Balanced armature receiver with liquid pressure relief hole

Abstract

The invention relates to a balanced armature receiver with a liquid pressure relief vent. A balanced armature receiver is provided comprising a gas permeable baffle located on a portion of the receiver defining a back cavity volume to provide a gas pressure relief. The baffle can be located in a wall portion of the receiver or in the diaphragm to vent the back cavity volume to the exterior of the receiver via the front cavity volume or via the nozzle. The gas permeable baffle is impermeable to liquid and can be configured to affect the low frequency response of the receiver.

Description

Technical Field

[0001] This disclosure generally relates to a balanced armature receiver, and more particularly to a balanced armature receiver having a barometric relief vent that provides improved liquid ingress protection. Background Technology

[0002] Balanced armature receivers (also referred to herein as "receivers") capable of generating sound output signals in response to electrical audio signals are commonly used in hearing devices such as in-canal (RIC) hearing aids, wired and wireless headphones, and true wireless stereo (TWS) devices. Such receivers typically include a diaphragm housed within a housing (also called a shell), which divides the interior into a front cavity volume and a rear cavity volume. A motor located within the housing actuates a portion of the diaphragm (called a paddle) to emit sound from a sound port acoustically coupled to the front cavity volume. The motor typically includes a coil wound around an armature having a movable end coupled to the paddle and balanced between permanent magnets held by a yoke. The free end portion of the armature oscillates between the magnets, thereby driving the paddle in response to an audio signal applied to the coil. Balanced armature receivers require an air path (called a pressure relief port) to equalize the air pressure in the rear cavity volume with the surrounding air pressure. In some receivers, the vent is a small perforation through the diaphragm located between the front and rear chamber volumes. The vent can also be a hole penetrating the housing to allow direct venting from the rear chamber volume to the outside of the receiver. However, these and other sound-generating transducers are susceptible to damage from liquid seeping into the rear chamber volume via the vent. Consumer demand for liquid-resistant hearing devices is growing, as liquid seepage can occur due to accidental or intentional exposure during bathing, swimming, and other activities. Summary of the Invention

[0003] This application relates in several aspects to a balanced armature receiver comprising: a housing; a diaphragm disposed within the housing and dividing the interior of the housing into a front cavity volume and a rear cavity volume; a sound port located between the front cavity volume and the exterior of the housing; a motor disposed within the housing and including a coil positioned close to an armature having a free end portion movably located between permanent magnets held by a yoke, the free end portion of the armature being coupled to a movable portion of the diaphragm; and a vent baffle located on a portion of the receiver defining the rear cavity volume, wherein the vent baffle is substantially impermeable to liquid and wherein the vent baffle provides pressure relief to the rear cavity volume of the housing. Attached Figure Description

[0004] The objects, features, and advantages of this disclosure will become fully apparent from the following detailed description taken in conjunction with the accompanying drawings and the appended claims. The drawings depict only exemplary embodiments and are therefore not intended to limit the scope of this disclosure.

[0005] Figure 1 This is a cross-sectional view of a balancing armature receiver, which may include a gas permeable barrier as disclosed herein.

[0006] Figure 2 It is a cross-sectional view of a receiver with a breathable baffle covered by a nozzle.

[0007] Figure 3 This is another cross-sectional view of a receiver with a breathable baffle covered by a nozzle.

[0008] Figure 4 It is a cross-sectional view of a receiver with a breathable baffle that allows direct exhaust to the outside of the housing.

[0009] Figure 5 It is a cross-sectional view of a receiver having a clamp structure for holding the breathable baffle within the receiver housing.

[0010] Figure 6 This is a more detailed view of a receiver with a clamp structure for holding the breathable baffle within the receiver housing.

[0011] Figure 7 yes Figure 6 Different views of the fixture structure.

[0012] Figure 8 yes Figure 6 Another view of the fixture structure.

[0013] Figure 9 It is a cross-sectional view of a receiver having a breathable baffle on a part of the diaphragm.

[0014] Figure 10 It is a cross-sectional view of a receiver with a breathable baffle on another part of the diaphragm.

[0015] Figure 11 It is a cross-sectional view of a receiver having a breathable baffle on another part of the diaphragm.

[0016] Figure 12 It is a cross-sectional view of a receiver having a breathable baffle on another part of the diaphragm.

[0017] Figure 13 It is a cross-sectional view of a receiver having a breathable baffle that is co-positioned with the terminal portion of the receiver.

[0018] Figure 14 These are characteristic frequency response curves for receivers with and without pressure relief holes.

[0019] Those skilled in the art will recognize that the accompanying drawings are for simplicity and clarity and may therefore not be drawn to scale and may not include well-known features; the order in which actions or steps occur may differ from the order described, and some actions or steps may be performed simultaneously unless otherwise specified; and the terms and expressions used herein have the meanings understood by those skilled in the art, unless different meanings are attributed to them herein. Detailed Implementation

[0020] This disclosure generally relates to balanced armature receivers with improved liquid impermeability, and more particularly, to balanced armature receivers with a pressure orifice that provides improved liquid impermeability. This orifice equalizes the pressure between the inside and outside of the receiver while providing a degree of liquid impermeability. Receivers are commonly used in in-canal receiver (RIC) hearing aids, wired and wireless headphones, true wireless stereo (TWS) devices, and other hearing devices that may be exposed to liquid contaminants.

[0021] A balanced armature receiver typically includes: a housing having a sound port located between its interior and exterior; and a diaphragm disposed within the housing, dividing the interior of the housing into a front cavity volume and a rear cavity volume. A motor, at least partially disposed within the housing, includes a coil positioned close to an armature having a free end portion that oscillates between permanent magnets held by a yoke in response to an audio signal applied to the coil; otherwise, it balances the armature between the magnets. The free end portion of the armature is coupled to a movable portion of the diaphragm that oscillates together with the armature to produce sound emitted from the sound port.

[0022] According to one aspect of this disclosure, the receiver includes a vent baffle located on a portion of a defined rear cavity volume of the receiver. The vent baffle forms a pressure relief orifice configured to provide pressure relief to the rear cavity volume of the housing to accommodate changes in temperature or ambient pressure. A lack of pressure equalization in the rear cavity volume leads to reed displacement, which can adversely affect receiver performance. Therefore, the pressure relief orifice must have an appropriate amount of acoustic impedance to equalize pressure over a short time period (e.g., one second) to avoid acoustic artifacts that may be perceptible to the user. Typically, the acoustic impedance of the pressure relief orifice is between about 5E9 Pa-s / m^3 and about 1E13 Pa-s / m^3. Acoustic impedance is determined by dividing the specific acoustic impedance of the baffle by the area of ​​the vent aperture. The MKS unit for specific acoustic impedance is Pa-s / m, also known as MKS Rayleigh, or simply Rayleigh. In one implementation, the pressure relief orifice is formed by a receiver consisting of a baffle positioned above an opening that penetrates the housing or diaphragm, and the diameter of the orifice can be between approximately 0.1 mm and 1.0 mm. In other implementations, the pressure relief orifice is more diffused, i.e., it spreads over a relatively large surface area; typical examples of this are described herein.

[0023] According to another aspect of this disclosure, the vented baffle is also substantially impermeable to liquids, thereby preventing liquid from seeping into the rear cavity volume. Substantially impermeable means that the baffle will prevent liquid from seeping into the rear cavity volume under specified equivalent water pressure and for a given duration. A common type of water pressure is the static head pressure caused by the weight of water due to its height above the object. A balanced armature receiver submerged in water will be subjected to this water pressure. Other types of water pressure are dynamic, where the water is moving and the water pressure is changing. Liquid resistance in these and other environments is typically defined according to the entry protection (IP) ratings of the International Electrotechnical Commission (IEC) 60529. For example, IPX5 specifies protection against low-pressure water jets, IPX6 against high-pressure heavy water jets, IPX7 against immersion in water up to 1 meter deep for 30 minutes, and IPX8 against immersion in water greater than 1 meter as specified by the manufacturer.

[0024] The pressure relief orifice provides liquid impermeability through a long, compact, tortuous path penetrating the hydrophobic baffle material. This liquid impermeability is typically associated with the specific acoustic impedance characteristics of the pressure relief orifice. A higher specific acoustic impedance generally provides greater liquid impermeability (i.e., impermeability at higher head pressures or for longer durations) because the higher impedance tortuous path is also less permeable to water. Based on currently available materials, a pressure relief orifice with a specific acoustic impedance of at least 5,000 MKS Rayleigh may be required for liquid impermeability sustained for 1 minute at a head of 3 meters. For liquid impermeability sustained for 1 minute at a head of 15 meters, a pressure relief orifice with a specific acoustic impedance of at least 00,000 MKS Rayleigh may be required. For liquid impermeability sustained for 1 minute at a head of 60 meters, a pressure relief orifice with a specific acoustic impedance of at least 00,000 MKS Rayleigh may be required. Liquid impermeability will require a corresponding amount of acoustic impedance for varying degrees of head pressure and exposure duration.

[0025] In one implementation, the breathable baffle is made of expanded polytetrafluoroethylene (ePTFE). Other impermeable breathable materials include thermoplastic polyurethane (TPF) films, meltblown fabrics, and nanospun materials. In principle, any known or future material or structure with pores or tightly wound fabrics is suitable for use as a breathable baffle, provided that the material is hydrophobic or coated with a hydrophobic material. In some implementations, the breathable baffle includes an oleophobic coating to reduce the adhesion of grease, oil, and other contaminants.

[0026] A venting baffle can be a patch fixed above a hole or opening in the housing. In one typical implementation, the rear cavity volume vents directly to the outside of the housing. In another typical implementation, the venting baffle is located between the rear cavity volume and the front cavity volume (e.g., on a portion of the diaphragm), wherein the rear cavity volume vents to the outside of the housing via the front cavity volume. In yet another typical implementation, the venting baffle is located between the rear cavity volume and a nozzle connected to the sound port, wherein the rear cavity volume vents to the outside of the housing via the nozzle. Combinations of these venting configurations are also considered in this disclosure. The entire receiver housing can be made of the material that serves as the venting baffle. A portion of the diaphragm can also be made of the venting baffle. Alternatively, the baffle can be a patch fixed above a hole or opening in the diaphragm. The baffle can be located on any wall portion of the housing, including end wall portions, any side wall portions, or top or bottom wall portions. The baffle can be located on the inner or outer surface of the housing wall portion. The precise position of the baffle may depend on how the receiver is mounted or integrated with the host device (e.g., wireless headphones) to ensure free airflow into and out of the housing and to avoid interference with other structures. Typical and non-limiting examples are further described herein with reference to the accompanying drawings.

[0027] Figure 1 This is a typical balanced armature receiver 100, in which a liquid-impermeable vent baffle can be implemented as further described herein. Other suitable receivers may take other forms. Receiver 100 typically includes: a housing 110, a diaphragm 120 disposed within the housing and dividing the interior of the housing into a front cavity volume 112 and a rear cavity volume 114. The front cavity volume is acoustically coupled to the outside of the housing via a sound port 116 located on an end wall portion. A typical receiver housing also includes a nozzle 118 disposed above the sound port 116 and coupled to the end wall portion on which the sound port is located. Other receivers do not include a nozzle. More generally, the sound port may be located on different portions of the housing. For example, the sound port may be located on a wall portion 111 parallel to the diaphragm and partially defining the front cavity volume. Alternatively, the sound port may be located on a wall portion defining another portion of the front cavity volume.

[0028] exist Figure 1 In the motor, located in the rear cavity volume, a coil 124 is supported by a bobbin 126 positioned around an armature 130. The armature has a free end portion 132 movably positioned between permanent magnets 140 and 142, which are spaced apart by a yoke 144. The free end portion of the armature is connected to a movable portion of the diaphragm (referred to as blade 122) via a drive rod or other linkage 146. Figure 1The armature in the armature is a U-shaped reed having a first arm 134 connected to the yoke and a second arm 138 extending therefrom a free end portion 132. The U-shaped portion 136 of the armature interconnects the first and second arms. Other receivers can have various other forms. For example, the armature can be an E-shaped reed or some other armature configuration, the coil does not need to be supported by a winding tube, and the motor can be located in the front cavity volume instead of the rear cavity volume.

[0029] In a receiver including a nozzle, a breathable baffle can be positioned between a portion of the nozzle and a lower wall portion of the housing defining a rear cavity volume: this wall portion secures the nozzle. Positioning the baffle between the nozzle and said wall portion simplifies baffle assembly, does not alter the overall external dimensions of the receiver, and provides a degree of protection for the baffle since it is not exposed. Figure 2 and Figure 3 In this receiver 200, a nozzle 210 is acoustically coupled to a sound port 202 of the receiver. The nozzle includes a sound tube portion 212 and a base portion 214 coupled to an end wall 216. A vent baffle 218 is disposed on a portion of the end wall 216 covered by at least a portion of the nozzle 210. The baffle covers a hole or opening 204 penetrating the end wall. Figure 2 In this process, the baffle is secured to the end wall 216, which has the opposite volume to the rear cavity, using adhesives or other fastening mechanisms. Figure 3 In the middle, the vent baffle 218 is clamped between the end wall 216 and the base part 214 of the nozzle.

[0030] In other implementations, a venting baffle is positioned on the outer wall portion defining the rear cavity volume, where the rear cavity volume directly exhausts air to the outside of the housing. Figure 4 and Figure 5 In the receiver 400, a breathable baffle 402 is mounted on the inner surface 410 of the outer wall portion of the housing 412. Figure 4 In this design, the baffle 402 covers the opening 414 extending through the outer wall portion and can be secured to the surface 410 by adhesive or other fastening mechanisms between the baffle and the surface. The adhesive can be a flat annular structure 416, such as a pressure-sensitive adhesive (PSA) located between the baffle and the surface 410. Alternatively, the adhesive can run around the baffle in an annular form 418. In one example, this annular form can be formed from cured epoxy resin. Alternatively, the baffle can be secured and / or sealed to the housing using both the flat annular structure 416 and the annular form 418.

[0031] exist Figure 5 In the middle, the baffle 402 covers the opening 404 that penetrates the outer wall portion and is held on the bottom surface 410 by a mechanical clamp. Figures 6 to 8 Various views of a typical clamping structure suitable for retaining a baffle on the inner surface of an outer wall portion are shown. Figure 6 In this design, the clamp includes a retaining plate 406 with a hole 407, which applies a clamping force to the top of a baffle 402 located above a hole 404 in the outer wall portion of the housing. The clamping force holds the baffle against the inner surface 410 of the housing 412. Figures 6 to 8 In this configuration, a tab 408 on the opposing sidewall portion of the housing 412 holds the retaining plate 406 in contact with the tab. In some implementations, the retaining plate may be bent to snap-fit ​​under the tab 408. For positioning purposes, the tab may also be positioned in a recess (not shown) formed in one or both of the bottom surfaces of the retaining plate or the housing. Alternatively, the retaining plate may be configured such that sufficient force is applied to position the tab without requiring a recess. Alternatively, in Figure 6 In this process, an adhesive layer 416, such as a pressure-sensitive adhesive (PSA), can position the baffle 402 and seal the baffle to the inner surface 410.

[0032] In other implementations, the venting baffle is integrated with or forms part of the diaphragm, wherein the rear cavity volume exhausts gas to the outside of the housing via the front cavity volume. The diaphragm includes rigid blades movably connected to the frame via a flexible diaphragm covering the gap between the blades and the frame. Figure 9 In this configuration, a breathable baffle 402 is located on the blade 122 of the diaphragm 120. The baffle covers the hole 123 penetrating the blade 122 and can be secured to the blade by adhesive or other fastening mechanisms. Figure 10 In this design, the breathable baffle 402 constitutes all or part of the blade. For example, the blade can be made of a rigid material that provides a liquid-resistant and breathable baffle. Figure 11 In this design, a breathable baffle forms part of the flexible diaphragm 125. In other words, the flexible diaphragm is made of a material that provides both liquid resistance and breathability. For example, the flexible diaphragm can be made of ePTFE or other flexible materials. In other implementations, the breathable baffle is located on or constitutes the frame of the diaphragm. Figure 12 In this configuration, a breathable baffle 402 is secured to a portion of the frame 121, and the baffle covers an opening 403 in the frame. The baffle can be secured to the frame by adhesive or other fastening mechanisms, or the baffle can be held in place by a portion of the frame. In other implementations, the baffle can be located on more than one portion of the diaphragm.

[0033] The receiver typically includes terminals located on an external portion or surface of the housing. These terminals include contacts electrically connected to a coil within the housing, accessible from the outside of the receiver for receiving audio signals applied to the coil. In some implementations, a vent baffle is co-positioned with the terminals, wherein the rear cavity volume vents to the outside of the housing through or near the terminals. The terminals may include holes aligned with openings in a wall portion of the housing to allow venting of the rear cavity volume through the terminals. Figure 13 In this receiver, a terminal 500 is located on the outer surface of an end wall 502 of the housing 110. The terminal is covered by a vent baffle 402 that covers an opening 504 through the end wall. The opening in the end wall communicates with an opening 506 in the terminal. Alternatively, the baffle may be a patch fixed to the outer surface of the terminal above the opening 506.

[0034] The frequency response of a receiver typically depends on the location and acoustic impedance of the pressure relief orifice. The orifice can be located between the rear and front chamber volumes of the receiver, or on the outer wall of the rear chamber volume that directly vents to the outside of the receiver. For an orifice located between the front and rear chamber volumes, as the acoustic impedance decreases, the low-frequency response of the receiver gradually attenuates (i.e., it will have a higher frequency roll-off), and vice versa. A pressure relief orifice directly venting to the outside of the receiver amplifies low frequencies to some extent. Reducing the acoustic impedance of the orifice directly venting to the outside of the housing will increase the frequency range where amplification occurs. Typical examples are further described in this paper.

[0035] exist Figure 14 In the first scenario shown, the extremely high acoustic impedance release orifice plot corresponds to a substantially blocked release orifice (i.e., virtually no air pressure release) and produces a relatively flat sound pressure level (SPL) at low frequencies. The extremely high acoustic impedance release orifice plot represents the receiver's characteristic frequency response. Figure 14 In the second scenario shown, the curve of 2.0E10 (Pa-s / m^3) acoustic impedance versus front cavity volume corresponds to the release orifice (e.g., the diaphragm of an exhaust pipe) between the rear and front cavity volumes, and shows the SPL attenuation at low frequencies. In this example, the frequency response shows a 3 dB drop at approximately 50 Hz compared to the characteristic frequency response. Reducing the acoustic impedance will increase the cutoff frequency and attenuation. Acoustic impedance depends on the aperture size of the baffle and the specific acoustic impedance. Figure 14 In the figure, the 2.5E10 (Pa-s / m^3) acoustic impedance external curve corresponds to the rear cavity volume with direct exhaust to the outside of the housing, and shows the increase in SPL at low frequencies due to the reduced acoustic stiffness of the rear cavity volume. The acoustic stiffness of the rear cavity volume can be reduced at low frequencies by decreasing the acoustic impedance of the release orifice. In this example, the frequency response increases by 3 dB at approximately 35 Hz compared to the characteristic frequency response. Figure 14The external acoustic impedance curve of 2.5E9 (Pa-s / m^3) shows that by further reducing the acoustic impedance of the release orifice, the response can be increased at low frequencies. In the final example, the frequency response is increased by 3 dB at approximately 200 Hz compared to the characteristic frequency response. In some implementations, the balanced armature receiver includes a pneumatic release orifice extending directly from the rear cavity volume to the outside of the housing, and another pneumatic release orifice between the rear and front cavity volumes, or between the rear cavity volume and the nozzle.

[0036] In RICs or other sound amplification devices, venting between the rear and front chamber volumes is generally preferable to venting directly from the rear chamber volume to the outside of the housing, where a microphone can detect sound and cause unwanted feedback. Therefore, when venting directly to the outside of the housing in a sound amplification device including a microphone, it is desirable to provide a pressure relief orifice with high acoustic impedance to reduce unwanted sound leakage detectable by the microphone. The breathable baffle described herein provides both high acoustic impedance and liquid impermeability.

[0037] In one implementation, one or more vents are configured and positioned such that the sound pressure level (SPL) deviation of the frequency response caused by air pressure release at 500 Hz is less than 3 dB compared to the characteristic frequency response of the balanced armature receiver in the absence of air pressure release. In another implementation, one or more vents are configured and positioned such that the frequency response deviation caused by air pressure release at frequencies less than 200 Hz is 3 dB compared to the characteristic frequency response of the balanced armature receiver in the absence of air pressure release. In yet another implementation, one or more vents are configured and positioned such that the frequency response deviation caused by air pressure release at frequencies less than 100 Hz is 3 dB compared to the characteristic frequency response of the balanced armature receiver in the absence of air pressure release. In yet another implementation, one or more vents are configured and positioned such that the frequency response deviation caused by air pressure release at frequencies less than 50 Hz is 3 dB compared to the characteristic frequency response of the balanced armature receiver in the absence of air pressure release.

[0038] While this disclosure and its content, which is now considered the best mode thereof, have been described in a manner that enables those skilled in the art to make and use them, it should be understood and appreciated that many equivalents exist for the typical embodiments described herein, and that various modifications and variations may be made to these embodiments without departing from the scope and spirit of the invention, and that such modifications and variations are not limited to the embodiments described, but rather to the appended claims and their equivalents.

Claims

1. A balanced armature receiver, the balanced armature receiver comprising: case; A diaphragm is disposed in the housing and divides the interior of the housing into a front cavity volume and a rear cavity volume; A sound port, the sound port being located between the front cavity volume and the outside of the housing; A motor, the motor being disposed within the housing, and the motor including a coil positioned close to an armature, the armature having a free end portion movably located between permanent magnets held by a yoke, the free end portion of the armature being coupled to a movable portion of the diaphragm; A breathable baffle is located on a portion of the receiver defining the rear cavity volume, wherein the breathable baffle is impermeable to liquid. The venting baffle provides air pressure release for the rear cavity volume of the housing. The housing includes a nozzle, which includes a sound tube portion and a base portion. The base portion is connected to a wall portion defining the volume of the rear cavity. The nozzle is acoustically connected to the sound port. A venting baffle is disposed on a portion of the wall portion covered by at least a portion of the nozzle and covers an opening penetrating the wall portion.

2. The balanced armature receiver according to claim 1, wherein, The breathable baffle has a specific acoustic impedance of 5,000 MKS Rayleigh or greater, and the breathable baffle forms a pressure relief hole in the rear cavity volume.

3. The balanced armature receiver according to claim 2, wherein, The acoustic impedance of the pressure relief orifice is between 5E9 Pa-s / m^3 and 1E13 Pa-s / m^3.

4. The balanced armature receiver according to claim 3, wherein, The pressure relief orifice includes a hole with a diameter between 0.1 mm and 1.0 mm.

5. The balanced armature receiver according to claim 1, wherein, The breathable baffle includes an oleophobic coating.

6. The balanced armature receiver according to claim 1, wherein, The breathable baffle is located inside the nozzle.

7. The balanced armature receiver according to claim 6, wherein, The venting baffle is held between the wall portion defining the rear cavity volume and the base portion of the nozzle.

8. The balanced armature receiver according to claim 1, wherein, The breathable baffle is located inside the housing and provides air pressure release directly to the outside of the housing.

9. The balanced armature receiver according to claim 8, wherein, The breathable baffle is mechanically clamped to the inner surface of the housing.

10. The balanced armature receiver according to claim 1, wherein, The breathable baffle is disposed on a portion of the diaphragm.

11. The balanced armature receiver according to claim 10, wherein, The breathable baffle is clamped between a portion of the diaphragm and the housing.

12. The balanced armature receiver according to claim 10, wherein, The diaphragm includes blades, which are movably connected to the frame via a flexible diaphragm, the flexible diaphragm including the breathable baffle.

13. The balanced armature receiver according to claim 10, wherein, The diaphragm includes blades that are movably connected to the frame via a flexible diaphragm, and the blades include the breathable baffles.

14. The balance armature receiver of claim 1, further comprising terminals secured to the housing, the terminals including contacts electrically connected to the coil, wherein, The terminal and the breathable baffle are positioned in coordination.

15. The balanced armature receiver according to claim 1, wherein, The pressure release results in a 3 dB deviation in the frequency response of the balanced armature receiver at frequencies below 200 Hz, compared to the characteristic frequency response of the balanced armature receiver in the absence of the pressure release.

16. The balanced armature receiver according to claim 1, wherein, Compared to the characteristic frequency response of the balanced armature receiver in the absence of the pressure release, the pressure release results in a 3 dB deviation in the frequency response of the balanced armature receiver at frequencies below 100 Hz.

17. The balanced armature receiver according to claim 1, wherein, Compared to the characteristic frequency response of the balanced armature receiver in the absence of the pressure release, the pressure release results in a 3 dB deviation in the frequency response of the balanced armature receiver at frequencies below 50 Hz.

18. The balanced armature receiver according to claim 1, wherein, The breathable baffle forms a pressure relief hole with an acoustic impedance of 5E9 Pa-s / m^3 or greater, and comprises a material with a specific acoustic impedance of at least 5,000 MKS Rayleigh.

19. The balanced armature receiver according to claim 8, wherein, The breathable baffle is fixed to the inner surface of the housing with adhesive.

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