Electroacoustic driver and loudspeaker including the same

Abstract

An electroacoustic driver that can be used in a loudspeaker system, which utilizes drivers with magnetic negative springs (MNS), such as reluctance-assisted drivers (RAD) and permanent magnet corona (PMC) drivers. The electroacoustic driver can be used for all audio frequencies, including subwoofer frequencies. The magnetic negative spring of the electroacoustic driver can cancel or partially cancel the large pressure on the sound panel (of an audio speaker), thereby enabling the efficient and economical generation of significant subwoofer notes in small / portable speakers. The electroacoustic driver can include a stabilizing / centering mechanism to overcome the unstable force of the MNS, which is too large for a separate voice coil to generate.

Description

[0001] Related Patent / Patent Application

[0002] This application claims priority to U.S. Patent Application No. 62 / 963,833, filed on January 21, 2020, U.S. Patent Application No. 63 / 022,125, filed on May 8, 2020, and U.S. Patent Application No. 63 / 048,393, filed on July 6, 2020, all of which have the invention title of "Electroacoustic Driver and Loudspeaker Incorporating the Same".

[0003] This application is related to U.S. Patent Application No. 63 / 034,556, filed on June 4, 2020, which has the invention title of "Voice Coil Actuator and Loudspeaker Incorporating the Same".

[0004] This application is related to U.S. Patent Application No. 62 / 932,971, filed on November 8, 2019 ("Pinkerton's 971 Patent Application") and U.S. Patent Application No. 62 / 962,770, filed on January 17, 2020 ("Pinkerton's 770 Patent Application"), both of which have the invention title of "Improved Electroacoustic Driver and Loudspeaker Incorporating the Same".

[0005] This application is also related to the international patent application with the serial number PCT / US19 / 30438, titled "Loudspeaker System and Method of Use Thereof", filed by Joseph F. Pinkerton et al. on May 2, 2019. This international patent application claims priority to (a) the U.S. Provisional Patent Application with the serial number 62 / 666,002, titled "Audio Loudspeaker", filed by Joseph F. Pinkerton et al. on May 2, 2018, and (b) the U.S. Provisional Patent Application with the serial number 62 / 805,210, titled "Loudspeaker System and Method of Use Thereof", filed by Joseph F. Pinkerton et al. on February 13, 2019.

[0006] This application is also related to the U.S. Patent with the serial number 9,826,313, titled "Compact Electroacoustic Transducer and Loudspeaker System and Method of Use Thereof", granted to Joseph F. Pinkerton et al. on November 21, 2017, and this U.S. Patent was granted based on the U.S. Patent Application No. 14 / 717,715, filed on May 20, 2015.

[0007] This application is also related to the international patent application titled "Stereo Speaker System and Method of Use Thereof" with serial number PCT / US19 / 057871, filed on October 24, 2019, by David A. Badger et al., which claims priority to the U.S. Provisional Patent Application titled "Stereo Speaker System and Method of Use Thereof" with serial number 62 / 749,938, filed on October 24, 2018, by David A. Badger et al.

[0008] All of the above patent applications are commonly assigned to the assignee of the present invention, and accordingly, their entire contents are incorporated herein by reference for all purposes. Technical Field

[0009] The present invention relates to electroacoustic drivers and speakers having and using such electroacoustic drivers, particularly drivers having a magnetic negative spring (MNS) (such as a reluctance assisted driver (RAD) and a permanent magnet corona (PMC) driver) and speakers having and using such drivers. Background Art

[0010] Figure 1 Shown is a prior art audio force sensor 100, which includes a fixed magnetic flux path 101 (soft iron) having a permanent magnet 102 and a moving coil bracket 103 having an electric coil 104. The permanent magnet 102 is separated from the electric coil 104 by an air gap 105. Magnetic force will cause the coil bracket 103 to slide inwards and outwards in the z-axis direction (as Figure 1 shown), which moves the panel of a speaker (not shown) to produce audible sound.

[0011] As Figure 1 shown, such a prior art audio force sensor cannot produce substantial subwoofer notes in small / portable speakers because they cannot generate the required force without being heavy, expensive, and high-powered. Due to the size of small / portable speakers, the amount of pressure required to move the (audio speaker's) sound panel to produce low-frequency sound is quite large; thus, the corresponding power to produce such subwoofer notes is also large. Since the power supply of small / portable speakers is typically a small mobile power source (such as a battery), the amount of power that can be used is limited, thereby restricting the generation of such subwoofer sounds. Otherwise, the small mobile power source will be quickly discharged, requiring a significant increase in the size and number of the mobile power source (i.e., a large increase in the use of batteries), which will significantly increase the size and weight of the device and / or the connection of the speaker to a non-mobile power source (such as being plugged in). For small / portable speakers and their use, all of these additional weights and power consumptions are generally undesirable.

[0012] Accordingly, it is desirable to cancel or partially cancel the large pressure on the sound panel (of an audio speaker) so that a substantial amount of subwoofer notes can be produced in a small / portable speaker. SUMMARY OF THE INVENTION

[0013] The present invention relates to electroacoustic drivers and speakers having and using such electroacoustic drivers, and in particular to drivers having a magnetic negative spring (MNS) (such as a reluctance assisted driver (RAD) and a permanent magnet corona (PMC) driver) and speakers having and using such drivers.

[0014] Generally, in one aspect, the present invention features a speaker including a sealed enclosure. The speaker also includes a sound panel mechanically connected to the sealed enclosure. The speaker also includes an actuator operable to convert electrical energy into mechanical energy. The actuator is mechanically connected to the sound panel. The speaker also includes a magnetic negative spring (MNS) mechanically connected to the sound panel.

[0015] Some embodiments of the present invention may include one or more of the following features:

[0016] The actuator may be a voice coil.

[0017] The voice coil and the MNS may share the same magnetic circuit.

[0018] The actuator may be an electromagnet.

[0019] The actuator may be a piezoelectric transducer.

[0020] The speaker may also include a position sensor for sensing the position of the sound panel.

[0021] The position sensor may be an infrared position sensor.

[0022] The position sensor may be a capacitive position sensor.

[0023] The position sensor may be an inductive position sensor.

[0024] The MNS may include at least one stationary magnet and a movable armature.

[0025] The stationary magnet may be a permanent magnet.

[0026] The stationary magnet may be a toroidal permanent magnet.

[0027] The toroidal permanent magnet may be a radially polarized magnet.

[0028] The stationary magnet may include at least four toroidal permanent magnets.

[0029] The stationary magnet may include at least six toroidal permanent magnets.

[0030] The stationary magnet can be an electromagnet.

[0031] The stationary magnet can be an electromagnet combined with a permanent magnet.

[0032] The movable armature can include a ferromagnetic element.

[0033] The ferromagnetic element can include at least one triangular steel element.

[0034] The ferromagnetic element can include a serrated steel ring.

[0035] The ferromagnetic element can include laminated steel.

[0036] The movable armature can include an armature permanent magnet.

[0037] When the armature is in the central position, the polarity of the armature permanent magnet can be opposite to the polarity of the stationary magnet.

[0038] For most positions of the armature, the polarity of the armature permanent magnet can be opposite to the polarity of the stationary magnet.

[0039] The armature permanent magnet can be triangular.

[0040] The armature permanent magnet can include an array of triangular elements.

[0041] The armature permanent magnet can be diamond-shaped.

[0042] The armature permanent magnet can include an array of diamond-shaped elements.

[0043] The movable armature can include a voice coil.

[0044] The movable armature can include a ferromagnetic element and a voice coil.

[0045] The movable armature can include an armature permanent magnet and a voice coil.

[0046] The armature permanent magnet can be triangular.

[0047] The armature permanent magnet can be diamond-shaped.

[0048] The loudspeaker can also include an armature centering mechanism.

[0049] The centering mechanism can include a motor.

[0050] The centering mechanism can include a gear motor.

[0051] The centering mechanism can include an air pump.

[0052] The loudspeaker can also include a flexible mechanical armature support.

[0053] The flexible mechanical armature support can share the same axis as the armature.

[0054] The flexible mechanical armature support can have an axis different from that of the armature.

[0055] Generally, on the other hand, the present invention features an electroacoustic transducer including a sound panel. The electroacoustic transducer further includes an actuator operable to convert electrical energy into mechanical energy. The actuator is mechanically connected to the sound panel. The electroacoustic transducer further includes a magnetic negative spring (MNS) mechanically connected to the sound panel.

[0056] Some embodiments of the present invention may include one or more of the following features:

[0057] The actuator can be a voice coil.

[0058] The voice coil and the MNS can share the same magnetic circuit.

[0059] The actuator can be an electromagnet.

[0060] The actuator can be a piezoelectric transducer.

[0061] The electroacoustic transducer can further include a position sensor.

[0062] The position sensor can be an infrared position sensor.

[0063] The position sensor can be a capacitive position sensor.

[0064] The position sensor can be an inductive position sensor.

[0065] The MNS can include a stationary magnet and a movable armature.

[0066] The stationary magnet can be a permanent magnet.

[0067] The stationary magnet can be an annular permanent magnet.

[0068] The annular permanent magnet can be a radially polarized magnet.

[0069] The stationary magnet can include at least four annular permanent magnets.

[0070] The stationary magnet can include at least six annular permanent magnets.

[0071] The stationary magnet can be an electromagnet.

[0072] The stationary magnet can be an electromagnet combined with a permanent magnet.

[0073] The movable armature can include a ferromagnetic element.

[0074] The ferromagnetic element may include at least one triangular steel element.

[0075] The ferromagnetic element may include a serrated steel ring.

[0076] The ferromagnetic element may include laminated steel.

[0077] The movable armature may include at least one armature permanent magnet.

[0078] When the armature is in the central position, the polarity of the armature permanent magnet may be opposite to the polarity of the stationary magnet.

[0079] For most positions of the armature, the polarity of the armature permanent magnet may be opposite to the polarity of the stationary magnet.

[0080] The armature permanent magnet may be triangular.

[0081] The armature permanent magnet may include an array of triangular elements.

[0082] The armature permanent magnet may be diamond-shaped.

[0083] The armature permanent magnet may include an array of diamond-shaped elements.

[0084] The movable armature may include a voice coil.

[0085] The movable armature may include a ferromagnetic element and a voice coil.

[0086] The movable armature may include an armature permanent magnet and a voice coil.

[0087] The armature permanent magnet may be triangular.

[0088] The armature permanent magnet may be diamond-shaped.

[0089] The electroacoustic transducer may further include an armature centering mechanism.

[0090] The centering mechanism may include a motor.

[0091] The centering mechanism may include a gear motor.

[0092] The centering mechanism may include an air pump.

[0093] The electroacoustic transducer may further include a flexible mechanical armature support.

[0094] The flexible mechanical armature support may share the same axis as the armature.

[0095] The flexible mechanical armature support may have an axis different from that of the armature.

[0096] Generally, on the other hand, the present invention features a system that includes the first electroacoustic transducer and the second electroacoustic transducer as described above. The first electroacoustic transducer is placed 180 degrees relative to the second electroacoustic transducer.

[0097] Generally, on the other hand, the present invention features an electroacoustic transducer that includes a sound panel. The electroacoustic transducer further includes an actuator operable to convert electrical energy into mechanical energy. The actuator is mechanically connected to the sound panel. The electroacoustic transducer further includes a magnetic negative spring (MNS) mechanically connected to the sound panel. The electroacoustic transducer further includes a centering mechanism.

[0098] Generally, on the other hand, the present invention features an electroacoustic transducer that includes a sound panel. The electroacoustic transducer further includes an actuator operable to convert electrical energy into mechanical energy. The actuator is mechanically connected to the sound panel. The electroacoustic transducer further includes a magnetic negative spring (MNS) mechanically connected to the sound panel. The electroacoustic transducer further includes a position sensor.

[0099] Generally, on the other hand, the present invention features an electroacoustic transducer that includes a sound panel. The electroacoustic transducer further includes an actuator operable to convert electrical energy into mechanical energy. The actuator is mechanically connected to the sound panel. The electroacoustic transducer further includes a magnetic negative spring (MNS) mechanically connected to the sound panel. The electroacoustic transducer further includes a flexible mechanical armature support.

[0100] Generally, on the other hand, the present invention features a method of manufacturing an electroacoustic transducer. The method includes the step of mounting a sound panel to a sealed housing. The method further includes the step of mounting a magnetic negative spring (MNS) having an armature to the sound panel. The method further includes the step of mounting an actuator operable to convert electrical energy into mechanical energy to the sound panel such that mechanical forces acting on the sound panel due to pressure changes within the sealed housing are at least partially canceled by magnetic forces from the MNS.

[0101] Some embodiments of the present invention may include one or more of the following features:

[0102] The electroacoustic transducer in the method is the electroacoustic transducer as described above.

[0103] Generally, on the other hand, the present invention features a method of using an electroacoustic transducer. The method includes the step of selecting an electroacoustic transducer as described above. The electroacoustic transducer is within a sealed chamber. The method further includes the step of using the electroacoustic transducer such that mechanical forces caused by pressure changes within the sealed housing are at least partially canceled by magnetic forces from the magnetic negative spring of the electroacoustic transducer.

[0104] Some embodiments of the present invention may include one or more of the following features:

[0105] The method may further include the step of monitoring electrical energy to automatically adjust the average position of the armature of the electroacoustic transducer to minimize the electrical energy consumption of the actuator.

[0106] The actuator may be a voice coil.

[0107] Generally, in another aspect, the present invention features a magnetic negative spring (MNS) including a stationary magnetic circuit. The MNS further includes a movable armature. The MNS further includes a position sensor. The MNS further includes a voice coil mounted to the movable armature. The MNS further includes a permanent magnet mounted to the movable armature. BRIEF DESCRIPTION OF THE DRAWINGS

[0108] Figure 1 is a schematic cross-sectional view of a prior art audio force sensor.

[0109] Figure 2A is a schematic cross-sectional view of an electroacoustic driver using a coil holder having a magnetic negative spring (MNS) utilizing a high magnetic permeability serrated cylindrical shell.

[0110] Figures 2B to 2C are respectively Figure 2A side view and perspective view of the coil holder in

[0111] Figure 3A is a schematic cross-sectional view of an alternative embodiment of an electroacoustic driver using a coil holder having a magnetic negative spring utilizing a pair of high magnetic permeability serrated cylindrical shells.

[0112] Figures 3B to 3C are respectively Figure 3A side view and perspective view of the coil holder in

[0113] Figure 4A is a schematic cross-sectional view of an alternative embodiment of an electroacoustic driver using a coil holder having a magnetic negative spring utilizing a high magnetic permeability serrated cylindrical shell concentric with the coil of the coil holder.

[0114] Figures 4B to 4C are respectively Figure 4A side view and perspective view of the high magnetic permeability serrated cylindrical shell portion of the coil holder in

[0115] Figures 4D to 4E are respectively Figure 4A side view and perspective view of the coil portion of the coil holder in

[0116] Figure 5ASchematic of a cross - sectional view of an alternative embodiment of an electro - acoustic driver using a coil carrier having a magnetic negative spring that can move a sound panel in opposite directions.

[0117] Figures 5B to 5C Are respectively focused on Figure 5A Side view and perspective view of the magnetic negative spring portion of the coil carrier in

[0118] Figure 6 Is using Figure 5A Schematic of a cross - sectional view of the sealed air chamber of the speaker of the electro - acoustic driver shown.

[0119] Figure 7A Schematic of a cross - sectional view of another alternative embodiment of an electro - acoustic driver using a coil carrier having a magnetic negative spring that can move a sound panel in opposite directions.

[0120] Figure 7B Is Figure 7A Schematic cross - sectional view (90 degrees with respect to the left side) of the electro - acoustic driver shown.

[0121] Figure 8 Photo of the magnetic negative spring prototype of the present invention.

[0122] Figure 9A Cross - sectional perspective view of an electro - acoustic driver using a magnetic circuit having a magnetic negative spring (MNS) including a permanent magnet crown.

[0123] Figure 9B Is Figure 9A Perspective view of the coil carrier shown.

[0124] Figure 10 Graph showing force versus displacement (for armature movement in one direction).

[0125] Figure 11 Schematic of a speaker driver assembly with MNS having repulsive and attractive MNS characteristics.

[0126] Figure 12 Illustration of a permanent magnet crown fully immersed in a repulsive magnetic field.

[0127] Figure 13 Photo of the MNS prototype of the present invention.

[0128] Figures 14A to 14B Photo of the repulsive MNS prototype.

[0129] Figures 15A to 15B Schematic of cross - sectional views of embodiments of repulsive / attractive MNS with upper - hung and lower - hung voice coils respectively.

[0130] Figure 16 Schematic of a cross-sectional view of another embodiment of a repulsive / attractive MNS with a suspended voice coil.

[0131] Figure 17 Shows Figure 16 Graph of the force of the repulsive / attractive MNS embodiment shown versus displacement (for armature movement in one direction) (total and components due to each movable permanent magnet array).

[0132] Figures 18A to 18C Schematic of a cross-sectional view of another embodiment of a repulsive / attractive MNS with voice coil armatures at different positions (centered, partially in the negative z-direction, centered, and fully in the negative z-direction).

[0133] Figure 18D Shows Figures 18A to 18C Illustration of a perspective view of certain parts (mainly permanent magnets) of the repulsive / attractive MNS shown.

[0134] Figure 19A Schematic of a cross-sectional view of another embodiment of a repulsive / attractive MNS with a voice coil armature in a centered position.

[0135] Figure 19B Is Figure 19A Top view of the coil bracket in

[0136] Figure 20 Schematic of an enclosure showing a loudspeaker in which an MNS embodiment of the present invention can be utilized.

[0137] Figure 21 Shows a graph of force versus displacement, showing how Figures 18A to 18C and Figures 19A to 19B of the MNS can be used to almost cancel the force on the sound panel.

[0138] Figures 22 to 23 Illustration of an MNS driver of the present invention. DETAILED DESCRIPTION

[0139] The present invention relates to electroacoustic drivers and loudspeakers having and using such electroacoustic drivers, particularly drivers having a magnetic negative spring (MNS) (such as a reluctance assisted driver (RAD) and a permanent magnet crown (PMC) driver) and loudspeakers having and using such drivers. It has been found that by using a magnetic negative spring as part of a reluctance assisted driver or a permanent magnet crown driver, a large pressure acting on the sound panel (of an audio loudspeaker) can be cancelled or partially cancelled.

[0140] Reluctance Assisted Driver (RAD)

[0141] Figure 2A is a schematic view of an electroacoustic driver 200 having a coil support 203 with a magnetically negative spring movable element 206 (a high magnetic permeability serrated cylindrical shell). As used herein, the term "reluctance assisted driver" (or "RAD") refers to an electroacoustic driver that utilizes a magnetically negative spring in combination with one or more voice coils. The coil support 203 is shown in more detail in Figures 2B to 2C . The coil support 203 is made of a non-magnetic / non-conductive material 205a - 205b (such as fiberglass), which mechanically supports the magnetic wire coils 204a - 204b (such as copper magnetic wire coils) and the magnetically negative spring movable element 206. The magnetically negative spring movable element 206 is a high magnetic permeability cylindrical shell (such as made of magnetic steel), which has a number of triangular protrusions parallel to the centerline of the electroacoustic driver 200.

[0142] Although not shown in Figure 2A , one side of the non-magnetic / non-conductive material 205a - 205b is attached to a sound panel, which produces sound when it moves. In the Figure 2A orientation (shown by the x - z axes therein, with the y direction perpendicular thereto), due to the sliding movement of the coil support 203 relative to the elements 201a - 201b (made of iron / steel) having permanent magnet rings 202a - 202d, the sound panel moves outward and inward in the z direction. Such movement is caused by the resulting magnetic field, as is known in the art and similar to that used in the audio force sensor 100.

[0143] When the sound panel is in its neutral / relaxed position, no force acts on the sound panel. When the sound panel (connected to the non-magnetic / non-conductive material 205b) moves in the positive z direction, this creates a partial vacuum in the sealed chamber of the audio speaker (not shown). In this case, for the audio speaker of the prior art audio force sensor 100, its sound panel actuator (voice coil, electromagnet, etc.) must overcome this large force and consume a large amount of electrical power for this purpose. However, in the electroacoustic driver 200 (which is a reluctance assisted driver since it utilizes a magnetically negative spring), this force can be partially or fully offset using the variable magnetic reluctance of the steel triangular parts of the magnetically negative spring movable element 206 entering the radial magnetic field. The variable magnetic reluctance is approximately proportional to the width of the triangle immersed in the magnetic field. Thus, this force increases as the steel triangle moves in the z direction (just as the pressure on the panel increases in the negative z direction as the panel moves in the positive z direction). When the panel pressure is towards the negative z direction, the variable magnetic reluctance is towards the positive z direction, so these forces can be made to cancel.

[0144] When the sound panel, the coil bracket 203, and the magnetic negative spring movable element 206 move in the negative z-direction, the panel pressure will be toward the positive z-direction and the magnetic force will be toward the negative z-direction. Therefore, these forces will similarly cancel each other out partially or completely.

[0145] For the above situation, the magnetic negative spring operates based on the interaction of the magnetic negative spring movable element 206 with the toroidal soft iron elements 201a - 201b and the permanent magnet rings 202a - 202d. Since the structures of the permanent magnet rings 202a - 202d, the toroidal soft iron elements 201a - 201b, and the magnetic negative spring movable element 206 consume approximately zero electric power to counteract a large pressure, the electroacoustic driver 200 will consume less power (10 to 100 times less) than prior art electroacoustic actuators to generate a given sound pressure level.

[0146] The active force actuator (usually a voice coil) can also be much smaller (and cheaper) because it needs to generate a much lower force. Although the magnetic negative spring movable element 206 and the magnet structure are Figures 2A to 2C shown as circular in

[0147] Figure 2A The coil bracket 203 with the magnetic negative spring movable element 206 and an integral voice coil (magnetic wire coils 204a - 204b) as an actuator for driving the sound panel is shown. In some embodiments, it may be advantageous to have the voice coil with its own magnetic circuit so that each magnetic circuit can be optimized. The magnetic negative spring movable element 206 and the voice coil (or other actuator, such as an electromagnetic actuator) can (and usually should) be mounted on the same movable structure connected to the sound panel.

[0148] No lever is required in this system to amplify mechanical motion, and the system can operate without position sensor feedback (when voice is used as the actuator). As can be seen in the electroacoustic driver 200 of FIG. 2, it is designed such that at any moment when the non-conductive cylindrical shell moves a measurable distance (the maximum amplitude of the motion) in the negative z-direction or the positive z-direction, the same amount of the voice coil is immersed in the magnetic field. This design will help keep the voice coil force approximately constant for a given current at all positions (since the voice coil force is always linearly related to the current, this will result in distortion-free music).

[0149] In some embodiments, the variable magnetic resistance of the magnetic negative spring movable element 206 (which is sometimes referred to as a high permeability serrated cylindrical shell) that interacts with the permanent magnets 202a - 202d will almost cancel out the air pressure (which changes the effective air volume of the sealed chamber due to the movement of the sound panel) and the mechanical spring force (due to the mechanical stiffness of the sound panel flexure support). If the net force (pressure plus spring force minus magnetic force) is linear with displacement in the z - direction, the system should be able to operate in an "open - loop" manner (without a position sensor or active position feedback).

[0150] The shared magnetic circuit (voice coil and magnetic negative spring movable element 206) can reduce size, weight, and cost. The incremental cost of the magnetic negative spring movable element 206 structure is low (since the voice coil requires a magnetic circuit), but it can significantly reduce the power loss in the voice coil and also reduce the size / cost of the voice coil (by reducing the net force that the voice coil has to generate).

[0151] The electro - acoustic driver 200 is designed such that the voice coil force depends on the position of the magnetic negative spring movable element. However, the shape of the teeth of the magnetic negative spring movable element can be made to compensate for this effect, so as to maintain a linear relationship between the voice coil current and the voice current force at all positions within a range of + / - a preset distance. The shape of the steel teeth of the magnetic negative spring movable element can be shaped to create an ideal force distribution for each speaker design.

[0152] Another way to compensate for this magnetic field variation effect is to reduce the density of the voice coil windings at the outer edge of the voice coil (since these coil elements will be subjected to a higher magnetic field than the central part of the coil).

[0153] Figure 3A FIG. is a schematic view of an alternative embodiment of an electro - acoustic driver 300 that utilizes a coil bracket 303 having a pair of magnetic negative spring elements 306a - 306b. The coil bracket 303 is shown in Figures 3B to 3C in more detail.

[0154] As Figure 3A shown, there is only one magnetic air gap, a pair of magnetic negative spring movable elements 306a - 306b, and a voice coil (using a magnet wire coil 304). The coil bracket 303 also includes a non - magnetic / non - conductive material 305 (such as fiberglass), which can be attached to the sound panel (not shown) and separates the magnet wire coil 304 from the pair of magnetic negative spring movable elements 306a - 306b. With this arrangement, the entire magnet wire coil 304 is immersed in the magnetic field at all positions (by the permanent magnets 302a - 302b), which can improve efficiency and maintain a linear relationship between current and force (which results in low - distortion music).

[0155] The voice coil requires the entire magnetic circuit (permanent magnets 302a - 302b plus element 301 (iron / steel)); the MNS movable elements 306a - 306b utilize this existing facility, thus adding very little cost / weight / size. Two separate magnetic negative spring movable elements 306a - 306b are used in the electro - acoustic driver 300, and this design reduces the number of pairs of toroidal magnets from two (in electro - acoustic driver 200) to one (in electro - acoustic driver 300).

[0156] Adding a pair of magnetic negative spring movable elements 306a - 306b increases the maximum force by an order of magnitude without increasing the electrical power consumption (of the voice coil or other active driver), or delivering the same force (or some combination of higher force and lower input power) at two orders of magnitude lower input power. These properties are highly desirable for battery - powered (portable) speakers.

[0157] The electro - acoustic driver 300 may also include one or more force - regulating coils (such as coils 307a - 307b). The force - regulating coils can increase or decrease the magnetic field in the air gap, thereby increasing or decreasing the voice - coil force per unit current and the variable magnetic resistance per unit displacement (since the variable magnetic resistance is proportional to the square of the magnetic field in the air gap).

[0158] Since the pressure depends on the sealed volume of the speaker air chamber and the mechanical stiffness of the sound - panel support (each of these forces is typically opposite to the voice - coil force and the variable magnetic resistance), it may be necessary to adjust the voice - coil force per unit current as well as the variable magnetic resistance per unit displacement to minimize the total electrical input power (which is equal to the voice - coil power plus the regulating - coil power) due to manufacturing tolerance issues. Self - testing can be used to optimize the regulating - coil current settings for each speaker.

[0159] Another benefit of the regulating coil is that it can ensure that the variable magnetic resistance never exceeds the opposing forces (mechanical stiffness plus pressure), in which case the movable element may get "stuck" at one extreme position or the other (in the negative z - direction and the positive z - direction).

[0160] Figure 3A One way in which the RAD can dispense with permanent magnets is further shown. If it is assumed that the N permanent magnet and the S permanent magnet (permanent magnets 302a and 302b respectively) are replaced by magnetic steel (this will reduce the material cost but increase the required electrical input power). Another option is that the N magnetic ring or the S magnetic ring can be replaced by magnetic steel (this will reduce the cost at the expense of sacrificing performance).

[0161] Figure 4ASchematic diagram of an electroacoustic driver 400 utilizing a coil support 403, which has a magnetic negative spring using a high magnetic permeability serrated cylindrical shell that is concentric with the magnetic wire coils 404a - 404b of the coil support. The high magnetic permeability serrated cylindrical shell portion of the coil support 403 is shown in more detail in Figures 4B to 4C and the voice coil portion of the coil support 403 is shown in more detail in Figures 4D to 4E . The high magnetic permeability serrated cylindrical shell has magnetic negative spring movable elements 406a - 406c near the permanent magnets 402a - 402d and may also include one or more force - regulating coils (such as coils 407a - 407b). The permanent magnets 402e - 402h are near the wire coils 404a - 404b. The coil support 403 also includes non - magnetic / non - conductive materials, such as non - magnetic / non - conductive materials 405a - 405c. The electroacoustic driver 400 also includes elements 401a - 401d (iron / steel).

[0162] One or more sound panels (not shown) can be connected to the movable coil support 403. The arrangement of the electroacoustic driver 400 roughly doubles the amount of force generated by the MNS at a given radius (relative to the electroacoustic driver 300) because the motion in the positive / negative z - direction engages two magnetic negative spring movable elements instead of one.

[0163] The magnetic wire coils 404a - 404b of the electroacoustic driver 400 also generate more than twice the force at a given radius (relative to the electroacoustic driver 300) because there are always two full magnet widths of the coils engaged at all positions. The wire coils 404a of the voice coil are wound in the opposite direction to the wire coils 404b because the first half of the voice coil is immersed in a magnetic field with an opposite polarity to the second half of the voice coil.

[0164] Optionally, the driver 400 can include a position and / or velocity sensor 412 (such as an optical or inductive position sensor), which can be used to provide position feedback to a control circuit that regulates the current in the force - regulating coils 407a - 407b. In an extreme case, the control circuit (using the position feedback from the position sensor 412) can adjust the current in the force - regulating coils 407a - 407b in real - time (about every millisecond) to minimize the total input power (equal to the voice coil power plus the regulating coil power) and ensure that the movable coil support 403 is never magnetically stuck in either extreme position ( Figure 4A the extreme positions in

[0165] the positive z - direction or the negative z - direction). Figure 4AIn [the figure], the magnetic negative spring movable elements 406a - 406c (which may also be referred to as "crowns" 406a - 406c) can be made of steel (or other ferromagnetic materials), and the stationary permanent magnets 402a - 402d (which may also be referred to as "magnetic poles" 402a - 402d) are radially polarized permanent magnets. In an alternative embodiment, the crowns 406a - 406c can be steel (or other ferromagnetic materials), and the magnetic poles 402a - 402d can be steel (or other ferromagnetic materials). In another alternative embodiment, the magnetic poles 402a - 402d are radially polarized permanent magnets, the crown 406b is made of steel (or other ferromagnetic materials), and the crowns 406a and 406c are made of radially polarized permanent magnetic materials. In yet another embodiment, the magnetic poles 402a - 402d are steel (or other ferromagnetic materials), and the crowns 406a - 406c are made of radially polarized permanent magnetic materials.

[0166] Figure 5A FIG. [is a schematic diagram of another alternative embodiment of the electroacoustic driver 500 that utilizes the coil holders 503a - 503b, which have magnetic negative springs that can move the sound panel in opposite directions. Figures 5B to 5C FIGS. [are a side view and a perspective view respectively focusing on a part of the coil holder 503a (showing the magnetic negative spring movable elements 506a - 506b). Figure 6 FIG. [is a schematic diagram of the electroacoustic driver 500 used in the sealed air chamber of the speaker 600, where the electroacoustic driver 500 can move the panels 610a - 610b in opposite directions. That is, when the electroacoustic driver 500 moves the panel 610b in the positive z - direction, it moves the panel 610a in the negative z - direction, and vice versa. Similar to the embodiments disclosed and taught in the Pinkerton'971 application and the Pinkerton'770 application, if they move in opposite directions with the same amplitude in this way, any inertial forces on the entire electroacoustic speaker 600 applied to the panels 610a - 610b are equal but in opposite directions, and thus will cancel each other out, making the inertial force of the entire electroacoustic speaker 600 approximately zero. This force cancellation has important benefits, including preventing the speaker from moving during use (by reducing vibration) and minimizing the distortion of the on - board microphone for voice control operations.

[0167] In an electroacoustic driver 500, the coil holder 503a has magnetically negative spring movable elements 506a - 506b (proximate to permanent magnets 502a - 502b), a magnet wire coil 504a (proximate to permanent magnets 502e - 502f), and non - magnetic / non - conductive material 505. The coil holder 503b has magnetically negative spring movable elements 506c - 506d (proximate to permanent magnets 502c - 502d), a magnet wire coil 504b (proximate to permanent magnets 502g - 502h), and non - magnetic / non - conductive material 505. Elements 501a - 501d are fixed (the coil holders 503a - 503b are movable relative to these fixed elements). The permanent magnets 502a - 502h are fixed to elements 501a - 501d.

[0168] For each magnetic circuit, the magnetic circuit of the magnetically negative spring and the voice coil are separate such that the position of the magnetically negative spring movable element does not change the magnetic field of the voice coil magnetic circuit (and thus the voice coil force is dependent on the position of the magnetically negative spring movable element).

[0169] In a device utilizing the electroacoustic driver 500 (relative to a device utilizing the electroacoustic driver 200 or the electroacoustic driver 300), the amount of magnet steel is reduced because the front / back RAD transducers can share a portion of the magnetic circuit.

[0170] Furthermore, relative to the electroacoustic driver 200 and the electroacoustic driver 300, a device utilizing the electroacoustic driver 500 separates the voice coil function and the MNS function, and thus can use a magnetic ring that is only width x (x = the mechanical movement amplitude of the sound panel, and 2x is the peak - to - peak movement). In contrast, a device using the electroacoustic driver 300 requires a magnet that is width 2.5x (which results in a back iron that is 2.5x thicker / heavier). This approach reduces the amount of steel and permanent magnetic material required to generate a given force. Additionally, the optimal air gap for the voice coil may be different from the optimal air gap for the MNS, thus allowing the separate magnetic circuits to be optimized individually.

[0171] Figures 7A to 7B An electroacoustic driver 700 is shown, which is an alternative embodiment of a magnetically negative spring. The electroacoustic driver 700 has a movable laminate structure 706, a shaft 705 (non - magnetic / non - conductive material), stationary laminate structures 704a - 704d, permanent magnets 702a - 702d, and force - regulating coils 707a - 707h. The electroacoustic driver 700 can be used to move a sound panel in opposite directions.

[0172] The shaft 705 is a movable shaft (which is connected to both the sound panel and an active force driver such as a voice coil), and it has a movable laminate structure 706 attached to it (which is the magnetically negative spring movable element). When the movable laminate structure 706 moves in the negative / positive z - direction, it is attracted to nearby stationary laminate structures (e.g., stationary laminate structures 704a and 704c, fromFigure 7A The positions shown are moved in the negative z direction). Since each of the stationary laminations 704a - 704d has an angle (as shown), as the movable lamination 706 moves in the z direction, the force will increase (to compensate for the increased pressure and mechanical spring force of the speaker). The magnetic field generated by the permanent magnets 702a - 702d can be adjusted using the force - regulating coils 707a - 707d.

[0173] If the permanent magnets 702a - 702d are not used, each of the stationary laminations 704a - 704d does not need to have an angle and can be straight as shown by lines 711a - 711d. In this case, a position sensor and active feedback would be required to generate the desired force distribution.

[0174] Figure 7B is a 90 - degree view relative to Figure 7A the left - hand portion of. In this view, the z - direction is in and out of the page (perpendicular to Figure 7B the x - direction and y - direction shown).

[0175] Laminations are used to reduce eddy - current losses, but are not absolutely necessary (solid magnetic steel can be used as an alternative).

[0176] The electro - acoustic driver 700 uses variable magnetic reluctance to create a "magnetic negative spring" that partially or fully cancels the forces that the speaker electro - acoustic transducer must overcome (mainly the sealed air - chamber pressure and the spring force of the electro - acoustic transducer's mechanical support). The variable magnetic reluctance can be fully passive (using permanent magnets), fully active (using active feedback and excitation coils), or a combination of active and passive. Partially or fully canceling the pressure / spring force of the audio speaker allows the active force sensor (such as the voice coil) to be smaller, lighter, and less costly, while using much less electrical power than prior - art devices.

[0177] Figure 8 is a photograph of the magnetic negative spring prototype of the present invention. Figure 8 A flat MNS is shown, which was tested to measure the force as a function of the position of the steel teeth. The total width of the steel - tooth member is 76 mm, and the maximum measured force is 80 N (about 1 N per mm length of the steel - tooth member). This force is quite large for the size of the device and does not require input power.

[0178] Permanent - magnet - crowned (PMC) driver

[0179] Referring again to Figure 4A, as discussed above, a permanent magnet crown (“PMC”) can be used in the actuator 400 (instead of a crown made of steel). In some embodiments, the crowns 406a - 406c are radially polarized permanent magnets (the outer crowns 402a and 402c have opposite polarities to the intermediate crown 402b), and the magnetic poles 402a - 402d are radially polarized permanent magnets. Additionally, for example, in some other embodiments, the crowns 406a - 406c can be radially polarized permanent magnets (the outer crowns 402a and 402c have opposite polarities to the intermediate crown 402b), and the magnetic poles 402a - 402d can be steel (or other ferromagnetic material).

[0180] In a PMC actuator, when one or the other or both of the excitation coils 407a - 407b are energized in one direction, the cylindrical housing of the electro - acoustic actuator 400 moves in one axial direction; when the excitation current is reversed, the direction of the axial force is reversed (even when the crowns 406a - 406c are in their central positions). Since the force generated by the excitation coils is bidirectional even in the central position, these embodiments do not require the wire coils 404a - 404b (which has benefits such as reduced cost, weight, etc.). Thus, in these PMC embodiments, the wire coils 404a - 404b are optional. Additionally, in these PMC actuator embodiments, less permanent magnetic material is required to generate a given force (which has benefits such as reduced cost).

[0181] Furthermore, since the permanent magnets have a permeability approximately the same as air, the total effective air gap of the excitation coil magnetic circuit can be reduced (which has benefits such as reduced power requirements for the excitation coils). Moreover, the amount of axial force generated per watt of excitation coil power is significantly higher than the force / watt ratio of a voice coil (improving efficiency and battery run - time). Since there are some inherent force instabilities in these PMC actuators (because the cylindrical housing of the electro - acoustic actuator 400 will move to the right or left on its own), a position and / or velocity sensor 412 should be used in conjunction with a feedback control loop to stabilize and operate the actuator 400.

[0182] Since the crowns in a PMC are made of permanent magnets (and the permanent magnets have a permeability similar to air as described above), a PMC actuator is not a magnetic damping actuator, but a magnetic negative spring. When an excitation coil is used, these can even be called “semi - active magnetic springs”. Additionally, when used with the voice coils 404a - 404b, the permanent magnet crown can act as a passive MNS, even when the device does not require the voice coils when using the excitation coil.

[0183] Figure 9A is a cross - sectional perspective view of an electro - acoustic actuator 900 utilizing a magnetic circuit having a magnetic negative spring (MNS) including permanent magnet crowns 906a - 906c.Figure 9B is a perspective view of the crown assembly 901, which includes the permanent magnet crowns 906a - 906c and the cylindrical shell 910.

[0184] As Figure 9A shown, there is no voice coil in the electro - acoustic driver 900, but there are two exciting coils, an outer exciting coil 907a and an inner exciting coil 907b. (Alternatively, one exciting coil can be used; however, generally, two exciting coils are more effective). The exciting coils 907a - 907b are wrapped in a ferromagnetic material, such as steel or ferrite. The coils and the ferromagnetic material form an electromagnet with a left pole piece and a right pole piece. There are three permanent magnet crown (PMC) structures (outer crown 906a, middle crown 906b, and outer crown 906c), which are mechanically attached to the cylindrical shell 910 (such as a shell made of carbon fiber epoxy), and this shell is attached to the sound panel ( Figures 9A - 9B not shown in the figure).

[0185] The permanent magnetic field of each crown 906a - 906c points towards the central axis or away from the central axis. If the magnetic fields of the outer crowns 906a and 906c point towards the central axis, then the magnetic field of the middle crown 906b points away from the central axis. In other words, if the outer crowns 906a and 906c have south magnetic poles on their outer diameters, then the middle crown 906b has north magnetic poles on its outer diameters.

[0186] When the current in the exciting coils 907a - 907b flows clockwise in the figure (in the Figures 9A - 9B orientation shown), it generates a north pole on the upper left pole piece and a south pole on the upper right pole piece. Assuming the above - mentioned PMC magnetic poles are in the Figures 9A to 9B orientation shown, then the PMC cylinder structure or "armature" will move in the positive z - axis direction (because the crown 906a with a south pole on its OD is attracted to the north pole of the upper left pole piece, etc.). If the exciting coil current is reversed (the current flows counter - clockwise in the Figures 9A - 9B orientation shown), then the armature will move in the negative z - axis direction. These results are shown in the force vs current graph in Figure 10 shown (which only shows the movement of the armature in one direction, i.e., the positive z - axis direction).

[0187] Once the armature (the cylindrical shell 910 with crowns 906a - 906c) moves even 0.1 mm in the (positive or negative) z - axis direction, there will be a passive magnetic negative spring (MNS) force (without the need for exciting coil current) to further move the armature along the z - axis direction. This passive negative spring force for moving in the positive z - axis direction is shown by Figure 10 line 1002 in

[0188] A current in one direction in the excitation coil (−1,360 A) generates the force shown by line 1003, while a current in the opposite direction (+1,360 A) generates the force shown by line 1001. The excitation coil current can generate a bi-directional force and can overcome the passive MNS force at any armature position (the armature cannot be “stuck” at one extreme position or the other). Curves 1004 - 1005 (for excitation currents of 136 A and −136 A respectively) show how the force caused by the excitation coil current reduces or increases the total force on the armature.

[0189] As previously mentioned, the passive MNS force serves to overcome the air pressure acting on the sound panel and any mechanical spring forces acting on the armature. The excitation coil current will be generated in response to position / velocity feedback from the position / velocity sensor and audio information from the music file to ensure that the sound panel is always in the correct position and at the correct velocity (always producing the correct sound).

[0190] Repulsive / Attractive MNS

[0191] The magnetic negative spring (MNS) generates significant forces to counteract forces mainly caused by air pressure changes during large armature / cone displacements. When playing music, the armature can move freely within the space between the reset contacts. Figure 11 Shown is a loudspeaker driver assembly 1100 with an MNS, which will be described in more detail below (and in combination with the repulsive and attractive MNS features of the present invention, i.e., repulsive / attractive MNS). When the user presses the off button on the loudspeaker (or it automatically turns off due to non-use), the geared motor will rotate the drive screw to move the reset contacts (in the positive z - direction or negative z - direction) to the right or left such that the disk mounted on the armature (located between the reset contacts) can “land” on one of the reset contacts.

[0192] For example, if the reset contacts move to the left, the armature disk will land on the right reset contact. When the loudspeaker is turned on, the reset contacts return to their central position to allow full - range movement of the armature / cone. In the case of an uncontrolled shutdown, the armature will drift significantly to the right or left (slightly more than the full amplitude of the armature movement) and land on one of the reset contacts.

[0193] Because the MNS can be inherently unstable (without active control, the armature will drift in the z-direction), mechanical stops are required to keep the armature (voice coil and movable magnetic element array bracket) roughly centered when the loudspeaker is turned off (otherwise the armature will drift to extreme positions and it will be difficult to center the voice coil alone). When the loudspeaker is reset (for example by cycling the power), the centering mechanism moves the armature back to the center position, the voice coil will take over the centering function, and the reset contact will then return to its center position. This reset operation requires the centering mechanism to generate the full force of the MNS plus the back pressure associated with moving the cone (up to several hundred Newtons, which is more than 10 times the maximum force of a typical voice coil). A gear motor can be used to generate the larger forces required by the centering mechanism. Alternatively, a small air pump can be used to create positive or negative pressure within the sealed enclosure, which will produce a large outward or inward force on the sound panel.

[0194] To counteract any destabilizing radial forces caused by the movable magnetic element array, a stabilizer / centralizer may be used. In some embodiments, the stabilizer / centering mechanism is a rigid bushing support; however, this can sometimes cause friction and audible noise. In other embodiments, a permanent magnetic crown (e.g. Figure 9B The permanent magnetic crown 906b shown in FIG. 1 is completely immersed in a repulsive magnetic field (e.g. Figure 12 ). This arrangement is referred to herein as "repulsive MNS". The permanent magnetic crown can also be immersed in a magnetic field that is both repulsive and attractive, an arrangement referred to herein as "repulsive / attractive MNS".

[0195] Figure 11 A speaker driver assembly 1100 having a MNS having both repulsive and attractive MNS characteristics (i.e., repulsive / attractive MNS) is shown. The speaker driver can be used as a component in a loudspeaker. The speaker driver assembly 1100 includes an outer ring 1101, a reflective surface 1102, a light sensor 1103, a motor 1104 (e.g., a 12GFN20E motor), a PCA 1105 (for the motor and light sensor), a drive screw 1106, and a reset contact 1107.

[0196] Conventional "spider" supports (instead of bushings), e.g. Figure 11The spider member 1108 shown can also be used well in conjunction with such a stabilizer / centering device design. Conventional speaker drivers typically use only one spider member, but for the embodiments of the present invention for stabilization / centering, two or more spider members are typically required to ensure that the armature does not move radially too much due to the small but non-zero radial force generated by the permanent magnet elements mounted on the movable armature. The gear motor 1104 can have an encoder for position feedback and may require some electronic components to be mounted on a circular circuit board. The armature position "photoelectric sensor" 1103 can be mounted on the circuit board together with some associated electronic components.

[0197] Routing the two conventional driver leads together with two input power leads (not shown) to terminals near a circuit board (not shown) will cause the speaker driver assembly of the present invention to operate like a conventional driver (but with approximately 10 times the force capability for the same power, or consuming approximately 10 times less power for the same force distribution).

[0198] Repulsive / Attractive MNS

[0199] As Figure 12 shown, in the repulsive MNS, when the PMC 1203 moves radially, the magnetic force tends to push it away from the center line 1201. When the PMC 1203 moves axially in either direction, it experiences a repulsive force that increases with the axial movement distance (to a point). The long voice coil (VC) 1202 can be placed on the movable armature next to the PMC 1203, in its own magnetic field, as Figure 12 shown.

[0200] Figure 13 is a photograph showing an array of permanent magnet (PM) disks embedded in an aluminum movable armature. In this embodiment, one of the two stationary PM rectangles is located above the disk array (such that when the north magnetic pole of the stationary PM faces down, the north poles of the permanent magnet disks face up, so that they repel each other).

[0201] Compared with a comparable MNS made of a movable steel element, the repulsive force generated by the repulsive MNS is more than twice the force for a given displacement (or stiffness). The repulsive force generated by the repulsive MNS is also higher than the attractive force generated by an attractive MNS that also uses a permanent magnet armature but in the attractive orientation. One reason for the higher stiffness of the repulsive MNS compared to the attractive MNS is that using a repulsive device allows for a smaller air gap between the stationary and movable elements (the magnetic force between two PM elements increases as the distance between the two PM elements decreases) (when the air gap is not relatively large, the attractive armature will bend and contact the stationary PM part).

[0202] The combination of higher stiffness (resulting in higher sound pressure levels in the speaker) and improved radial stability (enabling a simple, low-cost, and quiet armature support) allows the repulsive MNS to have the above advantageous characteristics.

[0203] Figures 14A to 14B Another embodiment of the repulsive MNS is shown, which can produce approximately ten times the sound pressure compared to a conventional subwoofer of the same size used in prior art speakers and consumes less electrical power while doing so. With this design, there is no need to use linear bearings (avoiding the undesirably high radial forces of the steel crown), and instead, one or two conventional "spider" supports 1401 are used for operation.

[0204] In Figures 14A to 14B the embodiment, dozens of commercially available generally crown-shaped permanent magnet discs are used and work well. Thus, there are some advantages (economics and others) to using this type of standard magnet. Alternatively, custom permanent magnets can be fabricated to achieve better performance.

[0205] In yet another embodiment, a combination of repulsive and attractive magnetic forces can be used in an attractive / repulsive MNS device, which is shown in Figures 15A to 15B Three stationary magnetic poles can be used together with two arrays of movable permanent magnet elements mounted on a coil bracket 1507 (one movable permanent magnet array having a north pole 1501a and a south pole 1501b, and the other movable permanent magnet array having a north pole 1502a and a south pole 1502b). The stationary magnetic poles include a permanent magnet having a north pole 1503a and a south pole 1503b, and metal magnetic poles 1504 - 1506 (such as steel) are arranged such that metal magnetic poles 1504 and 1506 are stationary north poles and metal magnetic pole 1505 is a stationary south pole. (In other embodiments, the north / south magnetic orientation can be reversed). Computer models and test results have shown that this three-magnetic-pole embodiment can produce high axial forces (and thus high sound pressure levels) using a relatively small amount of permanent magnetic material (one of the highest-cost items in a speaker device).

[0206] Embodiments can have a long (over-hung) voice coil (such as the voice coil 1515 shown in Figure 15A ) or a short (under-hung) voice coil (such as the voice coil 1516 shown in Figure 15B ), and can include a sensor 1516 for providing position or velocity feedback to a control circuit (such as a position and / or velocity sensor, which can be an optical or inductive sensor).

[0207] For Figures 15A to 15BThe shown orientation (where the permanent magnets have north poles 1501a, 1502a, and 1503a and south poles 1501b, 1502b, and 1503b, where metal poles 1504 and 1506 are north poles and metal pole 1505 is a south pole), the movable PMC north / south poles face the stationary north / south poles, and thus are in a repulsive mode. Magnetic flux axially exits from each stationary north pole 1503a, radially flows through each external metal pole (metal poles 1504 and 1506), crosses the air gap through the PMC, moves axially towards the central pole (metal pole 1505), and flows radially inwards across the voice coil ( Figures 15A to 15B which are voice coils 1506 and 1516 respectively in it), and then moves axially towards the south pole 1503b to complete the magnetic circuit.

[0208] When the coil holder 1507 is centered, all axial magnetic forces cancel out. When the coil holder 1507 moves in the negative z direction, the two PM crowns will be repelled by the metal poles in the negative z direction, and the PMC pole 1502a will be attracted by the metal pole 1505. When the coil holder 1507 moves in the positive z direction, the two PM crowns will be repelled by the steel poles in the positive z direction, and the PMC pole 1501a will be attracted by the metal pole 1505. Otherwise, the operation of the repulsive / attractive MNS is similar to that described above for the MNS embodiment. The embodiment with Figures 15A to 15B the shown design exhibits the force distribution as described above, where the peak exceeds 200 N.

[0209] Figure 16 An embodiment of a repulsive / attractive MNS (with a short voice coil 1616) is shown. This embodiment has a movable permanent magnet and a stationary permanent magnet. The movable permanent magnet has north poles 1601a and 1602a and south poles 1601b and 1602b, and the stationary permanent magnet has north poles 1603a, 1604a, 1605a, and 1606a and south poles 1603b, 1604b, 1605b, and 1606b. (Again, this polarity orientation can be reversed). Figure 16 This arrangement of Figure 17 shows a combination of permanent magnet repulsion and attraction (as

[0210] Figure 17 shown), which significantly increases the peak magnetic force as well as the amplitude of the armature movement (both of which contribute to an increase in the sound pressure level). Figure 17is shown by curve 1701 in. Similarly, the north pole 1602a of another movable permanent magnet is also repelled by the north pole 1606a of the stationary permanent magnet directly below it and is also attracted by the south pole 1605b of the central permanent magnet. Instead of just a pushing / rejecting magnetic force, the device also has a pulling / attracting magnetic force. This force is shown in Figure 17 by curve 1702 in. The total force (repulsion and attraction) is shown in Figure 17 by curve 1703 in. Figure 17 reveals a significant contribution of the attractive force to the total magnetic force.

[0211] Stabilize / Center

[0212] As described above, the MNS can exhibit radial instability. It has been found that when using steel / iron magnetic poles (as shown in Figure 15B ), the MNS may be radially unstable because when the coil bracket 1507 is not completely centered, the movable permanent magnet (located on the coil bracket 1507 including the movable voice coil 1516) may be attracted radially towards the steel. It has also been found that even when using permanent magnetic poles (such as 1603a in Figure 16 ), radial instability occurs when the coil bracket magnet moves outside the PM pole. When, for example, in Figure 16 the magnetic poles 1601a / 1601b move in the negative z direction instead of the positive z direction, this effect may be worse due to some magnetic field cancellation between the opposite magnetic poles 1603a and 1604b.

[0213] In some embodiments, Figure 11 the armature 1102 shown in can exhibit instability, which can be solved by using a harder material for the spider 1108. Even without using the spider 1108, radial stability can alternatively (or additionally) be achieved.

[0214] Figures 18A to 18C shows another embodiment of a repulsive / attractive MNS with voice coils 1815a - 1815b, and it can include a sensor 1816 (such as a position and / or velocity sensor, which can be an optical or inductive sensor) for providing position or velocity feedback to a control circuit. This embodiment has stationary magnetic poles (such as stationary magnetic north poles 1801a - 1804a and stationary magnetic south poles 1801b - 1804b) made of permanent magnets (instead of steel), so the oppositely polarized movable magnets (such as movable magnetic north poles 1805a - 1806a and movable magnetic south poles 1805b - 1806b) on the armature are radially repelled by the stationary magnetic poles (which provide radial stability). As shown in Figures 18A to 18CAs shown, the stationary magnetic pole is a permanent magnet ring (PMR), and the moving magnetic pole is a permanent magnet triangle (PMT). (The PMR can be a component of an arc segment, which, when combined, creates a toroidal magnet structure). Figure 18D is a perspective view showing the arrangement of the PMR and PMT of this embodiment.

[0215] Figures 18A to 18C Another advantageous feature of the MNS shown is that the moving permanent magnet elements on the armature (such as the moving magnetic north poles 1805a - 1806a and the moving magnetic south poles 1805b - 1806b) do not leave the "open" permanent magnetic pole edges, so there is always a repulsive force between the permanent magnetic poles and the armature permanent magnets, which makes the armature radially stable (this can be regarded as a permanent magnet - based radial passive magnetic bearing).

[0216] As Figures 18A to 18C shown (which shows the movement from the central position to the full negative z - direction), there is always one pole width of the voice coil immersed in the magnetic field (which makes the force per unit current input constant at all armature positions). Regardless of the position of the armature in the negative z - direction (as Figures 18A to 18C shown), the negative z - direction array of the armature permanent magnets (i.e., the moving magnetic north poles 1805a and the moving magnetic south poles 1805b) is always immersed in the oppositely - directed (repulsive) magnetic field of the stationary permanent magnets in the negative z - direction (the stationary magnetic north poles 1801a and 1803a and the stationary magnetic south poles 1801b and 1803b). This provides a radial stabilizing force that helps keep the armature centered within the air gap between the inner and outer permanent magnet rings.

[0217] When the armature is in the Figure 18A position shown (the centered position), the positive z - direction array of the PMT (the moving magnetic north poles 1806a and the moving magnetic south poles 1806b) is immersed in the oppositely - directed magnetic field of the positive z - direction PMR (the stationary magnetic north poles 1802a and 1804a and the stationary magnetic south poles 1802b and 1804b), and thus is radially stable.

[0218] When the armature is in the Figure 18BWhen in the position shown (partial negative z - direction), at this position, the positive z - direction array of the PMT (moving magnetic north pole 1806a and moving magnetic south pole 1806b) is partially immersed in the oppositely - directed magnetic field of the positive z - direction PMR (stationary magnetic north poles 1802a and 1804a and stationary magnetic south poles 1802b and 1804b), and remains radially stable. Since the positive z - direction array of the PMT (moving magnetic north pole 1806a and moving magnetic south pole 1806b) is repelled by the positive z - direction PMR (stationary magnetic north poles 1802a and 1804a and stationary magnetic south poles 1802b and 1804b) and attracted by the fringe magnetic field of the negative z - direction PMR (stationary magnetic north poles 1801a and 1803a and stationary magnetic south poles 1801b and 1803b), the axial / desired force in this position is high.

[0219] When the armature is in Figure 18C the position shown (fully negative z - direction), the positive z - direction array of the PMT (moving magnetic north pole 1806a and moving magnetic south pole 1806b) is not immersed in the oppositely - directed magnetic field of the positive z - direction PMR (stationary magnetic north poles 1802a and 1804a and stationary magnetic south poles 1802b and 1804b), but is partially immersed in the fringe magnetic field of the negative z - direction PMR (stationary magnetic north poles 1801a and 1803a and stationary magnetic south poles 1801b and 1803b) and this position still provides a certain degree of radial stability. In Figure 18C the position shown, the axial / desired force is also high because the positive z - direction array of the PMT is repelled by the fringe magnetic field of the positive z - direction PMR and attracted by the negative z - direction PMR.

[0220] By symmetry, when the armature moves in the positive z - direction from Figure 18A the position shown, the same stability will be provided.

[0221] The armature PMT only occupies approximately half of the axial width of the PMR magnetic poles, which provides enough space for two long voice coils, as Figures 18A to 18C shown. In addition, maintaining net magnetic stability in the radial direction at all armature positions is Figures 18A to 18C a beneficial feature of the present MNS embodiment shown, because it allows the use of conventional (low - cost, proven, etc.) rubber peripheries and "spider" supports.

[0222] Figures 19A to 19B Another MNS embodiment is shown, which shares Figures 18A to 18C many properties of the MNS embodiment of Figures 19A to 19BIn the embodiment, there are now three stationary outer PMRs (with stationary magnetic north poles 1901a - 1903a and stationary magnetic south poles 1901b - 1903b) and three inner PMRs (with stationary magnetic north poles 1904a - 1906a and stationary magnetic south poles 1904b - 1906b). Instead of two PMT arrays, the armature (with voice coils 1915a - 1915b) has only one moving permanent magnet array (moving magnetic north pole 1907a and moving magnetic south pole 1907b), which are diamond-shaped.

[0223] Use in a loudspeaker

[0224] The repulsive / attractive MNS as described above can be used in a loudspeaker, for example Figure 20 The schematic diagram of the loudspeaker 2000 shown. The loudspeaker 2000 has a sealed chamber 2001, a movable panel 2002 (which is connected to a flexible "surround" element 2005, made of rubber for example to allow the movable panel 2002 to move in the positive z-direction and the negative z-direction). The loudspeaker 2000 also includes an MNS 2003 and a voice coil 2004, which are placed to move the movable panel 2002 in the positive z-direction and the negative z-direction. The loudspeaker 2000 also includes a sensor 2006 (such as a position and / or velocity sensor, which can be an optical or inductive sensor) for providing position or velocity feedback to a control circuit.

[0225] Figure 21 Is a graph showing force versus displacement, reflecting how the Figure 20 MNS can be used to almost cancel the force on the sound panel. The line 2101 is the zero line. The main force on the sound panel 2002 when the sound panel moves in the z-direction is the air pressure, shown by the line 2102. (Since the chamber is a sealed chamber 2001, when the movable panel 2002 moves outwards in the positive z-direction, a force is generated due to vacuum / negative pressure). The flexible support 2005 also generates a force in the same negative z-direction as the sealed chamber pressure, shown by the line 2103. However, the MNS force is always opposite to the directions of the pressure and the flexible support force, and is shown by the line 2104. The total force (or also called the net force) is the sum of the pressure 2102, the MNS force 2104 and the flexible support force 2103, and is shown by the line 2105. As shown by the line 2105, regardless of the displacement direction of the movable panel, the net force is relatively close to the zero line 2101 (this is because the force provided by the MNS is opposite to the forces generated by the sealed chamber air pressure and the flexible support). For this reason, the loudspeaker 2000 only needs to generate a force of up to about 20 N (compared to a maximum of 200 N - 250 N) for the full movement of the movable panel. Therefore, the MNS significantly improves the efficiency of the loudspeaker.

[0226] Figures 22 to 23Further details of the MNS driver as described above are provided. As Figure 22 shown, the driver is more compact axially than previous MNS drivers because the spider 2201 is no longer on the same axis as the armature. The device shown can have an axial length of approximately 8 cm and also has an active sound panel area of approximately 150 cm 2 . A flat honeycomb panel 2202 can be used instead of a traditional cone, which also makes the device compact axially.

[0227] As Figure 23 shown, the device also uses a geared motor 2301 (for the centering mechanism described previously) that is not axially aligned with the armature, which also saves axial space. Since embodiments of the loudspeaker can use two MNS drivers in opposite directions (to cancel out the large vibrations caused by the moving armature), it is much easier to mount them in the loudspeaker enclosure when both drivers are axially compact. The position sensor can be an infrared sensor 2302 and it senses the position of a reflective element mounted to the honeycomb panel 2202. The device also has a gear train 2304 to transfer torque from the geared motor 2301 to a threaded element 2306. A temporary spacer 2303 is used during assembly to ensure that the armature is centered in the magnetic air gap while the spider 2201 and the sound panel 2202 are adhered to their respective bases.

[0228] The loudspeaker can also include control functions in the armature position controller that continuously adjust the average armature axial position to minimize the voice coil current (and thus minimize the voice coil electrical power). As previously mentioned, MNS creates a very strong unstable equilibrium; thus, if the armature moves (axially) slightly away from the zero MNS force point, it can accelerate in the direction of its displacement. The control function of the controller keeps the armature at this zero force point, even if this point does not correspond to the exact mechanical center point. Thus, if the loudspeaker is tilted 90 degrees, new forces will be created due to gravity, and the controller with the control function will automatically adjust the armature position so as to use the MNS force to cancel out the forces due to gravity (such that electrical power does not have to be wasted on the resistive forces due to gravity). The controller can also compensate for any temperature drift in the position sensor as well as any manufacturing defects.

[0229] While embodiments of the present invention have been shown and described, those skilled in the art can make modifications thereto without departing from the spirit and teachings of the present invention. The embodiments described herein and the examples provided are exemplary only and not restrictive. Many variations and modifications of the present invention disclosed herein are possible and within the scope of the present invention. Accordingly, other embodiments are within the scope of the following claims. The scope of protection is not limited by the above description but only by the appended claims, which includes all equivalents of the subject matter of the claims.

[0230] The disclosures of all patents, patent applications, and publications cited herein are hereby incorporated by reference in their entirety as long as they provide exemplary, procedural, or other details supplementary to the content described herein.

[0231] Quantities and other numerical data may be presented herein in a range format. It should be understood that the use of such range format is merely for convenience and brevity and should be interpreted flexibly as including not only the explicitly recited values as the limits of the range, but also all the individual values or sub-ranges subsumed within that range as if each value and sub-range were explicitly recited. For example, a numerical range of about 1 to about 4.5 should be interpreted as including not only the explicitly recited limits of 1 to about 4.5, but also individual numbers such as 2, 3, 4 and sub-ranges such as 1 to 3, 2 to 4, etc. The same principle applies to ranges recited with only one numerical value, such as "less than about 4.5", which should be interpreted as including all of the above values and ranges. Moreover, this interpretation should apply regardless of the breadth of the range or the nature of the property being described.

[0232] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the subject matter of this disclosure belongs. Although any methods, devices, and materials similar or equivalent to those described herein can be used in the practice or testing of the presently disclosed subject matter, representative methods, devices, and materials are now described.

[0233] In accordance with long-standing patent law convention, the terms "a" and "an" as used in this application (including the claims) denote "one or more".

[0234] Unless otherwise indicated, all numbers expressing quantities of ingredients, reaction conditions, etc. used in the specification and claims are to be understood as being modified in all instances by the term "about". Accordingly, unless indicated to the contrary, the numerical parameters set forth in this specification and the appended claims are approximations that may vary depending upon the desired properties sought to be obtained by the subject matter of this disclosure.

[0235] As used herein, when referring to a value or amount of mass, weight, time, volume, concentration, or percentage, the terms "about" and "substantially" mean a variation of ±20% in some embodiments, ±10% in some embodiments, ±5% in some embodiments, ±1% in some embodiments, ±0.5% in some embodiments, and ±0.1% in some embodiments from the specified amount, provided that such variation is suitable for performing the disclosed method.

[0236] As used herein, the terms "substantially perpendicular" and "substantially parallel" mean including variations within ±10° in the perpendicular and parallel directions, respectively, in some embodiments, within ±5° in the perpendicular and parallel directions, respectively, in some embodiments, within ±1° in the perpendicular and parallel directions, respectively, and within ±0.5° in the perpendicular and parallel directions, respectively, in some embodiments.

[0237] As used herein, the term "and / or" when used in the context of listing entities means that these entities are presented individually or in combination. Thus, for example, the phrase "A, B, C, and / or D" includes A, B, C, and D individually, as well as any and all combinations and sub - combinations of A, B, C, and D.

Claims

1. A loudspeaker, comprising: (a) A sealed enclosure; (b) A sound panel mechanically connected to the sealed enclosure; (c) An actuator operable to convert electrical energy into mechanical energy; and (d) A magnetic negative spring, wherein (i) The magnetic negative spring includes a stationary magnet and a movable armature, (ii) The movable armature includes a ferromagnetic element, (iii) The movable armature is mechanically connected to the sound panel and the actuator, and (iv) The magnetic negative spring is operable to generate a magnetic force that at least partially cancels out the mechanical force acting on the sound panel due to pressure changes within the sealed enclosure.

2. The loudspeaker according to claim 1, wherein, The actuator is a voice coil.

3. The loudspeaker according to claim 2, wherein, The voice coil and the magnetic negative spring share the same magnetic circuit.

4. The loudspeaker according to claim 1, wherein, The actuator is an electromagnet.

5. The loudspeaker according to claim 1, wherein, The actuator is a piezoelectric transducer.

6. The loudspeaker according to claim 1, further comprising a position sensor for sensing the position of the sound panel.

7. The loudspeaker according to claim 6, wherein, The position sensor is an infrared position sensor.

8. The loudspeaker according to claim 6, wherein, The position sensor is a capacitive position sensor.

9. The loudspeaker according to claim 6, wherein, The position sensor is an inductive position sensor.

10. The loudspeaker according to claim 1, wherein, The stationary magnet is a permanent magnet.

11. The loudspeaker according to claim 1, wherein, The stationary magnet is a ring-shaped permanent magnet.

12. The loudspeaker according to claim 11, wherein, The ring-shaped permanent magnet is a radially polarized magnet.

13. The loudspeaker according to claim 11, wherein, The stationary magnet includes at least four ring-shaped permanent magnets.

14. The loudspeaker according to claim 11, wherein, The stationary magnet includes at least six ring-shaped permanent magnets.

15. The loudspeaker according to claim 1, wherein, The stationary magnet is an electromagnet.

16. The loudspeaker according to claim 1, wherein, The stationary magnet is an electromagnet combined with a permanent magnet.

17. The loudspeaker according to claim 1, wherein, The ferromagnetic element includes at least one triangular steel element.

18. The loudspeaker according to claim 1, wherein, The ferromagnetic element includes a serrated steel ring.

19. The loudspeaker according to claim 1, wherein, The ferromagnetic element includes laminated steel.

20. The loudspeaker according to claim 1, wherein, The movable armature includes an armature permanent magnet.

21. The loudspeaker according to claim 20, wherein, When the armature is in the central position, the polarity of the armature permanent magnet is opposite to that of the stationary magnet.

22. The loudspeaker according to claim 20, wherein, For most positions of the armature, the polarity of the armature permanent magnet is opposite to that of the stationary magnet.

23. The loudspeaker according to claim 20, wherein, The armature permanent magnet is triangular.

24. The loudspeaker according to claim 20, wherein, The armature permanent magnet includes an array of triangular elements.

25. The loudspeaker according to claim 20, wherein, The armature permanent magnet is diamond-shaped.

26. The loudspeaker according to claim 20, wherein, The armature permanent magnet includes an array of diamond-shaped elements.

27. The loudspeaker according to claim 1, wherein, The movable armature includes a voice coil.

28. The loudspeaker according to claim 1, wherein, The movable armature includes a ferromagnetic element and a voice coil.

29. The loudspeaker according to claim 1, wherein, The movable armature includes an armature permanent magnet and a voice coil.

30. The loudspeaker according to claim 29, wherein, The armature permanent magnet is triangular.

31. The loudspeaker according to claim 29, wherein, The armature permanent magnet is diamond-shaped.

32. The loudspeaker according to claim 1, further comprising an armature centering mechanism.

33. The loudspeaker according to claim 32, wherein, The centering mechanism includes a motor.

34. The loudspeaker according to claim 32, wherein, The centering mechanism includes a gear motor.

35. The loudspeaker according to claim 32, wherein, The centering mechanism includes an air pump.

36. The loudspeaker according to claim 1, further comprising a flexible mechanical armature support.

37. The loudspeaker according to claim 36, wherein, The flexible mechanical armature support shares the same axis as the armature.

38. The loudspeaker according to claim 36, wherein, The flexible mechanical armature support has a different axis from the armature.

39. An electroacoustic transducer, comprising: (a) A sound panel connected to a sealed enclosure; (b) An actuator operable to convert electrical energy into mechanical energy; and (c) A magnetic negative spring, wherein (i) The magnetic negative spring includes a stationary magnet and a movable armature, (ii) The movable armature includes a ferromagnetic element, (iii) The movable armature is mechanically connected to the sound panel and the actuator, and (iv) The magnetic negative spring is operable to generate a magnetic force that at least partially cancels out the mechanical force acting on the sound panel due to pressure changes within the sealed enclosure.

40. The electroacoustic transducer according to claim 39, wherein, The actuator is a voice coil.

41. The electroacoustic transducer according to claim 40, wherein, The voice coil and the magnetic negative spring share the same magnetic circuit.

42. The electroacoustic transducer according to claim 39, wherein, The actuator is an electromagnet.

43. The electroacoustic transducer according to claim 39, wherein, The actuator is a piezoelectric transducer.

44. The electroacoustic transducer according to claim 39 further comprises a position sensor.

45. The electroacoustic transducer according to claim 44, wherein, The position sensor is an infrared position sensor.

46. The electroacoustic transducer according to claim 44, wherein, The position sensor is a capacitive position sensor.

47. The electroacoustic transducer according to claim 44, wherein, The position sensor is an inductive position sensor.

48. The electroacoustic transducer according to claim 39, wherein, The stationary magnet is a permanent magnet.

49. The electroacoustic transducer according to claim 39, wherein, The stationary magnet is an annular permanent magnet.

50. The electroacoustic transducer according to claim 49, wherein, The annular permanent magnet is a radially polarized magnet.

51. The electroacoustic transducer according to claim 39, wherein, The stationary magnet comprises at least four annular permanent magnets.

52. The electroacoustic transducer according to claim 39, wherein, The stationary magnet comprises at least six annular permanent magnets.

53. The electroacoustic transducer according to claim 39, wherein, The stationary magnet is an electromagnet.

54. The electroacoustic transducer according to claim 39, wherein, The stationary magnet is an electromagnet combined with a permanent magnet.

55. The electroacoustic transducer according to claim 39, wherein, The ferromagnetic element comprises at least one triangular steel element.

56. The electroacoustic transducer according to claim 39, wherein, The ferromagnetic element comprises a serrated steel ring.

57. The electroacoustic transducer according to claim 39, wherein, The ferromagnetic element comprises laminated steel.

58. The electroacoustic transducer according to claim 39, wherein, The movable armature comprises at least one armature permanent magnet.

59. The electroacoustic transducer according to claim 58, wherein, When the armature is in the central position, the polarity of the armature permanent magnet is opposite to that of the stationary magnet.

60. The electroacoustic transducer according to claim 58, wherein, For most positions of the armature, the polarity of the armature permanent magnet is opposite to that of the stationary magnet.

61. The electroacoustic transducer according to claim 58, wherein, The armature permanent magnet is triangular.

62. The electroacoustic transducer according to claim 58, wherein, The armature permanent magnet comprises an array of triangular elements.

63. The electroacoustic transducer according to claim 58, wherein, The armature permanent magnet is diamond-shaped.

64. The electroacoustic transducer according to claim 58, wherein, The armature permanent magnet comprises an array of diamond-shaped elements.

65. The electroacoustic transducer according to claim 39, wherein, The movable armature comprises a voice coil.

66. The electroacoustic transducer according to claim 39, wherein, The movable armature comprises a ferromagnetic element and a voice coil.

67. The electroacoustic transducer according to claim 39, wherein, The movable armature comprises an armature permanent magnet and a voice coil.

68. The electroacoustic transducer according to claim 67, wherein, The armature permanent magnet is triangular.

69. The electroacoustic transducer according to claim 67, wherein, The armature permanent magnet is diamond-shaped.

70. The electroacoustic transducer according to claim 39 further comprises an armature centering mechanism.

71. The electroacoustic transducer according to claim 70, wherein, The centering mechanism comprises a motor.

72. The electroacoustic transducer according to claim 70, wherein, The centering mechanism comprises a gear motor.

73. The electroacoustic transducer according to claim 70, wherein, The centering mechanism comprises an air pump.

74. The electroacoustic transducer according to claim 39 further comprises a flexible mechanical armature support.

75. The electroacoustic transducer according to claim 74, wherein, The flexible mechanical armature support shares the same axis with the armature.

76. The electroacoustic transducer according to claim 74, wherein, The flexible mechanical armature support has a different axis from the armature.

77. The electroacoustic transducer according to claim 39 further comprises a centering mechanism.

78. A system includes a first electroacoustic transducer and a second electroacoustic transducer, wherein, The first electroacoustic transducer and the second electroacoustic transducer are the electroacoustic transducers according to claim 39, and the first electroacoustic transducer and the second electroacoustic transducer are placed at 180 degrees.

79. A method of manufacturing an electroacoustic transducer, wherein, The method comprises the following steps: (a) Mounting a sound panel to a sealed housing; (b) Mounting a magnetic negative spring, wherein (i) the magnetic negative spring has a stationary magnet and a movable armature, (ii) the movable armature comprises a ferromagnetic element, (iii) the movable armature is mechanically connected to the sound panel; and (c) Mounting an actuator operable to convert electrical energy into mechanical energy to the sound panel, so that the mechanical force acting on the sound panel due to the pressure change in the sealed housing is at least partially offset by the magnetic force from the magnetic negative spring.

80. The method according to claim 79, wherein The electroacoustic transducer is the electroacoustic transducer according to any one of claims 39-77.

81. A method of using an electroacoustic transducer, wherein, The method comprises the following steps: (a) Selecting an electroacoustic transducer according to any one of claims 39-77, wherein the electroacoustic transducer is in a sealed chamber; (b) Using the electroacoustic transducer, so that the mechanical force caused by the pressure change in the sealed housing is at least partially offset by the magnetic force from the magnetic negative spring of the electroacoustic transducer.

82. The method according to claim 81 further comprises the step of monitoring electrical energy to automatically adjust the average position of the armature of the electroacoustic transducer to minimize the electrical energy consumption of the actuator.

83. The method according to claim 82, wherein, The actuator is a voice coil.

Images