PATENT DOCUMENT

Publication Number: US-9571936-B2
Application Number: US-201514702623-A
Country: US
Kind Code: B2

Title: Audio speaker having a high-saturation magnetic insert

Abstract:
An audio speaker having a magnetic system that includes a magnetic insert in a recess of a bottom plate, is disclosed. More particularly, embodiments of the magnetic system include a magnetic insert having a higher magnetic saturation level than the bottom plate. Other embodiments are also described and claimed.

Claims:
What is claimed is: 
     
       1. An audio speaker, comprising:
 a bottom plate having a support face and a recess, wherein the recess includes a recessed face below the support face, and wherein the bottom plate includes a first magnetic material having a first magnetic saturation level; 
 a center magnet on the support face and over the recess; 
 a lateral magnet on the support face and over the recess, the lateral magnet radially separated from the center magnet by a magnet gap; 
 a voicecoil for driving a diaphragm, the voicecoil aligned with the magnet gap; and 
 a magnetic insert in the recess on the recessed face, the magnetic insert below the lateral magnet and the center magnet to form a magnetic flux path from the lateral magnet to the center magnet, wherein the magnetic insert includes a second magnetic material having a second magnetic saturation level greater than the first magnetic saturation level. 
 
     
     
       2. The audio speaker of  claim 1 , wherein the magnetic insert includes an upper face overlapping respective lower faces of the lateral magnet and the center magnet to form the magnetic flux path from the lateral magnet into a first overlapping portion of the upper face and from a second overlapping portion of the upper face to the center magnet. 
     
     
       3. The audio speaker of  claim 2 , wherein the first overlapping portion of the magnetic insert is in contact with the lateral magnet. 
     
     
       4. The audio speaker of  claim 3 , wherein the recess is in the support face such that the support face and the recessed face both face a forward direction. 
     
     
       5. The audio speaker of  claim 3 , wherein the recess is in a rear face of the bottom plate opposite from the support face such that the support face faces a forward direction and the recessed face faces a rearward direction. 
     
     
       6. The audio speaker of  claim 2 , wherein the upper face includes a radial width between an outer edge under the lateral magnet and an inner edge, and wherein the radial width is wider than the magnet gap between the lateral magnet and the center magnet. 
     
     
       7. The audio speaker of  claim 6 , wherein the magnetic insert includes a thickness less than 1.5 mm. 
     
     
       8. The audio speaker of  claim 7 , wherein the upper face is ring-shaped such that the inner edge defines a central opening under the center magnet. 
     
     
       9. The audio speaker of  claim 2 , wherein the magnetic insert includes a laminate structure having a first layer and a second layer, and wherein the first layer is on the recessed face and the second layer is on the first layer. 
     
     
       10. The audio speaker of  claim 9 , wherein the first layer includes a first width, and wherein the second layer includes a second width different than the first width. 
     
     
       11. The audio speaker of  claim 2 , wherein the first magnetic material includes a magnetic steel material, and wherein the second magnetic material includes a high-saturation magnetic material. 
     
     
       12. The audio speaker of  claim 11 , wherein the second magnetic saturation level is at least 10% greater than the first magnetic saturation level. 
     
     
       13. The audio speaker of  claim 12 , wherein the high-saturation magnetic material is an iron-cobalt alloy. 
     
     
       14. An audio speaker, comprising:
 a voicecoil for driving a diaphragm along a central axis, the voicecoil disposed in a magnetic gap of a top plate; 
 a bottom plate having a support face and a plurality of recesses, each recess providing a radial gap between a central region of the support face and a lateral region of the support face, wherein the bottom plate includes a first magnetic material having a first magnetic saturation level; 
 a center magnet disposed between the top plate and the bottom plate on the central region; 
 a plurality of lateral magnets disposed between the top plate and the bottom plate on the lateral region, the lateral magnets disposed around the center magnet; and 
 a plurality of magnetic inserts in respective recesses of the plurality of recesses, each magnetic insert forming a magnetic flux path from a respective lateral magnet to the center magnet through a respective radial gap, wherein the magnetic insert includes a second magnetic material having a second magnetic saturation level greater than the first magnetic saturation level. 
 
     
     
       15. The audio speaker of  claim 14 , wherein the lateral magnets are symmetrically disposed around the center magnet. 
     
     
       16. The audio speaker of  claim 15 , wherein the plurality of recesses include one or more recessed faces facing a same direction as the support face. 
     
     
       17. The audio speaker of  claim 15 , wherein the plurality of recesses include one or more recessed faces facing an opposite direction as the support face.

Description:
BACKGROUND 
     Field 
     Embodiments related to audio speakers are disclosed. More particularly, an embodiment related to an audio speaker, which includes a magnetic system having a magnetic insert in a recess of a bottom plate, is disclosed. The magnetic insert may have a higher magnetic saturation level than the bottom plate. 
     Background Information 
     An audio speaker, such as a loudspeaker, converts an electrical audio input signal into an emitted sound. Audio speakers typically include a moving assembly that oscillates relative to a stationary assembly. For example, the moving assembly may include a diaphragm connected to a driving element, such as voicecoil. The stationary assembly may include a magnetic system having magnetic components, e.g., one or more permanent magnets sandwiched between a top plate and a bottom plate, to form a magnetic circuit through which a magnetic flux travels. More particularly, when an electrical audio input signal is input to the voicecoil, the electrical current reacts with a magnetic field of the magnetic system, and generates a mechanical force that moves the moving assembly from a neutral position in an axial direction relative to the stationary assembly. 
     SUMMARY 
     Electronic devices having audio speakers are becoming more compact, and as the form factors of these devices shrink, the space available for the audio speaker also reduces. Accordingly, the size of the magnetic system components must be reduced to fit within the audio speaker enclosure. However, as the magnetic components are miniaturized, e.g., as a top plate or a bottom plate of the magnetic circuit becomes thinner, the thinner magnetic components are unable to contain the applied magnetic field within the component cross-section. That is, when the magnetic field in the thinner component reaches a saturation limit, e.g., when the entire cross-section is saturated by the magnetic field, magnetic flux tends to leak out of the magnetic circuit into a surrounding environment. In some cases, this stray flux can leak into nearby low coercivity items, e.g., hotel keys, gift cards, and parking tickets. The stray flux may then cause the low coercivity items to demagnetize and lose stored data. Thus, a magnetic system having components with higher saturation limits may allow the magnetic field in the magnetic system to be increased and the stray magnetic flux to be reduced within a compact form factor. The increased magnetic field may generate a larger mechanical force on the voicecoil to improve acoustic performance of the audio speaker, and the reduced stray magnetic flux may prevent demagnetization of nearby magnetic strip cards. 
     In an embodiment, an audio speaker includes a magnetic circuit through one or more magnets and a magnetic insert in a bottom plate. The bottom plate may have a support face and a recess. A center magnet and a lateral magnet may be located on the support face over the recess and be radially separated from each other by a magnet gap aligned with a voicecoil to drive a diaphragm. The recess may include a recessed face below the support face, and the recess may be in the support face and/or a rear face of the bottom plate, opposite from the support face, such that the recessed face faces a same direction as the support face, i.e., a forward direction, and/or an opposite direction as the support face, i.e., a rearward direction. Thus, a magnetic insert may be located in the recess on the recessed face below the lateral magnet and the center magnet. Both the bottom plate and the magnetic insert may include a magnetic material, and the magnetic materials may differ. For example, the bottom plate may be formed from a magnetic steel material and the magnetic insert may be formed from a high-saturation magnetic material, e.g., an iron-cobalt (FeCo) alloy such as Hiperco®, Vacoflux®, or similar high permeability FeCo alloys. Thus, the magnetic saturation level of the magnetic insert may be greater, e.g., at least 10% greater, than the magnetic saturation level of the bottom plate. Accordingly, the magnetic insert may form a preferential magnetic flux path from the lateral magnet to the center magnet to contain the magnetic field within the audio speaker. 
     The magnetic system components may have a variety of relative positions and configurations. For example, the magnetic insert may include an upper face overlapping respective lower faces of the lateral magnet and the center magnet. The upper face may include a radial width between an outer edge under the lateral magnet and an inner edge, and the radial width may be wider than the magnet gap between the lateral magnet and the center magnet. Thus, the magnetic flux path may be directed from the lateral magnet into a first overlapping portion of the upper face and from a second overlapping portion of the upper face to the center magnet. In an embodiment, the overlapping portions of the magnetic insert may be in contact with the lateral magnet and/or the center magnet such that the magnetic flux path transitions directly from the magnets into the magnetic insert. 
     The magnetic insert may have a variety of shapes and dimensions. For example, the magnetic insert may have a thin, annular structure. Accordingly, the magnetic insert may have a thickness less than 1.5 mm. Furthermore, in an embodiment, the upper face of the magnetic insert may be ring-shaped such that the inner edge defines a central opening under the center magnet. 
     The magnetic insert may have a variety of structural configurations. For example, the magnetic insert may have a laminate structure that includes two or more layers. A first layer of the laminate structure may be located on the recessed face of the recess, and a second layer of the laminate structure may be located on the first layer. The layers may have differing widths. For example, the first layer may have a different width than the second layer, resulting in a cross-sectional profile with a stepped or tapered sidewall. 
     In an embodiment, an audio speaker includes a bottom plate with several recesses that provide radial gaps between a central region of the support face and a lateral region of the support face. The center magnet may be disposed on the central region and several lateral magnets may be disposed on the lateral region around the center magnet. Furthermore, several magnetic inserts may be located in respective recesses of the bottom plate to form a magnetic flux path from a respective lateral magnet to the center magnet through respective radial gaps of the recesses. The lateral magnets may be symmetrically disposed around the center magnet to generate a symmetric magnetic field. Furthermore, as described above, the recesses may include respective recessed faces that face a same or opposite direction as the support face. 
     In an embodiment, a method of fabricating an audio speaker includes forming a plate from a magnetic material, e.g., magnetic steel. The plate may include a support face and a recess. For example, forming the plate may include pressing the recess into the plate. The method further includes cutting a magnetic insert from a sheet of magnetic material, e.g., a high permeability FeCo alloy. For example, cutting the magnetic insert may include die-cutting the magnetic insert from the sheet of magnetic material. In an embodiment, the sheet of magnetic material is from a rolled sheet of magnetic material. The magnetic saturation levels of the plate and the magnetic insert may differ. For example, the magnetic saturation level of the magnetic insert may be greater than the magnetic saturation level of the plate. The method may further include inserting the magnetic insert into the recess and attaching one or more magnets to the support face. For example, the magnetic insert may be placed on a recessed face in the recess and a magnet may be attached adjacent to the support face. Accordingly, the magnetic insert in the recess may be disposed near the magnet to form a magnetic flux path from the magnet. 
     In an embodiment, an audio speaker includes a magnetic insert in a plate. The plate may have a support face and a recess. A magnet may be located adjacent to the support face and aligned with a voicecoil. The voicecoil may drive a diaphragm such that the voicecoil moves the diaphragm when a current in the voicecoil creates a first magnetic field that interacts with a second magnetic field created by the magnet. The recess may include a recessed face below the support face. Thus, a magnetic insert may be located in the recess on the recessed face, and be disposed near the magnet to form a magnetic flux path from the magnet. For example, the magnetic insert may be in contact with the magnet. Both the plate and the magnetic insert may include a magnetic material, and the magnetic materials may differ. For example, the plate may be formed from a magnetic steel material and the magnetic insert may be formed from a high-saturation magnetic material, e.g., an FeCo alloy such as Hiperco®, Vacoflux®, or similar high permeability FeCo alloys. Thus, the magnetic saturation level of the magnetic insert may be greater, e.g., at least 10% greater, than the magnetic saturation level of the plate. 
     The above summary does not include an exhaustive list of all aspects of the present invention. It is contemplated that the invention includes all systems and methods that can be practiced from all suitable combinations of the various aspects summarized above, as well as those disclosed in the Detailed Description below and particularly pointed out in the claims filed with the application. Such combinations have particular advantages not specifically recited in the above summary. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a pictorial view of an electronic device in accordance with an embodiment. 
         FIG. 2  is a schematic view of an electronic device having an audio speaker in accordance with an embodiment. 
         FIG. 3  is a perspective view of an audio speaker in accordance with an embodiment. 
         FIG. 4  is a cross-sectional view, taken about line A-A of  FIG. 3 , of an audio speaker in accordance with an embodiment. 
         FIG. 5  is a detail view, taken from Detail A of  FIG. 4 , of a magnetic flux path through an audio speaker in accordance with an embodiment. 
         FIG. 6  is a cross-sectional view, taken about line A-A of  FIG. 3 , of an audio speaker in accordance with an embodiment. 
         FIG. 7  is a cross-sectional view, taken about line A-A of  FIG. 3 , of an audio speaker in accordance with an embodiment. 
         FIG. 8  is a detail view, taken from Detail B of  FIG. 6 , of a magnetic flux path through an audio speaker in accordance with an embodiment. 
         FIG. 9  is a cross-sectional view, taken about line B-B of  FIG. 6 , of a magnetic system of an audio speaker in accordance with an embodiment. 
         FIG. 10  is a cross-sectional view, taken about line C-C of  FIG. 6 , of a magnetic insert of an audio speaker in accordance with an embodiment. 
         FIG. 11  is a cross-sectional view, taken about line C-C of  FIG. 6 , of a magnetic insert of an audio speaker in accordance with an embodiment. 
         FIG. 12  is a cross-sectional view, taken about line C-C of  FIG. 6 , of a magnetic insert of an audio speaker in accordance with an embodiment. 
         FIG. 13  is a perspective view of a bottom plate of an audio speaker in accordance with an embodiment. 
         FIG. 14  is a detail view, taken from Detail C of  FIG. 6 , of a magnetic insert in a recess of an audio speaker in accordance with an embodiment. 
         FIG. 15  is a detail view, taken from Detail C of  FIG. 6 , of a magnetic insert in a recess of an audio speaker in accordance with an embodiment. 
         FIG. 16  is a detail view, taken from Detail C of  FIG. 6 , of a magnetic insert in a recess of an audio speaker in accordance with an embodiment. 
         FIG. 17  is a flowchart of a method of manufacturing an audio speaker having a high-saturation magnetic insert in a recess of a bottom plate in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments describe audio speakers having magnetic systems that include a magnetic insert in a recess of a bottom plate, particularly for use in audio speaker applications. The magnetic insert may have a higher magnetic saturation level than the bottom plate. Some embodiments are described with specific regard to integration within mobile electronics devices having audio speakers, however, the embodiments are not so limited and certain embodiments may also be applicable to other uses. For example, an audio speaker as described below may be incorporated into other devices and apparatuses, including desktop computers, laptop computers, or motor vehicles, to name only a few possible applications. 
     In various embodiments, description is made with reference to the figures. Certain embodiments, however, may be practiced without one or more of these specific details, or in combination with other known methods and configurations. In the following description, numerous specific details are set forth, such as specific configurations, dimensions, and processes, in order to provide a thorough understanding of the embodiments. In other instances, well-known processes and manufacturing techniques have not been described in particular detail in order to not unnecessarily obscure the description. Reference throughout this specification to “one embodiment,” “an embodiment,” or the like, means that a particular feature, structure, configuration, or characteristic described is included in at least one embodiment. Thus, the appearance of the phrase “one embodiment,” “an embodiment,” or the like, in various places throughout this specification are not necessarily referring to the same embodiment. Furthermore, the particular features, structures, configurations, or characteristics may be combined in any suitable manner in one or more embodiments. 
     The use of relative terms throughout the description, such as “forward” and “rearward” may denote a relative position or direction. For example, a direction may be described as being “forward” from a diaphragm to denote a direction that sound propagates from the diaphragm toward a speaker port, while a “rearward direction” may be opposite to the forward direction. Nonetheless, such terms are not intended to limit the use of an audio speaker to a specific configuration described in the various embodiments below. For example, an audio speaker may be directed in any direction with respect to an external environment, including such that sound is directed upward, downward, sideways, etc., relative to a listener. 
     In an aspect, an audio speaker includes a magnetic system that provides a magnetic circuit that supports an increased magnetic field. More particularly, the magnetic system includes a high-saturation magnetic insert in a bottom plate, and the magnetic insert has a higher magnetic saturation level than the bottom plate. Furthermore, the magnetic insert may be shaped to cover saturation hot spots, e.g., at a location where a magnet corner would contact the bottom plate in the absence of the insert, to specifically increase the magnetic saturation level of those locations. Accordingly, the magnetic system supports a higher magnetic field before saturating, which may result in a higher drive factor and an improved acoustic performance for the audio speaker. 
     In an aspect, an audio speaker having a high-saturation magnetic insert covering saturation hot spots constrains the magnetic field within a magnetic flux path between opposing magnets of the magnetic system. For example, the magnetic insert may provide a flux bridge between a lateral magnet on one side of a magnetic gap and a center magnet on another side of the magnetic gap. Furthermore, the higher magnetic saturation level of the magnetic insert may reduce the likelihood of the saturation hot spots or the cross-section of the magnetic system becoming magnetically saturated. Thus, the magnetic flux may be constrained within the magnetic system between the offset magnets rather than leaking into the surrounding environment. Accordingly, the likelihood that stray flux will demagnetize low coercivity items, e.g., hotel keys, gift cards, parking tickets, etc., near the audio speaker may be reduced. 
     In an aspect, a method of manufacturing an audio speaker having a high-saturation magnetic insert to increase acoustic performance and decrease stray flux within a compact form factor is provided. Rather than forming an entire bottom plate of the audio speaker from high magnetic saturation material, which may be difficult to shape and costly to make, a high-saturation magnetic insert may be cut, e.g., die-cut, from a sheet of high saturation magnetic material, and inserted into the most critical regions of a stamped or forged bottom plate. Stamping and forging are known processes that may be used to mass produce bottom plates and die-cutting may be used for mass producing high-saturation magnetic inserts for a magnetic system of an audio speaker in a cost-efficient manner. The recess in the bottom plate may be formed either by forging, stamping, or by chemically etching a stamped plate. Furthermore, by inserting the magnetic insert into recesses in the bottom plate, the z-height of the bottom plate and the audio speaker may be limited. 
     Referring to  FIG. 1 , a pictorial view of an electronic device is shown in accordance with an embodiment. Electronic device  100  may be a smartphone device. Alternatively, it could be any other portable or stationary device or apparatus, such as a laptop computer or a tablet computer. Electronic device  100  may include various capabilities to allow the user to access features involving, for example, calls, voicemail, music, e-mail, internet browsing, scheduling, and photos. Electronic device  100  may also include hardware to facilitate such capabilities. For example, an integrated microphone  102  may pick up the voice of a user during a call, and an audio speaker  106 , e.g., a micro speaker, may deliver a far-end voice to the near-end user during the call. Audio speaker  106  may also emit sounds associated with music files played by a music player application running on electronic device  100 . A display  104  may present the user with a graphical user interface to allow the user to interact with electronic device  100  and/or applications running on electronic device  100 . Other conventional features are not shown but may of course be included in electronic device  100 . 
     Referring to  FIG. 2 , a schematic view of an electronic device having an audio speaker is shown in accordance with an embodiment. As described above, electronic device  100  may be one of several types of portable or stationary devices or apparatuses with circuitry suited to specific functionality. Thus, the diagrammed circuitry is provided by way of example and not limitation. Electronic device  100  may include one or more processors  202  that execute instructions to carry out the different functions and capabilities described above. Instructions executed by the one or more of processors  202  of electronic device  100  may be retrieved from a local memory  204 , and may be in the form of an operating system program having device drivers, as well as one or more application programs that run on top of the operating system, to perform the different functions introduced above, e.g., phone or telephony and/or music play back. For example, processor(s)  202  may directly or indirectly implement control loops and provide drive signals to a voicecoil of audio speaker  106  to drive a diaphragm motion and generate sound. 
     Referring to  FIG. 3 , a perspective view of an audio speaker is shown in accordance with an embodiment. An audio speaker  106  may be any type of loudspeaker. For example, audio speaker  106  may be a micro speaker. A micro speaker, also known as a microdriver, is a miniaturized implementation of a loudspeaker having a broad frequency range. Thus, audio speaker  106  may have a small form factor defined by an exterior surface of a housing  302 , a diaphragm  304 , and a surround  306  supporting the diaphragm relative to housing  302 . These components may have various geometries that combine to create an outer envelope of audio speaker  106 , and although the outer envelope is represented in  FIG. 3  as having essentially a rectangular cuboid shape, the outer envelope may be other shapes, e.g., cylindrical, to facilitate placement of audio speaker  106  within a corresponding internal space of electronic device  100 . 
     Referring to  FIG. 4 , a cross-sectional view, taken about line A-A of  FIG. 3 , of an audio speaker  106  is shown in accordance with an embodiment. The outer envelope of audio speaker  106  may surround a moving assembly and a stationary assembly. In an embodiment, the moving assembly includes the portion of audio speaker  106  that moves in conjunction with diaphragm  304  during sound generation. For example, the moving assembly may include surround  306 , diaphragm  304 , and a voicecoil  402 . Surround  306  may flex and deflect when diaphragm  304  oscillates along a central axis  404  during music or voice reproduction by electronic device  100 . Similarly, voicecoil  402  may be connected to diaphragm  304  to move and impart the driving force that causes diaphragm  304  to oscillate along central axis  404 . 
     In an embodiment, the stationary assembly of audio speaker  106  includes a magnetic system, which generates a magnetic field through which voicecoil  402  moves during sound creation. The magnetic system may include one or more magnets in a magnetic circuit. For example, each magnet may generate a magnetic field between opposing poles. In an embodiment, a center magnet  406  is laterally offset from one or more lateral magnets  410 . Center magnet  406  and lateral magnet(s)  410  may be permanent magnets, having respective opposite poles (denoted as “N” and “S” for “north” and “south” in  FIG. 4 ). Furthermore, the magnetic circuit may include a top plate  412  and a bottom plate  414  near respective poles of the magnets. Top plate  412  and bottom plate  414  may be formed from magnetic materials, e.g., magnetic steel, such that the magnetic field is directed through top plate  412  and bottom plate  414  between poles of the offset magnets. For example, magnetic flux may be directed along a path from an upper pole, e.g., a “north” pole, of center magnet  406 , into an inner region of top plate  412  intersected by central axis  404  and across a magnetic gap  408  to an outer region of top plate  412  radially outward of the inner region and near an upper pole, e.g., a “south” pole, of lateral magnet  410 . The magnetic flux path may be directed to an opposite pole of lateral magnet  410 , e.g., a “north” pole, and into bottom plate  414  toward the opposite pole, e.g., a “south” pole, of center magnet  406 . The magnetic field may be distributed through center magnet  406 , top plate  412 , lateral magnet  410 , and bottom plate  414  such that magnetic flux is concentrated in a radial direction across magnetic gap  408  within which voicecoil  402  is located. As such, when an electrical audio input signal is input to voicecoil  402 , the electrical current travels orthogonal to the magnetic flux (into or out of the page) in magnetic gap  408  and reacts with the magnetic field to generate the driving force that moves the moving assembly from a neutral position in an axial direction along central axis  404 . 
     Referring to  FIG. 5 , a detail view, taken from Detail A of  FIG. 4 , of a magnetic flux path through an audio speaker is shown in accordance with an embodiment. The magnetic system of audio speaker  106  may include transition points at which magnetic flux is directed from one magnetic component, e.g., lateral magnet  410 , into another magnetic component, e.g., bottom plate  414 . For example, a lower face  502  of lateral magnet  410  may be disposed on bottom plate  414 , and thus, a radially inward edge or corner of lateral magnet  410  may be in contact with an upper surface of bottom plate  414 . Furthermore, the magnetic field generated by the magnetic system may seek the shortest and/or least magnetically resistant path, and thus, the magnetic circuit may include a magnetic flux path  504  that converges at the corner, as shown. Each component of the magnetic circuit, however, includes a respective magnetic saturation level, which is the material state at which an increase in the magnetic field does not create a significant increase in the magnetic flux density. That is, as the magnetic field strength increases, the magnetic flux density in the bottom plate  414  at the junction of bottom plate  414  and the corner of lateral magnet  410  may reach a peak, and a continued increase in magnetic field causes magnetic flux path  504  to be directed along an alternate route between lateral magnet  410  and center magnet  406 . The magnetic flux path  504  may grow across a thickness of bottom plate  414  because the permeability of bottom plate  414  may be higher than a material, e.g., air, above or below bottom plate  414 . The bottom plate  414  may be a more attractive path for the magnetic flux due to this difference in magnetic permeability. Thus, magnetic flux path  504  may remain constrained within bottom plate  414  until the magnetic field is increased to a point at which a cross-section of bottom plate  414  is magnetically saturated. After the entire thickness of bottom plate  414  is saturated, however, magnetic flux may travel out of bottom plate  414  along a stray flux path  506  toward center magnet  406 . Accordingly, some of the magnetic field that is directed along stray flux path  506  may escape housing  302 . The escaped magnetic field may negatively affect nearby objects, e.g., by demagnetizing low coercivity objects. 
     Referring to  FIG. 6 , a cross-sectional view, taken about line A-A of  FIG. 3 , of an audio speaker is shown in accordance with an embodiment. An audio speaker  106  may include a magnetic system that allows the magnetic field to be increased without magnetically saturating components and causing stray flux to leak out of housing  302 . In an embodiment, audio speaker  106  is a micro speaker and includes the moving assembly components described above, i.e., diaphragm  304  arranged along central axis  404 , surround  306  supporting diaphragm  304  relative to housing  302 , and voicecoil  402  to move diaphragm  304  in a forward direction  602  and a rearward direction  606  during sound generation. Voicecoil  402  may be disposed within magnetic gap  408  of a stationary assembly of audio speaker  106 . More particularly, audio speaker  106  may include a magnetic system to generate a magnetic field, e.g., between center magnet  406  and lateral magnet(s)  410 , and magnetic flux of the magnetic field may be concentrated in magnetic gap  408  between inner and outer regions of top plate  412 . Voicecoil  402  may be located within the magnetic gap  408 . Additionally, center magnet  406  and lateral magnet  410  may be spaced apart from each other by a magnet gap  608 . For example, magnet gap  608  may be an air gap that radially separates lateral magnet  410  from center magnet  406 . In an embodiment, magnet gap  608  may be behind magnetic gap  408 , and thus, voicecoil  402  may be aligned with magnet gap  608  and/or be disposed within magnet gap  608 , i.e., in rearward direction  606  from magnetic gap  608  at a location radially offset from central axis  404  between lateral magnet  410  and center magnet  406 . 
     The magnetic field may circulate from a lower pole, e.g., a north pole, of lateral magnet  410  to a lower pole, e.g., a south pole, of center magnet  406  below the magnetic gap  408 . For example, magnetic flux path  504  may be directed from lateral magnet  410  to center magnet  406  in a radial direction across magnetic gap  608 . More particularly, the magnetic field may be directed through a magnetic insert  604  that provides a magnetic flux path  504  from lateral magnet  410  to center magnet  406  (or vice versa, depending upon the orientation of the magnet poles). 
     In an embodiment, magnetic insert  604  is located on a same side of bottom plate  414  as lateral magnet  410  and center magnet  406 . For example, lateral magnet  410  and center magnet  406  may be disposed over a support face  610 , which is located on an upper surface of bottom plate  414 . More particularly, lateral magnet  410  may be located on, and may be supported by, an outer region of support face  610 . Center magnet  406  may be located on, and may be supported by, an inner region of support face  610 . Similarly, magnetic insert  604  may be located above bottom plate  414 . For example, magnetic insert  604  may be located in a recess  612  formed in support face  610  of bottom plate  414 . Recess  612  may for instance be stamped or otherwise formed in support face  610  in a shape and size to accommodate magnetic insert  604 . Recess  612 , therefore, may include a recessed face  614  below support face  610 , i.e., recessed face  614  may be axially offset from support face  610  in rearward direction  606 . Thus, recessed face  614  and support face  610  may both face a same direction, e.g., forward direction  602 . In an embodiment, magnetic insert  604  may be disposed in recess  612  on recessed face  614 , and thus, may include an upper surface facing in the same direction as support face  610  and recessed face  614 , e.g., in forward direction  602 . 
     In an embodiment, lateral magnet  410  and/or center magnet  406  may be located over recess  612 . Center magnet  406  may be disposed on support face  610  and may at least partially overlap with recess  612  over a radial distance. That is, an axis parallel to central axis  404 , but radially offset from central axis  404 , may intersect both center magnet  406  and recess  612 . Accordingly, in an embodiment in which magnetic insert  604  fills recess  612 , the parallel axis may also intersect magnetic insert  604 . Similarly, lateral magnet  410  may be disposed on support face  610  and may at least partially overlap with recess  612  over a radial distance. That is, another axis parallel to central axis  404 , but radially offset from central axis  404 , may intersect lateral magnet  410 , recess  612 , and magnetic insert  604  disposed in recess  612 . Therefore, at least a portion of center magnet  406  and/or lateral magnet  410  may overlap magnetic insert  604 . 
     Referring to  FIG. 7 , a cross-sectional view, taken about line A-A of  FIG. 3 , of an audio speaker is shown in accordance with an embodiment. In an embodiment, lateral magnet  410  and/or center magnet  406  may be located on an opposite side of bottom plate  414  from magnetic insert  604 . For example, lateral magnet  410  and center magnet  406  may be disposed on support face  610  above bottom plate  414 , and magnetic insert  604  may be located below bottom plate  414 . For example, magnetic insert  604  may be located in recess  612  formed in a rear face  702  of bottom plate  414 . Therefore, support face  610  may be facing forward direction  602  along central axis  404  and recessed face  614  of recess  612  may be facing another direction, e.g., recessed face  614  may be facing rearward direction  606  along central axis  404 . 
     In an embodiment, lateral magnet  410  and/or center magnet  406  may be located over recess  612 , but may be located on an opposite side of bottom plate  414  from magnetic insert  604 . Center magnet  406  and lateral magnet  410  may be disposed on support face  610  and recess  612  may be formed in rear face  702 , on an opposite side of bottom plate  414  than support face  610 . Accordingly, an axis parallel to central axis  404 , but radially offset from central axis  404 , may intersect both center magnet  406  and recess  612  (or both lateral magnet  410  and recess  612 ). The parallel axis may also intersect magnetic insert  604  in recess  612 . Thus, the magnets  406 ,  410  and the magnetic inserts  604  may be overlapping in the radial direction even though the components are not on the same side of bottom plate  414 . 
     In an embodiment, audio speaker  106  may include bottom plate  414  having recesses  612  in both support face  610  and rear face  702 . Furthermore, magnetic inserts  604  may be located in the recesses  612  on both sides of bottom plate  414 . Thus, outward facing surfaces of magnetic inserts  604  may be directed in both forward direction  602  and rearward direction  606 . In an embodiment, an axis parallel to central axis  404 , but radially offset from central axis  404 , may intersect one or both magnetic inserts  604  on opposite sides of bottom plate  414 . For example, a magnetic insert  604  in a recess  612  formed in support face  610  may overlap one or both of lateral magnet  410  and center magnet  406 , and thus, may be intersected by the axis. The magnetic insert  604  in a recess  612  in rear face  702 , however, may be narrower than the upper magnetic insert  604 , and thus, may not overlap or be directly under one or both magnets such that the axis intersects the magnets and the upper insert  604 , but not necessarily the lower magnetic insert  604 . 
     Referring to  FIG. 8 , a detail view, taken from Detail B of  FIG. 6 , of a magnetic flux path through an audio speaker is shown in accordance with an embodiment. Magnetic insert  604  located below lateral magnet  410  and/or center magnet  406  (on an upper and/or lower side of bottom plate  414 ) may form a magnetic flux path  504  from lateral magnet  410  to center magnet  406 . In an embodiment, the magnetic flux path  504  may be preferentially directed between the magnet, e.g., lateral magnet  410 , and magnetic insert  604  (directly or via an intervening portion of bottom plate  414 ). That is, although lateral magnet  410  may be located above and/or be placed in contact with both magnetic insert  604  and bottom plate  414 , magnetic flux path  504  may preferentially travel from lateral magnet  410  into magnetic insert  604 , rather than traveling from lateral magnet  410  to center magnet  406  entirely through bottom plate  414 . 
     The preferential distribution of the magnetic field through magnetic insert  604  may be controlled by the material used to form magnetic insert  604  and bottom plate  414 . In an embodiment, magnetic insert  604  may be formed from a material having a magnetic permeability higher than the magnetic permeability of the material used to form bottom plate  414 . Additionally, the material used to form magnetic insert  604  may include a magnetic saturation level greater than a magnetic saturation level corresponding to the material used to form bottom plate  414 . Accordingly, in an embodiment, magnetic flux is preferentially distributed in magnetic insert  604 , rather than the adjacent bottom plate  414 . The respective materials of magnetic insert  604  and bottom plate  414  may include any two magnetic materials having different magnetic properties. For example, bottom plate  414  may be formed from a magnetic steel, and magnetic insert  604  may be formed from a high-saturation magnetic material. A high-saturation magnetic material may be considered a material with a magnetic saturation level higher than magnetic steel. For example, a high-saturation magnetic material may include a magnetic saturation level that is at least 10% greater than the magnetic saturation level of magnetic steel. In an embodiment, magnetic insert  604  from high-saturation magnetic material includes a magnetic saturation level that is at least 20% greater than the magnetic saturation level of bottom plate  414 . By way of example and not limitation, magnetic insert  604  may be formed from such high-saturation magnetic materials as iron-cobalt (FeCo) alloys, e.g., Hiperco®, Vacoflux®, or similar high permeability FeCo alloys. For example, high permeability FeCo alloys include Hiperco® 27, Hiperco® 50, Vacoflux® 17, and Vacoflux® 50, all of which are known materials. These materials and other similar high-saturation magnetic materials may have a magnetic saturation point between 2.0-3.0 Tesla, e.g., between 2.3-2.4 Tesla, as compared to magnetic steel materials that may typically include a magnetic saturation point between 1.0-2.2 Tesla, e.g., between 1.7-2.1 Tesla. 
     In an embodiment, magnetic insert  604  overlaps a portion of lateral magnet  410  and/or center magnet  406 . For example, an overlapping portion  802  of the magnetic system may include a region where lower face  502  of lateral magnet  410  overlaps an upper face  806  of magnetic insert  604 . The overlapping portion of upper face  806  of magnetic insert  604  below center magnet  406  may be in contact with the overlapping portion of the lower face of lateral magnet  410 . Similarly, a lower face of center magnet  406  may overlap upper face  806  of magnetic insert  604  (not shown) to form an overlapping region where center magnet  406  overlaps magnetic insert  604 . The overlapping portion  802  of the upper face  806  of magnetic insert  604  may be in contact with the overlapping portion  802  of the lower face of center magnet  406 . As such, magnetic flux path  504  may travel from lower face  502  of lateral magnet  410  into upper face  806  of magnetic insert  604  where the faces overlap. Similarly, magnetic flux path  504  may travel from upper face  806  of magnetic insert  604  into a lower face  502  of center magnet  406  where the faces overlap (not shown). In an embodiment, a radial width of overlapping portion  802 , e.g., a radial distance between an inward corner or edge of lateral magnet  410  and an outward corner or edge of magnetic insert  604  under lateral magnet  410 , may be at least 0.5 mm. More particularly, magnetic insert  604  may have a thickness  808  in an axial direction, and the radial width of overlapping portion  802  may be at least half as wide as thickness  808  is thick. For example, in an embodiment, thickness  808  may be 1 mm, and thus, overlapping portions  802  of lateral magnet  410  and magnetic insert  604  may have a radial width  1008  of at least 0.5 mm, e.g., 1 mm or more. In an embodiment, thickness  808 , and optionally the radial distance of overlapping portion  802 , may be less than 3 mm. For example, in an embodiment in which magnetic insert  604  includes a single layer that is die-cut from a sheet of high-saturation magnetic material, thickness  808  may be less than 1.5 mm, or less than 0.050 inch. 
     Referring to  FIG. 9 , a cross-sectional view, taken about line B-B of  FIG. 6 , of a magnetic system of an audio speaker is shown in accordance with an embodiment. The description above focuses on a cross-section of the magnetic circuit through center magnet  406 , top plate  412 , lateral magnet  410 , and magnetic insert  604  (and/or bottom plate  414 ), along any given radial plane emanating from central axis  404 . The magnetic field, however, may be symmetric about central axis  404 . For example, the magnetic field may be ring-shaped, e.g., toroidal, when viewed in three-dimensional space, as when audio speaker  106  includes a magnetic system with several lateral magnets  410  disposed around center magnet  406 . Center magnet  406  may be located between top plate  412  (not shown) and bottom plate  414 . Thus, magnetic flux may be directed in forward direction  602  from center magnet  406  into top plate  412  and then conveyed through top plate  412  radially toward a nearest lateral magnet  410 . The lateral magnets  410  may be disposed between top plate  412  and bottom plate  414 . More particularly, bottom plate  414  may include a central region upon which center magnet  406  is located, and a lateral region upon which lateral magnets  410  are located. Thus, the magnetic field may be directed into lateral magnets  410  in rearward direction  606  from top plate  412 , and then complete the magnetic circuit by radiating inward from lateral magnets  410  toward center magnet  406  along bottom plate  414 . 
     Bottom plate  414  may include several recesses  612  that at least partly overlap with center magnet  406  and one or more lateral magnets  410 . The recesses  612  may be depressions, grooves, counterbores, countersinks etc., located in support face  610  on which the magnets sit, and thus, a perimeter of each recess  612  may provide a radial gap between the center region of support face  610  and the lateral region of support face  610 . As described above, bottom plate  414  may be formed from or otherwise include a magnetic material having a magnetic saturation level, e.g., magnetic steel with a magnetic saturation level between 1.7-2.1 Tesla. Accordingly, bottom plate  414  may provide a pathway for the magnetic flux to travel from lateral magnet  410  to center magnet  406  around the inner surfaces of recesses  612 . 
     Several magnetic inserts  604  may be located in respective recesses  612  to provide preferential pathways for the magnetic flux to travel from lateral magnet  410  to center magnet  406 . More particularly, magnetic inserts  604  may have a magnetic saturation level higher than the magnetic saturation level of bottom plate  414 , e.g., between 2.3-2.4 Tesla. Thus, in an embodiment, the magnetic field preferentially distributes within magnetic insert  604  across the radial gap formed by the recesses  612  rather than travel around the inner surfaces of recesses  612  in bottom plate  414 . 
     Still referring to  FIG. 9 , recesses  612  may be in support face  610  of bottom plate  414 , and thus, recessed faces  614  of the respective recesses  612  (as well as an outward facing face of magnetic inserts  604  within recesses  612  in support face  610 ) may be directed in a same direction as support face  610 , e.g., in forward direction  602 . As described above, however, recesses  612  may be in rear face  702  of bottom plate  414 . Thus, recessed faces  614  of the respective recesses  612  (as well as an outward facing face of magnetic inserts  604  within recesses  612  in rear face  702 ) may be directed in an opposite direction as support face  610 . For example, support face  610  may be facing in forward direction  602  and recesses  612  face may be facing in rearward direction  606 . Accordingly, magnetic inserts  604  may provide a radial pathway for magnetic flux to travel between one or more lateral magnets  410  and center magnet  406 . The shape and configuration of magnetic inserts  604  to provide such radial pathways may be varied by one skilled in the art to satisfy design and manufacturing requirements. Several shapes and configurations are now described by way of example. 
     In an embodiment, one or more lateral magnets  410  are symmetrically disposed around center magnet  406 . For example, two magnetic inserts  604  shaped as straight, rectangular bars may be arranged in two recesses  612  on opposite sides of a radial plane that is parallel to and intersects central axis  404 . Referring again to  FIG. 9 , the straight magnetic inserts  604  may be parallel magnetic inserts  604 , such as the leftmost magnetic insert  604  shown and the rightmost magnetic insert  604  shown, and the magnetic inserts  604  may have a length to provide overlapping portions that extend below an entire length of center magnet  406  and an entire length of a respective lateral magnet  410 . That is, center magnet  406  and a respective lateral magnet  410  may have sidewalls that face each other across magnet gap  608 , and the sidewalls may intersect with a lower face of a respective magnet along a sidewall edge, e.g., a corner. Thus, magnetic insert  604  may have a length that is at least as long as the sidewall edges of both magnets to provide an overlapping portion with both lower faces of the magnets along the entire length of the sidewall edges. As such, respective magnetic inserts  604  provide a magnetic flux path radially between lateral magnet  410  and center magnet  406  along the entire sidewall lengths of the magnets. In an embodiment, the magnetic inserts  604  may extend beyond the lateral lengths of the magnets to also include an overlapping portion with lateral magnets  410  illustrated in the 12 o&#39;clock and 6 o&#39;clock position relative to center magnet  406  in  FIG. 9 . That is, the rightmost and leftmost magnetic inserts  604  may be parallel with each other and have a length that is sufficient to overlap with center magnet  406  and at least one lateral magnet  410  on each side of center magnet  406 , e.g., at the 12 o&#39;clock, 3 o&#39;clock, 6 o&#39;clock, or 9 o&#39;clock radial positions. 
     Referring to  FIG. 10 , a cross-sectional view, taken about line C-C of  FIG. 6 , of a magnetic insert of an audio speaker is shown in accordance with an embodiment. Several lateral magnets  410 , e.g., four lateral magnets  410 , may be arranged to form an essentially ring-shaped structure around central axis  404 . More particularly, each lateral magnet  410  may include an upper face with a respective inner edge  1002  or side. The inner edges  1002  may be arranged around central axis  404  to define a central opening  1004 . Furthermore, the inner edges  1002 , and thus the central opening  1004 , may be under center magnet  406 . That is, central opening  1004  may coincide with the central region of support face  610  upon which center magnet  406  is located. More particularly, central opening  1004  may be a space between inner edges  1002  of lateral magnets  410 , and the space may be filled by the central region of bottom plate  414  beneath support face  610  such that support face  610  is facing forward direction  602  away from central opening  1004 . 
     The upper face of each magnetic insert  604  may extend from the respective inner edge  1002  to a respective outer edge  1006  or wall separated from inner edge  1002  by a radial width  1008 . Radial width  1008  may be wider than the radial distance between the center magnet  406  and the lateral magnet  410  over magnetic insert  604 , i.e., radial width  1008  may be greater than a width of magnet gap  608 , such that magnetic insert  604  includes overlapping portions under both lateral magnet  410  and center magnet  406 . Alternatively, radial width  1008  may be less than a width of magnet gap  608  and magnetic insert  604  may include an overlapping portion under one of lateral magnet  410  or center magnet  406 , but may not overlap with the other magnet. 
     Referring to  FIG. 11 , a cross-sectional view, taken about line C-C of  FIG. 6 , of a magnetic insert of an audio speaker is shown in accordance with an embodiment. The magnetic system may include a single magnetic insert  604  having inner edge  1002  or wall radially separated from outer edge  1006  or wall by radial width  1008 . Inner edge  1002  and outer edge  1006  may both surround  306  central opening  1004 . Accordingly, the body of magnetic insert  604  in the radial direction may be ring-shaped, e.g., annular. Thus, the central opening  1004  may coincide with a central region of bottom plate  414  having support face  610  upon which center magnet  406  is located. Furthermore, radial width  1008  may be wide enough to allow magnetic insert  604  to overlap with one or both of lateral magnet  410  and center magnet  406 . Although the ring-shaped body of magnetic insert  604  is shown as having inner edge  1002  and outer edge  1006  with essentially rectangular shapes, the edges may have alternative shapes, e.g., circular shapes, and/or the shape of inner edge  1002  may differ from the shape of outer edge  1006 . Nonetheless, magnetic insert  604  may have a radial width  1008  on all radial planes emanating from central axis  404  such that at least a portion of magnetic insert  604  forms a continuous path around center magnet  406  to provide a magnetic flux path  504  radially between lateral magnets  410  distributed near outer edge  1006  to center magnet  406  located near inner edge  1002 . 
     Referring to  FIG. 12 , a cross-sectional view, taken about line C-C of  FIG. 6 , of a magnetic insert of an audio speaker is shown in accordance with an embodiment. The magnetic system may include at least two magnetic inserts  604  having respective inner edges  1002  or walls radially separated from respective outer edges  1006  or walls by radial width  1008 . In an embodiment, the magnetic inserts  604  may each have several linear or arcuate segments. For example, magnetic insert  604  may have a generally “L” shaped structure, i.e., may have two linear segments that intersect at a corner. The magnetic insert segments may have equal or different lengths or widths, e.g., a length or radial width  1008  of one segment may be less than a length or radial width  1008  of another segment, as shown. The segments may be perpendicular to one another as shown, or may be at an obtuse or acute angle. Thus, when a first magnetic insert  604  is paired with a second magnetic insert  604  having similar geometry, the combination of magnetic inserts  604  may form an essentially ring-shaped structure around central opening  1004 . The ring-shaped structure may be a rectangular annulus as shown, or may be a quadrilateral annulus with one or two parallel pairs of insert segments as in the case of similar “L” shaped inserts that meet at acute or obtuse angles. In an embodiment, the two magnetic inserts  604  may each follow a semi-circular path to combine to form a circular annulus around central opening  1004 . In any case, the two or more magnetic inserts  604  that combine to form an annulus structure around central opening  1004  may be separated from one another by two or more division slots  1202 . Accordingly, the annulus formed around central opening  1004  by one or more magnetic inserts  604  may have a discontinuity. Division slots  1202  allow for an essentially ring-shaped structure (albeit discontinuous) to be formed from multiple magnetic inserts  604  such that the individual magnetic inserts  604  may be formed using mass production methods such as die-cutting, without having to waste material that is originally contained within central opening  1004 . Reducing material waste can translate to cost reduction when using expensive materials such as high-saturation magnetic materials. 
     The thickness  808  (into the page) of insert(s)  604  may be equal or different than the depth of corresponding recesses  612  in bottom plate  414 . In an embodiment, thickness  808  of magnetic insert  604  is equal to the depth of recess  612  such that an outward facing surface of magnetic insert  604  is coplanar with either support face  610  or rear face  702  (whichever of those faces recess  612  is formed in). Alternatively, thickness  808  of magnetic insert  604  may be greater than the recess  612  depth to increase the likelihood that magnetic insert  604  will fully contact an overlapping portion of a magnet placed over recess  612 . Similarly, thickness  808  of magnetic insert  604  may be less than the depth of a corresponding recess  612 , as in the case where magnetic insert  604  is loaded into a recess  612  in support face  610  or rear face  702  and does not directly contact lateral magnet  410  or center magnet  406 . 
     Referring to  FIG. 13 , a perspective view of a bottom plate of an audio speaker is shown in accordance with an embodiment. Bottom plate  414  may be formed to receive one or more magnetic inserts  604 . For example, bottom plate  414  may be formed to receive two “L” shaped magnetic inserts  604  arranged in an essentially ring-shaped structure as shown in  FIG. 12 . Each recess  612  may be formed in support face  610  of bottom plate  414  (and/or in rear face  702  of bottom plate  414 ), and thus, may include a recessed face  614  below support face  610 . Furthermore, each recess  612  may have a sidewall surrounding recessed face  614 . For example, recess  612  may include a recess inner sidewall  1302  separated from a recess outer sidewall  1304  by a radial gap  1306 . For example, radial gap  1306  may be at least as wide as the radial width  1008  of magnetic insert  604  to allow magnetic insert  604  to be received within recess  612 . Recess  612  may also include recess end sidewalls  1308  on opposite ends of the recess  612  length, e.g., at opposite ends of the “L” shaped recess  612 . The distance along recess  612  around a central region  1310  of support face  610  may define a length of recess  612 . Furthermore, bottom plate  414  may include a division bridge  1312 , i.e., a segment of material extending from central region  1310  to a lateral region  1314  of support face  610 , which separates one recess end sidewall  1308  from another. Division bridge  1312  may have a width corresponding to, e.g., equal to or slightly smaller than, division slot  1202  so that magnetic inserts  604  may be received in the recesses  612  of bottom plate  414 . Accordingly, bottom plate  414  may be configured to receive an arrangement of magnetic inserts  604  that form a structure around central opening  1004  and at least partly overlap with lateral magnet  410  and center magnet  406  to form a magnetic flux path  504  between those magnets. 
     Referring to  FIG. 14 , a detail view, taken from Detail C of  FIG. 6 , of a magnetic insert in a recess of an audio speaker is shown in accordance with an embodiment. The magnetic system of audio speaker  106  may include center magnet  406  separated from lateral magnet  410  by magnet gap  608 . Furthermore, the magnets may be disposed on bottom plate  414  such that respective lower faces  502  of each magnet are in contact with bottom plate  414 . In an embodiment, magnetic insert  604  is disposed within recess  612  below the magnets, such that overlapping portion  802  of magnetic insert  604  is in contact with both lower faces  502  of the magnets. Thus, magnetic flux path  504  may be formed between lateral magnet  410  and center magnet  406 , and may be preferentially distributed in magnetic insert  604  (rather than in bottom plate  414  around inner surfaces of recess  612 ) because magnetic insert  604  may be formed from a material with a higher magnetic permeability or a higher magnetic saturation level than bottom plate  414 . In an embodiment, magnetic insert  604  may be sandwiched between, and in contact with, the magnets and recessed face  614  on bottom plate  414 . Furthermore, the magnetism of magnetic insert  604  may cause it to magnetically snap into place within recess  612  such that there are both magnetic and mechanical forces securing magnetic insert  604  in recess  612 . In an alternative embodiment, however, an adhesive  1402  may be placed within a gap between an outer sidewall of magnetic insert  604  and an adjacent sidewall of recess  612 , e.g., recess inner sidewall  1302 , recess outer sidewall  1304 , or recess end sidewall  1308 . Thus, adhesive  1402  may bond magnetic insert  604  to bottom plate  414  to fix magnetic insert  604  relative to bottom plate  414 . 
     Referring to  FIG. 15 , a detail view, taken from Detail C of  FIG. 6 , of a magnetic insert in a recess of an audio speaker is shown in accordance with an embodiment. In an embodiment, magnetic insert  604  may be held in place by magnetic forces, adhesive bonding, or mechanical loading from a surrounding structure. For example, insert  604  may be sandwiched between center magnet  406 , lateral magnet  410 , and bottom plate  414 . Additionally, bottom plate  414  may be deformed around magnetic insert  604  to provide an additional retention force. That is, bottom plate  414  may be deformed, e.g., by application of radial loading around the outer perimeter of bottom plate  414 , to cause recess inner sidewall  1302  and recess outer sidewall  1304  to bend inward and form tabs that pinch an outer sidewall of magnetic insert  604 . This pinching can press magnetic insert  604  against bottom plate  414  and prevent magnetic insert  604  from being removed from recess  612 . 
     Still referring to  FIG. 15 , magnetic insert  604  may include a laminate structure  1502 . For example, magnetic insert  604  may be multi-layered, e.g., may have a top layer  1504  and a bottom layer  1506 . Bottom layer  1506  may be disposed on recessed face  614  within recess  612 , and top layer  1504  may be disposed above and/or on bottom layer  1506  such that an outward facing surface of top layer  1504  is directed toward magnet gap  608 . More particularly, the outward facing surface of top layer  1504  may be in contact with lateral magnet  410  and/or center magnet  406  across overlapping portion  802  of magnetic insert  604 . Thus, laminate structure  1502  provides a magnetic insert  604  that fills recess  612  by combining several layers. Each layer may be formed from a high-saturation magnetic material cut from a material sheet. Thus, lamination of the layers allows for a magnetic insert  604  of a given overall thickness to be fabricated even when cutting of a thick sheet of the higher-saturation magnetic material having the given thickness is impractical. 
     Referring to  FIG. 16 , a detail view, taken from Detail C of  FIG. 6 , of a magnetic insert in a recess of an audio speaker is shown in accordance with an embodiment. In addition to allowing for a given thickness  808  of magnetic insert  604  to be achieved, laminate structure  1502  may provide for a magnetic insert  604  to be fabricated having a complex cross-sectional profile. Magnetic insert  604  may include laminate structure  1502  having top layer  1504  and bottom layer  1506  in recess  612  of bottom plate  414 . Top layer  1504  and bottom layer  1506  may, however, have different widths. For example, top layer  1504  may include a top width  1602  that is greater than a bottom width  1604  of bottom layer  1506 . As such, laminate structure  1502  may have a stepped profile. The stepped profile may provide for an overlapping portion  802  of top layer  1504  to be under and in contact with lateral magnet  410  and/or center magnet  406 . Bottom layer  1506 , however, may not be under lateral magnet  410  or center magnet  406  in the case where bottom width  1604  is narrower than a distance of magnet gap  608 . Thus, magnetic insert  604  may have a cross-sectional profile that is contoured to meet certain design goals. 
     Other types of contours may be achieved by forming magnetic insert  604  with laminate structure  1502 . For example, magnetic insert  604  may have a tapered cross-sectional profile. In an embodiment, several layers of magnetic insert  604  material may be laminated together and each layer may have a progressively narrower width. The layers may be centered over each other such that the edge of the laminate structure  1502  tapers inward progressively from each layer to the next (as shown in the two-layered embodiment of  FIG. 16 ). Subsequent machining operations, such as grinding of the edges, may be used to modify the edge shape from a stepwise taper to a smooth taper. Accordingly, magnetic insert  604  having laminate structure  1502  can be formed to include a desired thickness and/or contoured cross-sectional profile. 
     High-saturation magnetic materials can be difficult to shape by machining processes, and thus, laminate structure  1502  provides a practical and feasible solution to produce a contoured magnetic insert  604  formed from high-saturation magnetic material. The contoured profile may provide increased contact area between overlapping portion  802  of magnetic insert  604  and a respective magnet, and also includes a varying overall thickness  808  to reduce the likelihood of saturation of magnetic insert  604  between lateral magnet  410  and center magnet  406 . By reducing the likelihood of magnetic saturation of the entire cross-section of magnetic insert  604 , magnetic insert  604  constrains magnetic flux rather than leaking stray flux into the adjacent bottom plate  414 , magnet gap  608 , or surrounding environment. Furthermore, since the contoured surface can locate high-saturation magnetic material only where it is required to increase the magnetic saturation level, unnecessary use of high-saturation magnetic material may be limited, and thus, material costs may be reduced. 
     Referring to  FIG. 17 , a flowchart of a method of manufacturing an audio speaker having a high-saturation magnetic insert in a recess of a bottom plate is shown in accordance with an embodiment. At operation  1702 , bottom plate  414  may be formed from a magnetic material having a magnetic saturation level. For example, bottom plate  414  may be forged from a magnetic material, such as magnetic steel. Bottom plate  414  may be forged in a variety of shapes, and in an embodiment, bottom plate  414  includes a thickness in an axial direction of between 0.2-5 mm, e.g., between 0.3 to 1 mm. In an embodiment, the forging process used to form bottom plate  414  may include pressing or stamping recess  612  into bottom plate  414 . Thus, bottom plate  414  may be formed with recessed face  614  and support face  610 , facing a same or different direction. Although recess  612  may be formed in bottom plate  414  during a forging process, alternatively, bottom plate  414  may instead be formed using other processes, such as casting or stamping alone. For example, bottom plate  414  may be cast, stamped, or forged and then recess  612  may be formed in bottom plate  414  using subsequent operations. For example, recess  612  may be formed in bottom plate  414  using machining operations, e.g., by milling recess  612  into support face  610  and/or rear face  702 . Alternatively, recess  612  may be etched into bottom plate  414  in a subsequent operation. 
     At operation  1704 , magnetic insert  604  may be formed from a sheet of material having a higher magnetic saturation level than the material used to form bottom plate  414 . For example, magnetic insert  604  may be cut from a sheet of high-saturation magnetic material, e.g., Hiperco® 27. More particularly, magnetic insert  604  may be formed from a material that has a magnetic saturation level higher than that of the material used to form bottom plate  414 . In an embodiment, magnetic insert  604  may be die-cut from the sheet of magnetic material. Die-cutting is a low-cost method suitable to mass production, and thus, by die-cutting magnetic insert  604  from a sheet of material, e.g., a rolled sheet of material, the magnetic system of audio speaker  106  can be feasibly produced. Die-cutting of a high-saturation magnetic material can be achieved using material sheet thicknesses of up to 0.050 inch. Thus, magnetic insert  604  may be formed in a single layer having a die-cut thickness  808  up to 0.050 inch. Alternatively, multiple layers of die-cut material (or thicker layers using other cutting processes such as laser cutting) may be laminated to build laminate structure  1502 , and thus, magnetic insert  604  may have a total thickness  808  greater than 0.050 inch. Accordingly, the method of manufacturing audio speaker  106  may include laminating, e.g., bonding or otherwise attaching, multiple die-cut magnetic insert  604  layers together to form a composite magnetic insert  604  structure, i.e., laminate structure  1502 , having a desired thickness and shape. 
     At operation  1706 , magnetic insert  604  may be inserted into recess  612 . More particularly, magnetic insert  604  may be disposed in recess  612  and maintained in place by a magnetic attraction between magnetic insert  604  and bottom plate  414 . Optionally, low viscosity adhesive  1402  may be flowed into a gap between magnetic insert  604  and sidewalls of recess  612  to further retain magnetic insert  604 . In an embodiment, the adhesive  1402  is not applied between magnetic insert  604  and recessed face  614  to avoid increasing the vertical thickness  808 , i.e., the z-height, of audio speaker  106  any more than is necessary. As an alternative to, or in addition to, adhesive  1402 , bottom plate  414  may be deformed to pinch magnetic insert  604  along an edge and/or press and retain magnetic insert  604  against recessed face  614 . 
     At operation  1708 , lateral magnet  410  and center magnet  406  may be attached to support face  610  of bottom plate  414 . More particularly, one or both of the magnets may be bonded to bottom plate  414  or housing  302  using adhesives in locations that do not impede the magnetic field of the magnetic system. The lateral magnet  410  and/or center magnet  406  may be disposed over recess  612  such that magnetic insert  604  is under one or both magnets. For example, magnetic insert  604  may include overlapping portions  802  that are under and in contact with lateral magnet  410  and/or center magnet  406 . Accordingly, magnetic flux path  504  may be directed from lateral magnet  410  to center magnet  406  through the high-saturation magnetic insert  604 . Other components of audio speaker  106 , such as top plate  412  and the moving assembly, and housing  302  may be assembled to form audio speaker  106  having a desired form factor. Audio speaker  106  may then be integrated with other components to fabricate electronic device  100 . 
     In the foregoing specification, the invention has been described with reference to specific exemplary embodiments thereof. It will be evident that various modifications may be made thereto without departing from the broader spirit and scope of the invention as set forth in the following claims. The specification and drawings are, accordingly, to be regarded in an illustrative sense rather than a restrictive sense.

Metadata:
Filing Date: 20150501
Publication Date: 20170214
Grant Date: 20170214
Priority Date: 20150501
Inventors: PORTER SCOTT P.
WILK CHRISTOPHER
Assignee: APPLE INC
CPC Classifications: [{"code": "H04R9/025", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04R2209/024", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04R9/045", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04R31/006", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04R9/06", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04R9/025", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04R9/025", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04R2209/022", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04R9/06", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04R2209/024", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04R9/06", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04R2209/024", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04R2209/022", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04R9/045", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04R31/006", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 57205452