Bass loudspeaker

Abstract

A bass speaker includes: a frame; a diaphragm suspended to the frame by a first suspension element and a second suspension element; the first suspension element is attached to the frame at a first landing surface on the frame; a second suspension element attached to the frame at a second landing surface on the frame; a magnet unit fixed to the frame; the magnet unit comprises a permanent magnet and at least two flux guiding elements, and the flux guiding elements guide magnetic flux to cross the air gap; a voice coil rigidly connected to the diaphragm; the loudspeaker is operable to excite the voice coil to move the voice coil relative to the magnet unit along a movement axis, thereby moving the diaphragm along the movement axis to generate sound; the voice coil is configured to be located in the air gap when the diaphragm is stationary, wherein the center of mass of the voice coil has a position between the first landing surface and the second landing surface along the movement axis; the magnetic flux density at the outer periphery of the voice coil is 50% or less of the magnetic flux density at the inner periphery of the voice coil.

Description

[0001] This application claims priority to GB2209544.2 filed on June 29, 2022. Technical Field

[0002] The invention relates to a woofer comprising a frame, a diaphragm and a driving unit. Background Art

[0003] A typical conventional loudspeaker has a frame, a diaphragm and a drive unit for reproducing sound. In use, the drive unit moves the diaphragm, which acts as a piston, back and forth to generate pressure waves, i.e., sound.

[0004] The drive unit generally comprises a magnet unit attached to a frame and a voice coil attached to a diaphragm. The magnet unit defines a magnetic circuit including an air gap, across which magnetic flux is directed, and in which the voice coil is located when stationary. By exciting the voice coil, the magnet unit and the voice coil magnetically cooperate with each other, i.e., magnetically interact, to achieve displacement of the combination of the voice coil and the diaphragm, thereby generating sound.

[0005] The inventors have observed that, according to conventional principles, in order to efficiently utilize the magnetic circuit when the loudspeaker is in operation, the magnet unit generates magnetic flux in the air gap so that the associated magnetic flux density is as uniform as possible across the air gap. For example, for small bass loudspeakers, it is desirable that the magnetic flux density is as uniform as possible across the air gap in order to ensure efficient use of the magnetic circuit, because for these loudspeakers, the mass and size of the voice coil can be relatively maintained to suppress sway. Therefore, in conventional loudspeakers, the value of the magnetic flux density across the voice coil in the air gap will typically drop from an initial 100% to 90%, or possibly as low as 85%. Summary of the invention

[0006] A woofer is described herein that may be viewed as a departure from the conventional principles outlined in the background section above. More specifically, the woofer described has an air gap in which the magnetic flux density across the voice coil is significantly reduced by 50% or more. The woofer described also has improved anti-sway capabilities, which allows a wider range of voice coil parameters, particularly relatively large / heavy voice coils, to achieve the desired performance of the speaker.

[0007] According to a first aspect of the present invention, there is provided a bass speaker comprising: a frame; a diaphragm suspended to the frame by at least a first suspension element and a second suspension element, wherein the first suspension element is attached to the frame at a first landing surface on the frame, and the second suspension element is attached to the frame at a second landing surface on the frame; a magnet unit fixed to the frame, wherein the magnet unit comprises a permanent magnet and at least two flux guiding elements, the flux guiding elements being configured to guide magnetic flux across an air gap; a voice coil rigidly connected to the diaphragm; wherein the speaker is operable to excite the voice coil so that the voice coil moves relative to the magnet unit along a moving axis, thereby moving the diaphragm along the moving axis to produce sound; wherein the voice coil is configured to be located in the air gap when the diaphragm is stationary, wherein the center of mass of the voice coil has a position between the first landing surface and the second landing surface along the moving axis; and wherein the magnetic flux density at the outer periphery of the voice coil is 50% (percent) or less of the magnetic flux density at the inner periphery of the voice coil.

[0008] By making the magnetic flux density at the outer periphery of the voice coil 50% (percent) or less of the magnetic flux density at the inner periphery of the voice coil, the speaker is able to have a smaller or lighter magnet unit, thereby helping to make the entire speaker lighter (even if the coil is made heavier to compensate). By arranging the voice coil and suspension elements so that the center of gravity of the voice coil is located between the first landing surface and the second landing surface, rocking (e.g., as caused by having a heavier coil to compensate for the reduced flux across the air gap) can be suppressed. More specifically, the rocking mode of the speaker may be pushed outside the operating frequency range of the speaker. Therefore, the voice coil (e.g., size / weight) can be selected to compensate for the reduction in magnetic flux density without compromising desired performance, such as force factor.

[0009] The woofer as described above may be configured to produce sound having a frequency in a bass frequency range. The bass frequency range may include 60-80 Hz, where "Hz" represents the physical unit "Hertz". More preferably, the bass frequency range may include 40-100 Hz. By way of example, the bass frequency range may be 20 Hz-100 Hz.

[0010] The first suspension element may be arranged as a surround. The first suspension element may be attached directly or indirectly to the diaphragm. In some examples, the first suspension element may be fixed to an outer edge of the diaphragm.

[0011] The second suspension element may be configured as a spring (which may be referred to as a "centering spider"). The second suspension element may be attached directly or indirectly to the diaphragm. In some examples, the second suspension element may be fixed to the diaphragm at a position located inwardly relative to the outer edge of the diaphragm.

[0012] The voice coil is rigidly connected to the diaphragm so that when the loudspeaker is excited, the diaphragm and the voice coil move together (eg "as one") along the axis of movement. The voice coil may be rigidly connected to the diaphragm directly or indirectly.

[0013] The magnetic flux density in the air gap as referred to herein may be a radial magnetic flux density. The radial magnetic flux density may be the magnetic flux density measured in a direction perpendicular to the axis of movement.

[0014] If the voice coil is generally circular, the inner circumference of the voice coil may be referred to as the inner diameter of the voice coil, and the outer circumference of the voice coil may be referred to as the outer diameter of the voice coil.

[0015] The distance between the inner and outer circumferences in the radial direction (ie, in a direction perpendicular to the axis of movement) can be considered as the winding thickness of the voice coil. Therefore, as described above, the magnetic flux density passing through the voice coil may decrease over the winding thickness of the voice coil.

[0016] The extent to which the magnetic flux density drops across the voice coil (by 50% or more) may depend on design considerations, which may vary from speaker to speaker. In most cases, it is believed that the drop may be as high as 90% or even higher. If the drop is as high as 90%, the magnetic flux density at the outer periphery of the voice coil may be in the range of 10% to 50% of the magnetic flux density at the inner periphery of the voice coil.

[0017] The at least two flux guiding elements may define an air gap as a spatial volume between the at least two flux guiding elements.The voice coil may be located between the at least two flux guiding elements when the diaphragm is at rest such that the voice coil is located in the air gap.

[0018] The at least two flux guiding elements may comprise a washer and may comprise a yoke, the yoke being optionally arranged as a U-shaped yoke.The permanent magnet may be located between the washer and the yoke.

[0019] The yoke may include a base and a side wall extending from the base.The washer and the yoke may be arranged to define an air gap between the washer and the side wall of the yoke.

[0020] The thickness of the side wall of the yoke in the direction perpendicular to the movement axis may be smaller than the thickness of the voice coil in the direction perpendicular to the movement axis. In the case where the side wall has a uniform wall thickness (in the direction perpendicular to the movement axis), the thickness of the voice coil (in the direction perpendicular to the movement axis) may be greater than the (uniform) wall thickness. In the case where the side wall has a non-uniform wall thickness, the maximum value of the (non-uniform) wall thickness (in the direction perpendicular to the movement axis) may be smaller than the thickness of the voice coil (in the direction perpendicular to the movement axis).

[0021] The thickness of the side wall (eg as defined above) may be at least two times smaller than the thickness of the voice coil, more preferably three times, such as 3.15 times.

[0022] In some examples, the thickness of the sidewall (eg, as defined above) can be five or more times less than the thickness of the voice coil.

[0023] The average magnetic flux density within the at least two flux guiding elements may be between 1.5 T and 2 T, wherein "T" denotes the physical unit "Tesla", eg to avoid / reduce problems caused by saturation of the flux guiding elements.

[0024] The spacing between the first landing surface and the second landing surface may be defined as a distance between a position on the first landing surface and a position on the second landing surface measured in a direction parallel to the axis of movement.

[0025] The range of the voice coil measured in a direction parallel to the axis of movement (or the "height" of the voice coil) can be within the range of 85% and 100% of the spacing between the first landing surface and the second landing surface measured in a direction parallel to the axis of movement. This configuration can achieve a large linear displacement of the voice coil while effectively suppressing the rocking motion.

[0026] The magnet unit and the air gap may form a magnetic circuit. The magnetic circuit may provide a substantially closed circuit (or loop) for the magnetic flux generated by the permanent magnets and guided by the at least two flux guiding elements.

[0027] The magnetic circuit can have a relatively high reluctance. In particular, the reluctance can exceed the reluctance of conventional magnet units, which is usually kept low. For example, the reluctance of the magnetic circuit can be at least 2.5×10^6 [1 / H] or even 3×10^6 [1 / H], where "H" represents the physical unit "Henry". In contrast, conventional magnet units can have a reluctance of at most 1.5×10^6 [1 / H]. Therefore, the reluctance according to the present invention corresponds to or exceeds 166% or even 200% of the reluctance of a more conventional magnetic unit.

[0028] Most of the reluctance of the magnetic circuit is attributable to the air gap. For example, the air gap may have a reluctance of at least 2×10^6 [1 / H].

[0029] By utilizing a magnetic circuit with high reluctance, in particular a high reluctance air gap, relatively small flux guiding elements can be utilized. As a result, the weight of the magnet unit can be reduced. This weight reduction of the magnet unit can more than compensate for the weight of the large voice coil, which means that the relatively high reluctance of the magnetic circuit enables the design of particularly lightweight loudspeakers. This consideration may be particularly relevant for applications in, for example, the automotive industry.

[0030] The mass of the permanent magnet may be smaller than the mass of the voice coil. That is, the permanent magnet may have a first mass, the voice coil may have a second mass, and the first mass may be smaller than the second mass. The first mass may be at least two times smaller than the second mass, or even at least 2.5 times, such as 2.8 times.

[0031] In conventional loudspeakers, the mass of the permanent magnet may be large compared to the mass of the voice coil for the reasons outlined in the background section above. However, the present invention allows for a relatively heavy and therefore large / dense voice coil, which can be combined with a smaller / lighter permanent magnet (and therefore with the magnet unit). Thus, the combination of a smaller permanent magnet and a larger / dense voice coil can help achieve desired performance parameters while reducing the weight of the loudspeaker and the weight of the permanent magnet. Given the rising price of rare earth magnets, this can provide a more cost-effective configuration.

[0032] The diaphragm may include a first diaphragm body and a second diaphragm body, the second diaphragm body being centered relative to the first diaphragm body (eg relative to the axis of movement). The first diaphragm body may also be referred to as an outer diaphragm body, and the second diaphragm body may also be referred to as a central diaphragm body.

[0033] The outer film sheet body and the central film sheet body can be formed integrally. Alternatively, the outer film sheet body and the central film sheet body can be formed separately and bonded together, for example, using a suitable adhesive.

[0034] The outer film body may have a first radiating surface facing forward (eg, away from the frame) and a second radiating surface facing backward (eg, toward the frame).

[0035] The central diaphragm body may include an annular wall extending around the voice coil, the annular wall extending along the movement axis between the first end and the second end of the central diaphragm body. The first end may be further forward along the movement axis than the second end. The outer diaphragm body may be connected to the annular wall at a position between the first end and the second end of the central diaphragm body, so that the second end of the annular wall is separated from the position where the outer diaphragm is connected to the annular wall.

[0036] The outer diaphragm body may be connected to the first suspension element, for example at an outer edge of the outer diaphragm body.The second suspension element may be connected to the annular wall at or towards the second end of the central diaphragm body.

[0037] The central diaphragm body can provide an improved structure for attaching the suspension element. In particular, the second end of the annular wall of the diaphragm body provides a free end (i.e., the second end) extending away from the outer diaphragm body (in the rear and upward direction), and the suspension element can be attached to the free end. Therefore, the positioning of the suspension element can be improved and the swing can be suppressed.

[0038] Where the outer and central membrane bodies are arranged as separately formed bodies, this can provide an improved structure for assembly purposes. In particular, this can facilitate improved installation of leads during assembly, as the outer membrane body can be installed in a subsequent manufacturing step (i.e., after the central membrane body) and thus be easily accessible.

[0039] If the outer diaphragm body and the central diaphragm body are formed separately, these diaphragm bodies can be connected together by matching corresponding surfaces. For example, the outer diaphragm body can have an inner peripheral surface inclined relative to the movement axis, and the annular wall of the central diaphragm body can have an outer peripheral surface inclined relative to the movement axis. The inner peripheral surface and the outer peripheral surface can be inclined at approximately the same angle relative to the movement axis and fixed together, for example, using a suitable adhesive.

[0040] The angle or angles may be in the range of 3 to 35 degrees relative to the axis of movement, preferably between 3 and 20 degrees relative to the axis of movement.

[0041] The indicated angular range may improve the joining of the outer and central membrane bodies (where these membrane bodies are formed separately) and may improve the positioning of the second end of the annular wall (where the annular wall is straight) for the purpose of attaching the second suspension element.

[0042] The central diaphragm body may include a signal track to transmit electrical signals to or from the voice coil. The signal track may extend from a position on the outer peripheral surface of the annular wall of the central diaphragm along the annular wall and toward the voice coil. The position from which the signal track extends may be at the second end of the annular wall or toward the second end of the annular wall. The first pad may be provided at the position on the central diaphragm body from which the signal track extends. Here, "at the second end of the annular wall or toward the second end of the annular wall" may be understood to mean that the position is at the second end of the annular wall or between the second end and the position where the outer diaphragm body is attached to the annular wall.

[0043] In some examples, the signal track can extend to a second pad on the wall of the central diaphragm body close to the voice coil, for example to facilitate easy connection of the signal track to the voice coil. The second pad can be on an annular wall of the central diaphragm body or on another wall of the central diaphragm body. Preferably, the second pad is on the wall of the central diaphragm body, which wall can be approached after the central diaphragm has been fixed to the second suspension element, as this can facilitate connecting the voice coil to the second pad during installation. In some examples, the second pad is arranged on an inner annular wall that defines an aperture through the central diaphragm body. For example, the second pad can be located on the face of the inner annular wall facing the moving axis. Therefore, the second pad can be reached through the aperture.

[0044] Thus, the central diaphragm body can be used for the purpose of transmitting signals to and / or from the voice coil, replacing the lead wires used for part of the signal transmission. This can reduce the risk of strong cotton lead wire noise and can improve the installation of the lead wires during assembly, which can conventionally be cumbersome and difficult.

[0045] The axial extent of the central diaphragm body along the axis of movement may be greater than the spacing of the landing surfaces along the axis of movement.

[0046] The first end of the central diaphragm body may have a first extent in a direction perpendicular to the moving axis. The second end of the central diaphragm body may have a second extent in a direction perpendicular to the moving axis. The first extent may be smaller than the second extent.

[0047] The first end of the central diaphragm body may be closed. Additionally or alternatively, a dust cover may be located above the first end of the central diaphragm body.

[0048] Ingress to the loudspeaker may be partially or even completely prevented by closing the central diaphragm body by providing a closed first end or covering the central diaphragm body with a dust cover.

[0049] The speaker as described above may be arranged in a housing. The housing may define an internal volume in the range of 0.25 liters to 5 liters, with the speaker mounted in the internal volume. In some examples, the internal volume may be up to 1.5 liters.

[0050] According to another aspect of the present invention, there is provided a bass loudspeaker comprising: a frame; a diaphragm suspended to the frame by at least a first suspension element and a second suspension element, wherein the first suspension element is attached to the frame at a first landing surface on the frame and the second suspension element is attached to the frame at a second landing surface on the frame; a magnet unit fixed to the frame, wherein the magnet unit comprises a permanent magnet and at least two flux guiding elements, the flux guiding elements being configured to guide magnetic flux across an air gap; a voice coil rigidly connected to the diaphragm; wherein the loudspeaker is operable to excite the voice coil so that the voice coil moves along a movement axis relative to the diaphragm; The magnet unit moves, thereby moving the diaphragm along the moving axis to produce sound; wherein the diaphragm includes an outer diaphragm body and a central diaphragm body; wherein the central diaphragm body includes an annular wall extending around the voice coil, and the annular wall extends along the moving axis between the first end and the second end of the central diaphragm body; wherein the outer diaphragm body is connected to the annular wall at a position between the first end and the second end, so that the second end of the annular wall is separated from the position where the outer diaphragm is connected to the annular wall; wherein the first suspension element is connected to the outer diaphragm body; and wherein the second suspension element is connected to the annular wall at the second end of the central diaphragm body or toward the second end of the central diaphragm body.

[0051] The present invention includes the described aspects and preferred feature combinations unless such combinations are expressly impermissible or explicitly avoided. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Embodiments and experiments illustrating the principles of the present invention will now be discussed with reference to the accompanying drawings, in which:

[0053] Figure 1 is a cross-sectional view of an exemplary loudspeaker.

[0054] Figure 2 yes Figure 1 A cross-sectional view of a portion of a loudspeaker.

[0055] Figure 3 yes Figure 1 A cross-sectional view of a portion of a loudspeaker.

[0056] Figure 4 is an example Figure 1 A graph of the magnetic flux lines of a loudspeaker.

[0057] Figure 5 is an example Figure 1 A graph of the magnetic flux density of a loudspeaker.

[0058] Figure 6 yes Figure 1 A perspective view of a first portion of a diaphragm of a loudspeaker.

[0059] Figure 7 yes Figure 1 A cut-away perspective view of a second portion of the diaphragm of a loudspeaker.

[0060] Figure 8 yes Figure 1 A cross-sectional view of a portion of a loudspeaker.

[0061] Fig. 9 Includes back-to-back configuration Figure 1 A speaker assembly of two speakers.

[0062] Fig.10 is a side view of a car with an exemplary speaker. DETAILED DESCRIPTION

[0063] Aspects and embodiments of the present invention will now be discussed with reference to the accompanying drawings. Further aspects and embodiments will be apparent to those skilled in the art. All documents mentioned herein are incorporated herein by reference.

[0064] The present invention relates to a loudspeaker including a frame, a diaphragm and a driving unit. Prior to the detailed discussion of the present invention, an example of a conventional loudspeaker is discussed below in order to explain the background of the present invention.

[0065] In conventional loudspeakers, the depth of the cabinet is limited by the depth of the loudspeaker itself. Known loudspeakers are particularly designed to be shallow, such as those described in EP1654908B1, EP0912072B1, US7570780B2. In EP1654908B1, a loudspeaker is described as having a corrugated diaphragm comprising a V-shaped cone; the lower suspension part is positioned close to the magnet system to reduce the rocking motion of the moving components of the loudspeaker. In EP0912072B1, a similar loudspeaker using a tube suspension system is described. In US7570780B2, a further loudspeaker is described having a lower suspension member adjacent to the magnet system of the loudspeaker.

[0066] Each of the above-mentioned loudspeakers is configured to provide a magnetic flux of approximately uniform flux density across the air gap of the corresponding loudspeaker. As explained in the background section above, this corresponds to conventional principles of loudspeaker design. Therefore, a deviation from said conventional principles may be that a loudspeaker including a magnet unit with a relatively non-uniform flux density is described herein.

[0067] Furthermore, each of the above-mentioned loudspeakers uses a drive unit having a relatively small / light voice coil and a relatively large / heavy low reluctance magnet system. This may also correspond to conventional principles of loudspeaker design. In contrast, the magnet unit of the loudspeaker described herein is relatively light and has a relatively high reluctance, while the voice coil is relatively large / heavy.

[0068] The speakers described herein may provide a combination of many advantages over previously known speakers. For example, the speakers described herein are shallow, lightweight, and use relatively small amounts of rare earth materials in the magnet units. Furthermore, they are easily constructed using conventional machinery and may be constructed without increasing the number of parts compared to conventional speakers.

[0069] Figure 1 is a cross-sectional view of an exemplary speaker 100. The speaker 100 includes a frame 200, a diaphragm 300 suspended from the frame 200, and a driving unit 400.

[0070] The driving unit 400 has a translatable part 420 and a fixed part 440. The translatable part 420 is fixed to the diaphragm 300 and includes a voice coil 422. The fixed part 440 is fixed to the frame 200 and includes a magnet unit 441 configured to generate a magnetic field in the air gap 442. When the diaphragm 300 is stationary, the voice coil 422 is located in the air gap 442.

[0071] The speaker 100 is operable to excite the voice coil 422 so that the voice coil 422 moves relative to the magnet unit 441 along the movement axis 102. The voice coil 442 is rigidly connected to the diaphragm 300 so that the voice coil 442 and the diaphragm 300 move together. When the voice coil 442 is moved along the movement axis 102, the diaphragm 300 also moves along the movement axis 102, thereby generating sound.

[0072] More specifically, the diaphragm 300 has a first sound radiating surface 302 and a second sound radiating surface 304. The first sound radiating surface 302 faces in a forward direction 104 (away from the frame 200) and is used to generate sound in use. The second sound radiating surface 304 faces in a rearward direction 106, i.e., into the frame 200. The forward direction 104 and the rearward direction 106 are opposite directions parallel to the axis of movement 102. The direction perpendicular to the axis of movement 102 is also referred to as the radial direction 108.

[0073] The frame 200 of the loudspeaker 100 comprises a base 202 and an edge 204. The base 202 extends in the radial direction 108. The edge 204 of the frame 200 is positioned at the periphery of the base 202, radially outside the drive unit 400, and extends axially relative to the movement axis 102, i.e., at least partially along the movement axis 102.

[0074] The fixed part 440 of the drive unit 400 is fixed to the base 202 of the frame 200, while the diaphragm 300 and the translatable part 420 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, i.e., movement in a direction parallel to the movement axis 102, and to inhibit movement in the radial direction 104.

[0075] 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 configured as a rubber surround fixed to the outer edge 306 of the diaphragm 300. The second suspension element 540 is attached to the frame 200 at a second landing surface 240 defined by the edge 204 of the frame 200. The second suspension element 540 is configured as a spring fixed to the diaphragm 300 and extends radially outward relative to the axis of movement 102.

[0076] The first suspension element 520 and the second suspension element 540 are fixed to the diaphragm 300 such that the center of gravity of the translatable part 420 is located between the first landing surface 220 and the second landing surface 240. More specifically, the voice coil 422 is configured to be located in the air gap 442 when the diaphragm 300 is stationary, wherein the center of mass of the voice coil 422 has a position along the movement axis 102 between the first landing surface 220 and the second landing surface 240.

[0077] Figure 2 and Figure 3 is a cross-sectional view of a portion of speaker 100 . Figure 2 The diaphragm 300, voice coil 422 and suspension elements 520, 540 are shown. Figure 3 The voice coil 422 and the magnet unit 441 are shown.

[0078] The voice coil 422 has an axial extent along the moving axis 102 and a radial extent perpendicular to the moving axis 102. The axial extent of the voice coil 422 (also referred to as the height of the voice coil 422) is the distance between a pair of ends 425 of the voice coil 422. The radial extent of the voice coil 422 (also referred to as the winding thickness of the voice coil 422) is the distance between an inner periphery 423 of the voice coil 422 and an outer periphery 424 of the voice coil 422.

[0079] The height of the voice coil 422 is approximately 85% of the spacing between the first landing surface 220 and the second landing surface 240 measured in a direction parallel to the movement axis 102 .

[0080] The magnet unit 441 includes a permanent magnet 446, a (magnetic) washer 447 and a (magnetic) yoke 450. The permanent magnet 446 is configured as a rare earth magnet and may include more than one structural element. 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 a factor of two greater than the mass of the permanent magnet 446, i.e., the mass of the voice coil 422 is twice greater than the mass of the permanent magnet 446.

[0081] The washer 447 and the yoke 450 (configured as a U-shaped yoke in this example) are configured to guide the magnetic flux generated by the permanent magnet 446 to the air gap 442 between the washer 447 and the yoke 450. In particular, the washer 447 and the yoke 450 guide the magnetic flux across the air gap 442.

[0082] The magnet unit 441 is arranged in the speaker 100 such that the air gap 442 faces the front direction 104 , and receives the voice coil 422 extending in the rear direction 106 .

[0083] The magnet unit 441 and the air gap 442 form a magnetic circuit 443. The magnetic circuit 443 provides a closed loop for the magnetic flux generated by the permanent magnet 446 and guided across the air gap 442 by the two flux guiding elements 447, 450. In this example, the air gap 442 has a magnetic reluctance of 2.0×10^6 [1 / H], and the magnetic circuit 443 has a total reluctance slightly greater than the reluctance of the air gap 442.

[0084] The yoke 450 has a base 452 and a side wall 454 protruding from the base 452. The base 452 extends in the radial direction 108, while the side wall 454 extends axially with respect to the movement axis 102.

[0085] The sidewall 454 of the yoke 450 has a radially defined (uniform) thickness (i.e., in the radial direction 108). 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 sidewall 454 of the yoke 450. The ratio of the thickness of the voice coil 422 (i.e., "winding thickness") to the thickness of the sidewall 454 is preferably 3:1 or even 5:1. Conventional speakers of the same size may have a ratio as small as 0.2:1.

[0086] Loudspeaker 100 utilizes a relatively large voice coil 422 using many layers in magnetic circuit 443. Since air gap 442 is wider to accommodate a larger voice coil 442 than conventional speakers, the total magnetic resistance in magnetic circuit 443 is increased so much that the cross-section of flux guide washer 447 and yoke 450 can be thin.

[0087] This new configuration results in a relatively high voice coil mass and a relatively low magnet unit mass. However, the total mass of the drive unit 400 can be lower than, for example, the total mass of the known loudspeakers described above. The ratio of moving mass to total mass can be at most 1:3, preferably at most 1:2. Moreover, the ratio of magnet mass to voice coil winding mass can reach 1:2, preferably at most 1:4. This results in a surprisingly light weight woofer with a low resonance frequency in the enclosure.

[0088] The permanent magnet 446 , the washer 447 and the yoke 450 are axially symmetrical about the movement axis 102 , but other arrangements are possible.

[0089] Figure 4 and Figure 5 The magnetic flux generated by the magnet unit 441 is illustrated. In particular, Figure 4 4 shows a cross-sectional view of the drive unit 400 and illustrates the magnetic flux lines generated by the magnet unit 441, and Figure 5 is a graph showing the magnetic flux density across the voice coil 422 (“Coil ID” to “Coil OD”, ie, inner diameter / circumference 423 to outer diameter / circumference 424 ).

[0090] exist Figure 4 , the magnetic flux follows a tortuous path that spreads across the voice coil 422 in the air gap 442. Correspondingly, the magnetic flux density across the voice coil 422 decreases. Figure 5 The radial flux density Br is shown over the thickness of the winding of the voice coil 422, which shows a significant drop that is generally undesirable in speaker design. In a typical speaker, the magnetic flux density can be nearly constant and can drop to about 85% to 90% (percent) of the initial value. In contrast, according to the present invention, the radial flux density can drop by at least 50% over the thickness of the winding of the voice coil 422. In this example, the magnetic flux density at the outer periphery 424 of the voice coil 422 is about 37% of the magnetic flux density at the inner periphery 423 of the voice coil 422. In other words, the magnetic flux density drops by about 63% from the inner periphery 423 to the outer periphery 424 of the voice coil 422.

[0091] The relatively large reduction in magnetic flux density is associated with the relatively high magnetic resistance of the magnet unit 441 of the loudspeaker 100. The magnetic resistance can be estimated by calculations derived from simulations using the finite element method of a static magnetic circuit.

[0092] By taking the average magnetic field strength H inside the magnet av,m (H_av,m) multiplied by the height of the magnet h m (h_m) to calculate the magnetomotive force of the magnet in the circuit (F_m). The resulting unit is ampere [A].

[0093]

[0094] Estimate the total magnetic flux φ passing through the magnetic circuit by integrating the magnetic flux density across the open surface B (Phi_B). The integration is performed on the surface Sm (Sm), which is usually a cylindrical surface at the top or bottom of the magnet perpendicular to the magnetization direction. The magnetic flux density at the magnet is strictly axial, so that the radial component can be neglected. The resulting unit is Weber [Wb].

[0095]

[0096] Magnetomotive force Divided by the magnetic flux φ B Reluctance of the magnetic circuit (R_m). The resulting unit is one part Henry [1 / H].

[0097]

[0098] It has been found that having a magnetic reluctance higher than 2.5×10^6[1 / H] (or "2.5E6 1 / H"), preferably higher than 3×10^6[1 / H] (or "3E61 / H"), can produce a low-weight, high-efficiency loudspeaker. In contrast, performing the same calculation on the magnet system of a conventional loudspeaker shows that its magnetic reluctance cannot exceed 1.5×10^6[1 / H] (or "1.5E6 1 / H").

[0099] In this example, the flux guiding elements 447, 450 are made of steel, so that the magnetic resistance of the flux guiding elements can be neglected, since the relative magnetic permeability μ of steel is r >>1, and all the reluctance can be allocated to the air gap 442. With such a large reluctance air gap 442, the radial flux density is not constant in the air gap 442, as described above.

[0100] Figure 6 and Figure 7 Illustrated is a diaphragm 300. The diaphragm 300 includes an outer diaphragm body 320 (or "cone") and a central diaphragm body 340 (or "sub-cone").

[0101] exist Figure 6 , an outer film body 320 is shown. The outer film body 320 has an outer edge 322 and an inner edge 324. The inner edge 324 defines a central aperture 325 through the outer film body 320. When assembled, the central film body 340 is received in the central aperture 325.

[0102] The outer edge 322 of the outer diaphragm body 320 is connected to the first suspension element 520. In this example, the inner edge 322 of the outer diaphragm body 320 is connected to the central diaphragm body 340 because the diaphragm bodies 320, 340 are formed separately.

[0103] The inner edge 324 of the outer film body 320 is arranged at a certain angle relative to the movement axis 102. In this example, the angle is in the range of 5 degrees to 20 degrees. Thus, an upright edge portion at a certain angle to the movement axis 102 is provided.

[0104] exist Figure 7 , a central diaphragm body 340 is shown. The central diaphragm body 340 has a front end 341 and a rear end 342. The front end 341 and the rear end 342 are opposite ends of the central diaphragm body 340, which define the longitudinal extent of the central diaphragm body 340. The front end 341 faces the forward direction 104, and the rear end 342 faces the rearward direction 106.

[0105] The central diaphragm body 340 includes an outer annular wall 350 and an inner annular wall 370. The annular walls 350, 370 are concentrically arranged around the moving axis 102. In this example, the inner annular wall 370 and the voice coil 422 are sequentially arranged along the moving axis 102, and the outer annular wall 350 surrounds the inner annular wall 370 and the voice coil 422.

[0106] The inner annular wall 370 extends toward the voice coil 422 so that a mechanical and / or electrical connection can be made with the voice coil 422 or a voice coil former (where provided).

[0107] The inner annular wall 370 defines an aperture 372 that extends through the central diaphragm body 340 .

[0108] The central diaphragm body 340 and the outer diaphragm body 320 are located at a position 352 (see FIG. 35A ) where the outer annular wall 350 receives the outer diaphragm body 320. Figure 2 ) is connected. Position 352 is located between the front end 341 and the rear end 342 of the central diaphragm body 340. Therefore, the outer annular wall 350 has a free end 354 in the rearward direction 106 (see Figure 8 ). The second suspension element 540 is connected to the outer annular wall 350 , and in particular, to the free end 354 of the outer annular wall 350 .

[0109] The outer annular wall 350 of the central diaphragm body 340 is at a steep angle relative to the moving axis 102. In this example, the angle is in the range of 5 to 20 degrees, allowing a small inner diameter of the second suspension element 540. This ensures clearance above the yoke 450, allowing large axial displacements of the voice coil 422 and the entire moving assembly.

[0110] The inner edge 324 of the outer diaphragm body 320 and the outer annular wall 350 of the central diaphragm body 340 are disposed at similar steep angles relative to the axis of movement 102, for example within 3 degrees of each other, as this can improve the bonding of the diaphragm bodies 320, 340. Further, this design allows for undulation of the diaphragm 300, resulting in substantial strengthening of the entire downward portion of the outer diaphragm body 320 and the central diaphragm body 340, while allowing sufficient clearance to the bottom of the central diaphragm body 340 for wire connections.

[0111] Figure 8 A central diaphragm body 340 and a voice coil 422 are shown. The central diaphragm body 340 is used to transmit lead signals to and from the voice coil 422. More particularly, the central diaphragm body 340 includes a signal track 344, such as a copper strip, which is used to guide the signal to and from the voice coil 422. In practice, a minimum of two signal tracks 344 may be provided.

[0112] The signal track 344 extends from the radially outer surface 356 of the outer annular wall 350 toward the voice coil 422. Suitably, the signal track 344 is connected to a pair of solder pads 348 for connecting to the lead 380 at one end of the signal track 344 and to the voice coil 422 at the other end of the signal track 344. The first solder pad 348 is disposed on the radially outer surface 356 of the outer annular wall 350, the first solder pad 348 being positioned toward the rear end 342. The second solder pad 348 is disposed on the radially inner surface 374 of the inner annular wall 370.

[0113] In this example, the signal track 344 extends along a radially inner surface 358 of the outer annular wall 350 and along a radially outer surface 376 of the inner annular wall 370 .

[0114] The use of a signal track 344 may improve the ease of assembly of the loudspeaker 100. The signal track 344 may be provided as a thin self-adhesive copper strip glued along the central diaphragm body 340, along the inside or outside of the central diaphragm body 340. This may enable easy connection to the voice coil 422 at the top and to the leads 380 at the bottom by means of a solder connection or conductive glue. The flexible leads 380 may form an arc through the air, or be connected to the second suspension element 340, for example by sewing or gluing or even weaving in.

[0115] All electrical connections from the voice coil 422 to the signal tracks 344, leads 380, and lead terminals 382 can be made while the components are easily accessible without the outer diaphragm body 320 being present or without the need to flip the loudspeaker 100. The electrical connections to the voice coil 422 can be made through the aperture 372 of the center diaphragm body 340.

[0116] With regard to the known loudspeakers described above, it is noted that all three loudspeaker designs may suffer from relatively complex guidance of the leads connecting the voice coil winding to the terminals. EP0912072B1 allows large displacements because the inner diameter of the lower suspension is close to the outer diameter of the U-shaped yoke, but the construction and guidance of the leads using the tubular element and the coupling features to the cone may be cumbersome. In the case of EP1654908B1 and US7570780B2, the portion of the diaphragm that brings the connection surface to the spider close to the U-shaped yoke is under a shallow angle, resulting in a large inner diameter of the spider, thereby reducing the maximum excursion capability.

[0117] Fig. 9 Another exemplary loudspeaker 1000 is shown. Loudspeaker 1000 comprises two loudspeakers 100, as described above, mounted in a back-to-back configuration in a closed box volume of 3 liters, each loudspeaker being designed for a nominal excursion of ±10 mm (millimeters). Each loudspeaker 100 is configured as a 5 inch woofer for use up to 200 Hz (hertz) in a closed box as small as 1.5 liters net volume.

[0118] As described above, the magnet unit 441 consists of only three pieces: the U-yoke 450, the permanent magnet 446 (arranged as a disk) and the washer 447. The permanent magnet 446 has a diameter of 24 mm, a height of 8 mm and a weight of 28 g (grams). This may be unusually small for a woofer with such an application. The voice coil 422 has a winding height of 17 mm at a winding thickness of 6.4 mm. The weight of the winding is 75 g. In order to guide the flux through the winding efficiently, the washer 447 has a thickness of 3 mm and the U-yoke has a wall thickness of 2 mm (measured near half the height of the voice coil winding). These parameters result in a ratio of magnet weight to coil weight of 1:2.8. The ratio of winding thickness to U-yoke thickness is 3.15:1.

[0119] exist Fig. 9 In the embodiment of the invention, two of these loudspeakers 100 are mounted back to back in a closed box with a total net volume of 3 litres, allowing each loudspeaker 100 to act on a closed volume of 1.5 litres. Due to the small size, the box does not require additional internal ribbing or strengthening elements, which would otherwise increase the necessary external dimensions and total volume. The magnet units 441 are mounted back to back, mitigating the effects of any leakage flux towards the central surface contacted by the U-shaped yoke, as all flux is forced back into the flux guide steel, allowing the cross section to be minimized.

[0120] Since the loudspeakers 100 are joined back to back, the net force on the rear of each individual frame is zero and allows it to be thin and lightweight. The force factor of each motor system 400 is symmetrical to displacement and drops to 50% relative to the rest position at ±8mm, resulting in low deformation over a wide range of displacements. Having the steel flux guiding elements close to magnetic saturation at about 1.6T allows the inductance to be kept so low that it has little effect on the frequency response over the operating range up to 200Hz. In fact, the higher inductance and therefore lower inductance results in reduced higher order distortion compared to conventional loudspeakers with fewer windings, due to the reduced output for higher frequencies above 200Hz.

[0121] The moving mass of the loudspeaker 100 is approximately 100 g, the sum of the suspension and cabinet stiffness adds up to 15 N / mm, resulting in a cabinet resonant frequency of 62 Hz. The total mass of the loudspeaker 100 is less than 300 g.

[0122] It is worth noting that for two drivers back to back, the total mass of the drivers is under 600g, of which 200g are moving in opposite directions so that there is no net force on the enclosure. The mass of the overall assembly of two drivers in the enclosure is under 1.3kg.

[0123] This small size and weight and the absence of any cabinet vibrations allow placement in locations where sheer size previously prohibited applications. This could be, for example, near the bottom of an A-style or between the footwells in a car cabin in a high powered kick bass application.

[0124] The manufacturing possibilities according to the above invention can be easily understood. For example, the wire guidance and the subsequent placement of the dust cover can be improved. Fig. 9 , the speaker 100 is shown with a separate dust cover 390. This can allow for a traditional build starting with the frame and magnet system and adding the dust cover 390 last. Alternatively, the dust cover is integrated into the central diaphragm body 340 (see Figure 1 ), allowing pre-assembly with the voice coil 422 and installation of the signal track 344 before the magnet unit is inserted and centered via the fixture. The diaphragm 300 has a central portion covering the top of the voice coil, thereby acting as a dust cover. In this case, the entire loudspeaker can be manufactured around an alignment fixture that is initially inserted into the frame, which is eventually replaced by the magnet unit. Using this approach, the number of parts may not increase relative to traditional loudspeakers, while providing substantial benefits in terms of performance, as described above.

[0125] Figure 1540 at multiple locations. It is also conceivable that the leads are partially fixed to the underside of the diaphragm 300 and from there arc through the air toward the terminal 382. This can reduce the risk of strong cotton lead noise compared to an arc starting at the bottom of the central diaphragm body 340.

[0126] The voice coil 422 may have one (as described above) or multiple windings, which are driven from multiple amplifier channels via separate signal tracks 344 and lead wire 380 pairs. Also, the winding wire of the voice coil 422 may have a circular cross section or a rectangular cross section. These winding wire types allow for a higher conductivity ratio compared to the volume occupied by the winding (fill factor), and are particularly useful in the described loudspeakers with large coil volumes. The winding wire material is any suitable conductor material; preferably copper, but may also be aluminum or a mixture of the two, such as copper clad aluminum wire.

[0127] Both the outer diaphragm body 320 and the central diaphragm body 340 can be made of a material with high thermal conductivity (e.g., aluminum), effectively acting as a heat sink when they are connected near the voice coil 422 without a long voice coil frame. In this case, the signal track 344 is insulated from the outer diaphragm body 320 and the central diaphragm body 340. It is also conceivable to weld one electrical connection to the central diaphragm body 340 and one connection to the outer diaphragm body 320; in this case, electrical insulation between them can be provided by an adhesive between the diaphragm bodies 320, 340. Then, the lead 380 is also connected to the outer diaphragm body 320 and the central diaphragm body 340, respectively. Of course, a combination is also possible, in which, for example, only one connection is completed via the signal track 344, and the other connection is completed via the conductive central diaphragm body 340.

[0128] In fact, it is also possible to guide the lead wires of the winding wires or coils along the top surface of the central diaphragm body 340 to the bottom of the central diaphragm body 340 in order to connect to the leads. This is particularly interesting if the diaphragm 300 has an integrated dust cover and completely covers the wires. In the case where the central diaphragm body 340 is injection molded, the electrical connections along the central diaphragm body 340 can also be made by means of insert-molded conductors. Even a thin copper layer with only strips separating the conductive surfaces is an option, and the conductive surfaces are added to the otherwise insulating central diaphragm body 340 by means of vapor deposition. It can be seen that there are many ways to achieve the basic concept that the electrical connection is guided along the central diaphragm body 340 and is guided to the inner diameter of the second suspension element 540 and below the diaphragm 300.

[0129] Fig.10A car 2000 is shown. Any of the exemplary speakers described above may be installed in the car 2000. In this example, the speakers 100 described above are disposed between the footwells 2100 of the car 2000. Other locations are also contemplated, such as at or toward the bottom of the A-frame.

[0130] The features disclosed in the above description or the attached claims or drawings (expressed in their specific form or according to the device for performing the disclosed function, or the method or process for obtaining the disclosed result) can be used to realize the present invention in its different forms, either alone or in any combination of these features.

[0131] Although the present invention has been described in conjunction 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 to be illustrative rather than restrictive. Various changes may be made to the described embodiments without departing from the spirit and scope of the present invention.

[0132] For the avoidance of any doubt, any theoretical explanations provided herein are provided to improve the reader's understanding. The inventors do not wish to be bound by any of these theoretical explanations.

[0133] Any section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described.

[0134] Throughout the specification, including the following claims, unless the context requires otherwise, the words "comprises" and "comprising" and variations thereof will be understood to imply the inclusion of stated integers or steps or groups of integers or steps but not the exclusion of any other integers or steps or groups of integers or steps.

[0135] It must be noted that, as used in the specification and the appended claims, the singular forms "a", "an", and "the" include plural references unless the context clearly dictates 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 the one particular value and / or to the other particular value. Similarly, when a value is expressed as an approximation by using the antecedent "about", it should be understood that the particular value forms another embodiment. The term "about" in relation to a numerical value is optional and refers to, for example, + / - 10%.

[0136] References

[0137] In order to more fully describe and disclose the present invention and the prior art related to the present invention, many publications are cited above. The complete citations of these references are provided below. The entire contents of each of these references are incorporated herein.

[0138] EP1654908B1

[0139] EP0912072B1

[0140] US7570780B2

Claims

1. A woofer, comprising: frame; a membrane suspended to the frame by at least a first suspension element and a second suspension element, wherein the first suspension element is attached to the frame at a first landing surface on the frame and the second suspension element is attached to the frame at a second landing surface on the frame; a magnet unit fixed to the frame, wherein the magnet unit comprises a permanent magnet and at least two flux guiding elements configured to guide magnetic flux across an air gap; a voice coil rigidly connected to the diaphragm; wherein the speaker is operable to excite the voice coil to move the voice coil relative to the magnet unit along a movement axis, thereby moving the diaphragm along the movement axis to generate sound; wherein the voice coil is configured to be located in the air gap when the diaphragm is stationary, wherein a center of mass of the voice coil has a position along the axis of movement between the first landing surface and the second landing surface; and wherein a magnetic flux density at an outer periphery of the voice coil is 50% or less of a magnetic flux density at an inner periphery of the voice coil.

2. The woofer speaker according to claim 1, wherein: The magnetic flux density at the outer periphery of the voice coil is in a range of 10% to 50% of the magnetic flux density at the inner periphery of the voice coil.

3. The woofer according to claim 1 or 2, wherein: The magnet unit and the air gap form a magnetic circuit having a magnetic resistance of at least 2.5×10^6 [1 / H].

4. The woofer speaker according to claim 3, wherein: The air gap has a magnetic reluctance of at least 2×10^6 [1 / H].

5. A woofer according to any one of the preceding claims, in, The at least two flux guiding elements include a yoke including a base and a sidewall extending from the base, Wherein, a thickness of the voice coil in a direction perpendicular to the moving axis is greater than a thickness of the side wall of the yoke in the direction perpendicular to the moving axis.

6. A woofer according to any one of the preceding claims, in, The range of the voice coil along the axis of movement is within a range of 85% to 100% of the pitch of the landing surface along the axis of movement.

7. A woofer according to any one of the preceding claims, in, The permanent magnet has a first mass, the voice coil has a second mass, and the first mass is smaller than the second mass.

8. A woofer according to any one of the preceding claims, wherein: The diaphragm comprises an outer diaphragm body and a central diaphragm body; The central diaphragm body includes an annular wall extending around the voice coil, the annular wall extending along the movement axis between the first end and the second end of the central diaphragm body; wherein the outer membrane body is connected to the annular wall at a position between the first end and the second end, so that the second end is separated from the position where the outer membrane is connected to the annular wall; wherein the first suspension element is connected to the outer membrane body; and The second suspension element is connected to the annular wall at or towards the second end of the central diaphragm body.

9. A woofer according to any one of the preceding claims, wherein: The outer film body has an inner peripheral surface inclined relative to the moving axis, The annular wall of the central diaphragm body has an outer peripheral surface inclined relative to the moving axis, The inner circumferential surface and the outer circumferential surface are inclined at substantially the same angle relative to the moving axis and are fixed together.

10. A woofer according to any one of the preceding claims, wherein: in, The angle is in the range of 3 to 35 degrees relative to the movement axis, Preferably between 3 and 20 degrees relative to the axis of movement.

11. A woofer according to any one of the preceding claims, wherein: The central diaphragm body includes a signal track to transmit an electrical signal to or from the voice coil; The signal track extends from a position on the outer peripheral surface of the annular wall along the annular wall and toward the voice coil, The location from which the signal track extends is at or towards the second end of the annular wall.

12. A woofer according to any one of the preceding claims, in, The axial extent of the central diaphragm body along the movement axis is greater than the spacing of the landing surfaces along the movement axis.

13. A woofer according to any one of the preceding claims, The first end of the central diaphragm body has a first extent in a direction perpendicular to the movement axis, The second end of the central diaphragm body has a second extent in the direction perpendicular to the movement axis, The first range is smaller than the second range.

14. A woofer according to any preceding claim, wherein: The first end of the central diaphragm body is closed, Alternatively, the dust cover is located above the first end of the central diaphragm body.

15. An assembly comprising a woofer according to any one of the preceding claims and an enclosure, wherein: The woofer is mounted in the housing.

16. A woofer, comprising: frame; a membrane suspended from the frame by at least a first suspension element and a second suspension element, wherein the first suspension element is attached to the frame at a first landing surface on the frame and the second suspension element is attached to the frame at a second landing surface on the frame; a magnet unit fixed to the frame, wherein the magnet unit comprises a permanent magnet and at least two flux guiding elements configured to guide magnetic flux across an air gap; a voice coil rigidly connected to the diaphragm; wherein the speaker is operable to excite the voice coil to move the voice coil relative to the magnet unit along a movement axis, thereby moving the diaphragm along the movement axis to generate sound; Wherein, the diaphragm comprises an outer diaphragm body and a central diaphragm body; Wherein, the central diaphragm body comprises an annular wall extending around the voice coil, and the annular wall extends along the movement axis between the first end and the second end of the central diaphragm body; wherein the outer membrane body is connected to the annular wall at a position between the first end and the second end, so that the second end of the annular wall is separated from the position where the outer membrane is connected to the annular wall; wherein the first suspension element is connected to the outer membrane body; and Wherein, the second suspension element is connected to the annular wall at or towards the second end of the central diaphragm body.

Images