Patent Publication Number: US-9854364-B2

Title: Knurled speaker diaphragm

Description:
RELATED APPLICATION 
     The present application makes a claim of domestic priority to U.S. Provisional Patent Application No. 62/081,647 filed Nov. 19, 2014, the contents of which are hereby incorporated by reference. 
    
    
     SUMMARY 
     A planar magnetic (magnetic planar) speaker, in accordance with some embodiments, has a diaphragm positioned proximal to and separated from an array of magnets with the diaphragm consisting of a substrate and at least one patterned electrically conductive trace. A portion of the diaphragm is knurled to provide a ridge extending a height above the diaphragm that is at least twice a thickness of the diaphragm. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block representation of an example audio system arranged in accordance with various embodiments. 
         FIGS. 2A &amp; 2B  respectively show line representations of various portions of an example speaker configured in accordance with some embodiments. 
         FIGS. 3A-3E  respectively display different views of a portions of an example speaker constructed and operated in accordance with various embodiments 
         FIGS. 4A &amp; 4B  respectively depict line representations of different portions of an example knurling device configured in accordance with assorted embodiments. 
         FIGS. 5A-5D  respectively convey line representations of portions of an example knurling device arranged in accordance with some embodiments. 
         FIG. 6  provides an example diaphragm knurling routine carried out in accordance with assorted embodiments. 
         FIGS. 7A-7C  respectively are top view line representations of portions of an example diaphragm arranged in accordance with various embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     The proliferation of digital audio sources has increased the exposure of various types of music. For example, mobile computing devices, such as smartphones, music players, and hard drives, can provide music on demand anywhere in the world. The increase in music exposure correlates with heightened industry and consumer demand for optimal music reproducing equipment that is portable. While relatively non-portable audio equipment, such as floor standing speakers, are unhampered by size and power restrictions, configuring a portable audio speaker with accurate and rugged quality despite reduced power supplies is difficult. 
     In the past, various types of audio speakers have been utilized individually and in combination to provide sufficient range and balance for music reproduction. For instance, a dynamic driver can be utilized concurrently with electrostatic and/or ribbon drivers to separately reproduce predetermined ranges of audio frequencies. However, such multi-driver configuration is not practical in portable audio devices, like headphones, due at least to size and power requirements. The use of planar magnetic drivers has indicated promising portable audio device operation, but can be hampered by standing waves on the driver panel and inaccurate dampening that degrades accurate reproduction of audio signals. 
     With these issues and others in mind, a planar magnetic speaker is arranged with a diaphragm knurled to provide at least one ridge extending a height above the diaphragm that is at least twice the thickness of the diaphragm. Typically, the velocity of a sound wave in a diaphragm substrate is low relative to the velocity of sound in a conductor material portion of a diaphragm. The density of the conductor material is usually higher than the substrate material and the compliance of the substrate material is high relative to favorable conductor materials. Through the frequency range of interest, such as audible frequencies, the combination of mechanical properties can allow multiple localized resonance modes to occur on the surface of the diaphragm causing distortion and frequency response variations. 
     Resonant modes can result from localized wave reflections on the surface of the diaphragm or the supporting frame. Knurling decreases the transverse velocity of sound in the conductor and significantly raises its compliance relative to the substrate, which reduces abridges resonance areas on the surface of the diaphragm. The low compliance of some conductor materials, such as Cu, results in a higher than desired natural frequency for a small area planar magnetic transducer. Knurling of the conductor material raises the mechanical compliance of the conductor, which allows a lower natural frequency for a given diaphragm tension. 
     Thus, tuning the diaphragm material and knurled ridges allows resonance and dampening to be controlled, which results in optimized audio signal reproduction by reducing distortion and improving the transient and frequency response of the system. Knurling the diaphragm also lowers the panel resonance frequency, so smaller panels can produce increased bass output. The ability to knurl the diaphragm with patterns of multiple ridges of similar, or dissimilar, shapes and sizes allows the planar magnetic speaker to be customized for a variety of different enclosures and types of sound being reproduced. 
       FIG. 1  is a block representation of an example audio system  100  that may employ one or more knurled planar magnetic speakers  102  in accordance with some embodiments. As shown, at least one speaker  102  is positioned proximal to each ear  104  of a user  106 . The speakers  102  are housed in a headphone enclosure  108  that can be manipulated for fitment onto the user  106 . The headphone enclosure  108  may consist of one or more local controllers  110 , such as a microprocessor or application specific integrated circuit (ASIC), that directs audio reproduction by the speakers  102 . The controller  110  can be connected to any number of other local electrical components, such as amplifiers, capacitors, and memories, which enable the headphone enclosure  108  to provide mono and stereo audio generation from at least one audio signal source. 
     In some embodiments, the local controller  110  is connected to one or more remote hosts  112  via a wired or wireless network  114 . The ability to access remote hosts  112 , such as other controllers, nodes, servers, and software, can provide audio signals that are not stored proximal to the speakers  102 . As a non-limiting example, the user  106  may connect the headphone enclosure  108  to a local controller  110  resident in a smartphone that communicates with at least one remote host  112  to generate audio signals that are fed to and reproduced by the speakers  102 . Hence, the connectivity and robust computing capabilities of the audio system  100  allows for the speakers  102  to receive and reproduce diverse varieties of sound, such as spoken word and music. 
       FIGS. 2A and 2B  respectively provide different view line representations of portions of an example planar magnetic speaker  120  configured in accordance with various embodiments. In  FIG. 2A , the speaker  120  is shown as a flexible diaphragm  122  suspended between first  124  and second  126  arrays of magnets. The magnets can be any size, shape, and material to interact with electrical signals passing through the voice coil trace  128  of the diaphragm  122 . The diaphragm  122 , in some embodiments, is an insulating material, such as polyethylene terephthalate (PET), and the trace  128  is a continuous pattern of non-magnetic and electrically conductive material, such as aluminum, as shown in  FIG. 2B . It is contemplated that the electrically conductive trace  128  is positioned on a single side of the diaphragm  122 , as shown in  FIG. 2A , or on opposite sides of the diaphragm  122 , as illustrated by segmented traces  130   
     The placement of the voice coil trace  128  relative to the magnet arrays  124  and  126  allows audio signals to interact with the magnetic fields of the magnets to flex the diaphragm  122  and produce vibrations in a wide range of frequencies, such as 0.1-20 kHz. However, the relatively large surface area of the diaphragm  122  along with the strong magnetic fields and the physical presence of the magnet arrays  124  and  126  can result in standing waves, unwanted distortion, and negative pressure regions during and after audio signal reproduction that degrade audio quality. These audio quality inhibitors can, at least partially, be attributed to uncontrolled flexibility of the diaphragm  122  in response to received audio signals. It is noted that a single continuous trace  128  is positioned on the diaphragm  122 , but such configuration is not required or limiting as any number of separate traces, such as 2-5 traces, can increase the motor force on the diaphragm  122  compared to the single trace  128  embodiment of  FIG. 2B . 
     Although various diaphragm  122  configurations can crease, emboss, and pleat portions of the diaphragm  122  to control flexibility, the power handling capability, thermodynamic properties, and audio reproducing accuracy can remain volatile at the expense of audio quality. Hence, assorted embodiments construct the diaphragm  122  with a configuration that allows more aggressive knurled ridges to be incorporated to tune the tension of the diaphragm  122  to optimize sound reproduction without materially inhibiting or changing electrical and thermal conductance. 
       FIGS. 3A-3E  respectively depict various portions of an example speaker  140  constructed and operated in accordance with assorted embodiments. A cross-sectional view of the speaker  140  in  FIG. 3A  shows a diaphragm  142  knurled to provide a multitude of ridges  144  that have a tuned shape and size relative to the first  146  and second  148  arrays of magnets. 
     While not limiting, the knurled ridges  144  can have a thickness  150 , as measured along the Z axis, that continuously extends to a height  152  that is at least twice the thickness  150  of the diaphragm  142 . That is, each knurled ridge  142  can extend from a plane  154  that dissects the thickness  150  to a height  152  that is two or more times the size of the diaphragm thickness  150 . The knurled ridges  144  can be configured to maintain a minimum distance  156  from the magnets of the first  146  and second  148  arrays to allow ample diaphragm  142  excursion to replicate low frequency audio signals, such as below 200 Hz. 
     The position, shape, and size of the respective knurled ridges  144  can be tuned relative to the magnetic configuration of the various magnets of the respective arrays  146  and  148 . For example, a knurled ridge  144  may be configured to be closer to magnets that are arranged with a S-N dipole while other knurled ridges  144  are positioned farther away from magnets having a N-S dipole or monopole magnetic arrangement. Thus, with no magnetic arrangement being required, the diaphragm  142  can be tuned with respect to the magnet arrays  146  and  148  to control diaphragm flex and distortion that may occur as a result of uniform, or varying, magnetic arrangements in the various magnets. 
     In the non-limiting embodiment of  FIG. 3A , the knurled ridges  144  are positioned without contact with a voice coil trace. However, other embodiments can position one or more knurled ridges  144  in and around a voice coil trace, which may involve shaping the trace in a non-rectangular configuration. It is contemplated that a knurled ridge  144  can be positioned anywhere on the diaphragm  142  and continuously, or intermittingly, extend to partially, or completely, across the diaphragm  142 .  FIGS. 3B-3E  respectively show top views of various knurled ridge configurations that can be employed individually and collectively to tune the flexibility and sound reproduction quality of the diaphragm  142 . 
       FIG. 3B  depicts a plurality of knurled ridges  144  arranged in a pattern to cross the voice coil trace  158  multiple times. The ridge pattern may be configured with uniform spacing between the ridges  144  throughout the ridge&#39;s respective lengths in the X-Y plane. Yet, different portions of the diaphragm  142  may be more prone to unwanted distortion and flexibility, which can be accommodated by configuring the ridge pattern with multiple different ridge spacing distances, as shown by distances  160  and  162 . 
     It is noted that the ridge spacing distances are measured along the Y axis, but such measurement is not required and any measurement orientation can be used to describe uniform or non-uniform spacing between knurled ridges  144 . It is also noted that in order for the knurl to maintain its form over time, the metal traces  158  must be stiffer than the underlying diaphragm  142  substrate material, lest the substrate restore the material to its prior, unknurled, form, which corresponds with the diaphragm  142  retaining only minor creases that negligibly increase speaker performance. 
       FIG. 3C  provides an example knurled ridge  144  pattern with varying inter-ridge spacing in the X-Y plane. The various knurled ridges  144  are randomly positioned relative to one another and are confined to a predetermined portion of the diaphragm  142 . That is, the right half portion of the diaphragm  142  has no knurled ridges  144  while the left half portion of the diaphragm  142  has numerous knurled ridges  144  that are randomly arranged. Such random ridge  144  configuration corresponds with ridges  144  crossing each other, which may produce a different ridge shape and/or size at the intersection of the ridges  144  than at other points along the length of each ridge  144 . 
       FIG. 3D  illustrates how knurled ridges  144  can be continuously curvilinear across the diaphragm  142 . Various embodiments may utilize combinations of linear and curvilinear ridge  144  pathways across the diaphragm  142 , but the non-limiting embodiment of  FIG. 3D  shapes the various knurled ridges  144  with different radii of curvature. It is contemplated that the continuously curvilinear ridge  144  pathways provide varying ridge spacing distances  164  that can be manipulated to tune the structure and operation of the diaphragm  142 . In some embodiments, the knurled ridges  142  have a common origin point on the diaphragm  142 , which may correspond with a portion of the diaphragm  142  free of an operational voice coil trace  158 . 
       FIG. 3E  displays another knurled ridge  144  pattern. The pattern has a plurality of concentric circles that do not extend to the outer periphery of the diaphragm  142 . The various concentric circles may be ovals or any other shape, such as a rhomboid or triangle, that form a loop with each knurled ridge  144 . The ability to configure a knurled ridge  144  into a shape can allow the diaphragm  142  to be knurled similarly to a bullseye with concentric circles having a common origin. In the non-limiting embodiment shown in  FIG. 3E , the multiple different circle diameters and overlapping ridges  144  can create sophisticated diaphragm  142  tuning and flexibility control. 
     It is to be understood that while the various knurled ridge  144  patterns of  FIGS. 3B-3E  are shown in isolation, any aspect of any embodiment can coexist on a single diaphragm  142 . For example, a concentric circle can be positioned with any number of linear ridges  144  that may or may not overlap the circle. Regardless of whether or not multiple different ridge  144  patterns are utilized, different ridges  144  in a single pattern may have different shapes and/or sizes. For instance, a first ridge  144  may be knurled with a triangular shape, as shown in  FIG. 3A , and a second ridge  144  can have a rectangular or circular cross-sectional shape. 
       FIGS. 4A &amp; 4B  respectively provide line representations of portions of an example knurling device  180  that can be employed in accordance with some embodiments to create one or more knurled ridges. Although a diverse variety of equipment can manipulate a diaphragm to construct a knurled ridge, such as a rotating knurling tool, a diaphragm can be efficiently contorted to provide multiple shaped ridges by being pressed between first  182  and second  184  knurling plates. Each plate  182  and  184  can be constructed of any material, such as metals, polymers, ceramics, and combinations thereof, that mate with any number of protrusions  186  to manipulate a flexible diaphragm to permanently construct at least one knurled ridge corresponding with the shape of the protrusions  186 . 
     In accordance with a non-limiting embodiment, the first plate  182  has a substantially linear body while the second plate  184  has a curved body that is conducive to applying increased amounts of pressure as the second plate  184  across the protrusions  186  of the first plate  182 .  FIG. 4B  displays how the respective plates  182  and  184  can be configured to mechanically mate via securing features  188  that align along the Z axis. The securing features  188  can allow the plates  182  and  184  to remain interconnected while pressure is applied to one, or both, plates  182  and  184  without disturbing a diaphragm positioned there between. 
     The various protrusions  186  are shown to be similar sizes and shapes on each plate  182  and  184 . Such arrangement is not required or limiting as a knurling plate  182  and  184  can have multiple different protrusion configurations.  FIGS. 5A-5D  respectively depict cross-sectional line representations of different knurling device  200  configurations that can be utilized individually and concurrently on a single knurling plate or device in accordance with assorted embodiments. The example knurling device  200  of  FIG. 5A  has bottom  202  and top  204  knurling plates each having protrusions  206  defined by a continuously curvilinear sidewalls  208  that meet at a point  210 . 
     The various protrusions  206  of  FIG. 5A  can be tuned for height along the Z axis and width  212  along the Y axis between points  210  to control the aggressiveness of the knurled ridges the knurling device  200  can produce. The various points  210  can be rounded, in some embodiments, to mitigate the risk of puncturing or tearing a diaphragm or breaking a metal trace during a knurling process. Turning to  FIG. 5B , the protrusions  206  of the knurling plates  202  and  204  are configured with continuously linear valley  214  and peak  216  surfaces that are each aligned along the Y axis and connected by a linear sidewall  218 . The widths  220  and  222  of the respective valley  214  and peak  216  surfaces along the Y axis can be tuned to produce more, or less, aggressive knurled ridges. 
       FIG. 5C  illustrates how a knurling protrusion  206  can consist of a combination of curvilinear  224  and linear  226  surfaces to provide different peak and valley ridge shapes. Configuring a knurled ridge with curvilinear valleys and linear peaks can precisely tune diaphragm performance that cannot be produced by exclusively linear, or exclusively curvilinear, protrusion  206  defining surfaces. The protrusions  206  of  FIG. 5D  display how any shape and size can be utilized to form a knurled ridge. The finger protrusions  206  of  FIG. 5D  have a width  230 , linear sidewalls  232 , and continuously curvilinear mating surfaces  234  that interconnect to provide a diaphragm texture that can mitigate distortion, unwanted resonance, and inadvertent flexing. 
     With the nearly unlimited variety of knurling protrusion  206  shapes and sizes that can be provided by the knurling device  200 , it is noted that the material construction of the diaphragm is tantamount to the ability of the knurling device  200  to provide optimized diaphragm performance. In other words, an overly thin and/or incompatible material can be rendered inoperable if subjected to the various aggressive knurling protrusions  206  of  FIGS. 5A-5D  that produce knurled ridges extending at least twice as high as the thickness of the diaphragm. Hence, the knurling device  200 , knurled ridge pattern, and knurling protrusion  206  shape are tuned in concert to provide a diaphragm with increasingly robust flexibility and optimized sound reproduction performance. In general, the metal traces should be materially stiffer than the underlying substrate to ensure the shape of the knurled ridges is preserved over time. 
       FIG. 6  is a flowchart of an example diaphragm knurling routine  240  this is carried out in accordance with various embodiments to manufacture a hearing device, such as a headphone, loudspeaker, or in-ear monitor. Initially, step  242  positions a diaphragm between knurling plates. The diaphragm has a continuously uniform, or varying, thickness and is constructed of a non-magnetic, electrically insulating material, like PET. One or more predetermined amounts of pressure are applied onto the diaphragm in step  244  by knurling plates of a knurling device to permanently imprint a knurled ridge pattern onto selected portions of the diaphragm. 
     While a single knurled ridge pattern may be employed by the diaphragm, various embodiments can utilize one or more additional knurled ridge patterns. Decision  246  evaluates if an additional knurled ridge pattern is to be imprinted on the diaphragm. If a second pattern is called for, step  248  proceeds to form a second knurled pattern in the diaphragm. It is contemplated that the second knurled ridge pattern is provided by changing one, or both, knurling plates used in the execution of step  244 . At the conclusion of step  248 , or in the event that decision  246  chooses not to employ an additional knurled ridge pattern, step  250  suspends the knurled diaphragm between top and bottom magnet arrays with tuned tension. 
     Step  250  may further consist of tuning the individual magnets of at least one magnet array to provide a predetermined magnetic profile. For instance, magnets of a magnet array can be rotated so that the poles facing the diaphragm present a non-uniform polarity. With the diaphragm suspended between magnet arrays in a planar magnetic assembly, step  252  next assembles the planar magnetic assembly into a hearing device by incorporating the assembly into a housing, which may be any size, shape, type, and purpose. As such, the planar magnetic assembly can provide sound reproduction for portable apparatus, like headphones and in-ear monitors, as well as for fixed apparatus, such as loudspeakers and floor standing monitors. 
     Through the various steps and decision of routine  240 , a diaphragm can be tuned with one or more knurled ridges that optimize rigidity and mitigate unwanted resonance and distortion. However, the various aspects shown in  FIG. 6  are not required or limiting as anything can be changed and removed just as anything can be added. For example, one or more steps and decisions may be added to manufacture at least one voice coil trace onto the diaphragm in a selected pattern with a selected material, such as copper, that has a density and elasticity that can utilize the aggressive knurled ridges with a height that is at least twice as big as the thickness of the diaphragm. 
     In  FIGS. 7A-7C , various knurled ridge patterns are shown that can be implemented on portions of a diaphragm. The tuned shape, size, and pattern of the knurled ridges, as well as the knurling plates utilized to create the ridge pattern, can increase the compliance of the diaphragm, which optimizes bass response and transient performance. Greater diaphragm compliance corresponds with a smaller diaphragm physical size more readily responding to audio signal inputs to more accurately exert to reproduce low audio frequencies. Such increased compliance also reduces the space, weight, cost, and amplification requirements for reproducing high audio frequencies. 
     The tuning of knurled ridges in a diaphragm can significantly reduce distortion by allowing the diaphragm to move in a more ideal “flat piston” manner, which contrasts bowing or complex nonlinear diaphragm movements that are less ideal at accurately reproducing sound. The ability to provide flat piston movement can be particularly helpful in headphones with closed or semi-closed backs where diaphragm oscillations can produce resonances that degrade upper-bass and lower-midrange audio frequency reproductions. 
     The forming of the knurled ridges into the diaphragm can add a bit of surface area that equalizes diaphragm tension and improves consistency in diaphragm movement. For example, when a diaphragm is slightly tighter than desired before knurling and after knurling aggressive ridges, the substrate has been stretched to a larger size and a more relaxed tension, which contrasts a slightly too-relaxed diaphragm that will stretch less and will be slightly tightened due to the metal holding the diaphragm. 
     With the various embodiments of the present disclosure, it can be appreciated that a knurling device can be tuned to provide any knurled ridge geometry and pattern. A knurled ridge may continuously extent across all or part of a diaphragm and multiple ridge may be equally spaced from one another or have variable spacing. It is contemplated that knurled ridges have less aggressive heights and shapes proximal the edge of the diaphragm to mitigate potential diaphragm material failures. 
     As a non-exhaustive summary of some embodiments of the present disclosure, constructing voice coil traces of materials, like Cu and other materials with sufficient thickness to maintain a knurled for, with preferred combinations of density and elasticity allows thicker traces to be formed and deeper, more “aggressive” knurled ridges to be created compared to trace materials, like Al. Trace materials like copper allows a plethora of different knurled ridge shapes and sizes to be imprinted on the diaphragm to increase diaphragm compliance while reducing the resonant frequency. Such optimized diaphragm performance can be applied to legacy planar magnetic diaphragms to reduce distortion and enhance low frequency audio reproduction. 
     The ability to imprint any number of different knurled ridge patterns onto a diaphragm allows knurling to take place before, or after, formation of voice coil traces on the diaphragm. It is to be understood that even though numerous characteristics and configurations of various embodiments of the present disclosure have been set forth in the foregoing description, together with details of the structure and function of various embodiments, this detailed description is illustrative only, and changes may be made in detail, especially in matters of structure and arrangements of parts within the principles of the present disclosure to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed. For example, the particular elements may vary depending on the particular application without departing from the spirit and scope of the present technology.