Coating for improving the sound quality of speakers

Abstract

The present disclosure relates to coatings for improving the sound quality of speakers. Aspects of acoustic active coatings are disclosed herein. The coating is a highly porous coating having a thickness and comprising between 2% and 30% by mass of a binder and between 70% and 98% by mass of zeolite. The coating includes an irregular matrix formed by a plurality of convex shapes and having a distribution of pore sizes, the convex shapes being connected by concave connectors. Other embodiments are disclosed and protected by the claims.

Description

Technical Field

[0001] Aspects disclosed herein generally relate to audio speakers, and more particularly but not exclusively to coatings for improving speaker sound quality and audio speakers that use such coatings in a back cavity to improve speaker performance. Background Art

[0002] Speakers typically include a back cavity and a membrane or diaphragm that oscillates and emits sound when driven by an electromagnetic transducer. When the membrane is moved, a variety of different forces act on it, distorting its expected acceleration by the electromagnet and thus distorting the sound waves it emits. Reducing these additional membrane forces can improve sound quality.

[0003] One of the forces acting on the membrane is due to pressure fluctuations in the back cavity caused by the compression and decompression of the air in the back cavity as the membrane moves. These pressure fluctuations can be reduced by increasing the volume of the back cavity (e.g., making it larger). However, in handheld devices such as mobile phones, it is only possible to increase the size of the back cavity to a small extent because these devices should remain small and lightweight. Summary of the Invention

[0004] Aspects of the present invention are described. An audio speaker includes a housing that defines a back cavity located behind a speaker driver such that the speaker driver can convert an electrical audio signal into sound and the sound can propagate through the gas in the back cavity. A highly porous acoustically active coating is deposited on at least one inner surface of the back cavity, the highly porous coating comprising a binder and an adsorbent material.

[0005] Aspects of the acoustically active coating are described. In one aspect, the coating is a highly porous coating that has a thickness and comprises between 2% and 30% by mass of a binder and between 70% and 98% by mass of zeolite. The coating includes an irregular matrix formed by a plurality of convex shapes and has a pore size distribution, the convex shapes being connected by concave connectors. Other embodiments are disclosed and protected by the claims.

[0006] Aspects of a process are described, the process including preparing a slurry comprising a binder and zeolite. The slurry is sprayed through a nozzle having a nozzle diameter. A highly porous acoustically active coating is deposited on a substrate by guiding the sprayed slurry through the ambient to the substrate, the substrate being positioned at a distance from the nozzle. Brief Description of the Drawings

[0007] Non-limiting and non-exhaustive aspects of the present invention are described with reference to the following drawings, where like reference numerals refer to like components in the various views unless otherwise specified.

[0008] Figure 1 is a pictorial view of aspects of an electronic device.

[0009] Figures 2A to 2D is a cross-sectional view of an aspect of an audio micro-speaker for an electronic device.

[0010] Figure 3 is a schematic block diagram of an aspect of an electronic device, the aspect of the electronic device including an aspect of an audio micro-speaker, such as Figures 2A to 2D those shown.

[0011] Figure 4 is a cross-sectional view of an aspect of the back cavity of an audio micro-speaker, such as Figure 2A those shown in –2B, wherein an acoustically active coating is provided on at least one wall of the back cavity.

[0012] Figure 5 is a drawing of an aspect of a hardware setup for implementing a process for forming an acoustically active coating on a wall of a speaker back cavity, such as Figure 6 those shown.

[0013] Figure 6 is a Figure 5 flowchart of an aspect of a process for forming an acoustically active coating on a wall of a speaker back cavity, such as

[0014] Figure 7 is a scanning electron microscope (SEM) photograph of an aspect of a coating produced by the process Figures 5 - 6 shown.

[0015] Figure 8 is a graph showing the pore size distribution measured in a sample coating prepared according to Example 1.

[0016] Figures 9 - 12 is a graph showing the resonance frequency shift produced by the acoustically active coatings described in connection with Examples 1-4, respectively. DETAILED DESCRIPTION

[0017] The following disclosure describes an aspect of a speaker that includes a back cavity having an acoustically active coating on at least one of its inner walls. As used herein, the term "acoustically active coating" refers to a coating that can adsorb or desorb gas through a physical mechanism such as adsorption and thus has the following acoustic properties: when the coating is used in a speaker back cavity, the acoustic properties can cause the back cavity to behave as if it were larger than it actually is, thereby improving the sound quality of the speaker. Specific details are described to provide an understanding of the disclosed aspects, but those skilled in the art will recognize that the invention may be practiced without one or more of the described details or in combination with other methods, components, materials, etc. In some cases, well-known structures, materials, or operations are not shown or described in detail, but are still encompassed within the scope of the invention.

[0018] References throughout this specification to "one aspect" or "aspect" mean that the described feature, structure, or characteristic may be included in at least one of the aspects such that the appearances of "in one aspect" or "in an aspect" do not necessarily all refer to the same aspect. Additionally, the particular feature, structure, or characteristic may be combined in any suitable manner in one or more aspects.

[0019] One way to reduce the back cavity pressure fluctuations of a handheld device is to place an absorbent material such as carbon black or zeolite into the back cavity. It has been shown that these materials can in fact increase the back cavity - in other words, their presence in the back cavity enhances the speaker performance as if the back cavity of the speaker has physically become larger.

[0020] Loudspeaker

[0021] Figure 1 Aspects of the electronic device 100 are shown. In one aspect, the electronic device 100 may be a smart phone device, but in other aspects it may be any other portable device or stationary device or apparatus, such as a laptop computer or a tablet computer. The electronic device 100 may include various functions to allow a user to access functions related to, for example, calls, voicemail, music, email, Internet browsing, scheduling, and photos. The electronic device 100 may also include hardware to facilitate such capabilities. For example, the integrated microphone 102 may pick up the user's voice during a call, and the audio speaker 106 (e.g., a micro speaker) may deliver the remote voice to the end user during a call. The audio speaker 106 may also emit sounds associated with music files played by a music player application running on the electronic device 100. The display 104 may present a graphical user interface to the user to allow the user to interact with the electronic device 100 and / or the applications running on the electronic device 100. Other conventional features are not shown, but they may of course be included in the electronic device 100.

[0022] Figures 2A to 2DAspects of an audio speaker of an electronic device are shown. In an aspect, the audio speaker 106 includes a housing that supports a speaker driver 202, such as a speaker housing 204. The speaker driver 202 can be a speaker for converting an electrical audio signal into sound. For example, the speaker driver 202 can be a micro speaker having a diaphragm 206 supported relative to the housing 204 by a speaker surround 208. The speaker surround 208 can be flexible to allow the diaphragm 206 to move axially along a central axis 210. For example, the speaker driver 202 can have a motor assembly attached to the diaphragm 206 to axially move the diaphragm 206 in a piston-like motion (i.e., forward and backward) along the central axis 210. The motor assembly can include a voice coil 212 that moves relative to a magnetic assembly 214. In an aspect, the magnetic assembly 214 includes a magnet attached to a top plate on a front surface and a yoke on a rear surface, such as a permanent magnet. The top plate and the yoke can be formed of a magnetic material to create a magnetic circuit having a magnetic gap in which the voice coil 212 swings forward and backward. Thus, when an electrical audio signal is input to the voice coil 212, a mechanical force can be generated to move the diaphragm 206 to radiate sound forward along the central axis 210 into the surrounding environment outside the housing 204.

[0023] The movement of the diaphragm 206 to radiate sound forward into the surrounding environment can cause the sound to be pushed backward. For example, the sound can propagate through a gas filling the space enclosed by the housing 204. More specifically, the sound can travel through air in a back cavity 216 behind the diaphragm 206. The back cavity 216 can affect the acoustic performance. Specifically, the size of the back cavity 216 can affect the natural resonance peak of the audio speaker 106. For example, increasing the size of the back cavity 216 can result in the generation of greater bass.

[0024] In an aspect, the back cavity 216 within the housing 204 can be separated into several cavities. For example, in one aspect, the back cavity 216 can be separated into a rear cavity 218 and an absorption cavity 220 by a permeable separator 222 (see Figure 2A ), but other aspects may not require a permeable separator 222 at all, in which case the back cavity 216 can be a single cavity rather than multiple cavities (see Figure 2B ). The rear cavity 218 can be located directly behind the speaker driver 202. That is, the speaker driver 202 can be suspended or supported within the rear cavity 218 such that the sound radiating backward from the diaphragm 206 travels directly into the rear cavity 218. Thus, at least a portion of the rear cavity 218 can be defined by the back surface of the diaphragm 206 and similarly by the back surface of the speaker surround 208. Additionally, considering that the permeable separator 222 (if present) can extend across the cross-sectional area of the back cavity 216 between several walls of the housing 204, the rear cavity 218 can be further defined by the inner surface of the housing 204 and a first side 224 of the permeable separator 222.

[0025] In aspects where it is divided into multiple cavities (e.g., Figure 2A ), the back cavity 216 may include an adsorption cavity 220 separated from the rear cavity 218 by a permeable separator 222, i.e., the adsorption cavity 220 may be adjacent to the rear cavity 218 on the opposite side of the permeable separator 222. In an aspect, the adsorption cavity 220 is defined by the inner surface of the housing 204 surrounding the back cavity 216 and may also be defined by the second side 226 of the permeable separator 222 (if present). Thus, the rear cavity 218 and the adsorption cavity 220 may be adjacent to each other through the permeable separator 222. In aspects where the permeable separator 222 is absent, the rear cavity 210 and the adsorption cavity 220 together form a single back cavity 216 (e.g., Figure 2B ).

[0026] The audio speaker 106 may have a form factor with any number of shapes and sizes. For example, the audio speaker 106 and thus the housing 204 may have an external profile that appears to be a combination of a hexahedron, a cylinder, etc. For example, one such external profile may be a thin box. Additionally, the housing 204 may have thin walls, and thus, the cross-sectional area of a plane passing through the housing 204 at any point may have a geometry corresponding to the external profile, including rectangles, circles, triangles, etc. Thus, if present, the permeable separator 222 extending through the back cavity 216 within the housing 204 may also have various outer shapes. For example, in the case where the audio speaker 106 is a hexahedron, such as a low-profile box having a rectangular outer shape protruding in a direction orthogonal to the central axis 210, the permeable separator 222 may have a rectangular outer shape.

[0027] The acoustically active adsorption coating 232 may be encapsulated in the adsorption cavity 220 by forming a coating on at least one inner surface of the housing 204 with an acoustically active coating as further described below. The adsorption coating 232 may be any adsorption coating capable of adsorbing the gas located in the back cavity 216. For example, the adsorption coating 232 may be any of the highly porous adsorption coatings described below in connection with Figure 4 etc., which are configured to adsorb air molecules. In aspects without a permeable separator, the adsorption coating 232 may be formed at any position in the back cavity 216.

[0028] Figures 2C - 2D Another aspect of the audio speaker of the electronic device is shown. In various aspects, the rear cavity 218 and the adsorption cavity 220 may have different relative orientations. For example, in Figure 2A the aspect shown, the adsorption cavity 220 is located laterally of the rear cavity 218, i.e., laterally offset from the central axis 210 from the rear cavity 218. Thus, the sound emitted rearward from the diaphragm 206 may propagate directly to the rear wall of the rear cavity 218 rather than directly to the permeable separator 222.

[0029] However, in Figure 2C the aspect shown, the audio speaker 106 includes an axially arranged back cavity 216 cavity. For example, the suction cavity 220 may be located directly behind the rear cavity 218 such that the central axis 210 may intersect the rear cavity 218 behind the diaphragm 206 and the suction cavity 220 on the opposite side of the permeable separator 222. Thus, the permeable separator 222 may span the back cavity 216 along a plane such that the normal vector 250 exiting from the first side 224 and pointing towards the rear cavity 218 is oriented in a direction parallel to the central axis 210. For example, the rear cavity 218 and the suction cavity 220 may each be flat and thin, and the two are positioned front and back along the central axis 210. Therefore, the sound emitted backward by the diaphragm 206 may directly propagate along the central axis 210 through the rear cavity 218 and the permeable separator 222 and into the suction cavity 220.

[0030] Similar to Figure 2A the aspect shown, Figure 2C the aspect of does not need to include a permeable separator 222, in which case its back cavity 216 is a single cavity (see Figure 2D ). However, if present, the permeable separator 222 may be oriented at any angle with respect to the central axis 210. That is, although the first face may face a direction orthogonal or parallel to the central axis 210, in the aspect, the permeable separator 222 is oriented at an inclined angle with respect to the central axis 210. Therefore, within the scope of this specification, the suction cavity 220 may be some combination located laterally or directly behind the suction cavity 220. In any case, the rear cavity 218 and the suction cavity 220 may be adjacent to each other such that the opposite sides of the permeable separator 222 define a part of each cavity. Similar to Figure 2A the aspect of, an acoustically active adsorption coating 232 may be formed on at least one surface of at least one wall of the suction cavity 220.

[0031] Figure 3Aspects of an electronic device including a micro speaker are schematically illustrated. As described above, the electronic device 100 can be one of several types of portable or stationary devices or apparatuses having circuitry suitable for a particular function. Thus, the circuitry illustrated is provided by way of example and not limitation. The electronic device 100 can include one or more processors 902 that execute instructions to implement the different functions and capabilities described above. The instructions executed by the one or more processors 902 of the electronic device 100 can be retrieved from local memory 904, and these instructions can be in the form of an operating system program having device drivers, as well as in the form of one or more application programs running on top of the operating system to perform the different functions introduced above, such as making a call or dialing and / or music playback. For example, the processor 902 can directly or indirectly implement a control loop and provide a drive signal to the voice coil 212 of the audio speaker 106 to drive the diaphragm 206 to move and produce sound.

[0032] The audio speaker 106 having the above structure can include a back cavity 216 that is separated into two chambers by a sound-permeable barrier (e.g., a permeable separator 222, if present), the two chambers being: a rear chamber 218 located directly behind the speaker driver 202, and an adsorption chamber 220 adjacent to the rear chamber 218 across the permeable separator 222. Other aspects of the audio speaker 106 having an adsorption coating 232 can have a single-chamber back cavity 216, i.e., a back cavity in which there is no permeable separator 222. Additionally, the adsorption chamber 220 can be directly filled with an adsorption material such that the back cavity 216 has an adsorption volume that is exactly defined between the system housing 204 and the sound-permeable barrier. The adsorption volume can reduce the overall spring stiffness of the back cavity 216 and lower the natural resonance peak of the audio speaker 106. That is, the adsorption coating 232 can adsorb and desorb randomly traveling air molecules in response to the propagated sound when there are pressure fluctuations in the back cavity 216. Thus, compared to a speaker having a back cavity without an adsorption material, the audio speaker 106 can have higher efficiency at lower frequencies. Therefore, the overall output power of the audio speaker 106 can be increased. More specifically, the audio speaker output can be louder during dialing or music playback, especially in the low-frequency audio range. Thus, the audio speaker 106 having the above structure can produce a larger, richer sound in the bass range using the same form factor as a speaker back cavity without multiple chambers, or can produce an equivalent sound in the bass range with a smaller form factor. Additionally, since the adsorption chamber 220 is defined exactly in the middle between the housing 204 and the permeable separator 222 (which are sealed together), the form factor of the audio speaker 106 can be smaller than, for example, a speaker back cavity that holds a secondary container filled with an adsorption material, such as a mesh bag.

[0033] Back cavity configuration with acoustically active lining

[0034] Sound quality independent of orientation in a loudspeaker can be achieved by using a fixing preparation such as a fixing coating containing an adsorbent material such as zeolite, which adheres to the wall of the back cavity of the loudspeaker. However, simple coating techniques do not produce an acoustically active coating, i.e., do not produce an improved sound quality. Such conventional coating techniques produce a dense, non-porous coating, while an acoustically active coating is typically a highly porous structure. Surprisingly, however, such a porous coating can be prepared by applying a technique in which the atomized droplets are partially dried during flight before hitting the substrate. Through many experiments, it has been found that aqueous slurries containing especially zeolite and a binder form an acoustically active porous but mechanically stable coating - i.e., they improve the sound quality of the loudspeaker. A good measure of sound quality is the position of the resonance peak in an impedance measurement. The lower the frequency of the maximum impedance, the more output the loudspeaker can obtain in the low-frequency region. A high output in the low-frequency region is particularly desirable for a micro loudspeaker.

[0035] Figure 4 An aspect of the back cavity 400 is shown, which has an acoustically active coating applied to at least one of its inner walls. The back cavity 400 is a three-dimensional space defined by a plurality of walls 402a - 402d. Each of the walls 402b - 402d has an inner surface 403: wall 402b has an inner surface 403b, wall 402c has an inner surface 403c, and wall 402d has an inner surface 403d. In the aspect shown, one of the walls (in this instance wall 402a) is porous to allow gas to flow into and out of the back cavity, but in other aspects, wall 402a can be completely omitted. In the illustrated aspect, the back cavity 400 is a regular hexahedron, but in other aspects, it can be some other type of regular or irregular polyhedron. In other aspects, the back cavity 500 need not be a polyhedron, but can be composed of a combination of curved surfaces, a combination of flat surfaces, or a combination of both.

[0036] At least one inner surface 403 of the back cavity 400 is at least partially coated with an acoustically active coating 404, which can be any of the acoustically active coatings described below. An exemplary aspect has acoustically active layers 404 deposited on a plurality of inner surfaces: layer 404b is deposited on inner surface 403b, layer 404c is deposited on inner surface 403c, and layer 404d is deposited on inner surface 403d. Since wall 402a is porous, no layer 404 is deposited on its inner surface because this would prevent gas from flowing into and out of the back cavity 400. In aspects where wall 402a does not exist, of course no layer 404 exists thereon. In other aspects, layer 404 can be positioned on more or fewer inner surfaces 403 than the number of inner surfaces shown, ranging from a single inner surface of the back cavity to each inner surface, except for the inner surfaces of the porous walls of the back cavity. In the aspect shown, each coating 404b - 404d has a uniform thickness t: coating 404b has a uniform thickness tb, coating 404c has a uniform thickness tc, and so on. However, other aspects do not necessarily have coatings of uniform thickness. In one aspect, layers 404b and 404c can be tapered, for example, thinner near the porous wall 402a and becoming thicker towards wall 402d. The taper can be a smooth, continuous taper or a taper consisting of discrete steps. <(The text in should be translated according to its specific meaning. Since it's not clear from the context, it remains as here.)<(The text in

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[0038] here.)<(The text in Figures 5 - 6 should be translated according to its specific meaning. Since it's not clear from the context, it remains as Figures 5 - 6 here.)Shown together is a process for forming an acoustically active coating on a surface of a substrate such as the wall of a back cavity; <(The text in Figure 5 should be translated according to its specific meaning. Since it's not clear from the context, it remains as Figure 5 here.)Shown is one aspect of the hardware that can be used, while <(The text in Figure 6 should be translated according to its specific meaning. Since it's not clear from the context, it remains as Figure 6 here.)Shown in flowchart form is one embodiment of the process. <(The text in should be translated according to its specific meaning. Since it's not clear from the context, it remains as here.)<(The text in

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[0039] here.)<(The text in Figure 5 should be translated according to its specific meaning. Since it's not clear from the context, it remains as Figure 5 here.)Shows one aspect of a system 500 for forming an acoustically active coating. System 500 includes an environment 502 having an interior 504. In one aspect, environment 502 can be an enclosed space, such as a room in a building, but in other aspects, it can be a subset of a room or a specially constructed enclosure, such as a large box or cabinet. During operation of the process, the interior 504 is maintained at a known temperature, pressure, and relative humidity. In one aspect, the interior 504 can be maintained at standard temperature and pressure (STP), for example, the National Institute of Standards and Technology (NIST) STP, which is a temperature of 20 °C (293.15 K, 68 °F) and an absolute pressure of 1 atmosphere (14.696 psi, 101.325 kPa). This standard is sometimes also referred to as normal temperature and pressure (NTP). In other aspects, the temperature, pressure, or both can be different from STP. The relative humidity in the interior 504 can vary from 20% to 100%, or within any sub-range thereof, such as 40% to 70%. Different formulations of the slurry in the slurry reservoir 508 can use different temperatures, pressures, and / or relative humidities to obtain desired properties in the resulting acoustically active coating. Conversely, different environmental conditions can use different slurry formulations.

[0040] A sprayer 505 is positioned within the interior 504 of the environment 502. The sprayer includes a nozzle 506 fluidly coupled to the slurry reservoir 508 such that the slurry can flow from the reservoir to the nozzle. In one aspect, the sprayer 505 can be a commercially available device, such as an airbrush or paint spray gun. In another aspect, a swinging nozzle can be used to enhance the atomization of the slurry. If the nozzle 506 is a swinging nozzle, it can be vibrated, for example, by using an amplifier connected to a function generator at one or more frequencies. A pressure source 510 is fluidly coupled to the slurry reservoir 508 to push the slurry to the nozzle 506 and out of the nozzle. In one aspect, the pressure source 510 can be an air compressor, a high-pressure air tank, or other high-pressure air source fluidly coupled to the slurry reservoir 508.

[0041] A substrate 512 is positioned within the interior 504 of the environment 502 at a distance D from the outlet of the nozzle 506. In various aspects, the distance D can vary between 10 cm and 100 cm or any sub-range thereof (such as 15 cm - 20 cm). Distances D outside of this range (i.e., less than 10 cm or greater than 100 cm) are of course possible in other aspects. In some aspects, the distance D can be adjusted according to the composition of the slurry, the pressure in the pressure source 510, and the environmental conditions in the interior 504 of the environment 502. In other aspects, the adjustment can be made in other ways: the environmental conditions in the interior 504 can be adjusted according to the distance D.

[0042] In operation, the slurry from the slurry reservoir 508 is sprayed through the nozzle 506 towards the substrate 512 such that the sprayed slurry reaches the surface of the substrate 512. When the slurry is sprayed onto the surface of the substrate 512, it dries at least partially between the nozzle and the substrate, and when it impacts the substrate, it accumulates (i.e., it is deposited) until a slurry layer 514 of the desired thickness t is deposited on the substrate 512. The drying rate of the sprayed slurry can be controlled, for example, by changing the composition of the slurry, the pressure in the pressure source 510, and the environmental conditions (temperature, pressure, and relative humidity) inside 504. The final thickness t of the acoustically active coating 514 depends on the trade-off between mechanical robustness and adsorption / desorption characteristics: a thin coating (small t) is more mechanically stable and has less favorable adsorption / desorption characteristics, while a thick coating (large t) is less mechanically stable but has better adsorption / desorption characteristics. In various aspects, the thickness t of the acoustically active coating 514 can be in the micron range, for example, 40 microns - 60 microns.

[0043] Figure 6 Shows one aspect of a process 600 for fabricating a back cavity using an apparatus such as Figure 5 shown, the back cavity having at least one surface coated with an acoustically active coating, as Figure 4 shown. The process starts at block 602.

[0044] At block 604, an aqueous slurry or suspension (i.e., a semi-liquid mixture of fine particles suspended in a solvent (in this case water)) is formed by combining an adsorption / desorption material such as zeolite, a solvent, and a binder. The binder can be a polyacrylic acid or polyurethane emulsion. At block 606, the resulting slurry is mechanically agitated until fully mixed, and at block 608, the slurry is sieved or filtered to remove agglomerated particles (if any). The sieved / filtered slurry is then placed into the slurry reservoir 508 of the sprayer 505, and at block 610, the sprayer is placed inside the environment 502 at a desired distance D from the substrate 512 on which the acoustically active coating 514 is to be formed. At block 612, the slurry reservoir 508 is pressurized such that the slurry is forced through the nozzle 506, where the slurry is atomized (i.e., broken into slurry droplets) and ejected from the nozzle as a slurry spray.

[0045] At block 614, the slurry ejected from nozzle 506 is directed onto substrate 512 to form layer 514. At block 616, the process checks whether the current thickness of layer 514 matches the desired thickness. If, at block 616, the current thickness is less than the desired thickness, the process returns to block 614, where slurry continues to be ejected onto substrate 512. However, if, at block 616, the thickness of layer 514 is substantially equal to the desired thickness, the process moves to block 618, where ejection stops, and then to block 620, where the coating 514 is dried to form the slurry layer 514 into an acoustically active coating 514. In one aspect, layer 514 may not need to be dried at all after ejection, but in aspects where drying is needed, it may be allowed to air dry under the ambient conditions of environment 502. In other aspects, additional measures may be taken to dry layer 514 into an acoustically active coating 514, such as blowing heated or unheated air over or onto it, placing substrate 512 and coating 514 in an oven for a period of time, etc. Once coating 514 is dry and fixed to substrate 512, at block 622, the substrate / coating combination may be formed, for example by bending, into a speaker back cavity that will have at least one inner surface coated with acoustically active coating 514. The process ends at block 624.

[0046] Process example

[0047] Specific examples of blocks within process 600 are given in Examples 1 - 5 below; Examples 1 - 4 below describe the preparation of an acoustically active coating, and Example 5 describes the preparation of a cross-section of an acoustically active coating for SEM study. Examples 6 - 7 describe the analysis of coatings obtained using the slurry of Example 1.

[0048] Table 1 below gives an overview of the composition of the coatings obtained in Examples 1 - 4. For the aspects shown in Table 1, the acoustically active coating has a composition containing between 5 wt% and 10 wt% binder and between 90 wt% and 95 wt% adsorbent / desorbent material (in this case zeolite). However, other aspects may use different weight percentages of binder and adsorbent / desorbent material. For example, other aspects may include between 2 wt% and 30 wt% binder and between 70 wt% and 98 wt% adsorbent / desorbent material. Other aspects may include additional materials in addition to binder and adsorbent / desorbent material, and still other aspects do not have to use zeolite as the adsorbent / desorbent material.

[0049]

[0050]

[0051] Table 1: Coating Composition

[0052] Example 1

[0053] Place a binder containing 8.64 g of acrylic emulsion (28% solids content), 41.2 g of deionized water, 1 g of aqueous potassium hydroxide (KOH) (4 M) solution, and 46 g of MFI zeolite in a 100 ml beaker. Stir the slurry for 3 minutes and sieve (mesh size 100 μm) to remove agglomerates. A paintbrush gun with a 0.5 mm nozzle is loaded with the slurry and then the slurry is sprayed onto the acoustic fixture at a pressure of 2 bar and a spraying distance D of approximately 15 cm - 20 cm such that the resulting coating appears dry by visual inspection. Measure the acoustic properties of the fixture before and after applying the coating.

[0054] Example 2

[0055] The setup is the same as in Example 1, but the composition of the suspension is changed to 14.3 g of acrylic emulsion (28% solids content), 38.7 g of deionized water, 1 g of KOH (4 M), and 46 g of MFI zeolite.

[0056] Example 3

[0057] The setup is the same as in Example 1, but the composition of the suspension is changed to 6.05 g of acrylic emulsion (40% solids content), 43.79 g of deionized water, 1 g of aqueous KOH (4 M) solution, and 46 g of MFI zeolite.

[0058] Example 4

[0059] The setup is the same as in Example 1, but the composition of the suspension is changed to 10 g of acrylic emulsion (40% solids content), 41.2 g of deionized water, 1 g of aqueous KOH (4 M) solution, and 46 g of MFI zeolite.

[0060] Example 5

[0061] Spray the suspension of Example 1 onto an SEM sample carrier with a flat surface. Mix 500 mg of isophorone diamine and 600 mg of trimethylolpropane triglycidyl ether and stir for 30 seconds. These two compounds are standard materials for forming an epoxy resin after curing. Apply four drops of the mixture onto the zeolite coating on the sample carrier and then cure it at 50 °C for 2 hours. Cut the cured epoxy resin coating and analyze the cross-section by scanning electron microscopy (SEM).

[0062] The average thickness of the coating obtained in Example 1 was calculated by measuring the thickness at six points P1–P6 in each of three regions of the coating and calculating the mean value and standard deviation. The values obtained are shown in Table 2 below. The calculated average thickness was 58.8 ± 19.5 μm. The mass and area of the coating were 3.2 mg and 1.13E-4 m 2 . The density was calculated as 481 kg / m 3 .

[0063]

[0064]

[0065] Table 2: Measured thicknesses of the coating at different points

[0066] Since the compositions of the slurries in Examples 1–4 varied only by about 2% in solids content, it was assumed that the density of the coatings obtained with these slightly different slurry compositions would not differ by more than 2% from the values obtained here.

[0067] Example 6

[0068] The suspension from Example 1 was sprayed onto an acrylic glass plate using an airbrush gun with a 0.5 mm nozzle. The formed acoustically beneficial coating was carefully scraped off the plate with a scalpel and collected. The process was repeated until 1 g of material was collected. The porosity of the material was determined by mercury intrusion measurements.

[0069] Example 7

[0070] The suspension from Example 1 was poured onto an acrylic glass plate and dried at 60 °C. The layer was carefully scraped off the plate with a scalpel and collected. Similar layers did not exhibit beneficial acoustic effects. The process was repeated until 1 g of material was collected. The porosity of the material was determined by mercury intrusion measurements.

[0071] Result

[0072] Figure 7 An aspect of an acoustically active highly porous coating is shown, which is formed by using a slurry such as the slurry in Example 1 in a process such as Figures 5 - 6 the process shown. At the macroscopic level of observation (i.e., observation with the naked eye or at low magnification), the acoustically active coating appears smooth and integral, without voids. But when observed at high magnification, as shown in the SEM photograph of Figure 7 , it becomes clear that the resulting coating is a highly porous coating. The coating is described as a highly porous coating because it includes many pore sizes within a wide pore size range (see Figure 9)。The International Union of Pure and Applied Chemistry (IUPAC) defines micropores as pores with diameters from 0 nm to 2 nm, mesopores as pores with diameters from 2 nm to 50 nm, and macropores as pores with diameters greater than 50 nm. Figure 7 The coating is at least microporous because the zeolite (adsorption / desorption material) used contains micropores, but the coating is described herein as highly porous because it includes a wide range of pore diameters from micropores through mesopores to macropores. The porosity of the coating increases the effective surface area of the coating, thereby exposing more of the adsorption material (zeolite in this regard) to the gases in the back cavity and allowing better adsorption / desorption of those gases.

[0073] The highly porous coating 700 can be described in various ways. One description is that it is an irregular matrix of convex shapes 702 - irregular because the sizes and exact shapes of the convex shapes and their spacing within the matrix are non-uniform. In the aspect shown, the convex shapes 702 are irregularly joined to each other by concave connectors 704 to form an irregular matrix. As in Figure 7 can be seen, the irregular matrix (highly irregular in the illustrated aspect) means that there is a wide range and non-uniform distribution of pore sizes (see Figure 8 ). Considering the process 600 available for preparing it, the microporous coating 700 can also be described as a matrix or collection of spherical droplets and deformed droplets (both of different sizes) joined to each other. Figure 7 The microscopic appearance of the shown coating has various analogs in natural or biological structures. For example, the appearance of the highly porous coating 700 is reminiscent of some types of coral or certain fungi. The microscopic appearance also has analogs in other human-produced structures. Sintered metals can have a similar appearance, as can agglomerates within other powdered materials.

[0074] Figure 8 The porosity measurement results obtained for Examples 6 and 7 are graphically shown. The figure shows the pore radius in microns plotted against the pore volume in cubic millimeters per gram of coating. Since the highly porous coating is an irregular matrix, the pores in the matrix can be expected to have different sizes, sometimes very different sizes depending on the aspect. And this is what appears in the highly porous coating shown in the figure: there is a pore size distribution ranging from below 0.3 nm to about 100 microns. For the aspect of Example 6, most pore sizes are between 100 nm (0.1 micron) and 100 microns, with a peak near the 6 - 8 micron range. For the aspect of Example 7, the peak number of pores has a size of about 100 nm (0.1 micron). The cumulative pore volume between 1 and 20 μm radius for the sample obtained in Experiment 6 is 1290 mm 3 / g. The cumulative pore volume between 1 and 20 μm radius for the sample obtained in Example 7 is 134 mm3 / g; in other words, the coating obtained from Example 6 is much more porous than the coating obtained from Example 7.

[0075] Figures 9 - 12 The resonance frequency results of the acoustically active highly porous coatings disclosed herein are graphically illustrated. These figures are graphs of the impedance of speaker modules having the coatings of Examples 1 - 4 plotted against frequency. It can be seen that in each of the aspects shown, there is a downward shift in the resonance frequency, which translates to an improvement in the acoustic performance of the speaker, especially at lower frequencies.

[0076] Table 3 below summarizes the results graphically shown in Figures 9 - 12 comparing the acoustic resonance frequencies of the uncoated back cavity and the aspects of the back cavity coated with zeolite. The table also provides additional data on the coatings, including their mass and thickness calculated by density. The thickness of a particular coating is calculated by measuring the mass of the coating and using the average density determined in the description of Example 5 and the known substrate surface area of 1.39E - 3m 2 to calculate the thickness of a particular coating.

[0077]

[0078]

[0079] Table 3: Overview of coatings, thickness, and resonance frequency shift.

[0080] All coatings exhibit a significant shift in the resonance frequency towards the lower region, thus improving the sound quality of the speaker.

[0081] The above description of the aspects is not intended to be exhaustive or to limit the invention to the forms described. Specific aspects and examples of the invention have been described herein for illustrative purposes, but various modifications are possible. To assist the patent office and any readers of any patent issued from this application, the applicant wishes to note that they do not intend for any one of the appended claims or claim elements to invoke 35 U.S.C. § 112(f), unless the words "means for" or "step for" are expressly used in a particular claim.

Claims

1. An audio speaker, comprising: a housing that defines a back cavity behind a speaker driver, wherein the speaker driver is capable of converting an electrical audio signal into sound such that the sound can propagate through the gas in the back cavity; and a highly porous acoustic active coating deposited on at least one inner surface of the back cavity, the highly porous acoustic active coating comprising a binder and an adsorbent, wherein the highly porous acoustic active coating comprises an irregular matrix of connected particles.

2. The audio speaker according to claim 1, wherein the particles comprise an irregular matrix of convex shapes.

3. The audio speaker according to claim 2, wherein the convex shapes are connected by concave connectors.

4. The audio speaker according to claim 1, wherein the highly porous acoustic active coating has a pore size between 0.3 nanometers and 100 micrometers.

5. The audio speaker according to claim 4, wherein the largest proportion of the pore sizes is between 0.1 micrometer and 100 micrometers.

6. The audio speaker according to claim 1, wherein the acoustic active coating comprises a binder between 2% and 30% by mass and zeolite between 70% and 98% by mass.

7. The audio speaker according to claim 6, wherein the acoustic active coating comprises a binder between 5% and 10% by mass and zeolite between 90% and 95% by mass.

8. The audio speaker according to claim 1, wherein the thickness of the highly porous acoustic active coating is between 40 micrometers and 60 micrometers.

9. The audio speaker according to claim 1, wherein the adsorbent is zeolite.

10. The audio speaker according to claim 1, wherein the highly porous acoustic active coating is deposited on the at least one inner surface by spraying.

11. An acoustic active coating, comprising: a highly porous coating having a thickness and comprising a binder between 2% and 30% by mass and zeolite between 70% and 98% by mass, the coating comprising an irregular matrix formed by a plurality of convex shapes and having a pore size distribution, the plurality of convex shapes being connected by concave connectors.

12. The acoustic active coating according to claim 11, wherein the highly porous coating is formed by spraying a slurry comprising the binder and the zeolite.

13. The acoustic active coating according to claim 11, wherein the thickness of the highly porous coating is between 40 micrometers and 60 micrometers.

14. The acoustic active coating according to claim 11, wherein the highly porous coating has a pore size between 0.3 nanometers and 100 micrometers.

15. The acoustic active coating according to claim 14, wherein the largest proportion of the pore sizes is between 0.1 micrometer and 100 micrometers.

16. The acoustic active coating according to claim 11, wherein the acoustic active coating comprises a binder in an amount between 5% and 10% by mass and zeolite in an amount between 90% and 95% by mass.

17. A method for forming a highly porous acoustic active coating, comprising: preparing a slurry comprising a binder and zeolite; spraying the slurry through a nozzle having a nozzle diameter; and depositing the highly porous acoustic active coating on a substrate by guiding the sprayed slurry through an environment to the substrate, the substrate being positioned spaced apart from the nozzle, wherein the highly porous acoustic active coating comprises an irregular matrix of connected particles.

18. The method according to claim 17, wherein the environment has a relative humidity between 40% and 70%.

19. The method according to claim 18, wherein the environment is the National Institute of Standards and Technology (NIST) standard temperature and pressure (STP).

20. The method according to claim 17, wherein the acoustic active coating comprises a binder in an amount between 2% and 30% by mass and zeolite in an amount between 70% and 98% by mass.

21. The method according to claim 20, wherein the acoustic active coating comprises a binder in an amount between 5% and 10% by mass and zeolite in an amount between 90% and 95% by mass.

22. The method according to claim 17, wherein preparing the slurry comprises: combining the binder, the zeolite, and a solvent; thoroughly mixing the combined binder, zeolite, and solvent; and screening the slurry to remove agglomerated particles.

23. The method according to claim 17, wherein the distance between the nozzle and the substrate is between 15 cm and 20 cm.

24. The method according to claim 17, wherein the particle layer has a convex shape.

25. The method according to claim 24, wherein the convex shapes are connected by concave connectors.

26. The method according to claim 17, wherein the thickness of the highly porous acoustic active coating is between 40 microns and 60 microns.

27. The method according to claim 17, wherein the highly porous acoustic active coating has a pore size between 0.3 nm and 100 microns.

28. The method according to claim 27, wherein the largest proportion of the pore sizes is between 0.1 micron and 100 microns.

29. An audio speaker, comprising: a housing that defines a back cavity behind a speaker driver, wherein the speaker driver is capable of converting an electrical audio signal into sound such that the sound can propagate through the gas in the back cavity; and a highly porous acoustic active coating deposited on at least one inner surface of the back cavity, the highly porous acoustic active coating comprising a binder and an adsorbent material; wherein the highly porous acoustic active coating comprises an irregular matrix of connected particles; and, wherein the particles have a convex shape and are connected by concave connectors.

30. The audio speaker according to claim 29, wherein the highly porous acoustically active coating has a pore size between 0.3 nanometers and 100 micrometers.

31. The audio speaker according to claim 30, wherein the largest proportion of the pore sizes is between 0.1 micrometer and 100 micrometers.

32. The audio speaker according to claim 29, wherein the acoustically active coating comprises a binder in an amount between 2% and 30% by mass and zeolite in an amount between 70% and 98% by mass.

33. The audio speaker according to claim 32, wherein the acoustically active coating comprises a binder in an amount between 5% and 10% by mass and zeolite in an amount between 90% and 95% by mass.

34. The audio speaker according to claim 29, wherein the thickness of the highly porous acoustically active coating is between 40 micrometers and 60 micrometers.

35. The audio speaker according to claim 29, wherein the adsorbent material is zeolite.

36. The audio speaker according to claim 29, wherein the highly porous acoustically active coating is deposited on the at least one inner surface by spraying.

37. An acoustically active coating, comprising: a highly porous coating having a thickness and comprising a binder in an amount between 2% and 30% by mass and zeolite in an amount between 70% and 98% by mass, wherein the coating comprises an irregular matrix formed by a plurality of connected particles and has a pore size distribution, and wherein the plurality of connected particles are connected by concave connectors.

38. The acoustically active coating according to claim 37, wherein the highly porous coating is formed by spraying a slurry comprising the binder and the zeolite.

39. The acoustically active coating according to claim 37, wherein the thickness of the highly porous coating is between 40 micrometers and 60 micrometers.

40. The acoustically active coating according to claim 37, wherein the highly porous coating has a pore size between 0.3 nanometers and 100 micrometers.

41. The acoustically active coating according to claim 40, wherein the largest proportion of the pore sizes is between 0.1 micrometer and 100 micrometers.

42. The acoustically active coating according to claim 37, wherein the acoustically active coating comprises a binder in an amount between 5% and 10% by mass and zeolite in an amount between 90% and 95% by mass.

43. A method for forming a highly porous acoustically active coating, comprising: preparing a slurry comprising a binder and zeolite; spraying the slurry through a nozzle having a nozzle diameter; and depositing the highly porous acoustically active coating on a substrate by guiding the sprayed slurry through an environment to the substrate, the substrate being positioned at a distance from the nozzle; wherein the highly porous acoustically active coating comprises an irregular matrix of connected particles, and wherein the particles have a convex shape and are connected by concave connectors.

44. The method according to claim 43, wherein the environment has a relative humidity between 40% and 70%.

45. The method according to claim 44, wherein the environment is the National Institute of Standards and Technology (NIST) standard temperature and pressure (STP).

46. The method according to claim 43, wherein the acoustically active coating comprises a binder between 2% and 30% by mass and zeolite between 70% and 98% by mass.

47. The method according to claim 46, wherein the acoustically active coating comprises a binder between 5% and 10% by mass and zeolite between 90% and 95% by mass.

48. The method according to claim 43, wherein preparing the slurry comprises: combining the binder, the zeolite, and a solvent; thoroughly mixing the combined binder, zeolite, and solvent; and screening the slurry to remove agglomerated particles.

49. The method according to claim 43, wherein the distance between the nozzle and the substrate is between 15 cm and 20 cm.

50. The method according to claim 43, wherein the thickness of the highly porous acoustically active coating is between 40 microns and 60 microns.

51. The method according to claim 43, wherein the highly porous acoustically active coating has a pore size between 0.3 nm and 100 microns.

52. The method according to claim 51, wherein the largest proportion of the pore size is between 0.1 micron and 100 microns.

53. An electronic device, comprising: an audio speaker, comprising: a housing that defines a back cavity behind a speaker driver, wherein the speaker driver is capable of converting an electrical audio signal into sound such that the sound can propagate through the gas in the back cavity, a highly porous acoustically active coating deposited on at least one inner surface of the back cavity, the highly porous acoustically active coating comprising a binder and an adsorbent, wherein the highly porous acoustically active coating comprises an irregular matrix connecting particles, and wherein the particles are connected by concave connectors; and a processor coupled to the audio speaker and coupled to a memory having one or more applications stored therein, the applications comprising instructions that, when executed by the processor, transmit the electrical audio signal to the audio speaker for transduction into sound.

54. The electronic device according to claim 53, wherein the porous acoustically active coating has a pore size between 0.3 nm and 100 microns.

55. The electronic device according to claim 54, wherein the largest proportion of the pore size is between 0.1 micron and 100 microns.

56. The electronic device according to claim 53, wherein the thickness of the porous acoustically active coating is between 40 microns and 60 microns.

57. The electronic device according to claim 53, wherein the adsorbent is zeolite.

58. The electronic device according to claim 53, further comprising: A microphone, coupled to the processor; A radio frequency (RF) circuit, coupled to the processor; Or A display, coupled to the processor.

59. An audio speaker, comprising: A housing that defines a back cavity behind a speaker driver, wherein the speaker driver is capable of converting an electrical audio signal into sound such that the sound can propagate through the gas in the back cavity; And A porous acoustically active coating deposited on at least one inner surface of the back cavity, the porous acoustically active coating comprising convex particles connected by concave connectors, the convex particles and the concave connectors being made of a binder and an adsorbent material.

60. The audio speaker according to claim 59, wherein the porous acoustically active coating has a pore size between 0.3 nanometers and 100 micrometers.

61. The audio speaker according to claim 60, wherein the largest proportion of the pore size is between 0.1 micrometer and 100 micrometers.

62. The audio speaker according to claim 59, wherein the acoustically active coating comprises a binder between 2% and 30% by mass and zeolite between 70% and 98% by mass.

63. The audio speaker according to claim 62, wherein the acoustically active coating comprises a binder between 5% and 10% by mass and zeolite between 90% and 95% by mass.

64. The audio speaker according to claim 59, wherein the thickness of the porous acoustically active coating is between 40 micrometers and 60 micrometers.

65. The audio speaker according to claim 59, wherein the adsorbent material is zeolite.

66. A method for forming a porous acoustically active coating, comprising: Preparing a slurry comprising a binder and zeolite; Spraying the slurry through a nozzle having a nozzle diameter; And Depositing the porous acoustically active coating on a substrate by guiding the sprayed slurry through an environment to the substrate, the substrate being positioned at a distance from the nozzle, and the coating comprising convex particles connected by concave connectors.

67. The method according to claim 66, wherein the environment has a relative humidity between 40% and 70%.

68. The method according to claim 67, wherein the environment is the National Institute of Standards and Technology (NIST) standard temperature and pressure (STP).

69. The method according to claim 66, wherein the acoustically active coating comprises a binder between 2% and 30% by mass and zeolite between 70% and 98% by mass.

70. The method according to claim 69, wherein the acoustically active coating comprises a binder between 5% and 10% by mass and zeolite between 90% and 95% by mass.

71. The method according to claim 66, wherein preparing the slurry comprises: Combining the binder, the zeolite, and a solvent; Thoroughly mixing the combined binder, zeolite, and solvent; And Screening the slurry to remove agglomerated particles.

72. The method according to claim 66, wherein the distance between the nozzle and the substrate is between 15 cm and 20 cm.

73. The method according to claim 66, wherein the thickness of the porous acoustically active coating is between 40 microns and 60 microns.

74. The method according to claim 66, wherein the porous acoustically active coating has a pore size between 0.3 nanometers and 100 microns.

75. The method according to claim 74, wherein the largest proportion of the pore size is between 0.1 micron and 100 microns.

76. An electronic device, comprising: An audio speaker, comprising: A housing that defines a back cavity behind the speaker driver, wherein the speaker driver is capable of converting an electrical audio signal into sound such that the sound can propagate through the gas in the back cavity, and A porous acoustically active coating deposited on at least one inner surface of the back cavity, the porous acoustically active coating comprising convex particles connected by concave connectors, the convex particles and the concave connectors being made of a binder and an adsorbent; and A processor coupled to the audio speaker and coupled to a memory having one or more applications stored therein, the applications comprising instructions that, when executed by the processor, transmit the electrical audio signal to the audio speaker for transduction into sound.

77. The electronic device according to claim 76, wherein the porous acoustically active coating has a pore size between 0.3 nanometers and 100 microns.

78. The electronic device according to claim 77, wherein the largest proportion of the pore size is between 0.1 micron and 100 microns.

79. The electronic device according to claim 76, wherein the thickness of the porous acoustically active coating is between 40 microns and 60 microns.

80. The electronic device according to claim 76, wherein the adsorbent is zeolite.

81. The electronic device according to claim 76, further comprising: A microphone coupled to the processor; A radio frequency (RF) circuit coupled to the processor; Or A display coupled to the processor.

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