PATENT DOCUMENT

Publication Number: US-11176919-B2
Application Number: US-202016986061-A
Country: US
Kind Code: B2

Title: Acoustic filler including acoustically active beads and expandable filler

Abstract:
Aspects are disclosed of a filler for occupying a volume. The filler includes an expandable filler positioned in the volume so that it occupies a percentage of the volume. The expandable filler can permanently expand from a first dimension to a second dimension upon the application of an expansion trigger. The filler also includes an acoustic filler made up of a plurality of acoustically active beads positioned with the expandable filler in the volume so that the acoustic filler can adsorb gas flowing into the volume. Other embodiments are disclosed and claimed.

Claims:
What is claimed is: 
     
       1. A filler for occupying a volume, the filler comprising:
 an acoustic filler positioned in the volume of an electronic device so that the acoustic filler can adsorb gas flowing into the volume, the acoustic filler comprising a plurality of acoustically active beads; 
 an expandable filler positioned with the acoustic filler in the volume so that it occupies a percentage of the volume, wherein the expandable filler can permanently expand from a first dimension to a second dimension upon exposure to an expansion trigger to affect mobility of the acoustic filler, and wherein the expandable filler comprises a plurality of expandable beads mixed with the acoustically active beads. 
 
     
     
       2. The filler of  claim 1  wherein the expandable filler comprises an expandable coating positioned on at least one interior surface of the volume. 
     
     
       3. The filler of  claim 1  wherein a density of the expandable beads is within 90-110% of a density of the acoustically active beads. 
     
     
       4. The filler of  claim 1  wherein an average size of the plurality of expandable beads is within an order of magnitude of an average size of the plurality of acoustically active beads. 
     
     
       5. The filler of  claim 1  wherein the expandable filler occupies between 0.5% and 20% of the volume. 
     
     
       6. The filler of  claim 1  wherein the expandable filler occupies between 1% and 2% of the volume. 
     
     
       7. The filler of  claim 1  wherein the expansion trigger is heat, light, or ultraviolet radiation. 
     
     
       8. An electronic device comprising:
 an audio speaker to transduce electronic signals into sound; 
 a back volume coupled to the audio speaker, the back volume being positioned behind a speaker driver of the audio speaker; 
 a filler for occupying the back volume, the filler comprising:
 an acoustic filler positioned in the back volume so that the acoustic filler can adsorb gas flowing into the back volume, the acoustic filler comprising a plurality of acoustically active beads, and 
 an expandable filler positioned with the acoustic filler in the back volume so that it occupies a percentage of the back volume, wherein the expandable filler can permanently expand from a first dimension to a second dimension upon exposure to an expansion trigger to affect mobility of the acoustic filler, and wherein the expandable filler comprises a plurality of expandable beads mixed with the acoustically active beads; and 
 
 a processor coupled to the audio speaker and to a memory, the memory having stored therein one or more application programs including instructions that, when executed by the processor, transmit electronic signals to the audio speaker. 
 
     
     
       9. The electronic device of  claim 8  wherein the expandable filler comprises an expandable coating positioned on at least one interior surface of the back volume. 
     
     
       10. The electronic device of  claim 8  wherein a density of the expandable beads is within 90-110% of a density of the acoustically active beads. 
     
     
       11. The electronic device of  claim 8  wherein an average size of the plurality of expandable beads is within an order of magnitude of an average size of the plurality of acoustically active beads. 
     
     
       12. The electronic device of  claim 8  wherein the expandable filler occupies between 0.5% and 20% of the back volume. 
     
     
       13. The electronic device of  claim 8  wherein the expandable filler occupies between 1% and 2% of the back volume. 
     
     
       14. The electronic device of  claim 8  wherein the expansion trigger is heat, light, or ultraviolet radiation. 
     
     
       15. The electronic device of  claim 8  wherein the electronic device is a smartphone, a tablet, or a laptop computer. 
     
     
       16. The electronic device of  claim 8  wherein the application programs include one or more of a telephony application, a voicemail application, a sound playback application, an e-mail application, an internet browsing application, a scheduling application, and a photo application. 
     
     
       17. The electronic device of  claim 8 , further comprising one or more of a microphone coupled to the processor, radio frequency (RF) circuitry coupled to the processor, or a display coupled to the processor.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a division of pending U.S. application Ser. No. 16/184,888, filed Nov. 8, 2018. 
    
    
     TECHNICAL FIELD 
     The disclosed aspects relate generally to audio speakers and in particular, but not exclusively, to audio speakers that can use a combination of acoustically active and expandable fillers in their back volumes to improve loudspeaker performance. 
     BACKGROUND 
     Loudspeakers include a back volume and a membrane or diaphragm that oscillates and emits sound when driven by an electromagnetic transducer. A variety of different forces act on the membrane while it is being moved, distorting its intended acceleration by the electromagnet and thus distorting the sound wave it emits. Reduction of these additional membrane forces leads to improved sound quality. 
     One of the forces acting on the membrane results from pressure fluctuations in the back volume due to compression and decompression of air by the moving membrane. These pressure fluctuations can be reduced by increasing the space of the back volume—e.g., by making it larger. But in hand-held devices such as cell phones, increasing the size of the back volume is possible only to a minor degree because these devices should be kept conveniently small. 
     In the context of this disclosure, “acoustically active bead” means any entity with various geometrical shapes and capable of adand desorption. The sorptive material can for example comprise zeolites, active carbon or metal organic frameworks (MOFs). 
     SUMMARY 
     Aspects are described of an audio speaker. The audio speaker includes a housing defining a back volume behind a speaker driver, so that the speaker driver can convert an electrical audio signal into a sound and the sound can propagate through a gas in the back volume. A permeable partition divides the back volume into a rear cavity defined between the speaker driver, the housing, and the permeable partition and an adsorption cavity defined between the housing and the permeable partition. The permeable partition includes a plurality of holes that place the rear cavity in fluid communication with the adsorption cavity to allow the gas to flow between the rear cavity and the adsorption cavity. An expandable filler is positioned in the adsorption cavity so that it occupies a percentage of the volume of the adsorption cavity. The expandable filler can permanently expand from a first dimension to a second dimension upon the application of an expansion trigger. An acoustic filler is positioned with the expandable filler in the adsorption cavity to adsorb the gas, the acoustic filler comprising a plurality of acoustically active beads. 
     Aspects are described of a filler for occupying a volume. The filler includes an expandable filler positioned in the volume so that it occupies a percentage of the volume. The expandable filler can permanently expand from a first dimension to a second dimension upon the application of an expansion trigger. An acoustic filler is positioned with the expandable filler in the volume so that the acoustic filler can adsorb gas flowing into the volume. The acoustic filler comprises a plurality of acoustically active beads. 
     Aspects are described of a method including inserting an expandable filler in a back volume of an audio speaker, so that the expandable filler occupies a percentage of the back volume. An acoustic filler is inserted in at least a portion of the back volume not occupied by the expandable filler so that the acoustic filler can adsorb gas flowing into the back volume; the acoustic filler comprising a plurality of acoustically active beads. An expansion trigger is applied to the expandable filler and the acoustic filler so that the expandable filler permanently expands from a first dimension to a second dimension to reduce movement of the acoustically active beads in the back volume. 
     Aspects are described of an expandable material. The expandable material includes a solvent, a plurality of polymer granules mixed into the solvent, a polymeric binder, and a modifier that is a chemically inert density-regulating compound or a viscosity-regulating compound. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Non-limiting and non-exhaustive aspects of the present invention are described with reference to the following figures, wherein like reference numerals refer to like parts throughout the various views unless otherwise specified. 
         FIG. 1  is a pictorial view of an aspect of an electronic device. 
         FIGS. 2A-2B  are sectional views of aspects of an audio micro-loudspeaker for an electronic device. 
         FIG. 3  is a schematic of an aspect of an electronic device including an aspect of an audio micro-speaker such as the ones shown in  FIGS. 2A-2B . 
         FIGS. 4A-4C  are cross-sectional views of an aspect of an audio micro-loudspeaker back volume, such as the ones shown in  FIGS. 2A-2B , with acoustically active beads and expandable beads.  FIG. 4A  shows the expandable beads in their unexpanded state,  FIG. 4B  in their expanded state.  FIG. 4C  illustrates expansion of a single expandable bead. 
         FIGS. 5A-5B  are cross-sectional views of an aspect of an audio micro-loudspeaker back volume, such as the ones shown in  FIGS. 2A-2B , with an expandable coating on the walls of the back volume.  FIG. 5A  shows the coating in its unexpanded state,  FIG. 5B  in its expanded state. 
         FIG. 6  is a flowchart of an aspect of a process for making an aspect of expandable material for the uses shown in  FIGS. 4A-4C and 5A-5B . 
         FIG. 7  is a flowchart of an aspect of a process for using an expandable material for the uses shown in  FIGS. 4A-4C and 5A-5B . 
         FIGS. 8A-8D  are a perspective view and a series of side views of a simplified embodiment of a back volume, illustrating different orientations of the back volume. 
         FIG. 9  is a graph illustrating the resonance frequency shift produced by the back volume orientations shown in  FIGS. 8A-8D  when the back volume is without expandable beads. 
         FIG. 10  is a graph illustrating the resonance frequency shift produced by the back volume orientations shown in  FIGS. 8A-8D  when the back volume has expandable beads. 
     
    
    
     DETAILED DESCRIPTION 
     The disclosure below describes aspects of a loudspeaker including a back volume with an acoustic filler and an expandable filler. 
     Specific details are described to provide an understanding of the disclosed aspects, but one skilled in the art will recognize that the invention can be practiced without one or more of the described details or with other methods, components, materials, etc. In some instances, well-known structures, materials, or operations are not shown or described in detail but are nonetheless encompassed within the scope of the invention. 
     Reference throughout this specification to “one aspect” or “an aspect” means that a described feature, structure, or characteristic can be included in at least one described aspect, so that appearances of “in one aspect” or “in an aspect” do not necessarily all refer to the same aspect. Furthermore, the particular features, structures, or characteristics can be combined in any suitable manner in one or more aspects. 
     One approach to reducing back volume pressure fluctuations for handheld devices is to place absorbent materials like carbon black or zeolites into the back volumes. It has been shown that such materials can virtually increase the back volume—in other words, their presence in the back volume enhances loudspeaker performance as if the speaker&#39;s back volume had been made bigger. 
     Loudspeaker 
       FIG. 1  illustrates an aspect of an electronic device  100 . Electronic device  100  can be a smartphone device in one aspect, but in other aspects can be any other portable or stationary device or apparatus, such as a laptop computer or a tablet computer. Electronic device  100  can 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  can also include hardware to facilitate such capabilities. For example, an integrated microphone  102  can pick up the voice of a user during a call, and an audio speaker  106 , e.g., a micro loudspeaker, can deliver a far-end voice to the near-end user during the call. Audio speaker  106  can also emit sounds associated with music files played by a music player application running on electronic device  100 . A display  104  can 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 can of course be included in electronic device  100 . 
       FIGS. 2A-2B  illustrate aspects of an audio speaker of an electronic device. In an aspect, an audio speaker  106  includes an enclosure, such as a speaker housing  204 , which supports a speaker driver  202 . Speaker driver  202  can be a loudspeaker used to convert an electrical audio signal into a sound. For example, speaker driver  202  can be a micro speaker having a diaphragm  206  supported relative to housing  204  by a speaker surround  208 . Speaker surround  208  can flex to permit axial motion of diaphragm  206  along a central axis  210 . For example, speaker driver  202  can have a motor assembly attached to diaphragm  206  to move diaphragm  206  axially with piston-like motion, i.e., forward and backward, along central axis  210 . The motor assembly can include a voice coil  212  that moves relative to a magnetic assembly  214 . In an aspect, magnetic assembly  214  includes a magnet, such as a permanent magnet, attached to a top plate at a front face and to a yoke at a back face. The top plate and yoke can be formed from magnetic materials to create a magnetic circuit having a magnetic gap within which voice coil  212  oscillates forward and backward. Thus, when the electrical audio signal is input to voice coil  212 , a mechanical force can be generated that moves diaphragm  206  to radiate sound forward along central axis  210  into a surrounding environment outside of housing  204 . 
     Movement of diaphragm  206  to radiate sound forward toward the surrounding environment can cause sound to be pushed in a rearward direction. For example, sound can propagate through a gas filling a space enclosed by housing  204 . More particularly, sound can travel through air in a back volume  216  behind diaphragm  206 . Back volume  216  can influence acoustic performance. In particular, the size of back volume  216  can influence the natural resonance peak of audio speaker  106 . For example, increasing the size of back volume  216  can result in the generation of louder bass sounds. 
     In an aspect, back volume  216  within housing  204  can be separated into several cavities. For example, back volume  216  can be separated by a permeable partition  222  into a rear cavity  218  and an adsorption cavity  220 . Rear cavity  218  can be located directly behind speaker driver  202 . That is, speaker driver  202  can be suspended or supported within rear cavity  218  so that sound radiating backward from diaphragm  206  propagates directly into rear cavity  218 . Accordingly, at least a portion of rear cavity  218  can be defined by a rear surface of diaphragm  206 , and similarly, by a rear surface of speaker surround  208 . Furthermore, given that permeable partition  222  can extend across a cross-sectional area of back volume  216  between several walls of housing  204 , rear cavity  218  can be further defined by an internal surface of housing  204  and a first side  224  of permeable partition  222 . 
     Back volume  216  can include adsorption cavity  220  separated from rear cavity  218  by permeable partition  222 —i.e., adsorption cavity  220  can be adjacent to rear cavity  218  on an opposite side of permeable partition  222 . In an aspect, adsorption cavity  220  is defined by an internal surface of housing  204  that surrounds back volume  216 , and can also be defined by a second side  226  of permeable partition  222 . Thus, rear cavity  218  and adsorption cavity  220  can be immediately adjacent to one another across permeable partition  222 . 
     In an aspect, adsorption cavity  220  can be placed in fluid communication with the surrounding environment through a fill port  228 . For example, fill port  228  can be a hole through a wall of housing  204  that places adsorption cavity  220  in fluid communication with the surrounding environment. The port can be formed during molding of housing  204 , or through a secondary operation, as described further below. To isolate adsorption cavity  220  from the surrounding environment, a plug  230  can be located in fill port  228 , e.g., after filling adsorption cavity  220  with an adsorptive filler  232 , to prevent leakage of the adsorptive filler  232  into the surrounding environment. Thus, adsorption cavity  220  can be partially defined by a surface of plug  230 . 
     Audio speaker  106  can have a form factor with any number of shapes and sizes. For example, audio speaker  106 , and thus housing  204 , can have an external contour that appears to be a combination of hexahedrons, cylinders, etc. One such external contour could be a thin box, for example. Furthermore, housing  204  can be thin-walled, and thus, a cross-sectional area of a plane passing across housing  204  at any point can have a geometry corresponding to the external contour, including rectangular, circular, and triangular, etc. Accordingly, permeable partition  222  extending across back volume  216  within housing  204  can also have a variety of profile shapes. For example, in the case where audio speaker  106  is a hexahedron, e.g., a low-profile box having a rectangular profile extruded in a direction orthogonal to central axis  210 , permeable partition  222  can have a rectangular profile. 
     Adsorptive filler  232  can be packaged in adsorption cavity  220  by directly filling, e.g., packing, adsorption cavity  220  with a loose adsorptive material and/or by coating inner surfaces of housing  204  with an adsorptive material. Directly filling adsorption cavity  220  can be distinguished from indirectly filling adsorption cavity  220  in that the loose adsorptive material can be poured, injected, or other transferred into adsorption cavity  220  in a loose and unconstrained manner such that the adsorptive material can move freely within adsorption cavity  220 . That is, the adsorptive material can be constrained only by the walls that define adsorption cavity  220 , e.g., an inner surface of housing  204 , and not by a separate constraint, e.g., a bag, pouch, box, etc. that is filled with adsorptive material prior to or after inserting the separate constraint into adsorption cavity  220 . In an aspect, at least a portion of the space of adsorption cavity  220  is filled with adsorptive filler  232 , and at least a portion of an inner surface of housing  204  within adsorption cavity  220  is covered by adsorptive filler  232 . The adsorptive filler  232  can be any appropriate adsorptive material that is capable of adsorbing a gas located in back volume  216 . For example, adsorptive filler  232  can include acoustically active beads described below in connection with  FIGS. 4A-4B and 5A-5B , which are configured to adsorb air molecules. The adsorptive material can be in a loose granular form. More particularly, the adsorptive filler  232  can include unbound particles that are able to move freely within adsorption cavity  220 , e.g., the particles can shake around during device use. Thus, permeable partition  222  can act as a barrier to prevent adsorptive filler  232  from shaking out of adsorption cavity  220  into rear cavity  218  behind speaker driver  202 . 
       FIG. 2B  illustrates another aspect of an audio loudspeaker of an electronic device. Rear cavity  218  and adsorption cavity  220  can have different relative orientations in various aspects. For example, in the aspect shown in  FIG. 2A , adsorption cavity  220  is located lateral to rear cavity  218 , i.e., is laterally offset from rear cavity  218  away from central axis  210 . As a result, sound emitted rearward from diaphragm  206  can propagate directly toward a rear wall of rear cavity  218 , rather than be radiated directly toward permeable partition  222 . 
     But in the aspect shown in  FIG. 2B , audio speaker  106  includes axially arranged back volume  216  cavities. For example, adsorption cavity  220  can be located directly behind rear cavity  218 , so that central axis  210  can intersect rear cavity  218  behind diaphragm  206  and adsorption cavity  220  on an opposite side of permeable partition  222 . Accordingly, permeable partition  222  can cross back volume  216  along a plane such that normal vector  250  emerging from first side  224  and pointing into rear cavity  218  is oriented in a direction that is parallel to central axis  210 . For example, rear cavity  218  and adsorption cavity  220  can each be flat and thin and positioned forward-and-behind along central axis  210 . Thus, sound emitted rearward by diaphragm  206  can propagate along central axis  210  directly through rear cavity  218  and permeable partition  222  into adsorption cavity  220 . 
     Permeable partition  222  can be oriented at any angle relative to central axis  210 . That is, although first face can face a direction orthogonal to, or parallel to, central axis  210 , in an aspect, permeable partition  222  is oriented at an oblique angle relative to central axis  210 . Thus, adsorption cavity  220  can be some combination of lateral to, or directly behind, adsorption cavity  220  within the scope of this description. In any case, rear cavity  218  and adsorption cavity  220  can be adjacent to one another such that opposite sides of permeable partition  222  define a portion of each cavity. 
       FIG. 3  schematically illustrates an aspect of an electronic device that includes a micro speaker. As described above, electronic device  100  can 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  can include one or more processors  902  that execute instructions to carry out the different functions and capabilities described above. Instructions executed by the one or more processors  902  of electronic device  100  can be retrieved from local memory  904 , and can 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  902  can directly or indirectly implement control loops and provide drive signals to voice coil  212  of audio speaker  106  to drive diaphragm  206  motion and generate sound. 
     Audio speaker  106  with the structure described above can include back volume  216  separated by an acoustically transparent barrier, e.g., permeable partition  222 , into two cavities: rear cavity  218  directly behind speaker driver  202  and adsorption cavity  220  adjacent to rear cavity  218  across permeable partition  222 . Furthermore, adsorption cavity  220  can be directly filled with an adsorptive material such that back volume  216  includes an adsorptive volume defined directly between a system housing  204  and the acoustically transparent barrier. The adsorptive volume can reduce the overall spring rate of back volume  216  and lower the natural resonance peak of audio speaker  106 . That is, adsorptive filler  232  can adsorb and desorb randomly traveling air molecules as pressure fluctuates within back volume  216  in response to a propagating sound. As a result, audio speaker  106  can have a higher efficiency at lower frequencies, as compared to a speaker having a back volume  216  without adsorptive material. Thus, the overall output power of audio speaker  106  can be improved. More particularly, audio speaker output can be louder during telephony or music play back, especially within the low-frequency audio range. Accordingly, audio speaker  106  having the structure described above can produce louder, richer sound within the bass range using the same form factor as a speaker back volume without multiple cavities, or can produce equivalent sound within the bass range within a smaller form factor. Furthermore, because adsorption cavity  220  is defined directly between housing  204  and permeable partition  222 , which are sealed together, the form factor of audio speaker  106  can be smaller than, e.g., a speaker back volume that holds a secondary container, e.g., a mesh bag, filled with an adsorbent material. 
     Back-Volume Configurations with Expandable Fillers 
     If a back volume is not entirely and densely filled with acoustically active beads, the use of beads can lead to a varying sound quality. This is mainly caused by undesirable movements of the beads inside the back volume. For example, upon changing the spatial orientation of a loudspeaker module, the sound quality might change because the beads occupy the lowest possible space inside the cavity. However, it is preferable to have constant sound quality regardless of the spatial orientation. 
     A simple approach to immobilize the acoustically-active beads would be to glue them together. But since the acoustically-active beads comprise a highly porous structure which is needed for improving the acoustic properties, it is impossible to glue them together and not lose acoustic performance. The bead&#39;s pores would be at least partly blocked by the glue because it would penetrate the pores and, when solidified, would hinder any gas transport through or gas storage in these pores. And, unfortunately, capillary forces favor such penetration of pores by glue—i.e., glue tends to block small pores of beads more likely than just immobilizing beads by gluing them together. Another approach to immobilize beads would be to fill the back volume completely. But in a production process slight variations of the filling density are extremely difficult to control and can hardly be avoided. 
     By numerous experiments performed by the inventors, it was shown that the addition to the bead assemblage a second kind of material comprising an expandable filler, and the expansion of this material, can prevent the bead assemblage from moving. By the correct amount of volume expansion of such material, the beads are compressed and/or squeezed together, so that they are immobilized. Thus, the variation of the sound quality because of the different spatial orientations of a loudspeaker can be mitigated or completely suppressed. 
       FIGS. 4A-4C  illustrate an aspect an expandable filler including a plurality of expandable beads in an audio speaker back volume  400 .  FIG. 4A  illustrates the expandable beads before expansion and  FIG. 4B  after expansion.  FIG. 4C  illustrates the expansion of a single expandable bead. 
     Back volume  400  is a three-dimensional space bounded by a plurality of walls  402   a - 402   d . At least one of the walls, wall  402   a  in this instance, is porous so as to allow gas to flow in and out of the back volume. In the illustrated aspect back volume  400  is a hexahedron, but in other aspects it can be some other type of polyhedron, regular or irregular. In still other aspects, back volume  400  need not be a polyhedron but can instead be made up of a combination of curved surfaces, plane surfaces, or both. 
     Back volume  400  is filled partially by an expandable filler made up of a plurality of expandable beads  404  and partially filled by an acoustic filler comprising a plurality of acoustically active beads  406 . Acoustically active beads  406  are those that have sorption properties that allow them to adsorb or desorb gases driven by the driver parts of the speaker into back volume  400  through porous wall  402   a . In the illustrated aspect expandable beads  404  and acoustically active beads  406  have the same shape—both are spherical in this instance—but in other aspects the two types of beads need not have the same shape. 
     In one aspect, the average size of the plurality of expandable beads  404  is similar to the average size of the plurality of acoustically active beads  406 , meaning that the sizes of the beads are within an order of magnitude of each other, in another aspect, are within 90-110% of each other. The density of expandable beads  404  is also similar to the density of acoustically active beads  406 , meaning that their densities are within 90-110% of each other. When expandable beads  404  and acoustically active beads  406  are mixed inside back volume  400 , or mixed before being inserted into the back volume, it is desirable for the expandable beads to be uniformly distributed among the acoustically active beads, or vice versa. Similarity of size and density of expandable beads  404  and acoustically active beads  406  can be desirable to reduce or prevent separation of the two types of beads when mixed; big differences in size or density can allow gravity or other inertial forces, such as those caused by shaking, to separate the two types of beads from each other. Having the expandable beads possess similar size and density as the acoustically active beads is also advantageous as the existing process for filling in the beads can be used without or with only minor modifications. 
     For example, a mixture of two kinds of spheres with at least an order of magnitude different sizes would rapidly separate on shaking, and the smaller spheres would fall through the voids between the larger ones and collect themselves in the bottom. In some aspects, however, it is possible to use expandable and acoustically active beads of different sizes and densities, for example, if the mixing of the both types of beads takes place directly before the filling of the loudspeaker back volume. 
       FIG. 4B  illustrates expandable beads  404  in their expanded state. As further explained below, expandable beads  404  are formulated so that they permanently expand from a first dimension to a larger second dimension upon the application of an expansion trigger to the beads. The expansion trigger can be heat, light, electromagnetic radiation such as ultraviolet (UV) radiation, alternating magnetic fields, or some other trigger. When expandable beads  404  expand, they reduce the space into which acoustically active beads  406  are packed, exerting a mechanical force on the acoustically active beads and thus substantially reducing or eliminating movement or mobility of the acoustically active beads within back volume  400 . Put differently, when expanded the expandable beads  404  partially or fully lock or fix acoustically active beads  406  into position. In one aspect, when expanded the expandable beads  404  can occupy between 0.5% and 20% of the back volume, e.g., more particularly between 1% and 2% of the back volume. The acoustically active beads occupy at least part of the remainder of the back volume. Persons skilled in the art will appreciate that the percentages of back volume  400  occupied by the expandable beads and the acoustically active beads will not add up to 100% of the back volume because of the presence of interstitial spaces between beads. 
       FIG. 4C  illustrates the expansion of a single expandable bead  404 . Upon application of the expansion trigger, bead  404  expands from radius ra to radius rb, and thus its volume increases from volume Va to volume Vb. Depending on formulation of the beads and the expansion factor defined by f=Vb/Va, with Vb being the volume after expansion and Va the volume before expansion, the free volume inside the back volume is reduced. The assemblage of a plurality of acoustically-active beads is squeezed together, resulting in a block in which all beads are mostly or totally fixed. Generally, the higher f is, the higher is the degree of fixation. 
     Acoustically active beads  406  can be any of various known formulations. In one aspect, they can have a formulation that includes a polymer binder and zeolite, but other bead formulations are possible. Examples of sorptive materials that can be used include zeolites, active carbon or metal organic frameworks (MOFs). Since the expandable formulation does not contribute to the increase of virtual volume which is the purpose of the zeolite beads, an optimum percentage of this formulation in the acoustic beads exist which allows a reasonable fixation and a satisfactory acoustic performance. It is advantageous to use between 0.5% and 20% by mass of the expandable formulation, more advantageous to use between 1% and 5% by mass of the expandable formulation, and the most advantageous is to use between 1% and 2% by mass of the expandable formulation. 
       FIGS. 5A-5B  illustrate another aspect in which an expandable filler can be applied into a back volume  500  as a layer or a sheet comprising expandable parts which can be laid into the back volume. 
     Like back volume  400 , back volume  500  is a three-dimensional space bounded by a plurality of walls  502   a - 502   d . Each of walls  502   b - 502   d  has an interior surface  503 : wall  502   b  has interior surface  503   b , wall  502   c  has interior surface  503   c , and wall  502   d  has interior surface  503   d . At least one of the walls, wall  502   a  in this instance, is porous so as to allow gas to flow in and out of the back volume. In the illustrated aspect back volume  500  is a regular hexahedron, but in other aspects it can be some other type of polyhedron, regular or irregular. In still other aspects, back volume  500  need not be a polyhedron, but can instead be made up of a combination of curved surfaces, plane surfaces, or both. 
     Back volume  500  is partially filled by an expandable filler comprising a plurality of expandable layers or sheets  504  deposited on the interior surfaces  503  of at least one wall  502 . Back volume  500  is also partially filled by an acoustic filler including a plurality of acoustically active beads  406 . Acoustically active beads  406  are those that have sorption properties that allow them to adsorb or desorb gases driven by the driver parts of the speaker into back volume  500  through porous wall  502   a.    
     The illustrated aspect has layers  504  deposited on multiple interior surfaces: layer  504   b  is deposited on interior surface  503   b , layer  504   c  is deposited on interior surface  503   c , and layer  504   d  is deposited on interior surface  503   d . Because wall  502   a  is porous, no layer  504  is deposited on its interior surface because it would prevent the flow of gas into and out of back volume  500 . In other aspects, layers  504  can be positioned a greater or lesser number of interior surfaces  503  than shown, ranging from a single interior surface to every interior surface of the back volume except the interior surface of the back volume&#39;s porous wall. 
       FIG. 5B  illustrates expandable layers  504  in their expanded state. As further explained below, expandable layers  504  are formulated so that they permanently expand from a first dimension t to a larger second dimension T upon application of an expansion trigger: layer  504   b  expands from thickness tb to thickness Tb, layer  504   c  expands from thickness tc to thickness Tc, and so on. The expansion trigger can be heat, light, electromagnetic radiation such as ultraviolet (UV) radiation, alternating magnetic fields, or some other trigger. When the layers  504  expand, they reduce the volume into which acoustically active beads  406  are packed, exerting a mechanical force on the acoustically active beads and thus substantially reducing or eliminating their movement or mobility within back volume  500 . Put differently, when expanded, the layers  504  partially or fully lock or fix acoustically active beads  406  into position. In one aspect, when expanded the expandable filler can occupy between 0.5% and 20% of the back volume, and for example, more particularly, the expandable filler can be between 1% and 2% of the back volume. The acoustic filler occupies at least part of the remainder of the back volume. Persons skilled in the art will appreciate that the percentages of back volume  500  occupied by the expandable layers  504  and the acoustically active beads  406  will not add up to 100% of the back volume because of the presence of interstitial spaces between acoustically active beads. 
     Expandable Filler Manufacturing Process 
       FIG. 6  illustrates an aspect of a process  600  for making an expandable filler for an audio speaker back volume, such as the ones shown in  FIGS. 4A-4B and 5A-5B . Blocks shown in dashed lines are optional. The process starts at block  602 . 
     At block  604 , an aqueous slurry (i.e., a semiliquid mixture of fine particles suspended in a solvent, in this case water) of an expandable polymeric material is formed by combining commercially available expandable polymer microspheres, optionally a density regulator, a solvent, and a polymeric binder. The binder can be a polyacrylic or polyurethane sol; unexpectedly, using a polymeric binder such as an acrylic or polyurethane sol leads to mechanically stable beads that retain their geometrical shape upon expansion. 
     At block  606 , two different process options are available depending on whether the expandable filler will be a paste that can be used for coating the interior surface of a back volume, as in  FIGS. 5A-5B , or whether it will be formed into expandable beads for use in the back volume, as shown in  FIGS. 4A-4B . If the expandable material will be a paste, then at block  608  a thickener or viscosity-regulating compound is added to the slurry to adjust the viscosity of the slurry or to produce a stable gel. Slurries with a viscosity similar to glues used in commercial processes have the advantage that existing equipment for the application of glues can be used. In one embodiment the viscosity-regulating compound can be fumed silica, but in other aspects a different viscosity-regulating compound can be used. At block  610  the resulting slurry is mechanically stirred until thoroughly mixed. If the stirred mixture is not already the desired consistency, then it is allowed to rest or is otherwise processed to thicken it into a paste. The process ends at block  611   
     If the expandable filler will be expandable beads, then at optional block  612 , a density-regulating compound is added to the slurry to adjust the density of the expandable beads to be similar to the density of the acoustically active beads with which they will be mixed. The density of such beads can be increased by adding to the slurry compounds of relatively high density, for example finely dispersed metal oxides. Oxides that can be used include, among others, Zinc oxide (ZnO), Tin oxide (SnO 2 ), Titanium oxide (TiO 2 ), Bismuth oxide (Bi 2 O 3 ), Zirconium oxide (ZrO 2 ), or Hafnium oxide (HfO 2 ). The density of many oxides, especially the above-listed ones, is higher than the density of typical polymers, so that the addition of these oxides increases the density of the final beads. 
     At block  614  the slurry is mechanically stirred until thoroughly mixed. At block  616  the slurry is pressurized and forced through an oscillating nozzle to produce droplets of the slurry. For instance, the slurry can be pressurized with air and pushed through an oscillating nozzle with a suitable diameter, powered by an amplifier connected to a function generator. At block  618 , the droplets emerging from the nozzle in block  616  are frozen, for instance by dropping them through a cooling tower. For instance, the droplets can be dropped into a cooling tower of ca. 3 meters height, cooled continuously by a mixture of nitrogen and air to a temperature in the top, for example, of −20±5° C. and in the bottom of −50±5° C. 
     At block  620  the frozen droplets are collected from the cooling tower and at the frozen droplets are freeze-dried at block  624  by subjecting them to a vacuum, to cause any remaining water in the droplets to sublimate. For instance, the frozen droplets can be collected in a round-bottom flask that was precooled to about −20° C. and subjected to a vacuum until the water (ice) was completely removed from the frozen droplets by sublimation, thus freeze drying the frozen droplets into beads. Additionally or instead of freeze-drying at block  622 , the frozen droplets or freeze-dried beads can be collected and heated at block  624  to obtain the final beads. For instance, the freeze-dried beads can be collected on a steel tray, heated in a forced convection air oven to a suitable temperature, kept at that temperature for a certain amount of time, and then cooled. 
     At block  626  the beads are mechanically filtered or sieved to obtain beads similar in size to the acoustically active beads that will be used. The process ends at block  628 . Further details of specific aspects of process  600  are given in examples 1-3 below. 
     Example 1 
     Into a 0.5 L beaker were placed 100.0 g of acrylic emulsion, 56.0 g of deionized water, 34.0 g of fine zinc oxide, 2.00 g of 15% KOH solution, and 33.0 g of F-48D expandable microspheres. The slurry was stirred for 1 hour and dropped using an electronically controlled oscillating nozzle into an excess of liquid nitrogen. The frozen droplets were freeze-dried and sieved to obtain the fraction with pellet diameter 0.355-0.400 mm. A small fraction of about 100 mg was separated from the batch and when heated to 115° C. for about 2 min, the bead volume expanded several fold without losing their round shape and integrity. 
     Example 2 
     Into a 0.5 L beaker were placed 100.0 g of acrylic emulsion, 60.0 g of deionized water, 32.0 g of fine zinc oxide, 2.00 g of 15% KOH solution, and 35.0 g of EML101 expandable microspheres. The slurry was stirred for 1 h, and dropped using electronically controlled oscillating nozzle into an excess of liquid nitrogen. The frozen droplets were freeze-dried and sieved to obtain the fraction with beads diameter 0.355-0.400 mm. A small fraction of about 100 mg was separated from the batch and heated to 115° C. for about 2 min, the bead volume expanded several fold without losing their round shape and integrity. 
     The beads obtained as above were mixed with acoustically active beads in ratio of 1:49, and a back volume of a loudspeaker was filled with this mixture. The relative amount of the expandable beads should, on one hand, be sufficient to fix the acoustic beads after the expansion, on the other hand, as the expandable beads are neutral material, it should not be too large to diminish significantly the acoustic performance of the whole assemblage. The loudspeaker was heated several minutes at 115° C., and its acoustic performance in horizontal and vertical was measured. The loudspeaker containing the expanded beads demonstrated the same performance independently on its spatial orientation. 
     Example 3 
     In a beaker, to 5.00 g acrylic emulsion was added 0.15 g of fumed silica (particle size &lt;7 nm), and 5.00 g of F-48D expandable microspheres. The components were carefully mixed with a spatula to obtain a thick paste. About 40 mg of such paste was placed as a stripe in the corner of the back volume of a loudspeaker, and dried at 70° C. for 1 h. The back volume of the loudspeaker was filled with the acoustic beads, sealed and heated for several minutes at 115° C. The loud-speaker with the expanded stripe in the back volume demonstrated the same performance in vertical and horizontal positions. 
       FIG. 7  illustrates an aspect of a process  700  by which an expandable filler can be used in an audio speaker back volume. The process starts at block  702 . At block  704 , different process options are available depending on whether the application will use a paste to coat an interior surface of a back volume, as in  FIGS. 5A-5B , or will use expandable beads in the back volume, as shown in  FIGS. 4A-4B . 
     If a paste will be used to coat interior surfaces of the back volume, then at block  706  the paste is deposited as an expandable layer or sheet on at least one interior surface of the back volume (see  FIGS. 5A-5B ). The application of the paste can be done by various means, such as doctor blading, jetting, or printing. Using such a paste is advantageous because the location of the unexpanded and then expanded material can be precisely determined, whereas in the mixture of expandable beads and acoustically active beads the expansion takes place statistically throughout the mixture of acoustically active and expandable beads. 
     At block  708 , the deposited expandable layers are allowed to dry on the surfaces on which they were deposited, and at block  710  the remaining part of the back volume is filled with acoustically active beads. The back volume is then closed so that the acoustically active beads do not flow out. At block  712  the expansion trigger is applied to the back volume to cause the expandable layers to permanently expand, thus constricting the acoustically active beads into a smaller volume and substantially immobilizing them. The expansion trigger can be heat, but other triggers as, for example, electromagnetic waves or an alternating magnetic field are also possible. The process ends at block  714 . 
     If expandable beads will be used in the back volume, then at block  716  the expandable beads are mixed with the acoustically active beads in the desired ratio. At block  718 , the bead mixture is inserted into the back volume (see  FIGS. 4A-4B ) and the back volume is then closed so that the beads do not flow out. In other aspects of the process, the expandable beads can be inserted into the back volume before or after acoustically active beads are inserted. At block  720  the expansion trigger is applied to the back volume to cause the expandable beads to permanently expand, thus constricting the acoustically active beads into a smaller volume and substantially immobilizing them. The expansion trigger can be heat, but other triggers as, for example, electromagnetic waves or an alternating magnetic field are also possible. The process ends at block  722 . 
     Results 
       FIGS. 8A-8D  are a perspective views and three cross-sectional views illustrating orientations of a simplified representation of a back volume  800  of an audio speaker in a smartphone such as an iPhone. The representation of back volume  800  does not necessarily represent the exact shape of the back volume, but instead illustrates three back volume orientations used to test whether the immobilized acoustically active beads are effective in maintaining uniform sound from an audio speaker. 
     Volume  800  is hexahedral and has three pairs of surfaces: a pair of surfaces  1  with maximum area, a pair of surfaces  3  with minimum area, and a pair of surfaces  2  with an area in between surfaces  1  and  3 .  FIGS. 8B-8D  illustrate the three orientations used. In  FIG. 8B , surfaces  3  are horizontal, while surfaces  1  and  2  run vertically. In  FIG. 8C , surfaces  2  are horizontal while surfaces  1  and  3  run vertically. And in  FIG. 8D , surfaces  1  are horizontal while surfaces  2  and  3  run vertically. 
       FIG. 9  illustrates the loudspeaker performance of a loud-speaker (e.g., micro-speaker) whose back volume includes no expandable filler. A loudspeaker back volume built from transparent plastics was filled with acoustically active beads—but not very densely, so that the beads could slightly move inside during shaking—and was sealed. The acoustic performance in various spatial orientations was measured. In the vertical position ( FIG. 8B ), a small free space in the loudspeaker back volume appeared after some time, as the beads assemblage slightly densified on having been shaken by acoustic waves. The loud-speaker acoustic performance in vertical ( FIG. 8B ) and horizontal ( FIG. 8D ) orientations was therefore different. 
       FIG. 9  shows the electric impedance plotted against the frequency of a loudspeaker module filled with acoustical active beads in three different orientations. Curve  1  was recorded with the module in the orientation of  FIG. 8B ; curve  2  was recorded with the module in the orientation of  FIG. 8D ; and curve  3  was recorded with the same spatial alignment as used for curve  1  but with the opposite surface  3  at the top. Variations in the resonance frequency were recorded to be as high as 74 Hz by a change of the loudspeaker orientation. 
       FIG. 10  illustrates results of using the expandable filler shown in  FIGS. 4A-4B . The diagram shows the electrical impedance plotted against the frequency of a loudspeaker module filled with a mixture of acoustical active beads and expanded beads in two different orientations. 
     The expandable beads obtained from Example 1 above in the unexpanded state were mixed with acoustically active beads in a ratio between 1:4 and 1:200. A back volume of a loudspeaker was filled with this mixture and sealed. The loudspeaker was heated for several minutes at a temperature sufficient to trigger the expansion of the beads, and its acoustic performance in horizontal and vertical orientations was measured. The expandable beads fixed the acoustically active bead assemblage and prevented the acoustically active beads from gathering in one part of the loudspeaker back volume. The loudspeaker containing the expanded beads demonstrated the same performance independently on its spatial orientation. Curve  1  was recorded with the module in the orientation of  FIG. 8D , while curve  2  was recorded with the orientation of  FIG. 8B . The curves are within measurement errors and in the low frequency region below 1000 Hz are substantially identical. 
     The above description of aspects is not intended to be exhaustive or to limit the invention to the described forms. Specific aspects of, and examples for, the invention are described herein for illustrative purposes, but various modifications are possible. To aid the Patent Office and any readers of any patent issued on this application in interpreting the claims appended hereto, applicants wish to note that they do not intend any of the appended claims or claim elements to invoke 35 U.S.C. § 112(f) unless the words “means for” or “step for” are explicitly used in the particular claim.

Metadata:
Filing Date: 20200805
Publication Date: 20211116
Grant Date: 20211116
Priority Date: 20181108
Inventors: GAVRYUSHIN, Andrey
WAGNER, Veronika
SAUER, JUERGEN
Assignee: APPLE INC
CPC Classifications: [{"code": "H04R1/288", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04R31/00", "inventive": true, "first": false, "tree": "[]"}, {"code": "G10K11/002", "inventive": true, "first": true, "tree": "[]"}, {"code": "C08J2333/04", "inventive": false, "first": false, "tree": "[]"}, {"code": "G10K11/002", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04R1/288", "inventive": true, "first": true, "tree": "[]"}, {"code": "C08J2203/22", "inventive": false, "first": false, "tree": "[]"}, {"code": "G10K11/162", "inventive": true, "first": false, "tree": "[]"}, {"code": "C08J9/32", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04R2499/11", "inventive": false, "first": false, "tree": "[]"}, {"code": "G10K11/165", "inventive": true, "first": false, "tree": "[]"}, {"code": "C08J9/0066", "inventive": true, "first": false, "tree": "[]"}, {"code": "G10K11/161", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04R31/00", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04R1/02", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04R1/02", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04R1/2811", "inventive": false, "first": false, "tree": "[]"}, {"code": "G10K11/161", "inventive": true, "first": false, "tree": "[]"}, {"code": "G10K11/162", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04R1/02", "inventive": true, "first": false, "tree": "[]"}, {"code": "G10K11/002", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04R31/00", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 70550335