Loudspeaker motor with internal permanent magnets

Abstract

The present invention relates to a motor for an electrodynamic loudspeaker and an electrodynamic loudspeaker comprising the motor. The motor comprises a magnetic circuit assembly arranged around a motor axis, the magnetic circuit assembly comprising a magnetically permeable top plate, a magnetically permeable bottom plate, a magnetically permeable member arranged between the magnetically permeable top plate and the magnetically permeable bottom plate and magnetically coupled to the magnetically permeable top plate and the magnetically permeable bottom plate, a central pole piece, and an air gap for accommodating a voice coil, the motor further comprising an outwardly protruding magnetically permeable member or cap arranged above the top of the air gap. The central pole piece comprises a permanent magnet, such as a neodymium magnet or a ferrite magnet, extending axially at least from the bottom of the air gap to the magnetically permeable bottom member or the magnetically permeable bottom plate.

Description

[0001] This invention relates in one aspect to a motor for an electrodynamic loudspeaker and an electrodynamic loudspeaker including the motor. The motor includes a magnetic circuit assembly arranged around a motor axis, the magnetic circuit assembly comprising: a magnetically conductive top plate; a magnetically conductive bottom plate; a magnetically conductive member disposed between and magnetically connected to the magnetically conductive top plate and the magnetically conductive bottom plate; a central pole piece; and an air gap for receiving a voice coil. The motor also includes an outwardly extending magnetically conductive member or cap-like portion disposed above the top of the air gap. The central pole piece includes a permanent magnet, such as a neodymium magnet or a ferrite magnet, extending axially from at least the bottom of the air gap to the magnetically conductive bottom member or the magnetically conductive bottom plate. Background Technology

[0002] An electrodynamic loudspeaker has a motor that converts electrical energy into mechanical motion. The most common operating principle involves moving a coil, where an electrical input or driving current flows through the voice coil of the loudspeaker. The voice coil is suspended in a permanent magnetic field with a strong radial component. The driving current through the voice coil and the radial magnetic field generate a so-called Lorentz force along the axis of the voice coil. The voice coil is typically rigidly attached to the diaphragm or membrane of the electrodynamic loudspeaker. Therefore, the Lorentz force causes the diaphragm to shift outward and inward based on motion, thereby generating sound pressure.

[0003] The Lorentz force, or driving force, on the diaphragm is the product of the driving current I, the flux density B in the air gap, and the length l of the cable inside the radial magnetic field. More precisely, it is I times the integral of the radial component of B over the length of the voice coil cable.

[0004] This integral is typically designated as the product of the motor's Bl or force factor. In both electrical and mechanical fields, motors convert (transform) energy in two directions. Therefore, motors also act as generators, causing mechanical motion to produce electrical energy. The voltage (EMF) generated by the magnetic field in the voice coil is proportional to the speed of the voice coil and diaphragm assembly. This proportionality factor is also the force factor. The actual motors in electrodynamic loudspeakers exhibit several significant nonlinear mechanisms, which produce undesirable linear and nonlinear distortions in the generated sound pressure levels.

[0005] One nonlinear distortion mechanism is caused by the position / displacement-dependent change of the B*l product of the motor, resulting in the B*l product varying with the position of the voice coil in the magnetic gap. With zero drive current in the voice coil, the force factor gradually decreases from its maximum value, which typically occurs at the rest position of the voice coil. This first nonlinear distortion mechanism is static, i.e., it depends only on the position of the voice coil.

[0006] Another dynamic nonlinear distortion mechanism exists. The driving current in the voice coil generates its own magnetic field in response to the current flow. A portion of the magnetic field generated by the voice coil circulates in the magnetic circuit, meaning the voice coil behaves as a core inductor with the magnetic circuit at its core. The magnetic flux generated by the voice coil current is superimposed on the permanent magnetic flux in the magnetic gap, causing the magnetic flux in the magnetic gap to change undesirably with the coil current, thus creating nonlinear distortion.

[0007] Because the force factor itself has become dependent on the voice coil current, the force on the voice coil and diaphragm is no longer exactly proportional to the voice coil current (i.e., the drive current). This effect depends on the position of the voice coil, but the nonlinearity is due to the superposition of the two magnetic fields rather than to the mobility of the voice coil. Based on the description of the problem, force factor modulation is also known as position-dependent inductance, flux modulation, and magnetoresistance. This force factor modulation is described in detail in the AES paper "Force Factor Modulation in Electrodynamic Loudspeakers," presented at the 141st session held from September 29th to October 3rd, 2016.

[0008] Force factor modulation results in a second-order nonlinear distortion in the form of a force component that is proportional to the square of the voice coil current.

[0009]

[0010] Where L is the position-dependent generalized inductance of the coil as defined in the AES paper, x is the coil position and i is the coil current.

[0011] In other words, second-order nonlinear distortion is proportional to the square of the voice coil current and the spatial derivative of the coil inductance. Variable voice coil inductance also produces distortion in another way. The voice coil inductance is part of the voice coil's resistivity, such that when it is driven by a voltage source (in most cases), the voice coil current becomes position-dependent on the applied driving voltage. The 2016 AES paper described above shows that the equation for the nonlinear components of the force can be generalized to include the frequency dependence of the voice coil inductance. As previously stated, the magnetic circuit acts as the core of the voice coil, meaning that when the permeability of a portion of the magnetic circuit is frequency-dependent, the voice coil inductance becomes frequency-dependent.

[0012] The reason for frequency-dependent permeability is the introduction of eddy currents. When the magnetic flux of the voice coil changes, eddy currents flow through all conductive parts or components (such as ferrous parts) of the magnetic circuit or system due to changes in current or due to coil movement. The flow of eddy currents will counteract the change in magnetic flux (Lenz's law), or in other words, the eddy currents act as short-circuit coil turns, thereby reducing the inductance of the voice coil.

[0013] Because the conductivity of the material in which these eddy currents flow is limited, the current decays when the coil flux remains static for a period of time. That is, at DC, 0Hz, or very low frequencies, there are no eddy currents to counteract the inductance. Therefore, the voice coil inductance at DC is determined solely by the geometry and permeability of the magnetic circuit material. At higher frequencies, the eddy currents become more pronounced, reducing the inductance to below that observed at DC.

[0014] Some existing electrodynamic loudspeakers already include so-called short-circuit rings around the poles and voice coil. These rings are made of a conductive but non-magnetic material, such as copper or aluminum. The purpose is to reduce the voice coil inductance, at least at higher frequencies. Because copper or aluminum has a lower resistivity than iron, most of the eddy currents flow in the short-circuit rings rather than in the iron. For the same reason, the eddy currents are larger and therefore more strongly counteract the changes in the magnetic field that the voice coil attempts to induce or form in the magnetic circuit. This reduces force factor modulation, at least at higher frequencies. Another advantage is the reduced inductance, which means higher sensitivity to a given voltage applied to the voice coil and reduced nonlinear inductance caused by hysteresis in the iron. This does not mean that the short-circuit ring (regardless of placement) will unconditionally improve linearity. Since force factor modulation is equivalent to the positional dependence of the generalized voice coil inductance, at high frequencies it is possible to reduce inductance while increasing the spatial gradient of the inductance (the absolute change in inductance per millimeter of motion). At low frequencies, existing short-circuit rings have no effect. The lower the frequency at which the desired effect is desired, the larger the cross-section of the short-circuit ring must be at lower frequencies, which is too large for the amount of available space inside the magnetic circuit of the actual loudspeaker.

[0015] The inventors have realized that if the motor and magnetic circuit of an electrodynamic loudspeaker are designed or configured such that the voice coil inductance is displacement / position-dependent, then both nonlinear distortion caused by force factor modulation and nonlinear distortion caused by voice coil current modulation are eliminated. Therefore, an ideal motor for an electrodynamic loudspeaker exhibits a constant voice coil inductance, meaning that the voice coil inductance does not change with the displacement of the voice coil and is therefore position-dependent.

[0016] Therefore, one object or objective of the present invention is to provide an electrodynamic speaker motor that, compared to prior art speaker motors, substantially eliminates or at least significantly reduces the harmful displacement dependence of the voice coil inductance. For the reasons stated above, this reduction will improve the linearity of the motor, thereby reducing various types of nonlinear distortion in the corresponding electrodynamic speaker incorporating this speaker motor. Thus, for example, the objective performance and subjective sound quality of the corresponding electrodynamic speaker can be improved by reducing harmonic and intermodulation distortion. Summary of the Invention

[0017] A first aspect of the invention relates to a motor for an electrodynamic loudspeaker, the motor including a magnetic circuit assembly arranged around a motor axis. The magnetic circuit assembly includes: a magnetically conductive top plate; a magnetically conductive bottom plate; a magnetically conductive member disposed between and magnetically connected to the magnetically conductive bottom plate and the magnetically conductive top plate; a central pole piece; and an air gap for receiving a voice coil; wherein the air gap is formed by an inner axially extending wall of the magnetically conductive top plate facing an axially extending peripheral wall section of the central pole piece to define the width, bottom, top, and height of the air gap. The motor also includes an outwardly extending magnetically conductive member or cap-like portion disposed above the top of the air gap. The central pole piece includes a permanent magnet, such as a neodymium magnet or a ferrite magnet, extending at least axially from the bottom of the air gap to the magnetically conductive bottom member or the magnetically conductive bottom plate. Those skilled in the art will understand that, in some embodiments, the magnetically conductive component and the magnetically conductive base plate can be formed as separate parts mechanically joined together, or alternatively as a single, integrally formed element or component. The latter embodiment reduces motor assembly time and thus lowers costs.

[0018] A significant advantage of this motor is that the material of the conductive magnetic components is arranged outside the central pole piece. Figure 1 Compared to existing motors that arrange the material of the conductive magnetic component within the voice coil, this arrangement reduces the increase in inductance of the voice coil relative to a corresponding air voice coil. Another advantage of this motor is its reduced outer diameter compared to corresponding motors that replace the conductive magnetic component with a corresponding ferrite component.

[0019] In this specification, the term "AC permeability" for magnetic components (such as permanent magnets with central pole pieces) refers to the slope of the tangent line to the curve relating flux density B to magnetic field strength H under zero voice coil current. The term "relative AC permeability" μ... r This refers to "AC permeability" expressed as a multiple of the vacuum permeability μ0. The tangent can be viewed as a linearized small-signal model or AC model around the DC operating point of the magnetic component. The slope of the tangent is the permeability of the small-signal model of the magnetic component, i.e., the "AC permeability" of the magnetic component. Under high magnetic field strength (e.g., greater than 1.5 Tesla), this BH curve becomes flatter, meaning that the AC permeability decreases as the material of the magnetic component becomes saturated. Permanent magnets are inherently highly magnetically saturated and therefore typically have an AC permeability not much greater than that of air. Neodymium magnets that can form the permanent magnets of this motor can exhibit relative AC permeability below 1.5 or below 1.1. Therefore, the permanent magnets of the central pole piece can exhibit relative AC permeability below 2 or 1.5, or even below 1.1.

[0020] Therefore, the low AC permeability of the permanent magnet, combined with the outwardly extending conductive magnetic member, provides a synergistic effect by significantly reducing the increase in voice coil inductance when the voice coil is shifted inward. Furthermore, the slight increase in residual voice coil inductance is compensated by arranging the outwardly extending conductive magnetic member above the top of the air gap. This geometry ensures that the voice coil inductance also increases in almost the same proportion when the voice coil is shifted outward as it does when shifted inward, thus making the displacement-dependent change in voice coil inductance very small, as discussed in further detail below with reference to the accompanying figures.

[0021] The outwardly extending conductive magnetic component can be generally arranged inside or outside the outwardly extending plane or surface defined by the axially extending peripheral wall section of the central pole piece, as discussed in further detail below with reference to the accompanying drawings, such as Figure 2. Figure 4 The motor implementation shown in Figure 8.

[0022] In one embodiment of the motor, the central pole piece includes a magnetically conductive top member that extends axially from the bottom of the air gap to the top of the air gap, thereby forming or defining an axially extending peripheral wall section of the central pole piece. An outwardly extending magnetically conductive member or a magnetically conductive cap may be disposed on top of the magnetically conductive top member and may be integrally formed with or configured as a separate element coupled to or adjacent to the upper surface of the magnetically conductive top member, as discussed in further detail below with reference to the accompanying drawings. The magnetically conductive top member and / or the outwardly extending magnetically conductive member may include or be made of, for example, a ferromagnetic material (such as AISI CR1010 steel) of high permeability or an isotropic, high-resistivity soft magnetic composite (SMC) material, as discussed in further detail below with reference to the accompanying drawings. Similarly, the magnetically conductive member may include or be made of, for example, a ferromagnetic material (such as AISI CR1010 steel) of high permeability or an isotropic, high-resistivity soft magnetic composite (SMC) material.

[0023] According to another embodiment of the motor, the height of the outwardly extending magnetically conductive member exceeds the height of the magnetically conductive top plate, for example, by 1.5 times the height of the magnetically conductive top plate.

[0024] According to another embodiment of the motor, the height of the magnetic component of the central pole is greater than the difference between the height of the voice coil and the height of the air gap.

[0025] Additional embodiments of the invention are set forth in the appended dependent claims.

[0026] A second aspect of the invention relates to a corresponding electrodynamic loudspeaker, namely an electrodynamic loudspeaker incorporating a motor, and the electrodynamic loudspeaker includes:

[0027] -frame,

[0028] - A motor according to any of the above-described embodiments of the motor and / or according to any of the following embodiments of the motor described in conjunction with the accompanying drawings. The electrodynamic loudspeaker also includes a movable diaphragm or membrane attached to the voice coil, wherein the voice coil is arranged in the air gap of the motor, for example, freely suspended in the air gap.

[0029] The magnetic circuit assembly of the electrodynamic loudspeaker is preferably configured such that, when measured at 31 Hz, the change in inductance of the voice coil is less than 10%, such as less than 7.5%, or even less than 5%, within a predetermined displacement range defined by outward and inward displacement limits; wherein the displacement range corresponds to 0.5 times the difference between the height of the voice coil and the height of the air gap. Those skilled in the art will understand that the outward and inward displacement limits may be symmetrical about the voice coil's rest or neutral position. The magnetic circuit assembly of the electrodynamic loudspeaker is preferably configured such that, at one or more additional test frequencies selected from the group consisting of 1 Hz, 100 Hz, 316 Hz, 1 kHz, and 3.16 kHz, the change in inductance of the voice coil within the predetermined displacement range falls within the same proportional limit. Attached Figure Description

[0030] Preferred embodiments of the present invention will now be described in further detail with reference to the accompanying drawings, in which:

[0031] Figure 1 This is a schematic cross-sectional view of a prior art motor for an electric loudspeaker.

[0032] Figure 2 is a schematic axial cross-sectional view of a motor for an electric loudspeaker according to a first embodiment of the present invention.

[0033] Figure 3 This is a schematic axial cross-sectional view of a motor for an electric loudspeaker according to a second embodiment of the present invention.

[0034] Figure 4 This is a schematic axial cross-sectional view of a motor for an electric loudspeaker according to a third embodiment of the present invention.

[0035] Figure 5 This is a schematic axial cross-sectional view of a motor for an electric loudspeaker according to a fourth embodiment of the present invention.

[0036] Figure 6 This is a schematic axial cross-sectional view of a motor for an electric loudspeaker according to a fifth embodiment of the present invention.

[0037] Figure 7 This is a schematic axial cross-sectional view of a motor for an electric loudspeaker according to a sixth embodiment of the present invention.

[0038] Figure 8A This is a schematic axial cross-sectional view of a motor for an electric loudspeaker according to a seventh embodiment of the present invention.

[0039] Figure 8B This is a schematic axial cross-sectional view of a motor for an electric loudspeaker according to an eighth embodiment of the present invention.

[0040] Figure 9 A schematic axial cross-sectional view of a corresponding exemplary electrodynamic loudspeaker incorporating a motor according to any of the above embodiments of the present invention is shown.

[0041] Figure 10 A graph comparing the voice coil inductance with the inward and outward displacement of the voice coil at 1Hz is shown, based on a finite element analysis simulation of an exemplary motor design or structure according to the eighth embodiment of the present invention, and a corresponding motor design without the conductive magnetic "cap" 215.

[0042] Figure 11 A graph showing the force factor (i.e., B*l product) of an exemplary motor design or structure according to the eighth embodiment of the present invention, simulated by finite element analysis, is compared with the inward and outward displacements of the voice coil. This is a comparison of the force factor (i.e., B*l product) of the motor design without the conductive magnetic "cap" 215. Detailed Implementation

[0043] In the following description, several exemplary embodiments of this motor for an electric loudspeaker are illustrated with reference to the accompanying drawings. Those skilled in the art will understand that these drawings are schematic and simplified for clarity, and therefore only details essential for understanding the invention are shown, while other details are omitted. Throughout the application, the same reference numerals refer to the same elements or components. Therefore, it is not necessary to describe similar elements or components in detail for each drawing. It should also be understood that certain actions and / or steps may be described or depicted in a specific order of occurrence, and those skilled in the art will understand that such specificity related to the described order is not actually required.

[0044] Figure 1This is a schematic cross-sectional view of a prior art motor 100 for an electrodynamic loudspeaker. The voice coil inductance is directly proportional to the square of the number of windings in the voice coil and inversely proportional to the magnetic reluctance of the magnetic circuit. The number of windings is fixed, while the magnetic reluctance of the magnetic circuit can vary with the displacement of the voice coil, and therefore also with the displacement of the diaphragm attached to the voice coil position, due to the change in the amount of material near the voice coil with a higher permeability than air. Another way to describe this is that the effective permeability is adjusted by the displacement of the voice coil. The voice coil surrounds a central iron pole. When the voice coil shifts inward toward the base plate (i.e., as shown, from the rest position 0 toward the negative X position (-X), the voice coil inductance is higher due to the increased amount of iron material within the voice coil. This position of the voice coil increases the effective permeability. Conversely, when the voice coil is displaced outward along the direction of the motor's diaphragm (i.e., from the rest position 0 toward the positive X (+X) position as shown in the figure), the voice coil inductance is lower because the voice coil moves outward in free air with low permeability.

[0045] Figure 2A A schematic axial cross-sectional view of a motor 200 for an electrodynamic loudspeaker (not shown) according to a first embodiment of the invention is shown. The electrodynamic loudspeaker may be a so-called 6.5-inch size, with a diaphragm diameter of approximately 120 mm. Compared to prior art loudspeaker motors, this motor 200 and its magnetic circuit assembly, as well as other motor embodiments described below, are configured or designed to minimize or reduce displacement-related variations in the inductance of the voice coil. Therefore, for reasons discussed in detail above in the background section of the invention, both nonlinear distortion due to force factor modulation and nonlinear distortion due to voice coil current modulation are minimized.

[0046] Motor 200 is rotationally symmetrical about its central motor axis 205. Motor 200 includes a magnetic circuit assembly configured to generate a radially oriented, substantially static magnetic field within an annular air gap 220. The magnetic circuit assembly includes a conductive magnetic member 240, a conductive magnetic top plate 235 (e.g., formed as an annular disk), a conductive magnetic bottom plate or yoke 230, and a central pole piece 245. Air gap 220 is shaped and sized or configured to receive a mating annular or ring-shaped voice coil 225, which may form part of the diaphragm assembly of an electrodynamic loudspeaker. The annular or ring-shaped voice coil 225 is freely suspended within the annular air gap 220 and can therefore be displaced outwards along the central motor axis 205 away from the magnetic circuit assembly and inwards toward the magnetic circuit assembly relative to a rest position 0 of the voice coil. The rest position corresponds to zero DC current in the annular voice coil 225 and preferably corresponds to the central position of the annular voice coil 225 within the air gap 220. The resting position of the annular voice coil 225 is schematically represented by the "0" on the "X" arrow in the attached figure, while the outward displacement of the voice coil 225 away from the magnetic circuit assembly corresponds to the positive / + direction of X, and the inward displacement of the voice coil 225 towards the magnetic circuit assembly corresponds to the negative / - direction of X. The conductive magnetic member 240 may have an annular shape and form the outer periphery of the motor 200. The conductive magnetic member 240 may be magnetically connected or coupled to the conductive magnetic top plate 235 and the conductive magnetic yoke 230, and does not have a permanent magnet or any other type of magnet.

[0047] Those skilled in the art should understand that Figure 2A and Figures 3 to 7 The schematic diagram of the motor embodiment shows the total cross-sectional area of ​​the conductive magnetic components 240, 340, 440, 540, 640, and 740 perpendicular to a plane along the central axis of the motor. This total cross-sectional area is larger than the cross-sectional area of ​​the corresponding central pole piece. This cross-sectional area ratio can be applied to various embodiments of this motor. However, Figure 2A and Figures 3 to 7 The cross-sectional area of ​​the conductive magnetic components 240, 340, 440, 540, 640 and 740 of the alternative motor embodiments described above can be less than 66.6% of the cross-sectional area of ​​the corresponding central pole piece, or more preferably about 50% or less.

[0048] The magnetically conductive top plate 235 can be made of a high-permeability material, such as a ferromagnetic material (e.g., CR1010 steel), and its height is between one-sixth and two-thirds of the height of the toroidal voice coil 225. The magnetically conductive bottom plate or yoke 230 can be made of a high-permeability material, such as a ferromagnetic material (e.g., AISI CR1010 steel), and its height or thickness is between 4 mm and 16 mm, depending on the external dimensions of the motor 200.

[0049] The central pole piece or central pole assembly includes a magnetic member 250 extending from the bottom 220b of the air gap 220 to a magnetically conductive bottom member 245, which may be formed as an upwardly extending columnar protrusion 245 integrally formed with a magnetically conductive base plate or yoke 230. The magnetically conductive bottom member 245 is physically and magnetically coupled to the lower surface of the magnetic member 250. Thus, in this embodiment of the motor 200, the magnetic member 250 is arranged between the top of the magnetically conductive pole 210 and the magnetically conductive bottom member 245, wherein the top of the magnetically conductive pole may be formed as a flat disk. In other embodiments of the magnetic circuit assembly, the magnetic member 250 may extend axially from the bottom 220b of the air gap 220 to the magnetically conductive base plate or yoke 230. The height of the magnetic member 250 is preferably at least 0.5 times the height of the outer annular magnetically conductive member 240, for example, greater than 0.7 or 0.9 times the height of the outer annular magnetically conductive member 240. Alternatively or additionally, the height of the magnetic component 250 is greater than the difference between the height of the voice coil and the height of the air gap 220. Each of these limitations will generally ensure that the height of the magnetic component 250 is large enough to significantly reduce the inductance of the voice coil during inward displacement due to the reduction in the amount of conductive magnetic material within the voice coil.

[0050] The top 210 of the conductive magnetic pole extends from the bottom 220b of the air gap 220 (reference). Figure 2B An axially extending peripheral wall section 236 of the central pole piece 245 extends axially to the top 220a of the air gap 220, forming a wall or surface (e.g., circular or elliptical) within the air gap 220. Another wall of the air gap 220 is formed by an axially extending wall 242 (e.g., circular or elliptical) inside the conductive magnetic top plate 235, wherein the axially extending wall 242 faces the axially extending peripheral wall section of the central pole piece 245 to define the width, bottom 220b, top 220a, and height of the air gap 220. Those skilled in the art will understand that the height and / or width of the air gap 220 can be scaled according to the overall dimensions of the motor 200 and the voice coil 225. The conductive magnetic pole top 210 can be made of a high-permeability material, such as a ferromagnetic material (e.g., AISI CR1010 steel).

[0051] The conductive pole top 210 includes an outwardly extending portion or protrusion 215 or "cap" 215 disposed above the top 220a of the air gap 220 (i.e., outside the top of the air gap). Therefore, in this embodiment, the outwardly extending portion or protrusion 215 is also disposed above the flat upper surface 237 of the conductive pole top member 235. The outwardly extending "cap" 215 is disposed inside an outwardly extending plane or surface (not shown) defined by the axially extending peripheral wall section 217 of the central pole piece 245, i.e., towards the central motor axis 205. This allows for unrestricted axial displacement of the voice coil 225.

[0052] Therefore, the conductive pole top 210 may include a first columnar portion or segment 212 defining the inner wall (axially extending peripheral wall section) 236 of the air gap 220 discussed above. The conductive pole top 210 of the central pole piece 245 also includes the outwardly projecting protrusion 215 described above, which in this embodiment is formed by a second columnar portion of the conductive pole top 210, which is disposed on top of the first columnar portion 212 and integrally formed with or configured as a separate element attached to or adjacent to the top surface of the first columnar portion 212. Those skilled in the art will understand that the outwardly projecting protrusion 215 is not necessarily columnar. For example, it may be a columnar ferrite member of a suitable shape milled or machined, or other high-permeability materials (such as AISI CR1010 steel) or isotropic, high-resistivity soft magnetic composite (SMC) materials (such as...). Materials), such as those made from The Somaloy 1P, Somaloy 3P, or Somaloy 5P manufactured and sold by AB can have their first and second columnar portions 212 and 215 of the conductive pole top 210 integrally formed. The cross-sectional area of ​​the second columnar portion 215 can be smaller than that of the first columnar portion or segment 212 to define a recessed upper outer circular wall 215a relative to the inner wall 236 of the conductive pole top 210, thereby defining the inner surface or inner wall 236 of the magnetic gap 220. In other words, the outwardly extending protrusion 215 extends outward in the upward direction of the magnetic gap 220 along the axial direction 205 of the motor 200.

[0053] In some alternative embodiments, the first columnar portion and the second columnar portions 212, 215 may each have the same diameter to eliminate the recessed characteristic of the upper outer circular wall 215a.

[0054] The magnetic component 250 may exhibit a relative AC permeability of less than 10 (e.g., less than 5 or less than 2). In some embodiments, the magnetic component 250 comprises or is made of a permanent magnet, such as a neodymium magnet or a ferrite magnet. In other embodiments of the motor 200, which are described in further detail below, the magnetic component 250 comprises a magnetically conductive material (e.g., an isotropic, high-resistivity soft magnetic composite (SMC) material) that is driven to DC magnetic saturation by at least one of the permanent magnet and the magnetic field coil. The SMC material may include those discussed above. Material.

[0055] As schematically shown in the figure, the magnetic component 250 is axially magnetized by magnetic field lines that drive magnetic flux through the magnetic circuit assembly and across the air gap, thus subjecting the air gap to a radially oriented magnetic field. The outer annular conductive magnetic component 240 may comprise a high-permeability material or an isotropic, high-resistivity soft magnetic composite (SMC) material, or be made of a high-permeability material or an isotropic, high-resistivity soft magnetic composite material, such as a ferromagnetic material like AISICR1010 steel, and the soft magnetic composite material may include ferrite magnets or neodymium magnets.

[0056] The arrangement of the magnetically conductive outwardly protruding or cap-shaped portion 215 increases the inductance of the voice coil 225 when the voice coil 225 is shifted outward (i.e., a positive "X" value), so that the increase in inductance effectively offsets or compensates for the increase in inductance of the voice coil 225 when it is shifted inward.

[0057] The reduced cross-sectional area of ​​the conductive magnetic cap 215 guides the DC magnetic flux (i.e., static DC magnetic flux) of the magnetic circuit assembly to flow in the air gap 220. This feature ensures that the DC magnetic flux is concentrated in the air gap 220 and that the magnetic field strength in the conductive magnetic cap 215 is low. This feature, in turn, ensures that the conductive magnetic cap 215 remains outside of magnetic saturation, thereby resulting in higher permeability and more effective compensation for the displacement-dependent inductance L(x) of the voice coil 225.

[0058] Conversely, the magnetic pole member 250 disposed below the bottom 220b of the air gap 220 (e.g., the upper surface of the magnetic pole member substantially aligned with the bottom 220b of the air gap 220) preferably exhibits or has a small relative AC permeability as described above, in order to reduce the displacement dependence of the voice coil inductance. A small relative AC permeability can be achieved in various ways, such as through high DC or static magnetic saturation, for example by using a permanent magnet or by using a soft magnetic material (such as a ferromagnetic material) driven to DC saturation by a permanent magnet or magnetic field coil, as described below. In both cases, the relative AC permeability can be very small, for example, less than 10 or less than 5.

[0059] The increase in voice coil inductance as described above when the voice coil 225 is shifted inward is partly due to the reduced distance between the voice coil 225 and the conductive magnetic base plate or yoke 230, including the upwardly extending columnar protrusion 245. Another significant contribution to the increase in voice coil inductance when the voice coil 225 is shifted inward in prior art motor designs is the high permeability of the ferromagnetic material of the central pole piece.

[0060] Those skilled in the art will understand that the combined characteristics of the magnetic component 250 and the conductive magnetic cap 215 greatly eliminate or at least significantly reduce the expected increase in voice coil inductance when the voice coil 225 of the motor 200 is displaced inward. The small AC relative permeability of the magnetic component 250 (in some embodiments, it can be comparable to free air, i.e., μ) r =1.0) This reduces the presence of conductive magnetic material within the voice coil 225, at least when shifted inward. Because the conductive top member 210 and the yoke 235 still contribute to shortening the magnetic field lines compared to free air, the voice coil inductance may still be at its maximum when the voice coil 225 is fully pulled inward. Importantly, the voice coil inductance is significantly reduced compared to a design with a conductive magnetic central pole piece close to the coil.

[0061] Therefore, the magnetic pole member 250 and the conductive magnetic cap 215 provide a synergistic effect by first significantly reducing the voice coil inductance when the voice coil 225 is shifted inward via the magnetic pole member 250, and further by compensating for the small amount of residual voice coil inductance that increases during inward shift by arranging the conductive magnetic cap 215 above the top of the air gap 220, such that the voice coil inductance also increases when the voice coil 225 is shifted outward. In other words, the combination of the conductive magnetic cap 215 and the magnetic pole member 250 arranged in the central pole piece 245 is perfectly suited for this purpose due to the small AC permeability of the magnetic pole member.

[0062] Figure 3 A schematic axial cross-sectional view of a motor 300 for an electrodynamic loudspeaker (not shown) according to a second embodiment of the present invention is shown. An outwardly extending conductive magnetic member 315 is supported by a non-magnetic spacer 343 disposed between the top surface of the conductive magnetic pole top 310 of the central pole piece 345 and the conductive magnetic cap-shaped portion 315. Although the conductive magnetic cap-shaped portion 315 is not directly physically or magnetically connected to the central pole piece, its higher permeability still compensates for the displacement-related inductance of the voice coil 325 when it is displaced outward or at the displaced position, for the reasons described above.

[0063] Figure 4A schematic axial cross-sectional view of a motor 400 for an electrodynamic loudspeaker (not shown) according to a third embodiment of the present invention is shown. The conductive magnetic top plate 435 of the magnetic circuit assembly includes an annular conductive disk-shaped protrusion 415. The annular conductive disk 415 may be integrally formed with the conductive magnetic top plate 435. The inner circular peripheral wall 415a of the annular conductive disk 415 is arranged outside the outwardly extending plane defined by the axially extending wall 436 inside the conductive magnetic pole top 410. Although the annular conductive cap-shaped portion 415 is completely arranged outside the outwardly extending plane defined by the inner axially extending wall 436, and thus outside the voice coil 425, its proximity and high permeability still compensate for the displacement-related inductance of the voice coil 425 when it is displaced outwards or at the displaced position.

[0064] Figure 5 A schematic axial cross-sectional view of a motor 500 for an electrodynamic loudspeaker (not shown) according to a fourth embodiment of the present invention is shown. The motor 500 is substantially the same as the motor 200 according to the first embodiment discussed above, but additionally includes a first conductive ring 547 disposed below the bottom of an air gap 520 and surrounding a central pole piece 545. The central pole includes a magnetic member 500, a conductive pole top 510, and a conductive pole bottom member 545. The motor 500 may also include a second conductive ring 546 abutting against an outwardly oriented surface of the conductive pole top 510 and surrounding an outwardly extending conductive pole cap-like portion 515. Thus, the second conductive ring 546 is disposed above the top of the air gap 520 and inside an outwardly extending plane or surface defined by the axially extending peripheral wall section 517 of the central pole piece. Each of the first conductive ring and the second conductive rings 547, 546 operates as a so-called short-circuit ring and preferably comprises a conductive but non-magnetic material (such as copper or aluminum). For the reasons mentioned above, the advantage of short-circuit rings 547 and 546 is that they reduce the increase in voice coil impedance at higher frequencies (e.g., above 10 Hz) by reducing the eddy currents flowing in the magnetic circuit assembly.

[0065] Figure 6A schematic axial cross-sectional view of a motor 600 for an electrodynamic loudspeaker (not shown) according to a fifth embodiment of the present invention is shown. The central pole piece of the motor 600 includes a magnetic pole member 650 that extends axially from the top of an air gap 620 to a conductive magnetic base plate or yoke 630. The central pole piece 645 of this magnetic circuit lacks the previously described conductive magnetic pole tops 210, 310, 410, and 510. Therefore, in the motor 600 of this embodiment, the axially extending peripheral wall section 636 of the magnetic member 650 forms an axially extending peripheral wall section 636 on the inner side of the central pole piece (e.g., circular or elliptical). Another wall of the air gap 620 is formed by an axially extending wall section 642 on the interior (e.g., circular or elliptical) of the conductive magnetic base plate 635, such that these two axially extending wall sections together define the size of the air gap 620. Magnetic component 650 may include a permanent magnet or may be formed in a saturated soft magnetic material (such as a ferromagnetic material), for example, the isotropic, high-resistivity soft magnetic composite (SMC) material discussed earlier. Magnetic component 650 may be driven to DC saturation by a permanent magnet (not shown) or an internal or external magnetic field coil (not shown). Magnetic component 650 is driven to DC magnetic saturation by a suitable magnetic flux such that the relative AC permeability of the magnetic pole component 650 is preferably less than 5 or less than 2. Motor 600 includes an outwardly extending conductive magnetic component 615 supported by and preferably coupled to the upper surface of magnetic component 650 and arranged above the top of magnetic gap 620. In a variation of motor 600 of this embodiment, magnetic component 650 includes an axially extending (i.e., along axis 605) through-hole or aperture (not shown) for reducing the effective cross-sectional area of ​​magnetic component 650 by, for example, more than 30% or 50%. The axially extending through-hole or aperture of the magnetic component 650 can be used to promote DC magnetic saturation of the material of the magnetic component 650 (such as the SMC material discussed above). The conductive magnetic component 640 can have an annular shape and provide the outer periphery of the motor 600. The conductive magnetic component 640 can be magnetically connected or coupled to the conductive magnetic top plate 635 and the conductive magnetic yoke 630.

[0066] Figure 7A schematic axial cross-sectional view of a motor 700 for an electrodynamic loudspeaker (not shown) according to a sixth embodiment of the invention is shown. The central pole piece 745 of the motor 700 includes an annular columnar magnetic member 750 arranged around a central motor axis 705. The annular columnar magnetic member 750 is made of a magnetically conductive material, preferably an isotropic, high-resistivity soft magnetic composite (SMC) material discussed above. The central pole piece 745 also includes a disk-shaped permanent magnet 750a (e.g., a neodymium magnet) extending downward from the bottom of an air gap 720 to the upper surface of the annular columnar magnetic member 750. The disk-shaped permanent magnet 750a is configured to drive the annular columnar magnetic member 750 to DC magnetic saturation. The DC magnetic saturation of the annular columnar magnetic member 750 results in a low relative AC permeability of the annular columnar magnetic member 750 (e.g., less than 5 or less than 2). The axially oriented through-hole 751 of the annular columnar magnetic member 750 reduces the effective cross-sectional area of ​​the magnetic member 750 and thus helps to induce appropriate DC magnetic saturation in the magnetic member 750.

[0067] The central pole piece of the magnetic circuit also includes a conductive magnetic pole top 710, which conducts magnetic flux and guides the magnetic flux radially through the air gap 725. The conductive magnetic pole top 710 is preferably integrally formed with an outwardly extending and recessed portion or protrusion 715 or "cap" disposed above the top of the air gap 720 (i.e., outside the top of the air gap) in a manner similar to that of the first embodiment of the invention discussed above.

[0068] Figure 8A A schematic axial cross-sectional view of a motor 800 for an electrodynamic loudspeaker (not shown) according to a seventh embodiment of the present invention is shown. The motor 800 includes a conductive magnetic member 835 disposed between and magnetically coupled to a conductive magnetic top plate 835 and a conductive magnetic bottom plate 830 to provide a closed loop through which magnetic flux passes via a magnetic circuit assembly. The magnetic circuit assembly of the motor 800 is arranged about a motor axis 805 and includes: a conductive magnetic top plate 835, a conductive magnetic bottom plate 830, one or more conductive magnetic members 833, a central pole piece, and an air gap for receiving a voice coil 825.

[0069] The motor 800 is rotationally symmetrical about its central motor axis 805. The magnetic circuit assembly is preferably configured to generate a radially oriented, substantially static magnetic field within a substantially annular air gap 820. The air gap 820 is configured to receive a ring-shaped or annular voice coil 825, which can form... Figure 9This is part of the diaphragm assembly of an electrodynamic loudspeaker, schematically described in Figure 2. An annular or ring-shaped voice coil 825 is freely suspended in an annular air gap 820, and can therefore be displaced outwards along the central motor axis 805 away from the magnetic circuit assembly and inwards toward the magnetic circuit assembly around the rest position 0 of the voice coil schematically shown in Figure 2. The rest position corresponds to zero DC current in the annular voice coil 825, and preferably corresponds to the center position of the annular voice coil 825 in the air gap 820.

[0070] The magnetically conductive top plate 835 can be made of a high-permeability material, such as a ferromagnetic material (e.g., CR1010 steel), and its height is between one-sixth and two-thirds of the height of the toroidal voice coil 825. The magnetically conductive bottom plate or yoke 830 can be made of a high-permeability material, such as a ferromagnetic material (e.g., AISI CR1010 steel), and its height or thickness is between 4 mm and 16 mm, depending on the external dimensions of the motor 800. Similarly, the magnetically conductive member 833 can also be comprised of or made of a high-permeability material, such as a ferromagnetic material (e.g., AISI CR1010 steel). The magnetically conductive member 833 can be formed as a single columnar member. Those skilled in the art will understand that the magnetically conductive member 833 can be integrally formed with one or both of the magnetically conductive top plate 835 and the magnetically conductive bottom plate 830, as schematically shown. This can be achieved by machining or manufacturing these as single coherent articles of a magnetically conductive material. Alternatively, the magnetically conductive top plate 835, the magnetically conductive bottom plate 830, and the magnetically conductive component 833 may be separate articles that are joined together using suitable reagents to form a physical bond and magnetic connection or connection between the individual components.

[0071] The central pole piece or central pole assembly includes a permanent magnet 850 (i.e., the central pole magnet) such as a neodymium magnet or a ferrite magnet and preferably extends from the bottom b of the air gap 820 to a magnetically conductive bottom member 845, which may be formed as an upwardly extending columnar protrusion 845 integrally formed with a magnetically conductive base plate or yoke 830. Preferably, the magnetically conductive bottom member 845 is physically and magnetically coupled to the lower surface of the permanent magnet 850. Thus, the permanent magnet 850 of the motor 800 is arranged between the magnetically conductive pole top 810 and the magnetically conductive bottom member 845, which may be a flat disk. In other embodiments of the magnetic circuit assembly, the permanent magnet 850 may extend axially from the bottom of the air gap 220 to the magnetically conductive base plate or yoke 830. The height of the permanent magnet 850 may be greater than the difference between the height of the voice coil 825 and the height of the air gap 820. Each of these constraints will typically ensure that the height of the permanent magnet 850 is large enough to significantly reduce the inductance of the voice coil 825 when it is shifted inward due to the reduction in the amount of magnetically conductive material within the voice coil.

[0072] The conductive pole top 810 can be made of or formed from a high-permeability material, such as a ferromagnetic material (e.g., AISI CR1010 steel). The conductive pole top 810 includes an outwardly extending portion or protrusion 815 or "cap" 815 disposed above the top of the air gap 820 (i.e., outside the top of the air gap). Thus, the cap 815 is also disposed above the flat upper surface 837 of the conductive magnetic top member 835 of the magnetic circuit assembly. The outwardly extending "cap" 815 can be disposed inside an outwardly extending plane or surface (not shown) defined by the axially extending peripheral wall section 817 of the central pole piece, i.e., towards the central motor axis 805. This allows for unrestricted axial displacement of the voice coil 825. The height of the cap 815 is preferably at least 1.5 times the height or thickness of the conductive magnetic top plate 835, such as at least 1.75 or 2.0 times. The height or thickness of the magnetically conductive top plate 835 depends on the size of the motor 800, but can be between 3mm and 10mm.

[0073] The conductive pole top 810 may include a first columnar portion or section defining the inner wall (axially extending peripheral wall section) 836 of the air gap 820 discussed above. The conductive pole top 810 of the central pole piece may include the integrally formed, outwardly projecting cap 815 described above, which in the motor 800 is formed by a second columnar portion of the conductive pole top 810 and disposed on top of the first columnar portion, and is integrally formed with or configured as a separate element coupled to or adjacent to the upper surface of the first columnar portion, for example by milling or machining. Those skilled in the art will understand that the outwardly projecting protrusion 815 may have shapes other than columnar. Each of the conductive pole top 810 and the cap 815 may include a high-permeability material (such as AISI CR1010 steel) or an isotropic, high-resistivity soft magnetic composite (SMC) material, such as… Materials, such as those made from Somaloy 1P, Somaloy 3P, or Somaloy 5P are manufactured and sold by AB. The cross-sectional area of ​​the cap-shaped portion 815 may be smaller than the cross-sectional area of ​​the conductive pole top 810 to define a recessed upper outer circular wall 815a relative to the inner surface or inner wall 836 of the defining magnetic gap 820 of the conductive pole top 810. In other words, the outwardly extending protrusion 815 extends outward in the upward direction of the magnetic gap 820 along the axial direction 805 of the motor 800.

[0074] In some alternative embodiments, the first columnar portion and the second columnar portions 810, 815 may each have the same cross-sectional area (e.g., diameter) to eliminate the recessed characteristic of the upper outer circular wall 815a. As schematically shown in the figure, the permanent magnet 850 is preferably axially magnetized by magnetic field lines to drive a DC magnetic flux through the magnetic circuit assembly and through the air gap 820, which thereby receives a radially oriented magnetic field.

[0075] The arrangement of the outwardly extending cap-shaped portion 815 increases the inductance of the voice coil 825 when it shifts outward (i.e., the positive "X" value shown in Figure 2a), effectively offsetting or compensating for the increase in inductance when the voice coil 825 shifts inward. The reduced cross-sectional area of ​​the magnetically conductive cap-shaped portion 815 guides the DC magnetic flux (i.e., the static DC magnetic flux) of the magnetic circuit assembly to flow in the air gap 820. This feature ensures that the DC magnetic flux is concentrated in the air gap 820 and that the magnetic field strength in the cap-shaped portion 815 is low. This feature, in turn, ensures that the magnetically conductive cap-shaped portion 815 remains outside of magnetic saturation, resulting in higher permeability and more effective compensation for the displacement-related inductance L(x) of the voice coil 825.

[0076] Conversely, the permanent magnet 850, disposed below the bottom of the air gap 820 (e.g., the upper surface of the permanent magnet is substantially aligned with the bottom of the air gap 820), preferably exhibits or has a small relative AC permeability as described above in order to reduce the displacement dependence of the voice coil inductance. The AC relative permeability of the permanent magnet 850 can be very small, for example, less than 10 or less than 5. The increase in voice coil inductance mentioned above during the inward displacement of the voice coil 825 is partly due to the reduced distance from the voice coil 825 to the conductive magnetic base plate or yoke 830, which includes the upwardly extending columnar protrusion 845. Another significant contribution to the increase in voice coil inductance during the inward displacement of the voice coil 825 in prior art motor designs is the high permeability of the ferromagnetic material of the central pole piece.

[0077] Those skilled in the art will understand that the combined characteristics of the permanent magnet 850 and the cap 815 greatly eliminate or at least significantly reduce the expected increase in voice coil inductance when the voice coil 825 of the motor 800 is shifted inward. During inward shift, the small AC relative permeability of the permanent magnet 850 (which in some embodiments can be comparable to free air, i.e., μ) r =1.0) at least reduces the presence of conductive magnetic material within the voice coil 825. Because the conductive magnetic top member 810 and the yoke 835 still contribute to shortening the magnetic field lines compared to free air, the voice coil inductance can still reach its maximum value when the voice coil 825 is fully pulled inward. Importantly, the voice coil inductance is significantly reduced compared to a design with a conductive magnetic central pole arranged close to the voice coil.

[0078] Therefore, the magnetic member 850 and the cap-shaped portion 815 provide a synergistic effect by significantly reducing the voice coil inductance during the inward displacement of the voice coil 825, primarily via the magnetic pole member 850. Furthermore, by arranging the cap-shaped portion 215 above the top of the air gap 820, the slight increase in residual voice coil inductance during inward displacement is compensated, causing the voice coil inductance to increase during the outward displacement of the voice coil 825. In other words, the combination of the cap-shaped portion 815 with the permanent magnet 850 within the central pole piece is perfectly suited for this purpose due to the small AC permeability of the permanent magnet.

[0079] Figure 8B A schematic axial cross-sectional view of an eighth embodiment of a motor 800 for an electrodynamic loudspeaker (not shown) is shown. Those skilled in the art will understand that this motor can be substantially the same as the motor 800 of the seventh embodiment described above in terms of materials and dimensions, except for the details of the conductive magnetic top plate 835. The difference between the eighth and seventh embodiments of the motor 800 is that the conductive magnetic top plate 835 can be considered integrated into the conductive magnetic member 840, such that the top portion of the conductive magnetic member extends upward to the top of the air gap 820. This means that the outer peripheral wall of the annular air gap 820 is formed by the uppermost section of the conductive magnetic member 840. Alternatively, those skilled in the art can consider this eighth embodiment as a motor design without any conductive magnetic top plate. Those skilled in the art will understand that at least some of the various embodiments of the motor described above can have similar integration of corresponding conductive magnetic top plates and conductive magnetic members.

[0080] Figure 9A schematic axial cross-sectional view of an exemplary electrodynamic loudspeaker 979 incorporating a motor according to any one of the embodiments of motors 200, 300, 400, 500, 600, 700, and 800 described above is shown. The electrodynamic loudspeaker 979 or driver generally includes a frame 971 mounted to a motor 900 and a diaphragm 975. The diaphragm 975 is attached to or coupled to the frame 971 by a flexible surrounding portion 976, which may include an outer edge 984 of a peripherally upward-oriented circular surface bonded to or otherwise fixedly attached to the frame 971. This causes the diaphragm 975 to vibrate in response to the vibration of a voice coil 925. The voice coil 925 may be supported by a hollow cylindrical molding 974, which is also attached to a voice coil spider 973. The voice coil positioner 973 is a flexible, corrugated support that holds the voice coil 925 at the center of the air gap 920 of the motor 900 while allowing the voice coil 925 to move freely in both upward and downward directions. The voice coil positioner 973 can be attached to the outer surface of the molded part 974 and the voice coil positioner platen 983 located on the inner portion of the frame 971 by various means, such as adhesives. In the embodiments described herein, the frame 971 has a generally circular shape. However, in other embodiments, the frame 971 and other elements of the speaker 979 can be of different forms, such as rectangular or elliptical profiles or shapes. The molded part 974 can be securely attached to the inner circular surface area of ​​the diaphragm 975 by adhesives or other bonding mechanisms. The diaphragm 975 can be made of any suitable material (such as fabric, plastic, paper, or lightweight metal) having sufficient rigidity and weight. The frame 971 can be made of any suitable material (such as metallic or non-metallic materials).

[0081] Figure 10A graph comparing the voice coil inductance at 1 Hz with the inward and outward displacement of the voice coil, simulated by finite element analysis modeling of a motor design 800 according to the eighth embodiment of the present invention and a corresponding motor design without the magnetically conductive "cap" 215. The x-axis represents the sound displacement relative to its rest or neutral position, in millimeters. The y-axis represents the voice coil inductance at 1 Hz, in mH. The curve drawn with a solid line represents the simulated inductance of the motor design according to the eighth embodiment, which includes the magnetically conductive outwardly protruding protrusion or "cap". The curve drawn with a dashed line represents the simulated inductance of the same motor design but without the magnetically conductive "cap" 215. It is clear from the first curve 1010 that, with a peak-to-peak displacement range of 10 mm around the voice coil in its rest position (x = 0), the inductance change of the voice coil in the eighth embodiment is only about 0.1 mH. It is evident from the second dashed curve, which does not have a "cap-like" section, that the inductance of the voice coil changes much more significantly and by approximately 0.32 mH within the same peak-to-peak displacement range of 10 mm around the voice coil when it is in a stationary position (X=0).

[0082] Figure 11 A graph showing the force factor (i.e., B*l product) versus the inward and outward displacement of the voice coil, simulated by finite element analysis, for an exemplary motor design or structure according to an eighth embodiment of the present invention. The x-axis represents the sound displacement relative to its rest or neutral position, in millimeters. The y-axis represents the force factor. The first curve 1110 represents the simulated B*l product of a motor design including a magnetically conductive, outwardly projecting protrusion or "cap" disposed above the top of the air gap (i.e., outside the top of the air gap). The second curve 1120 represents the simulated B*l product of a motor design of the same type but without the magnetically conductive "cap" 215.

Claims

1. A motor for an electric loudspeaker, the motor comprising: A magnetic circuit assembly, arranged around a motor axis, includes: a magnetically conductive top plate; a magnetically conductive bottom plate; a magnetically conductive member disposed between the magnetically conductive top plate and the magnetically conductive bottom plate and magnetically connected to the magnetically conductive top plate and the magnetically conductive bottom plate; a central pole piece; and an air gap for accommodating a voice coil. The air gap is formed by the inner axially extending wall of the conductive magnetic top plate, and the inner axially extending wall faces the axially extending peripheral wall section of the central pole piece to define the width, bottom, top and height of the air gap. An outwardly extending, magnetically conductive cap-shaped portion is positioned above the top of the air gap; The central pole piece includes a permanent magnet extending axially from at least the bottom of the air gap to the conductive magnetic base plate, wherein the height of the permanent magnet is at least 0.5 times the height of the conductive magnetic member, and wherein the permanent magnet exhibits a relative AC permeability of less than 10. The magnetic circuit assembly is configured such that, when measured at 31 Hz, the change in inductance of the voice coil is less than 10% within a predetermined displacement range defined by outward and inward displacement limits, and wherein the displacement range corresponds to 0.5 times the difference between the height of the voice coil and the height of the air gap.

2. The motor for an electric loudspeaker according to claim 1, wherein, The permanent magnet is a neodymium magnet or a ferrite magnet.

3. The motor for an electric loudspeaker according to claim 1, wherein, The height of the permanent magnet is 0.7 times or 0.9 times the height of the magnetically conductive component.

4. The motor for an electric loudspeaker according to claim 1, wherein, The permanent magnet of the central pole piece extends outward to the top of the air gap to define the axially extending peripheral wall section of the central pole piece.

5. The motor for an electric loudspeaker according to claim 1, wherein, The central pole piece includes a magnetically conductive top component; The magnetically conductive top member extends axially from the bottom of the air gap to the top of the air gap to define the axially extended peripheral wall section of the central pole piece.

6. The motor for an electric loudspeaker according to claim 5, wherein, The outwardly extending conductive magnetic cap-shaped portion is arranged inside the outwardly extending plane or surface defined by the axially extending peripheral wall section of the central pole piece.

7. The motor for an electric loudspeaker according to claim 5, wherein, The magnetically conductive top component and the outwardly extending magnetically conductive cap-shaped portion are integrally formed from a single piece of magnetically conductive material.

8. The motor for an electric loudspeaker according to claim 6, wherein, The magnetically conductive top component and the outwardly extending magnetically conductive cap-shaped portion are integrally formed from a single piece of magnetically conductive material.

9. The motor for an electric loudspeaker according to claim 7, wherein, The magnetically conductive top component includes the axially extending peripheral wall section defining the central pole piece and the disc-shaped or columnar element extending outward into the magnetically conductive cap-like portion.

10. The motor for an electric loudspeaker according to claim 8, wherein, The magnetically conductive top component includes the axially extending peripheral wall section defining the central pole piece and the disc-shaped or columnar element extending outward into the magnetically conductive cap-like portion.

11. The motor for an electric loudspeaker according to claim 1, wherein, The outwardly extending conductive magnetic cap-like portion defines a recessed outer wall relative to the axially extending peripheral wall section of the central pole piece.

12. The motor for an electric loudspeaker according to any one of claims 9 to 11, further comprising a non-magnetic spacer disposed between the top of the central pole piece and the outwardly extending conductive magnetic cap-like portion.

13. The motor for an electric loudspeaker according to any one of claims 1 to 11, wherein, The outwardly extending conductive magnetic cap-shaped portion is located outside the outwardly extending plane defined by the inner axially extending wall of the conductive magnetic top plate.

14. The motor for an electric loudspeaker according to any one of claims 1 to 11, further comprising at least one of the following: - A conductive ring disposed below the bottom of the air gap and surrounding the central electrode; and - A conductive ring disposed above the top of the air gap and surrounding the outwardly extending magnetically conductive cap-like portion, the conductive ring being inside the outwardly extending plane or surface defined by the axially extending peripheral wall section of the central pole piece.

15. The motor for an electric loudspeaker according to any one of claims 1 to 11, wherein, The height of the outwardly extending magnetic cap-shaped portion is at least 1.5 times the height of the magnetic top plate.

16. The motor for an electric loudspeaker according to any one of claims 1 to 11, wherein, When measured in a plane perpendicular to the axis of the central motor, the cross-sectional area of ​​the conductive magnetic component is less than half the cross-sectional area of ​​the central pole piece.

17. The motor for an electric loudspeaker according to any one of claims 1 to 11, wherein, At least one of the magnetically conductive top plate and the magnetically conductive bottom plate is integrally formed with the magnetically conductive component.

18. The motor for an electric loudspeaker according to claim 7 or 8, wherein, The magnetically conductive material is a ferromagnetic material.

19. The motor for an electric loudspeaker according to claim 18, wherein, The ferromagnetic material is CR1010 steel.

20. The motor for an electric loudspeaker according to claim 16, wherein, When measured in a plane perpendicular to the axis of the central motor, the cross-sectional area of ​​the conductive magnetic component is less than one-third of the cross-sectional area of ​​the central pole piece.

21. The motor for an electric loudspeaker according to any one of claims 1 to 11, wherein, The change in inductance of the voice coil is less than 7.5%.

22. The motor for an electric loudspeaker according to any one of claims 1 to 11, wherein, The change in inductance of the voice coil is less than 5%.

23. An electrodynamic loudspeaker, comprising: - Framework; - The motor according to any one of claims 1 to 22; - A movable diaphragm is attached to the voice coil, which is arranged in the air gap of the motor.

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