, unless such combinations are clearly impermissible or expressly avoided. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Embodiments and experiments illustrating the principles of the present invention will now be discussed with reference to the accompanying drawings, in which:

[0062] Figure 1 is a cross-sectional view of a conventional loudspeaker.

[0063] Figure 2 is Figure 1 a cross-sectional view of the drive unit of the conventional loudspeaker.

[0064] Figure 3 is a cross-sectional view of the drive unit of another conventional loudspeaker.

[0065] Figure 4 is a cross-sectional view of a loudspeaker according to the present invention.

[0066] Figure 5 is Figure 4 a cross-sectional view of a part of the loudspeaker.

[0067] Figure 6 is Figure 4 a cross-sectional view of the drive unit of the loudspeaker.

[0068] Figure 7 is a cross-sectional view of a loudspeaker assembly according to the present invention.

[0069] Figure 8 is Figure 7 a cross-sectional view of a pair of drive units of the loudspeaker assembly.

[0070] Figure 9 is Figure 7 another cross-sectional view of a pair of drive units of the loudspeaker assembly.

[0071] Figure 10 is illustrative of Figure 7 the performance parameters of the loudspeaker assembly.

[0072] Figure 11 is illustrative of Figure 7 the performance parameters of another loudspeaker assembly.

[0073] Figure 12 is a cross-sectional view of another drive unit.

[0074] Figure 13 is Figure 12 a perspective view of the drive unit.

[0075] Figure 14 is Figure 12 another cross-sectional view of the drive unit.

[0076] Figure 15 is a graph showing the performance parameters of the drive unit Figure 12 illustrated.

[0077] Figure 16 is a partially cut-away perspective view of a speaker having a Figure 12 drive unit.

[0078] Figure 17 is Figure 16 a cross-sectional view of the speaker.

[0079] Figure 18 is a cross-sectional view of another drive unit.

[0080] Figure 19 shows a Figure 6 drive unit provided with a structured cooling element.

[0081] Figure 20 is a side view of a car having a speaker. DETAILED DESCRIPTION

[0082] The present invention relates to a speaker including a frame, a diaphragm, and a drive unit. Before presenting a detailed discussion of the present invention, an example of a conventional speaker is discussed in detail below to illustrate the background of the present invention.

[0083] Figure 1 and Figure 2 illustrate a conventional speaker 10. In the conventional speaker 10, a voice coil 11 is suspended in an air gap 12 between an inner rigid part 13 and an outer rigid part 14, and the air gap guides the magnetic flux of a permanent magnet 15 through the voice coil 11. A speaker cone 16 is connected to the voice coil 11 via a voice coil former 17. Two suspension elements are connected to the voice coil former and the cone; a spider 18 is connected to the voice coil former 17, and a surround 19 is connected to the cone 16.

[0084] The mass of the voice coil 11 is usually smaller than that of the permanent magnet 15, or can be in the same range. Generally, the moving mass of the speaker (i.e., the total mass displaced during operation) is smaller than the total mass of the speaker including the magnet unit and the frame (not shown).

[0085] The force generating element with respect to the frame of the speaker 10 is the voice coil winding 20 (Lorentz force). The center of gravity 21 of these windings 20 is located outside the volume between two landing surfaces 22, 23 on the frame, where the spider 18 and the surround 19 are attached to the frame. This makes the structure prone to causing the entire assembly to sway, which may potentially result in the coil rubbing against the steel parts and damaging the speaker, especially for heavy coils and / or shallow speaker structures.

[0086] Figure 3Shows an alternative conventional construction, also known as an open magnet system, in which two permanent magnets 15 are magnetized in opposite directions and push flux lines through the washer 13 therebetween. Alternatively, the washer may be absent and the permanent magnets 15 are separated by non-magnetic elements.

[0087] In an open magnet system, the center of gravity of the voice coil can be made to lie between the suspension elements, but such a magnet system can be inefficient because it presents a large magnetic resistance to the flux lines (not shown) due to the relatively long path through air. To have an acceptable magnet permeance coefficient and an available linear BL(x) in terms of the displacement of the cone by the force factor, the magnet must be tall - and thus large in volume - and therefore expensive. A thin magnet would not be suitable for an open magnet system because the linear displacement is limited when the winding enters the region of reverse magnetic flux density for large offsets.

[0088] For efficient low-frequency reproduction, the moving mass and the force factor must be large enough to counteract the effect of the stiffness from the air volume that a small closed box imposes on the speaker cone. Typically, such large moving mass and large force factor are generated by means of a voice coil having 2 to 6 layers and a strong, large, and expensive rare-earth magnet in a low-magnetic-resistance magnetic circuit that requires thick steel parts to guide the magnetic flux. To increase the moving mass, a heavy object, such as a brass dust cap, is typically added. The dust cap or a heavy diaphragm can also be used to shift the center of gravity of the entire moving assembly closer to the two suspensions, thus reducing the risk of rocking in the application.

[0089] A known way to increase the moving mass is to use a voice coil winding wire having a rectangular or square cross-section instead of a circular cross-section. This increases the motor strength, but increases the risk of rocking because most of the moving mass is concentrated away from the suspension elements.

[0090] Since the voice coil moves in a conventional loudspeaker, flexible leads must connect the voice coil winding to the terminals on the frame. The leads are prone to generating ticking noises, being overstretched during operation, having to be connected to the winding, for example, via a soldered connection on the voice coil former, and are generally to be avoided.

[0091] For a heavy moving mass woofer as described above, the reaction forces on the frame and the enclosure are large. It is known to mount two speakers on opposite faces of the enclosure (i.e., in a back-to-back configuration) to cancel out the net force on the enclosure. However, when mounted in this way, due to the depth of the speakers, this results in a necessary long elongation of the enclosure along the main axis of the speakers.

[0092] For a woofer having a nominal diameter of, for example, 5 to 6 inches, the above considerations impose severe limitations on the loudspeaker designer. In the market, we can hardly see loudspeakers in this range that have a moving mass greater than 100 g (grams) or are suitable for enclosures smaller than two liters. However, this moving mass must achieve a resonant frequency inside the enclosure close to or below 50 Hz (hertz) suitable for woofer applications. If such loudspeakers are designed, they typically have large and expensive magnet systems to allow reasonable control of the high moving mass with a quality factor Qtc < 3 inside the enclosure, making them suitable for music reproduction. The current world market price of rare earths required for high-temperature stable magnets with high remanent flux density (such as NdFeB+Dy magnets) has hindered the widespread use of such loudspeakers in automotive or consumer applications.

[0093] Accordingly, there is a need for an improved loudspeaker. The examples discussed below may provide one or more low-cost, lightweight, shallow (woofer) drivers that have a high moving mass but rocking stability, are easy to manufacture, and are suitable for back-to-back mounting for force cancellation operation.

[0094] As will now be referred to Figures 4 to 19 discuss aspects and embodiments of the present invention. The present invention relates to low-frequency sound reproduction, and more particularly to music playback from a loudspeaker with a small, closed-box volume. Additional aspects and embodiments will be apparent to those skilled in the art. All documents mentioned herein are incorporated herein by reference.

[0095] Figure 4 is a cross-sectional view of an exemplary loudspeaker 100. The loudspeaker 100 includes a frame 200, a diaphragm 300 suspended from the frame 200, and a drive unit 400.

[0096] The drive unit 400 has a fixed part 420 and a translatable part 440. The fixed part 420 is fixed to the frame 200 and includes a voice coil 422. The translatable part 440 is fixed to the diaphragm 300 and includes a magnet unit 441 configured to generate a magnetic field in an air gap 442. When the diaphragm 300 is stationary, the voice coil 422 is located in the air gap 442.

[0097] The loudspeaker 100 is operable to excite the voice coil 422 to cause the magnet unit 441 to move relative to the voice coil 422 along a movement axis 102, thereby moving the diaphragm 300 along the movement axis 102 to produce sound.

[0098] The diaphragm 300 has a first sound radiating surface 302 and a second sound radiating surface 304. The first sound radiating surface 302 faces forward 106 (away from the frame 200) and is used to generate sound during use. The second sound radiating surface 304 faces backward 108, that is, into the frame 200. The forward 106 and the backward 108 are opposite directions parallel to the movement axis 102.

[0099] Note that the air gap 442 faces backward, and it inhibits the accumulation of dust without the need for a dust cover as seen in some conventional speakers.

[0100] The frame 200 of the loudspeaker 100 includes a base 202 and an edge 204. The base 202 extends radially outward relative to the movement axis 102. The edge 204 extends axially relative to the movement axis 102, that is, at least partially along the movement axis 102. The edge 204 of the frame 200 is located at the periphery of the base 202 and is located radially outside the magnet unit 441.

[0101] The fixed part 420 of the drive unit 400 is fixed to the base 202 of the frame 200, while the diaphragm 300 and the translatable parts 440 of the drive unit 400 are suspended from the frame 200 by means of suspension elements 520, 540. The suspension elements 520, 540 are configured to allow movement along the movement axis 102, that is, movement in a direction parallel to the movement axis 102, and to inhibit movement in the radial direction 104 ( Figure 5 as shown in), that is, movement in a direction perpendicular to the movement axis 102.

[0102] The first suspension element 520 is attached to the frame 200 at a first landing surface 220 defined by the edge 204 of the frame 200. The first suspension element 520 is arranged to be fixed to a surround of the outer edge 306 of the diaphragm 300.

[0103] The second suspension element 540 is attached to the frame 200 at a second landing surface 640 defined by the edge 204 of the frame 200. The second suspension element 540 is arranged to be fixed to the surround of the translatable part 440 of the drive unit 400 and extends radially outward relative to the movement axis 102.

[0104] Figure 5 is a cross-sectional view of a part of the loudspeaker 100 and shows the diaphragm 300, the drive unit 400 and the suspension elements 520, 540.

[0105] The diaphragm 300 and the second suspension element 540 are fixed to the translatable part 440 of the drive unit 400 such that the center of gravity 443 of the translatable part 440 indicated by the checkerboard pattern disk lies between the first landing surface 220 and the second landing surface 240. That is to say, the first landing surface 220 and the second landing surface 240 are spaced apart along the movement axis 102, and the center of gravity 443 of the translatable part 440 lies between them.

[0106] The magnet unit 441 is suspended by the second suspension element 540 which, in this example, is arranged as a flexure connecting the magnet unit 441 to the frame 200. The magnet unit 441 is also suspended via the diaphragm 300 which, in this example, is arranged as a cone, and the first suspension element 520 which, in this example, is arranged as a rubber surround and is also connected to the frame 200. Thus, the center of gravity 443 of the magnet unit 441 is positioned along the movement axis 102 and lies between the two landing surfaces 220, 240 of the suspension elements 520, 540 to the frame 200.

[0107] The diaphragm 300 has an inner edge 308. The inner edge 308 defines the diaphragm aperture 310, i.e., bounds the diaphragm aperture 310. The diaphragm aperture 310 extends through the diaphragm 300, i.e., from the first sound radiating surface 302 to the second sound radiating surface 304.

[0108] The translatable part 440 of the drive unit 400 extends through the diaphragm aperture 310. Thus, the exposed part 444 (or "first part") of the translatable part 440 lies on one side of the diaphragm 300, while the interior 445 (or "second part") of the translatable part 440 lies on the other side of the diaphragm 300. More particularly, the exposed part 444 faces forward 106, and the interior 445 faces rearward 108. The exposed part 444 of the translatable part 440 lies outside the volume enclosed by the frame 200 and the diaphragm 300 in use, i.e., is exposed to the surrounding air.

[0109] Some conventional loudspeakers are mounted with the magnet unit facing the interior of the frame / cabinet. This causes the temperature in the cabinet to rise, thus limiting the power handling of the loudspeaker, especially when there is also active electronics (such as an amplifier). The exemplary loudspeaker 100 has the magnet unit facing the outside of the frame / cabinet which can allow much better heat radiation. It also allows the translatable part 440 to be equipped with cooling fins (see Figure 19 ), or a metal cone (such as made of aluminum) to be used as an additional heat sink as it is directly connected to the translatable part 440 while keeping the air gap 442 protected within the cabinet / frame; away from dust and debris.

[0110] Figure 6It is a cross-sectional view of the translatable part 440. In this example, the translatable part 440 of the drive unit 400 corresponds to the magnet unit 441.

[0111] The magnet unit 441 is arranged in the loudspeaker 100 in use such that the air gap 442 opens towards the frame 200, as Figure 4 shown, and the voice coil 422 extends into the air gap 442 on the forward direction 106.

[0112] The magnet unit 441 includes a permanent magnet 446, a (magnetic) washer 447, and a (magnetic) yoke 450. The permanent magnet 446, the washer 447, and the yoke 450 are axially symmetric about the moving axis 102, but other arrangements are also possible.

[0113] The permanent magnet 446 is provided as a rare earth magnet. The mass of the permanent magnet 446 is less than the mass of the voice coil 422. In this example, the mass of the voice coil 422 is two times greater than the mass of the permanent magnet 446, that is, the mass of the voice coil 422 is twice as large as the mass of the permanent magnet 446.

[0114] The washer 447 and the yoke 450 (which are provided as a U-shaped yoke in this example) are configured to direct the magnetic flux generated by the permanent magnet 446 to the air gap 442 between the washer 447 and the yoke 450.

[0115] The yoke 450 has a base 452 and side walls 454 protruding from the base 452. The base 452 extends in the radial direction 104, while the side walls 454 extend axially with respect to the moving axis 102.

[0116] Since the suspension elements 520, 540 are mounted on the outside of the side walls 454 of the yoke 450, the center of gravity 443 of the moving force generating element - in this case the magnet unit 441 - can be located between the second suspension element 540 (surround) and the first suspension element 520 (spider), which can result in excellent rocking stability and pure axial movement. Moreover, arranging the suspension adjacent to the yoke 450 radially allows for a very shallow design, enabling back-to-back force cancellation operations in a small enclosure, as referenced Figure 7 described.

[0117] The side walls 454 of the yoke 450 have a radially (i.e., in the radial direction 104) defined (uniform) thickness. The voice coil 422 also has a radially defined (uniform) thickness. The thickness of the voice coil 422 is greater than the thickness of the side walls 454 of the yoke 450. The ratio of the thickness of the voice coil 422 (i.e., the "winding thickness") to the thickness of the side walls 454 is preferably 3:1 or even 5:1. Conventional loudspeakers of the same size can have a ratio as small as 0.2:1.

[0118] The loudspeaker 100 utilizes a particularly large voice coil using many layers in the magnetic circuit. However, since the air gap is much wider compared to conventional loudspeakers to accommodate the large voice coil, the total magnetic resistance in the magnetic circuit increases so much that the cross-sections of the flux guiding washer and the yoke part can be very thin.

[0119] This new configuration results in a relatively high voice coil mass and a relatively low magnet unit mass. Therefore, it has been found beneficial to fix the voice coil 422 to the frame 200 and allow the magnet unit 441 to oscillate freely by means of two or more suspension elements 520, 540, because more of the total mass of the loudspeaker 100 is effective and moving.

[0120] The drive unit 400 results in a high moving mass at a low total driver mass. The ratio of the moving mass to the total mass can be at most 1:3, preferably at most 1:2. Moreover, the ratio of the magnet mass to the voice coil winding mass can reach 1:2, preferably at most 1:4. This results in a surprisingly lightweight subwoofer that has a low resonance frequency within the enclosure.

[0121] Figure 7 is a cross-sectional view of an exemplary loudspeaker assembly 1000 according to the present invention. The loudspeaker assembly 1000 includes the first loudspeaker 100 and the second loudspeaker 100 as described above, which are arranged in a back-to-back configuration and face in opposite directions.

[0122] The frames 200 of the loudspeakers 100 are joined at their respective bases 202. In this example, the bases 202 are formed separately and joined by means of an adhesive. It is also conceivable that the bases 202 can be formed integrally with each other. The resulting configuration of the loudspeaker assembly 1000 causes the bases 202 to serve as a separator between the volumes enclosed by the respective loudspeakers 100.

[0123] The edges 204 of the loudspeakers 100 extend in opposite directions from the respective bases 202 of the frames 200.

[0124] The diaphragm 300 is located on the opposite sides of the loudspeaker assembly 1000.

[0125] The drive unit 400 of the loudspeaker 100 is located between the diaphragms 300. The translatable part 440 of the drive unit 400 can move along the movement axis 102 shared by the two loudspeakers 100.

[0126] The speaker assembly 1000 is operable to excite the voice coils 422 of the first speaker 100 and the second speaker 100 so that the magnet units 441 of the first speaker 100 and the magnet units 441 of the second speaker 100 move along the moving axis 102, thereby moving the diaphragms 300 of the two speakers 100 and generating sound. In this example, the voice coils 422 of the speakers 100 are configured to receive the same signal to excite the voice coils 422.

[0127] The speakers 100 are set as 5 - inch (12.7 cm) subwoofers, which are used for up to 100 Hz in an enclosure (sealed box) with a net volume of approximately 1.5 liters per speaker 100. In Figure 8 this case, two speakers 100 are mounted back - to - back in a total sealed - box volume of 3 liters and are designed for a nominal stroke of ±10 mm (millimeters).

[0128] The gasket 447 of each speaker 100 has a thickness of 3 mm, which can effectively guide the magnetic flux through the voice - coil winding. The thickness of the side wall 454 of the yoke 450 adjacent to half the height of the voice - coil winding is 2 mm. In this example, the side wall 454 has a uniform thickness.

[0129] The permanent magnet 446 has a diameter of 24 mm (millimeters), a height of 8 mm, and a weight of 28 g (grams). This is considered a particularly small and lightweight magnet for a subwoofer in this application.

[0130] The moving mass of each speaker 100 (i.e., the mass of the movable parts 440 of each speaker 100) is approximately 160 g.

[0131] The voice coil 422 of each speaker 100 wound around the voice - coil former 424 fixed to the corresponding frame 200 has a winding height of 17 mm along the moving axis 102 and a winding thickness of 6.4 mm in the radial direction 104. The weight of the voice - coil winding is 75 g.

[0132] These parameters result in a ratio of magnet weight to coil weight of 1:2.8. The ratio of the voice - coil winding thickness to the thickness of the side wall 454 of the yoke 450 is 3.15:1.

[0133] The frame 200 of each speaker 100, which is made of plastic in this example, weighs 50 g.

[0134] The total mass of each speaker is less than 300 g, while the total mass of the speaker assembly 1000 is less than 600 g, and the total moving mass is 320 g. In operation, the moving mass of each speaker 100 of 160 g moves in opposite directions, resulting in no net force on the enclosure. Thus, a maximum output and resonance frequency equivalent to or comparable to that of a relatively heavy high-performance single 8-inch (20.32 cm) subwoofer in an approximately 15-liter volume can be obtained from the speaker assembly 1000 with a 3-liter volume. This substantial reduction in enclosure size and reduction in enclosure vibration allows the subwoofer to be placed in locations where the shear size previously prohibited subwoofer applications. This can be, for example, near the bottom of an A-style or between the footrest spaces in a vehicle cabin.

[0135] Figure 8 and Figure 9 are cross-sectional views of the drive unit 400 of the speaker assembly 1000, illustrating the magnetic flux in different configurations of the drive unit 400. In Figure 8 , the drive unit 400 is shown at rest, i.e., the voice coil 422 is not energized, and the translatable parts 440 of each drive unit 400 are in their corresponding rest positions. In Figure 9 , the translatable parts 440 are displaced towards each other. That is, in Figure 9 , the displacement is negative.

[0136] In the case where two drive units 400 are mounted back-to-back, there is an additional force acting on the magnet unit 441. Due to the large air gap 442 in the separate magnet units 441 with the same magnetic poles facing each other, the separate leakage fluxes of the magnet units 441 may push the magnet units 441 apart. To mitigate this effect of the speaker 100 during the rest position and normal operating range, a magnetic shielding member 1100 is added. In this example, the magnetic shielding member 1100 is provided as a low-carbon steel sheet with a diameter of 50 mm and a thickness of 0.5 mm.

[0137] The magnetic shielding member 1100 is disposed at the junction between the two speaker frames 200, i.e., at the connection of the bases 202 (see Figure 7 ). The magnetic shielding member 1100 shields the two magnet units 441 from each other. According to this example, the magnetic shielding member 1100 is configured to shield until the point where the magnet units 442 are very close to each other, beyond the normal operating range (e.g., a displacement of approximately -10 mm). In this example, this is the limit of normal operation, and displacements beyond it are not expected.

[0138] The magnetic shielding member 1100 is configured such that beyond the nominal displacement, the magnetic shielding member 1100 is fully saturated by the leakage fluxes of the two magnet units 441. For example, the thickness of the low-carbon steel sheet can be selected such that full saturation occurs accordingly.

[0139] When the magnetic shielding member 1100 is fully saturated, the two magnet units 441 push each other apart through the magnetic shielding member 1100. In this example, this can generate a force of up to -50 N (Newtons) relative to the frame 200 (or 100 N relative to the magnet units 441 relative to each other). This additional force can make it difficult or even impossible for the magnet units 441 to collide with the frame 200 for negative displacement even when operating at peak power, thus ensuring safe operation even during peak power operation.

[0140] Figure 10 and Figure 11 A graph showing the performance parameters of the exemplary speaker assembly 1000 is shown.

[0141] Figure 10 The force acting on the translatable part 440 relative to the frame 200 is illustrated. The solid line represents the restoring force of the trapped air volume acting on the cone, 1.5 L, 108 cm 2 . The dashed line represents the restoring force of the mechanical suspension element. The dashed line represents the restoring force of the magnetic interaction between the magnet units.

[0142] Figure 11 The force factor BL(x) of each drive unit 400 relative to the corresponding frame 200 is illustrated.

[0143] The trapped air within the enclosure (i.e., the closed box) serves as additional axial stiffness on the diaphragm 300 (set as the cone) of each speaker 100. For a displacement of ±13 mm of the effective radiation surface area of 108 cm 2 (square centimeters) at 1.5 liters, this results in forces of up to -150 N and +130 N respectively. In contrast, the forces of the suspension elements 520, 540 are small, up to ±25 N.

[0144] Since the speakers are linked back-to-back, the net force on the base 202 of each individual frame 200 is zero, and allows the frame 200 to be thin and light. The force factor of each drive unit 400 is symmetric with respect to displacement and drops to 50% relative to the rest position at ±8 mm, resulting in low distortion over a wide displacement range.

[0145] Bringing the magnetic shielding member 1100 close to magnetic saturation at approximately 1.6 Tesla allows the inductance to be kept so low that it has little effect on the frequency response within an operating range of up to 100 Hz. In fact, compared to conventional speakers with fewer windings, the higher inductance and thus lower inductance results in reduced higher-order distortion due to the reduced output for higher frequencies above 100 Hz.

[0146] Figure 12 and Figure 13Shows another example of the drive unit 600. Figure 12 is a cross-sectional view of the drive unit, while Figure 13 is a perspective view of the drive unit 600. For ease of assembly, the above Figure 4 magnet unit can be preferred, which consists of only three separate components. However, alternative configurations of magnet units with other advantages can be envisioned.

[0147] The drive unit 600 is similar to the above drive unit 400, and the detailed description of the similar parts is omitted.

[0148] The drive unit 600 includes a fixed part 620 and a translatable part 640. The fixed part 620 includes a voice coil 622. The translatable part 640 includes a magnet unit 641.

[0149] The magnet unit 641 includes two permanent magnets 646, which are arranged in such a way that the same magnetic poles face each other. The two permanent magnets 646 are fixed to a washer 647 that radially pushes the flux. Two U-shaped yokes 650 are used to guide the flux around the voice coil winding and radially through the voice coil winding. This arrangement can allow for a voice coil with a smaller inner diameter, as the permanent magnet volume can be distributed over two permanent magnets 646 that act in parallel on the same voice coil winding.

[0150] In this example, the voice coil 622 is radially fixed to the frame 200 by an arm 626 that protrudes through a slit 656 in the U-shaped yoke. The arm 626 that protrudes through the slit 656 also helps with the lead wires 628 of the voice coil 622. The term "lead wire" is understood to mean wiring that is not flexible, which is different from leads that are understood to be flexible.

[0151] The said arrangement can be shallower than the arrangement described with reference to Figures 4 to 11 but is still similar in height to a conventional loudspeaker. Moreover, the rocking resistance can be significant, as the suspension elements can be spaced further apart than in a conventional loudspeaker.

[0152] Figure 14 and Figure 15 illustrate Figure 12 and Figure 13 the magnetic characteristics of the drive unit 600.

[0153] The symmetric arrangement of the permanent magnets 646 results in a symmetric BL(x) curve, and there is little leakage flux despite the relatively large air gap. Moreover, a gap 658 can be introduced between the side walls 654 (or "outer") of the U-shaped yoke 650 to reduce the moving mass and cost of the parts, as the flux lines will anyway take the path of least magnetic resistance that enters the side walls 654 at an angle rather than strictly radially.

[0154] Compared with traditional open magnet systems or U-shaped yoke magnet systems for magnets, the two permanent magnets 646 have a higher magnetic flux coefficient because they are both loaded by a magnetic circuit with a U-shaped yoke 650 with a relatively low total magnetic resistance. Moreover, the large surface areas of the two U-shaped yokes 650 can be used as very effective heat sinks. The good heat dissipation characteristics and high magnetic flux coefficient of this design both allow the use of low-cost permanent magnets with low demagnetization resistance, such as neodymium magnets.

[0155] Figure 16 and Figure 17 shows an exemplary loudspeaker 700 including the drive unit 600 described with reference to Figures 12 to 15 More particularly, Figure 16 is a cutaway perspective view of the loudspeaker 700, while Figure 17 is a cross-sectional view of the loudspeaker 700.

[0156] The loudspeaker 700 is similar to the loudspeaker 100 described above with reference to Figure 4 The detailed description of the corresponding parts is omitted.

[0157] The loudspeaker 700 includes a frame 800, a diaphragm 300, and a drive unit 600. The fixed part 620 of the drive unit 600 is fixed to the frame 800. The diaphragm 800 and the translatable part 640 of the drive unit 600 are suspended from the frame 800. In this example, a third suspension element 560 is provided, which is fixed to the translatable part 640 of the drive unit 600.

[0158] The drive unit 600 extends from the front of the loudspeaker 700 to the rear of the loudspeaker 700. More particularly, the drive unit 600 extends along the movement axis 102 from the diaphragm 300, passing through the rear slot 562 in the third suspension element 560. The third suspension element 560 is disposed in the base slot 806 of the base 802 of the frame 800. The translatable part 640 projects rearward 108 from the rear slot 562.

[0159] In operation, when the loudspeaker 700 is operated, the rear part of the loudspeaker 700 defined by the second suspension element and the translatable part 640 also moves.

[0160] Figure 18 is a cross-sectional view of another exemplary drive unit 900. The drive unit 900 is similar to the drive units 400, 600, and the detailed description of the same parts is omitted.

[0161] The drive unit 900 has a fixed part 920 and a translatable part 940. The translatable part 940 includes a magnet unit 941, which includes a single permanent magnet 946 configured to generate a magnetic field in the air gap 942.

[0162] The fixing part 420 includes a first voice coil 922 and a second voice coil 924. When the diaphragm is stationary, the voice coils 922, 924 are located in the air gap 942. Therefore, the drive unit utilizes one permanent magnet and two voice coils.

[0163] The permanent magnet 946 is located between two washers 947 for guiding the flux lines through to the two voice coil windings, where the cylindrical yoke 950 is adjacent to the outer sides of the voice coils 922, 924. The cylindrical yoke 950 does not have a base 425 extending in the radial direction 104 as described for the reference yoke 450. Instead, the cylindrical yoke 950 only extends axially.

[0164] The interior of the magnet unit 941 (i.e., the permanent magnet 946 and the washers 947) is mechanically connected to the outer side of the yoke 950 by at least one non-magnetic member 960 ( Figure 18 the dashed line in) to ensure that the flux lines are guided through the voice coil windings. In this example, the non-magnetic member 960 is provided as an annular bracket.

[0165] The arrangement is symmetric and can provide all the advantages that allow the suspension element and the diaphragm to be fixed to the outer side of the magnet unit. The arrangement also has the benefit that the voice coils 922, 924 are connected (or wound in opposite winding directions) in such a way that their inductances partially cancel each other out, which can improve performance, especially at higher frequencies.

[0166] Figure 19 Shown is Figure 6 the magnet unit 441, but it is provided with optional cooling features.

[0167] The magnet unit 441 is as described above with reference to Figure 6 However, the exposed part 444 is provided with structured cooling elements 456, 458 to increase the surface area of the exposed part 444. In this example, the structured cooling elements 456, 458 are provided as cooling fins 456 and cooling channels 458.

[0168] Considering the exemplary drive units 400, 600, 900, a person skilled in the art can easily imagine additional examples where the magnetic flux is split into main parts by means of one or more washers (split washer design) or gaps or by introducing main winding parts into the voice coil windings (split windings) to shape the resulting BL(x) curve that trades off linearity with the force factor at the rest position.

[0169] Figure 20 Shown is the vehicle 2000. Any of the exemplary speakers described above can be installed in the vehicle 2000. In this example, with reference to the above Figure 4The described loudspeaker 100 is arranged between the footrest spaces 2100 of the vehicle 2000. Other positions are also conceivable, for example at the bottom of the A-pillar or towards the bottom of the A-pillar.

[0170] The above-described exemplary loudspeaker can be manufactured using existing tools. The exemplary loudspeaker utilizes conventional loudspeaker components built into a single frame, thereby allowing production on existing production lines with existing machines, jigs, and fixtures.

[0171] Each loudspeaker can be easily and independently constructed with a single jig inserted into the bottom of the frame, first aligning the magnet unit parts towards each other and relative to the frame. Adding the surround and cone assembly is straightforward and similar to the construction of conventional loudspeakers. In fact, connecting the cone to the magnet unit no longer requires a dust cap, and a coil operating without flexible leads can make the construction easier than that of conventional loudspeakers.

[0172] The voice coil of the drive unit is made of square wire (i.e., wire having a square cross-section). Since using rectangular wire does not shift the center of gravity of the moving components downward (since the coil is fixed to the frame anyway), this is a convenient way to increase the motor strength with no drawbacks other than cost. Moreover, the fill factor of the winding formed by square wire is significantly higher than that of a conventional helical winding using round wire. With the continuously increasing price of neodymium raw materials, when trading off costs between components for the same performance, this "exotic" coil becomes increasingly viable as an alternative.

[0173] The voice coil of the drive unit can be made of any suitable material. In this example, the wire forming the voice coil is made of copper. Suitable metals or metal alloys, such as aluminum, are also conceivable.

[0174] The diaphragm is formed of aluminum, which is a thermal conductor with high thermal conductivity.

[0175] The diaphragm (i.e., the cone) is made of 0.4 mm thick aluminum and thus effectively serves as a heat sink, thereby giving the loudspeaker excellent power handling capabilities.

[0176] The translatable parts of the drive unit include a thermal conductor having a high thermal conductivity (e.g., at least 40 watts / (meter × Kelvin)), and heat generated due to operation can be removed from the loudspeaker more efficiently. Suitably, the washer and the yoke are made of steel, but other materials are also possible. Since the steel parts direct the flux lines away from the magnet, the height of the magnet is independent of the linearity of the motor system, which is different from an open magnet system (see Figure 3 ; a high magnet is required to avoid flux line cancellation in the voice coil). This allows the use of a small volume of high-grade neodymium, such as N55, which typically results in the lowest cost.

[0177] Some or all of the following aspects may be present in the above examples:

[0178] - A magnet unit having at least one permanent magnet and at least two flux guiding elements.

[0179] - A magnet unit suspended in a frame and axially free to oscillate.

[0180] - A diaphragm directly or via an intermediate member connected to the magnet unit and intended for sound radiation in air.

[0181] - At least one voice coil winding directly or via an intermediate member (such as a voice coil former) fixed to the frame.

[0182] - The voice coil winding is 50% thicker than the outside of the yoke.

[0183] - The voice coil winding is 50% heavier than the permanent magnet.

[0184] - The center of gravity of the magnet unit is between the landing surfaces, thus effectively pushing the rocking mode outside the operating frequency range of the speaker.

[0185] Features disclosed in the above specification or the appended claims or the drawings (expressed in their specific form or according to the means for performing the disclosed function, or the method or process for obtaining the disclosed result) may be suitably used alone or in any combination of these features to implement the present invention in its different forms.

[0186] Although the present invention has been described in connection with the above exemplary embodiments, many equivalent modifications and variations will be apparent to those skilled in the art when the present invention is given. Therefore, the above exemplary embodiments of the present invention are considered illustrative rather than restrictive. Various changes may be made to the embodiments without departing from the spirit and scope of the present invention.

[0187] To avoid any doubt, any theoretical explanations provided herein are for improving the reader's understanding. The inventors do not wish to be limited by any of these theoretical explanations.

[0188] Any section headings used herein are for organizational purposes only and should not be construed as limiting the subject matter described.

[0189] Throughout the specification, including the following claims, unless the context requires otherwise, the words "comprising" and "including" and their variants shall be understood to imply the inclusion of the stated whole or step or group of wholes or steps but not the exclusion of any other whole or step or group of wholes or steps.

[0190] It should be noted that, as used in the specification and the appended claims, the singular forms "a", "an" and "the" include plural referents unless the context clearly indicates otherwise. Ranges may be expressed herein as from "about" one particular value and / or to "about" another particular value. When such a range is expressed, another embodiment includes from one particular value and / or to another particular value. Similarly, when values are expressed as approximations by use of the antecedent "about", it should be understood that the particular value forms another embodiment. The term "about" associated with a numerical value is optional and means, for example, + / - 10%.

[0191] References

[0192] To more fully describe and disclose the present invention and the prior art related thereto, a number of publications have been cited above. The complete citations of these references are provided below. The entire contents of each of these references are incorporated herein by reference.

[0193] US2003 / 0044041A1.

Claims

1. A loudspeaker (100), comprising: a frame (200), a diaphragm (300) suspended from the frame, and a drive unit (400); wherein the drive unit has a fixed part (420) fixed to the frame and a translatable part (440) fixed to the diaphragm; wherein the translatable part of the drive unit includes a magnet unit (441), the magnet unit (441) includes at least one permanent magnet (446), a washer (447), and a yoke (450), wherein the magnet unit is configured to generate a magnetic field in an air gap (442) between the washer and a side wall (454) of the yoke, and wherein the at least one permanent magnet, the washer, and the yoke are configured to direct magnetic flux provided by the at least one permanent magnet to the air gap; wherein the fixed part of the drive unit includes a voice coil (442), the voice coil being configured to be located in the air gap when the diaphragm is stationary; wherein the at least one permanent magnet has a first mass, the voice coil has a second mass, and the first mass is less than the second mass; wherein the loudspeaker is operable to excite the voice coil to move the magnet unit relative to the voice coil along a movement axis (102), thereby moving the diaphragm along the movement axis to generate sound; the loudspeaker further includes: a first suspension element (520) attached to the frame at a first landing surface (220) on the frame; and a second suspension element (540) attached to the frame at a second landing surface (240) on the frame; wherein a position of a center of gravity of the translatable part of the drive unit is along the movement axis between the first landing surface and the second landing surface; wherein the loudspeaker is provided as a subwoofer, the subwoofer being configured to generate sound having frequencies in a low frequency range.

2. The loudspeaker according to claim 1, wherein, The first suspension element is fixed to an outer edge (306) of the diaphragm, and wherein the second suspension element is fixed to the translatable part of the drive unit.

3. The loudspeaker according to claim 1, wherein, the diaphragm has a first radiation surface (302) facing forward (106) and a second radiation surface (304) facing backward (108); the yoke is a U-shaped yoke (450); the U-shaped yoke of the translatable part of the drive unit is located in a slot (310) passing through the diaphragm; and an exposed portion (444) of the U-shaped yoke of the translatable part of the drive unit faces the forward direction, and an interior (445) of the U-shaped yoke of the translatable part faces the backward direction.

4. The loudspeaker according to claim 3, wherein, The exposed portion of the U-shaped yoke of the translatable part includes a structured cooling element for dissipating heat to the surrounding air.

5. The loudspeaker according to claim 4, wherein, The structured cooling element (456, 458) includes cooling fins (456) or cooling channels (458).

6. The loudspeaker according to any one of the preceding claims, wherein, The wire forming the voice coil has a rectangular cross-section.

7. The loudspeaker according to any one of claims 1 to 5, wherein, The first mass is at least two times smaller than the second mass.

8. The loudspeaker according to any one of claims 1 to 5, wherein, The yoke includes a base (452), and the side walls extend from the base, wherein the thickness of the voice coil in a direction perpendicular to the movement axis is greater than the thickness of the side walls of the yoke in a direction perpendicular to the movement axis, wherein the air gap is formed between the gasket and the yoke, and wherein the yoke is a U-shaped yoke (450).

9. The loudspeaker according to claim 8, wherein, The thickness of the voice coil is at least three times greater than the thickness of the side walls.

10. The loudspeaker according to any one of claims 1 to 5, wherein, The bass frequency range includes 60 Hz to 80 Hz.

11. A loudspeaker assembly (1000) comprising a first loudspeaker (100) according to any one of the preceding claims and a second loudspeaker (100) according to any one of the preceding claims, wherein, The first speaker and the second speaker are arranged in a back-to-back configuration such that the first speaker and the second speaker face opposite directions; wherein the speaker assembly is operable to excite the voice coil of the first speaker and the voice coil of the second speaker so that the magnet units of the first speaker and the second speaker move in opposite directions along the movement axis, thereby causing the diaphragms of the first speaker and the second speaker to move to produce sound.

12. The speaker assembly according to claim 11, comprising a magnetic shielding member (1100) disposed between the first speaker and the second speaker to magnetically shield the magnet unit of the first speaker and the magnet unit of the second speaker from each other.

13. The loudspeaker assembly according to claim 12, wherein, The magnetic shielding member is configured to become magnetically flux saturated when the magnet unit of the first speaker and the magnet unit of the second speaker approach the magnetic shielding member, thereby causing mutual repulsion of the magnet units.

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