阅读说明：本技术 用于麦克风系统的滤波器、麦克风系统、微型电子装置以及装备印刷电路板的方法 (Filter for a microphone system, microelectronic device and method for equipping a printed circuit board ) 是由 M·魏贝尔 P·波特曼 A·施莱辛格 于 2017-05-05 设计创作，主要内容包括：本发明涉及一种用于微型电子装置(10)的麦克风系统(16)的滤波器(34’、34")。所述滤波器(34’、34")包括声音入口和声音出口,其中,所述滤波器(34’、34")适合于安装在印刷电路板(14)的表面上。(The invention relates to a filter (34', 34") for a microphone system (16) of a miniature electronic device (10). The filter (34', 34") comprises a sound inlet and a sound outlet, wherein the filter (34', 34") is adapted to be mounted on a surface of a printed circuit board (14).)

1. A filter (34; 34', 34') for a microphone system (16) of a microelectronic device (10), the filter (34; 34', 34') having a sound inlet and a sound outlet, wherein the filter (34; 34', 34') is adapted to be mounted on a surface of a printed circuit board (14).

2. The filter (34; 34', 34") according to claim 1, wherein the filter (34; 34', 34") is adapted to be mounted on the surface of the printed circuit board (14) in such a manner that the sound discharge opening of the filter (34; 34', 34") faces a portion of the printed circuit board (14) where a through hole (38) is formed.

3. The filter (34; 34', 34") according to claim 1 or 2, wherein the filter (34; 34', 34") is an acoustic low-pass filter or an acoustic band-pass filter.

4. The filter (34; 34', 34") according to one of the preceding claims, wherein the filter (34; 34', 34") is an SMD component adapted to be mounted by machine on the surface of the printed circuit board (14) by means of a pick-and-place process.

5. The filter (34) according to one of the preceding claims, comprising a sound tube (42) for coupling the sound inlet opening to the sound outlet opening.

6. The filter (34) according to one of claims 2 to 5, wherein the sound tube (42) is adapted to be mounted on the printed circuit board (14) in such a way that a longitudinal direction of the sound tube (42) passes through the through hole (38) formed in the printed circuit board (14).

7. The filter (34) of claim 6 wherein the acoustic tube (42) includes a flange (44) adapted to be mounted on a portion of the printed circuit board (14) surrounding the through hole (38).

8. The filter (34) according to one of the preceding claims, further comprising a seal (45) comprising an elastic material, the seal (45) surrounding the sound tube (42) in at least a part of the sound entry opening of the filter (34).

9. the filter (34) according to claim 8, wherein the length of the seal (45) in the direction of the sound tube (42) is tailored to exceed the length of the sound tube (42).

10. The filter (34) according to one of the preceding claims, wherein the sound tube (42) is made of plastic.

11. The filter (34) of claim 10 wherein the acoustic tube (42) is mounted on the printed circuit board (14) by means of adhesive bonding.

12. The filter (34) according to one of claims 1 to 9, wherein the sound tube (42) is made of metal.

13. The filter (34) of claim 12 wherein the acoustic tube (42) is mounted on the printed circuit board (14) by means of soldering or gluing.

14. The filter (34) according to one of claims 8 to 13, wherein the seal (45) is formed in a conical shape.

15. The filter (34) according to one of claims 5 to 14, further comprising at least one of an acoustic filter component (50) and a protective cover (52) accommodated into at least a portion of the sound tube (42) or located at a sound inlet or a sound outlet of the sound tube.

16. The filter (34; 34', 34") according to one of the preceding claims, wherein the miniature electronic device is a hearing aid (10).

17. The filter (34) according to one of claims 8 to 16, wherein the seal (45) is sized to provide an acoustically tight coupling between a sound entry channel (32', 32") of the microelectronic device (10) and the sound entry port.

18. A microphone system (16), the microphone system comprising: a printed circuit board (14); the filter (34') according to one of the preceding claims mounted on a first surface of the printed circuit board (14); at least one microphone (36') mounted on a second surface of the printed circuit board (14), wherein a sound input of the microphone (36') is acoustically coupled to the sound outlet of the filter (34') via a through hole formed in the printed circuit board (14).

19. Microphone system (16) according to claim 18, wherein the microphone system (16) comprises a further microphone (36") and a further filter (34") mounted on opposite surfaces of the printed circuit board (14), the further filter (34") being a filter (34") according to one of claims 1 to 17, wherein a sound input of the further microphone (36") is acoustically coupled to a sound outlet of the further filter (34") via a further through hole formed in the printed circuit board (14).

20. Microphone system (16) according to claim 18 or 19, wherein the microphone (36, 36', 36") is a dynamic microphone, a capacitive microphone, an electret capacitive microphone or a MEMS microphone.

21. A microelectronic device (10), comprising: a housing (12) formed with at least one sound inlet; -a printed circuit board (14) equipped with at least one processing device (18); and a microphone system (16) according to one of claims 18 to 20.

22. The microelectronic device (10) according to claim 21, wherein the filter (34, 34', 34") comprises a seal (45) adapted to prevent sound leakage.

23. The microelectronic device (10) according to claim 21 or 22, wherein the microelectronic device is a hearing aid (10).

24. Method for equipping a printed circuit board (14) with a filter (34; 34', 34") according to one of claims 1 to 17, comprising the steps of: the filter (34; 34', 34') is mounted to the surface of the printed circuit board (14) by means of a pick-and-place process.

Technical Field

The invention relates to a filter for a microphone system, a microelectronic device and a method of equipping a printed circuit board.

Background

Hearing devices are commonly used to improve the hearing ability or communication ability of a user. The hearing device may pick up surrounding sounds with a microphone of the hearing device, process the microphone signal to take account of the hearing preference of the user of the hearing device, and provide the processed sound signal to the auditory canal (commonly referred to as a receiver) of the user via a micro-speaker. The hearing device may also receive sound from alternative inputs such as an inductive coil or a wireless interface.

Hearing devices comprising a microphone are known, wherein the microphone is protected at the acoustic input by means of two mesh-like, acoustically transparent acoustic input filters. Thus, demands are made on the volume inside the hearing device in front of the microphone. This may lead to a complex mechanical solution, resulting in a loss of sensitivity and a change in the frequency response and phase of the sound delivered to the microphone.

Known hearing devices may be equipped with micro-electromechanical systems (MEMS) microphones. Disadvantages of MEMS microphones may include non-linear frequency response and high sensitivity to ultrasonic noise. MEMS microphones can be mounted on printed circuit boards by surface mounting or more precisely by automated pick and place (automated pick and place) processes and do not grant the same degrees of freedom as for example in hand soldered electret microphones with nozzles and ducts.

The output of the microphone may be coupled to an electrical Low Pass Filter (LPF) that may reduce non-linearity up to 10 kHz. In the example, an R-C filter is used. The R-C filter may result in higher Total Harmonic Distortion (THD), phase distortion, higher output impedance, lower sensitivity, and higher power consumption.

In the case of coupling a low-pass filter to the output of the MEMS microphone, the problem of high sensitivity to ultrasonic noise still remains.

It is therefore an object of the present invention to provide a filter for a microphone system of a miniature electronic device, which filter solves the problems known in the art.

Disclosure of Invention

It is noted that the term "hearing device" is to be understood not only as a device to be used for improving the hearing of hearing impaired patients, but also as a communication means to improve communication between individuals. In addition, the term "hearing device" includes currently available hearing device types, such as, for example, behind-the-ear (BTE), in-ear (ITE), in-canal (ITC), and deep-canal (CIC) hearing devices. Furthermore, the hearing device may also be fully implanted or partially implanted.

The present invention is directed to a filter for a microphone system of a microelectronic device, wherein the filter comprises a sound inlet and a sound outlet, wherein the filter is adapted to be mounted on a surface of a printed circuit board. Accordingly, a filter is proposed which can be easily and reliably mounted on one surface of a printed circuit board when a microphone is mounted on the opposite surface of the printed circuit board.

In an embodiment, the filter is adapted to be mounted on the surface of the printed circuit board in the following manner: the sound outlet of the filter faces a portion of the printed circuit board where a through-hole is formed. The filter may be mounted in such a manner that a central axis of the filter is aligned with a central axis of the through-hole.

In an embodiment, the filter is an acoustic low-pass filter or an acoustic band-pass filter. Therefore, the provision of an electrical low-pass or band-pass filter (LPF, BPF) at the output of the microphone can be omitted, while non-linearity can be reduced and efficiency can be improved without drawbacks. Furthermore, omitting an electrical filter at the output of the microphone may increase the density of the printed circuit board. A surface mounted filter allows to provide a certain distance between e.g. the diaphragm of a microphone and an acoustic low pass filter or an acoustic band pass filter provided by the filter itself. This increases the efficiency of the filter. Furthermore, the loss of sensitivity can be reduced.

In an embodiment, said filter is an SMD component adapted to be mounted on said surface of said printed circuit board by machine by a pick and place process. The filter of the present invention enables fast, safe and accurate placement and mounting on the surface of the printed circuit board, thereby providing a reliable and fast interchangeable or adaptable mechanical interface for sound pickup.

In an embodiment, the proposed filter further comprises a sound tube for coupling the sound inlet to the sound outlet. The size of the sound tube may be defined to allow for an optimal acoustic filter matching or rather requirements.

In an embodiment of the proposed filter, the sound tube is adapted to be mounted on the printed circuit board in the following way: the longitudinal direction of the sound tube passes through the through-hole formed in the printed circuit board.

In an embodiment of the proposed filter, the sound tube comprises a flange adapted to be mounted on a portion of the printed circuit board surrounding the through hole. The flange allows for a quick and correct placement and fixation of the filter on the surface of the printed circuit board.

In an embodiment, the filter further comprises a sealing member comprising an elastic material, the sealing member surrounding the sound tube in at least a part of the sound inlet of the filter. The sealing member may be provided with a hole formed through the sealing member in a longitudinal direction of the sealing member. The filter may be provided with the seal by simply mounting the seal via its aperture on the sound tube. In an example, the filter may be mounted on a surface of the printed circuit board with the seal already pre-assembled to the sound tube. In another example, the filter may be mounted on a surface of the printed circuit board, and the sealing member is assembled to the sound tube in a subsequent process step, i.e., a process step after the mounting step. Since the seal surrounds the sound tube in at least a part of the sound inlet of the filter, acoustic leakage can be prevented. Another benefit of the proposed solution is that the seal allows radial sealing, which is more robust than e.g. face-to-face sealing.

In an embodiment of the proposed filter, the length of the sealing member in the direction of the sound tube is tailored to exceed the length of the sound tube. The length may be tailored to engage, for example, a sound inlet of the housing of the hearing device in an acoustically sealed manner. Due to the resilient material of the sealing member, at least a distal end of the sealing member may engage, for example, a sound inlet of the housing of the hearing device in a snug fit connection. Thus preventing acoustic leakage.

In an embodiment of the proposed filter, the sound tube is made of plastic. Thus, costs may be reduced while still exhibiting improved acoustic characteristics.

In an embodiment of the proposed filter, the sound tube is mounted on the printed circuit board by gluing. In this embodiment, the sound tube, which may comprise plastic, may be easily mounted on the surface of the printed circuit board. In an example, the top layer of a multilayer printed circuit board may be removed (blanked out) to create a sink region (sink) that is customized to accommodate the flange of the filter. In this example, the diameter of the flange of the filter is equal to or less than the diameter of the dip zone.

In another embodiment of the proposed filter, the sound tube is made of metal.

In an embodiment of the proposed filter, the sound tube is mounted on the printed circuit board by means of soldering or gluing. In this embodiment, the sound tube, which may comprise metal, may be easily mounted on the surface of the printed circuit board by means of soldering or gluing. The soldering may comprise reflow soldering or rather SMD soldering, as may already be used in an automated SMD pick and place process. Advantageously, the filter can be soldered in a highly accurate manner directly on the surface of the printed circuit board, for example via its sound tube, flange or the like. To allow for proper positioning, an additional copper ring may be added to the top layer of the printed circuit board. In an example, the top layer of a multilayer printed circuit board may be removed or, more precisely, recessed to create a sinker, which may be provided with an additional copper ring at its bottom. In this example, the diameter of the flange of the filter is equal to or less than the diameter of the dip zone. If the sound tube is made of metal, such a metal sound tube may be directly bonded to the printed circuit board or recessed into a depression in the printed circuit board.

In an embodiment of the proposed filter, the seal is formed in a conical shape. The conical shape of the sealing member, optionally in combination with the elastic properties of the sealing member, may enable a tight fitting connection to e.g. a sound inlet of a housing of the hearing device. The sound inlet of the housing may comprise an acoustic channel to the environment.

In an embodiment, the filter further comprises at least one of an acoustic filter component and a protective cover accommodated into at least a part of the sound tube or at a sound entrance or a sound exit of the sound tube. The acoustic filter component may be configured to compensate for a possible reduction in sensitivity. In addition, the sensitivity to ultrasound can be reduced.

In an embodiment of the proposed filter, the miniature electronic device is a hearing aid.

In an embodiment of the proposed filter, the seal is dimensioned to provide an acoustically tight coupling between the sound inlet channel of the microelectronic device and the sound inlet. Thus, acoustic leakage can be prevented. Furthermore, the seal may provide a reliable radial seal against the sound entry passage.

The invention also relates to a microphone system comprising: printed circuit board, a filter according to one of the preceding claims mounted on a first surface of the printed circuit board, at least one microphone mounted on a second surface of the circuit board, wherein a sound input of the microphone is acoustically coupled to the sound outlet of the filter via a through hole formed in the printed circuit board. The microphone system of the present invention allows for a smaller and easier mechanical design, providing reduced cost and improved performance and efficiency.

In an embodiment, the microphone system comprises a further microphone and a further filter according to one of claims 1 to 17 mounted on opposite surfaces of the printed circuit board, respectively, wherein a sound input of the further microphone is acoustically coupled to the sound outlet of the further filter via a further through hole formed in the printed circuit board. In case the microphone system comprises more than one microphone and associated filters, the microphones may be mounted on the same surface of the printed circuit board or on opposite surfaces, respectively. The same is true of the associated filters, in turn.

In an embodiment of the proposed microphone system, the microphone is a dynamic microphone, a capacitive microphone, an electret capacitive microphone or a MEMS microphone. Other still known or upcoming microphones may be used as well.

The invention also relates to a microelectronic device comprising: housing formed with at least one sound inlet, printed circuit board equipped with at least one processing means and microphone system according to one of claims 18 to 20. The sound inlet may be any opening in the housing to allow sound to enter the interior of the housing. In an example, the opening may be any opening that may be assigned additional uses (e.g., technical and/or mechanical uses). In an example, the opening for sound to enter may be an opening exposed adjacent to the shift button. In another example, the opening may be a pin insertion hole for the purpose of maintenance or the like.

In an embodiment of the proposed microelectronic device, the filter comprises a seal adapted to prevent sound leakage. Thus, the microelectronic device may allow sound from the environment to enter the acoustic input of the microphone directly via the filter without acoustic leakage.

In an embodiment, the proposed miniature electronic device is a hearing aid. Thus, a hearing aid is provided which exhibits reduced non-linearity at the output of the one or more microphones even if the respective filters are omitted.

Furthermore, the invention relates to a method for assembling a filter according to one of claims 1 to 17 to a printed circuit board, wherein the method comprises the following steps: the filter is mounted to the surface of the printed circuit board by means of a pick and place process. The pick and place process may include a process of reflow soldering or bonding components to the surface of the printed circuit board. The method of the invention may allow the use of different MEMS microphones having the same mechanical and/or acoustic properties. The pick and place process is a simple, reliable and accurate process, which further achieves cost savings.

It is explicitly pointed out that any combination of the above embodiments is the subject of further possible embodiments. Only those embodiments that would cause a conflict are excluded.

Drawings

The present invention is further described with reference to the accompanying drawings, which jointly illustrate various exemplary embodiments that will be considered in conjunction with the detailed description below. Shown in the drawings are:

Fig. 1 schematically depicts a cross-sectional view of a hearing aid in an embodiment of the invention; and

Fig. 2 schematically depicts a cross-sectional view of a microphone system in an embodiment of the invention.

Detailed Description

Fig. 1 is a schematic cross-sectional view of a hearing aid 10. The hearing aid 10 comprises a housing 12 for accommodating a printed circuit board 14 constituted by a microphone system 16 (shown enclosed by a dashed line in the figure). The microphone system 16 further comprises two microphone devices 17', 17 "which will be explained in more detail below. Although the microphone system 16 is shown as comprising two microphone devices 17', 17", the microphone system 16 may comprise one or more than two microphone devices. The printed circuit board 14 may be provided with processing means 18. The processing means 18 may be a digital signal processor or an analog signal processor. Although the printed circuit board 14 is shown as being integrally constructed, the printed circuit board 14 may include more than one circuit board, wherein, for example, one of the circuit boards thereof may be used to support one or more microphone devices. The hearing device 10 also includes a battery 20, the battery 20 being used to power hearing aid components (e.g., the processing device 18, the microphone system 16, etc.). The hearing aid 10 is also equipped with an ear canal plug 22 to be inserted into the ear of the user. The plug 22 may include a receiver 24 for transmitting sound into the ear canal of the user. The receiver 24 may be connected to a receiver device (not shown) comprised in the housing 12 of the hearing aid 10 via a connection wire 26, which connection wire 26 may be configured as an electrical connection or as a sound tube.

the hearing aid 10 further comprises electrical switching means 28, for example for switching between different modes of the hearing aid 10, adjusting the loudness etc. The electrical switching apparatus 28 includes a control button 30 which can be operated by a user from outside the housing 12. In the shown example, the control buttons 30 are shift buttons that can be shifted up and down, e.g. to shift the user between different hearing aid menus, adjust the loudness, etc.

While the control button 30 of the electrical switching apparatus 28 may substantially cover the interior of the housing 12 relative to the environment, there may be a portion between the housing 12 and the control button 30 that is open to the environment. In an example, a portion at the top and bottom of the control button 30 (on the right and left side when viewed in the figure) may be vented to the environment. These openings allow sound (e.g., speech) to enter the interior of the housing 12, as schematically depicted by the two dashed arrows a', a ". Inside the housing 12, sound entering the housing 12 via the above-mentioned opening can be guided by means of two sound entry channels 32', 32 ". The sound inlet channels 32', 32 "may comprise, for example, wall portions formed by the housing 12 and/or the electrical switching apparatus 28.

As mentioned above, in the example shown, the microphone system 16 comprises two microphone arrangements 17', 17 ". The microphone devices 17', 17 "may comprise filters 34', 34" and microphones 36', 36", respectively. The filters 34', 34 "each include a seal formed in a conical shape, as described in more detail below. The filters 34', 34 "are mounted on a first surface of the printed circuit board 14 and the microphones 36', 36" are correspondingly mounted on a second surface of the printed circuit board 14. The first and second surfaces of the printed circuit board 14 are opposite to each other. Through holes, which will be described in more detail below, are formed in the portions of the printed circuit board 14 that are sandwiched between the filters 34', 34 "and the microphones 36', 36", respectively.

The filters 34', 34 "disposed on the first surface of the printed circuit board 14 each include a sound inlet and a sound outlet, wherein the filters 34', 34" are mounted such that the sound inlets are exposed to the sound inlet passages 32', 32 "to pick up sound, and the sound outlets face portions of the printed circuit board 14 in which the through holes are formed. On the other hand, the microphones 36', 36 ″ provided on the second surface of the printed circuit board 14 are mounted in the following manner: the respective acoustic inputs of the microphones 36', 36 "face the portions of the printed circuit board 14 where the through holes are formed. Thus, sound picked up from the environment may be coupled to the acoustic inputs of the respective microphones 36', 36 "via the filters 34', 34" and the through holes.

Accordingly, the filters 34', 34 "and the microphones 36', 36" are stacked on each other correspondingly with the printed circuit board 14 interposed therebetween while sound transmission is achieved via the through holes. This arrangement allows for more efficient use of the space of the printed circuit board 14, the volume inside the housing 12, etc. The sound may pass through a filter assembly of filters 34', 34 "(described below). The filter assembly may comprise acoustic filter components and/or a protective cover for filtering out dust, dirt, foreign objects etc. and thus preventing them from entering the microphones 36', 36 ".

The conical shape of the seal may be such as to provide an acoustically tight coupling with the sound inlet passages 32', 32 ". In other words, each sound entry passage 32', 32 "tightly engages the surface of the respective seal in an acoustically sealed manner by its distal end. This seal may be further enhanced due to the resilient nature of the seal. In an example, the acoustically-tight coupling may be established during assembly of a first housing portion (e.g., a half-housing) of the housing 12 to a second housing portion (e.g., a counterpart of the half-housing). The first housing part may be provided with one or two sound inlet passages 32', 32", or may be part of the sound inlet passage.

Although fig. 1 shows two filters 34', 34 "mounted on the same surface (e.g., a first surface) of the printed circuit board 14 and microphones 36', 36" mounted on an opposite surface (e.g., a second surface), this arrangement may be reversed. In other words, the filters 34', 34 "may be mounted on opposite surfaces of the printed circuit board 14, respectively, and the microphones 36', 36" may be mounted on opposite surfaces of the printed circuit board 14, respectively, in reverse. This arrangement allows sound arriving from opposite sides (e.g. left/right, front/back, etc.) of the hearing aid 10 to be picked up. Therefore, the definition can be improved.

Fig. 2 shows the microphone system 16 in an enlarged view. In fig. 2, the same or similar components as those already shown and described with reference to fig. 1 are referenced with the same or similar reference numerals. The microphone system 16 includes a filter 34 and a microphone 36 mounted on opposite surfaces of the printed circuit board 14, respectively, and the printed circuit board 14 provided with a through hole 38 is inserted. In an example, the filter 34 may be an acoustic low pass filter or an acoustic band pass filter. Therefore, the provision of the electric filter can be omitted without suffering from acoustic disadvantages such as an increase in nonlinearity or the like.

The filter 34 may be configured as an SMD component filter. Therefore, the SMD component filter can be accurately mounted on the surface of the printed circuit board 14 by means of the pick-and-place process. The filter 34 comprises a filter component 40 arranged within a sound tube 42. The sound tube 42 may in turn be mounted on the printed circuit board 14 by means of its flange 44, the flange 44 surrounding the sound tube at its bottom end of the sound tube 42. The filter 34 further comprises a seal 45 surrounding the sound tube 42. The seal 45 may be formed in a conical shape, wherein the seal 45 is mounted on the sound tube 42 in such a way that the cone tapers at the end directed towards the top. The seal 45 may be made of an elastic material (e.g., rubber). The central axis of the conical seal 45 may be provided with a passage formed to engage with the sound tube 42 by simply attaching the seal 45 to the sound tube 42 from above. Due to the elasticity of the material of the sealing member 45, the sound tube 42 and the sealing member 45 may be simply fixed to each other by friction. Thus, fixing means such as adhesive may be omitted.

As mentioned above, the filter 34 is connected to the surface of the printed circuit board 14 by means of the sound tube 42, in particular by means of the flange 44 of the sound tube 42. In doing so, the sound tube 42 may be mounted on the surface of the printed circuit board 14 by means of a first adhesive portion 46', which may comprise solder (i.e., solidified solder) or adhesive. In the example, it is assumed that the sound tube 42 is made of plastic, and the sound tube 42 is mounted on the surface of the printed circuit board 14 by means of adhesion. On the other hand, assuming that the sound tube 42 is made of metal, the sound tube 42 is mounted on the surface of the printed circuit board 14 by means of soldering or bonding. If the sound tube 42 is mounted on the surface of the printed circuit board 14 by means of soldering, an additional copper ring (not shown) may be provided on the surface of the printed circuit board 14. In an example, the surface of the printed circuit board 14 may be recessed to create a sunken region 47, wherein the sunken region 47 may receive the first adhesive 46' (solder or adhesive). In the case of welding, sinker 47 may include an additional copper ring (not shown) at its bottom. The diameter of flange 44 is equal to or less than the diameter of countersink 47.

A portion of the surface of the printed circuit board 14 opposite the filter 34 is provided with a microphone 36. The microphone 36 may be mounted on the surface of the printed circuit board 14 by means of a second adhesive portion 46", which may comprise (cured) solder or an adhesive. The first 46' and second 46 "adhesive portions may be identical, i.e. both comprise (cured) solder or adhesive, or may be different from each other. The filter 34 and microphone 36 may be mounted on respective surfaces of the printed circuit board 14 in the following manner: the central axis of the acoustic pipe 42 of the filter 34 and the central axis of the acoustic input portion 48 of the microphone 36 both pass through the through hole 38. In an example, the two axes are substantially aligned with each other. In another example, both axes extend along the same straight line. The microphone 36 is provided at its acoustic input 48 with a back plate 49 provided with a plurality of holes. Incoming sound pressure waves passing through the holes in the back plate 49 may cause a diaphragm (not shown) included with the microphone 36 to move in proportion to the amplitude of the compressional and rarefaction waves. This movement changes the distance between the diaphragm and the back plate 49 and thus the capacitance. This change in capacitance can in turn be converted into an electrical signal.

The above-mentioned filter member 40 may include an acoustic filter member 50 disposed inside the sound tube 42. The acoustic filter component 50 may be adapted to reduce non-linearities and/or sensitivity to ultrasound, etc. In the sound tube 42, the distance between the acoustic filter member 50 and the back plate 49 can be adjusted so as to optimize the filter characteristic of the filter 34. Since the acoustic filter component 50 may become clogged with contaminants (e.g., dust, dirt, foreign matter, etc.), a protective cover 52 may be provided to prevent the contaminants from entering. The protective cover 52 is disposed upstream of the acoustic filter section 50 when viewed in the sound entry direction indicated by the arrow. The protective cover 52 may be designed as a washable or easily reproducible inlet filter.