Microelectromechanical Systems (MEMS) Microphone Assembly

Abstract

In at least one embodiment, a microphone assembly is provided that includes a housing, a first printed circuit board (PCB), and a microphone assembly. The microphone assembly includes a sub-casing, a microelectromechanical system (MEMS) transducer, and a second PCB. The MEMS transducer is disposed within the sub-casing, and the second PCB supports the MEMS transducer. The first PCB defines a first acoustic path disposed beneath the second PCB and the MEMS transducer. The second PCB defines a first audio port disposed beneath the MEMS transducer. The housing defines a first acoustic opening disposed beneath the first acoustic path to allow an audio input signal to reach the underside of the MEMS transducer. The housing defines a second acoustic opening disposed a distance of 3 to 30 mm from the first acoustic opening.

Description

[Technical field]

[0001] Aspects disclosed herein generally relate to microphones, such as microelectromechanical systems (MEMS) microphones for microphone assemblies, that can be adapted to form microphones having different directional patterns (e.g., unidirectional vs. omnidirectional) and / or frequency response shapes. The disclosed MEMS microphone assemblies can be used in any number of applications, including, but not limited to, active noise cancellation (ANC) technology and voice pickup in hands-free phone applications. These and other aspects are discussed in more detail herein. [Background technology]

[0002] U.S. Patent No. 10,154,330 to Baumhauer et al. provides a microelectromechanical system (MEMS) microphone assembly. The assembly includes a housing, a MEMS transducer, and a plurality of substrate layers. A single MEMS transducer is disposed within the housing. The plurality of substrate layers support the single MEMS transducer. The plurality of substrate layers define a first transfer mechanism that enables a first side of the single MEMS transducer to receive an audio input signal, and a second transfer mechanism that enables a second side of the single MEMS transducer to receive an audio input signal.

[0003] U.S. Patent No. 9,955,246 to Reese et al. provides a microelectromechanical system (MEMS) microphone assembly. The assembly includes a housing, a single microelectromechanical system (MEMS) transducer, a substrate layer, and an application housing. The single MEMS transducer is disposed within the housing. The substrate layer supports the single MEMS transducer. The application housing supports the substrate layer and defines at least a portion of a first transfer mechanism that enables a first side of the single MEMS transducer to receive an audio input signal and at least a portion of a second transfer mechanism that enables a second side of the single MEMS transducer to receive an audio input signal. Summary of the Invention [Means for solving the problem]

[0004] In at least one embodiment, a microphone assembly is provided that includes a housing, a first printed circuit board (PCB), and a microphone assembly. The microphone assembly includes a sub-casing, a microelectromechanical system (MEMS) transducer, and a second PCB. The MEMS transducer is disposed within the sub-casing, and the second PCB supports the MEMS transducer. The first PCB defines a first acoustic path disposed beneath the second PCB and the MEMS transducer. The second PCB defines a first audio port disposed beneath the MEMS transducer. The housing defines a first acoustic opening disposed beneath the first acoustic path to allow an audio input signal to pass through the first audio port to an underside of the MEMS transducer. The housing defines a second acoustic opening disposed at a distance of 3 to 30 mm from the first acoustic opening.

[0005] In at least another embodiment, a microphone assembly is provided that includes a housing, a first printed circuit board (PCB), a post, and a microphone subassembly. The microphone subassembly includes a subcasing, a microelectromechanical system (MEMS) transducer, and at least one port hole. The microelectromechanical system (MEMS) transducer is disposed within the subcasing for receiving an audio input signal. The at least one port is disposed on a top surface of the subcasing. The post is disposed over the at least one port hole to seal the subcasing.

[0006] In at least another embodiment, a microphone assembly is provided that includes a housing, a first printed circuit board (PCB), and a microphone subassembly. The microphone subassembly includes a subcasing, a microelectromechanical system (MEMS) transducer, at least one port hole, and a cover. The microelectromechanical system (MEMS) transducer is disposed within the subcasing to receive an audio input signal. The at least one port is disposed on a top surface of the subcasing. A cover is disposed over the at least one port hole and is movable about the first port hole to provide a plurality of frequency responses based on a position of the cover relative to the first port hole.

[0007] Embodiments of the present disclosure are pointed out with particularity in the appended claims, however other features of the various embodiments will become more apparent and will be best understood by reference to the following detailed description taken in conjunction with the accompanying drawings. The present specification also provides, for example, the following items: (Item 1) 1. A microphone assembly comprising: A housing and a first printed circuit board (PCB); 1. A microphone subassembly comprising: A subcasing; a microelectromechanical system (MEMS) transducer disposed within the subcasing; a second PCB supporting the MEMS transducer; the microphone subassembly including: Equipped with the second PCB defines a first audio port located directly beneath the MEMS transducer; the first PCB is disposed below the second PCB and the MEMS transducer and defines a first acoustic path axially aligned with the first audio port; the housing defines a first acoustic opening disposed beneath the first acoustic path to allow an audio input signal to pass through the first audio port to an underside of the MEMS transducer; The housing defines a second acoustic opening disposed at a distance of 3 to 30 mm from the first acoustic opening. The microphone assembly. (Item 2) 2. The microphone assembly of claim 1, wherein the first acoustic opening and the second acoustic opening are disposed on the same surface of the housing. (Item 3) 2. The microphone assembly of claim 1, wherein the first acoustic opening and the second acoustic opening are disposed on different surfaces of the housing. (Item 4) 2. The microphone assembly of claim 1, further comprising a first acoustic resistor disposed around the first acoustic opening and a second acoustic resistor disposed around the second acoustic opening. (Item 5) 2. The microphone assembly of claim 1, wherein the sub-casing defines at least one port hole disposed on an upper side thereof. (Item 6) 6. The microphone assembly of claim 5, wherein the at least one port hole includes a plurality of port holes spaced apart from one another on the top side of the sub-casing. (Item 7) 6. The microphone assembly of claim 5, wherein the housing includes a post disposed over the at least one port hole to seal the sub-casing. (Item 8) 8. The microphone assembly of claim 7, wherein the post extends from the top side of the sub-casing to an underside of the top side of the housing. (Item 9) 6. The microphone assembly of item 5, further comprising a cover disposed on an upper side of the sub-casing. (Item 10) 10. The microphone assembly of claim 9, wherein the cover slides against the at least one port hole to provide the assembly with multiple frequency responses. (Item 11) 1. A microphone assembly comprising: A housing and a first printed circuit board (PCB); Post and 1. A microphone subassembly comprising: A subcasing; a microelectromechanical system (MEMS) transducer disposed within the subcasing for receiving an audio input signal; At least one port hole disposed on the upper side of the subcasing; the microphone subassembly including: Equipped with the post is disposed over at least one port hole to seal the subcasing; The microphone assembly. (Item 12) Item 12. The microphone assembly of item 11, further comprising a second PCB that supports the MEMS transducer and defines a first audio port. (Item 13) the first PCB defines a first acoustic path disposed beneath the second PCB and the MEMS transducer; the housing defines a first acoustic opening disposed beneath the first acoustic path and the first audio port to allow the audio input signal to pass through the first acoustic port to an underside of the MEMS transducer; Item 13. A microphone assembly as described in item 12. (Item 14) Item 14. The microphone assembly of item 13, wherein the housing defines a second acoustic opening that allows the audio signal to pass to a top side of the MEMS transducer. (Item 15) Item 15. The microphone assembly of item 14, wherein the second acoustic opening is positioned at a distance of 3 to 30 mm from the first acoustic opening to increase sensitivity of the MEMS transducer and minimize a difference in sound pressure amplitude of the audio input signal at the first acoustic opening and the second acoustic opening. (Item 16) Item 14. The microphone assembly of item 13, wherein the first acoustic opening and the second acoustic opening are disposed on the same surface of the housing. (Item 17) Item 14. The microphone assembly of item 13, wherein the first acoustic opening and the second acoustic opening are disposed on different surfaces of the housing. (Item 18) Item 12. The microphone assembly of item 11, wherein the post extends from the top side of the sub-casing to an underside of the top side of the housing. (Item 19) 1. A microphone assembly comprising: A housing and a first printed circuit board (PCB); 1. A microphone subassembly comprising: A subcasing; a microelectromechanical system (MEMS) transducer disposed within the subcasing for receiving an audio input signal; At least one port disposed on an upper side of the subcasing; a cover disposed over the at least one port hole and movable about the first port hole to provide a plurality of frequency responses based on a position of the cover relative to the first port hole; the microphone subassembly including: The microphone assembly. (Item 20) 20. The microphone assembly of claim 19, wherein the cover slides against the at least one port hole to provide the multiple frequency responses. [Brief description of the drawings]

[0008] [Figure 1] 2 shows an example of a microphone amplitude response curve.

[0009] [Diagram 2] 1 shows examples of different cutoff frequencies in various automotive audio applications.

[0010] [Diagram 3] 1 shows an example of a MEMS microphone for achieving a single cutoff frequency.

[0011] [Figure 4] 1 illustrates an example of a microphone assembly.

[0012] [Diagram 5] 1 illustrates a microphone assembly according to one embodiment.

[0013] [Figure 6] 1 illustrates a detailed implementation of a microphone subassembly according to one embodiment.

[0014] [Figure 7] 4 illustrates an example of a frequency response curve according to one embodiment.

[0015] [Figure 8] 4 illustrates an example of various frequency response curves according to one embodiment.

[0016] [Figure 9] 1 illustrates an example of various directivities according to one embodiment.

[0017] [Figure 10] 1 illustrates another detailed implementation of a microphone assembly according to one embodiment.

[0018] [Figure 11] 1A and 1B show respective top views of a sub-casing of a microphone subassembly according to one embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Where necessary, detailed embodiments of the present invention are disclosed herein, but it will be understood that the disclosed embodiments are merely examples of the invention that may be embodied in various and alternative forms. The figures are not necessarily to scale, and some features may be exaggerated or minimized to show details of specific components. Therefore, specific structural and functional details disclosed herein should not be construed as limiting, but merely as a representative basis for teaching those skilled in the art to variously use the present invention.

[0020] It will be appreciated that directional terms that may be referred to herein (e.g., "upper," "lower," "inner," "outer," "top," "bottom," etc.) simply refer to the orientation of the various components of the transducer assembly in relation to the microphone assembly as illustrated in the accompanying figures. Such terminology is provided for the context and understanding of the embodiments disclosed herein.

[0021] A microphone assembly may include, but is not limited to, a microphone subassembly that includes a microelectromechanical system (MEMS) based microphone element (such as a transducer) or an electret condenser microphone (ECM), a printed circuit board (PCB) assembly to which the microphone element is mounted, and a housing (or casing) that encloses the aforementioned features. It is therefore understood that the microphone assembly is larger in size than the MEMS microphone element package (or ECM).

[0022] Customer applications may require microphone elements that provide different frequency response shapes and / or directivities. This means that different microphone element models may be required across microphone assemblies for different specific applications. The embodiments described herein seek to extend the acoustic design parameters from the microphone element level (e.g., MEMS microphone package design) (or subassembly level) to the assembly level. That is, a single common microphone element package can be used across multiple microphone subassembly designs by modifying the structural and geometric parameters of the assembly housing / casing. For example, the design of a vehicle microphone assembly may currently require different dedicated MEMS microphone elements to satisfy hands-free communication and active noise cancellation (ANC) applications. The embodiments described herein may provide a single common MEMS microphone element model that can be used for both applications, requiring only changes to a few design features at the module housing level.

[0023] In automotive applications, the entire microphone assembly may include a protective housing and is mounted to the vehicle body. In other applications, the microphone element and PCB may be mounted directly to the product housing (such as a cell phone). In this case, the end product housing (e.g., a cell phone) may encapsulate (or encase) the microphone assembly in its protective housing.

[0024] FIG. 1 shows an example of a microphone amplitude response curve as a function of frequency. The curve typically begins at the lowest frequency defined in the plot and exhibits a rising response shape characterized by a cutoff frequency. The cutoff frequency of a microphone is typically defined as the frequency point at which the sensitivity is 3 dB (or other suitable value) below the normal sensitivity measured at 1 kHz. FIG. 2 shows an example of cutoff frequencies for various applications (e.g., microphones used in conjunction with ANC or in conjunction with a hands-free communication implementation). These microphone-based applications may be applicable to vehicles. As shown, microphones used in ANC have cutoff frequencies below 20 Hz, while microphones used in hands-free applications have cutoff frequencies above 200 Hz.

[0025] FIG. 3 shows an example of a MEMS microphone transducer 100 for achieving a single cutoff frequency. The transducer 100 includes a diaphragm 102, a backplate 104, and a baffle 106. The diaphragm 102 generally moves under sound pressure excitation. The backplate 104 is provided with a number of holes, which allows acoustic waves to pass therethrough, which is considered acoustically transparent. The diaphragm 102 and the backplate 104 form a capacitor that transfers the mechanical motion of the diaphragm 102 to the electrical (e.g., voltage) output of the transducer 100. The diaphragm 102 defines a path 108 that generates the cutoff frequency of the audio output signal. When assembled into a MEMS microphone package (or microphone assembly), the baffle 106 and package casing (not shown in FIG. 3) ensure that external sound waves can only reach one side of the diaphragm 102 through the path 108 to the other side. It may be easier for low frequency sound waves with longer wavelengths to pass through the path 108 and reach both sides of the diaphragm 102. This may result in less or no net pressure difference between the two sides of the diaphragm 102 at low frequencies than at high frequencies (e.g., no net movement). This may effectively form a first order low pass filter with a cutoff frequency proportional to the size of the path 108. Thus, to change the cutoff frequency of the MEMS microphone transducer 100, the size of the path 108 must be adjusted. As such, existing implementations may require the use of different MEMS elements for each individual application with a specific cutoff frequency target or specific frequency response.

[0026] 4 illustrates an example of a microphone assembly 200 (or assembly 200). The microphone assembly 200 includes a protective housing or enclosure 202, a microphone subassembly 204, electronic circuitry 206, and a printed circuit board (PCB) 208. The electronic circuitry 206 is mounted on the PCB 208 along with the microphone subassembly 204 and may perform any number of audio processing applications, such as, but not limited to, ANC, hands-free operation, etc. The electronic circuitry 206 may interface with the microphone subassembly 204 to perform operations related to the aforementioned audio applications.

[0027] The microphone subassembly 204 includes a subcasing 220, a MEMS transducer (or microphone) 222, an application specific integrated circuit (ASIC) 224, and a PCB base 226. The MEMS transducer 222 and the ASIC 224 are disposed on the PCB base 226. The subcasing 220 surrounds the MEMS transducer 222, the ASIC 224, and is sealed (typically by soldering) along its periphery to the PCB base 226. It will be appreciated that the MEMS transducer 222 may also be implemented as an ECM. The PCB base 226 defines a first audio port 228. The PCB 208 defines a first acoustic path 230, and the base portion of the housing 202 defines a first acoustic opening 237. The first acoustic path 230 and the first acoustic opening 237 are axially aligned perpendicular to the first audio port 228. Although not shown, the MEMS transducer 222 includes a diaphragm that vibrates or is excited in response to sound pressure acting on the diaphragm. The underside of the diaphragm is exposed to the environment and allows audio signals to enter a first audio port 228 provided by the PCB base 226, a first acoustic path 230 provided by the PCB 208, and a first acoustic opening 237 provided by the housing 202. The ASIC 224 provides an electrical output indicative of the sound captured by the MEMS transducer 222.

[0028] 5 illustrates a microphone assembly 300 according to one embodiment. The assembly 300 includes a protective housing 202, a microphone subassembly 204, electronic circuitry 206, and a PCB 208. Similarly, as described above in connection with FIG. 4, the electronic circuitry 206 is mounted on the PCB 208 along with the microphone subassembly 204 and may perform any number of audio processing applications, such as, but not limited to, ANC, hands-free operation, etc. The electronic circuitry 206 may interface with the microphone subassembly 204 to perform operations related to the aforementioned audio applications.

[0029] Similarly, as described in relation to FIG. 4, the microphone assembly 204 includes a sub-casing 220, a microphone transducer 222 (MEMS or ECM), an ASIC 224, and a PCB base 226. The MEMS transducer 222 and the ASIC 224 are disposed on the PCB base 226. The PCB base 226 defines a first audio port 228a disposed directly below the microphone transducer 222. A first acoustic path 230 is defined by the PCB 208. The base 227 of the housing 202 defines a first acoustic opening 237a and a second acoustic opening 237b. When assembled, the first audio port 228a provided by the PCB base 226, the first acoustic path 230 provided by the PCB 208, and the first acoustic opening 237a provided by the housing 202 are axially aligned in the vertical direction. The second acoustic opening 237b opens directly into the cavity or volume 302 defined by the housing 202. The first acoustic opening 237a and the second acoustic opening 237b may be located on the same surface of the housing 202 (e.g., the base 227) and separated by a distance d. The distance d may preferably be in the range of 3 to 30 mm. If the microphone assembly 300 is configured as a unidirectional microphone, the output sensitivity of the microphone is proportional to the value of d. If d is too small, the sensitivity of the microphone may be very low and not optimal. If the microphone assembly 300 is configured as an omnidirectional microphone with different cutoff frequencies, the assembly 300 relies on the sound pressure amplitudes exhibited by the first and second acoustic openings 237a, 237b being similar to each other. If d is too large, there may be differences in the sound pressure amplitudes exhibited by the first and second acoustic openings 237a, 237b. It will be appreciated that the second acoustic opening 237b may also be located along any of the vertically extending side walls of the housing 202 while maintaining the cumulative distance d within the preferred range.

[0030] The first acoustic opening 237a, the first acoustic path 230, and the first audio port 228a allow the underside of the microphone transducer 222 to be vented to a sound field outside the assembly 300. The sub-casing 220 defines at least one second audio port 228b (hereinafter port hole 228b) located on its upper side. Similarly, the second acoustic opening 237b can allow the sound field outside the assembly 300 to enter the cavity or volume 302 defined by the housing 202. This can then allow the top side of the microphone transducer 222 to be vented to the external sound field through the port hole 228b. If the microphone assembly 300 is configured as an omnidirectional microphone with a variable cutoff frequency, the size of the opening area of ​​the port hole 228b determines the cutoff frequency. If the port hole 228b is circular, the preferred diameter range is between 0.01 mm and 1 mm. This provides a cutoff frequency suitable for hands-free microphone applications. If the port holes 228b have other geometries and / or multiple configurations, the total effective open area is preferably in the range equivalent to that provided by a circular port hole having a diameter of 0.01 mm to 1 mm.

[0031] The post 304 may be disposed on the top side of the subcasing 220 and directly attached to the top of the port hole 228b. The post 304 may be integral with the housing 202. The post 304 extends from the top side of the subcasing 220 to the underside of the top 309 of the housing 202. The post 304, if provided, may function as a sealing mechanism and seal the port hole 228b. The first acoustic resistance element 310a (e.g., fabric, sintered material, foam, micromachined or laser drilled hole array, etc.) may be disposed below the base 227 of the housing 202. The first acoustic resistance element 310a may be disposed directly below or above the first acoustic opening 237a. The second acoustic resistance element 310b (e.g., fabric, sintered material, foam, micromachined or laser drilled hole array, etc.) may also be disposed below the base 227 of the housing 202. The second acoustic resistive element 310b can be located directly below or directly above the second acoustic opening 237b. The addition of the first acoustic resistive element 310a and the second acoustic resistive element 310b also serves as an ingress protection mechanism to prevent foreign objects and moisture from the external environment from entering the interior of the microphone assembly 300.

[0032] It is recognized that any one or more of the post 304, the first acoustic resistive element 310a, and the second acoustic resistive element 310b may or may not be utilized on the assembly 300. The utilization of the post 304, the first acoustic resistive element 310a, and the second acoustic resistive element 310b may provide the assembly 300 with a different frequency response or directional pattern. For example, if the post 304, the first acoustic resistive element 310a, and the second acoustic resistive element 310b are not implemented in the assembly 300, the port hole 228b is not sealed and both sides of the microphone diaphragm are exposed to the external sound field. In this case, the port hole 228b effectively functions as the path 108 described in connection with FIG. 3. Thus, the microphone subassembly 204 allows for a rising frequency response with a cutoff frequency determined by the size of the opening area of ​​the port hole 228b. The microphone assembly 300 functions as an omnidirectional microphone with a rising frequency response as shown in the waveform 402 of the plot shown in FIG. 7. Waveform 402 exhibits a cutoff frequency above 200 Hz that is desirable for applications such as hands-free communication.

[0033] A post 304 is used to seal the port hole 228b of the assembly 300, and in the absence of the first acoustic resistive element 310a and the second acoustic resistive element 310b, only the underside of the microphone diaphragm is exposed to the external sound field. In such a case, the microphone subassembly 204 and microphone assembly 300 function as an omnidirectional microphone with a flat frequency response, as shown in the waveform 404 of the plot shown in Figure 7. The waveform 404 shows a cutoff frequency that is below 20Hz, which may be suitable for applications such as ANC.

[0034] If the microphone assembly 300 is arranged as an omnidirectional microphone with various cutoff frequencies, either by utilizing the posts 304 or not utilizing the posts 304, it may not be necessary to implement the first and second acoustic resistive elements 310a, 310b. However, in practice it may be preferable to include the first and second acoustic resistive elements 310a, 310b, which have a low resistance value, to act as an ingress protection mechanism to prevent the ingress of foreign objects and moisture.

[0035] In the absence of the post 304 and the presence of the first and second acoustic resistive elements 310a and 310b, the microphone assembly 300 may also be configured to provide a unidirectional (cardioid) response characteristic. If a sound source or speaker is present on the left side of the assembly 300, it may be desirable to direct the pickup sensitivity beam (polar pattern) to the left (θ=0°) but to distinguish from picking up unwanted sounds from other directions (e.g., from the right or rear of the microphone assembly 300). In the absence of the post 304, the microphone assembly 300 allows external sounds or audio signals to enter the first acoustic opening 237a and thereby reach the underside (and thus the diaphragm) of the transducer 222. Similarly, external sounds or audio signals are transmitted through the second acoustic opening 237b and thereby reach the upper side (and thus the diaphragm) of the transducer 222. The output of the microphone subassembly 204 may be a function of the subtraction or "acoustic gradient" between the two sound pressures impinging on either side of the transducer 222 (or diaphragm). Differences in the transmission paths result in a relative phase delay that corresponds to the time difference when the sound source arrives on either side of the transducer 222. Such phase delays allow the microphone assembly 300 to achieve desired performance, such as a particular polar pattern.

[0036] To achieve the desired cardioid directional pattern, a certain amount of acoustic resistance level R of the second acoustic resistive element 310b is sb is the delay distance d and the acoustic compliance Cv In general, R sb d / C v must be proportional to the quotient of v The value of is determined by the combined air volumes of the second acoustic opening 237b, the cavity 302, the port hole 228b, and the volume 231 enclosed by the sub-casing 220 of the microphone element 204. It should be noted that the first acoustic resistive element 310a may be omitted or included. The acoustic resistance value of the first acoustic resistive element 310a may be smaller than the acoustic resistance value of the second acoustic resistive element 310b and may be used to prevent the ingress of foreign objects and moisture.

[0037] Figure 8 shows an example of a simulated frequency response shape of the microphone assembly 300 when configured as a unidirectional microphone as shown in Figure 5, according to one embodiment. Specifically, Figure 8 plots the frequency response ratio in dB of the electrical output of the microphone assembly 300 to an acoustic input delivered versus frequency from various directions, indicated by θ relative to the first acoustic opening 237a.

[0038] FIG. 9 is a simulated plot illustrating an example of cardioid polar directivity or spatial filtering resulting from the microphone assembly 300 described above in connection with FIG.

[0039] 6 shows a detailed view of the microphone subassembly 204 according to one embodiment. The transducer 222 includes a diaphragm 102 that is movable and a backplate 104 that is fixed but acoustically transparent due to a number of through holes distributed in the backplate 104. The transducer 222 and the ASIC 224 are disposed on a PCB base 226 and enclosed within a cavity 231 formed by a subcasing 220. As mentioned above, the PCB base 226 defines a first audio port 228a and the subcasing 220 defines a port hole 228b. An external audio signal can reach the underside of the diaphragm 102 through the first audio port 228a and the cavity 231 sealed between the transducer 222 and the PCB base 226. Similarly, an external audio signal can reach the top surface of the diaphragm 102 through the port hole 228b and the cavity 231 sealed between the transducer 222, the subcasing 220, and the PCB base 226. Additionally, the audio signal can also reach from one side of the diaphragm 102 to the other side through the path 108 defined by the diaphragm 102. The diaphragm 102 is excited by the net sound pressure applied (i.e., the pressure difference between the two sides). As mentioned above, for an external audio signal, both the path 108 and the audio port 228b act as leakage paths with cutoff frequency values ​​based on their relative sizes. This aspect can result in a rise frequency response shape of the microphone assembly 300. Since it is generally more difficult to change the size of the passage 108 in addition to the overall size of the microphone subassembly 204, the microphone assembly 300 discloses an approach to adjust the cutoff frequency of the rising response by adjusting the sealed or unsealed state (i.e., the opening area) of the port hole 228b. For example, the passage 108 defined by the transducer 222 of the microphone subassembly 204 may be omitted or ignored if the port hole 228b is kept small such that the cutoff frequency of the rising response of the microphone subassembly 204 can be below 20 Hz with the port hole 228b sealed.

[0040] In light of the above, the assembly 300 provides multiple frequency response shapes or directivities while utilizing a single microphone subassembly 204 in which the overall size of the path 108 defined by the diaphragm 102 is fixed. Depending on the utilization of the posts 304, the first acoustic resistive element 310a, and the second acoustic resistive element 310b, and the values ​​of the first acoustic resistive element 310a and the second acoustic resistive element 310b, the microphone assembly 300 can operate as an omnidirectional microphone with a flat frequency response (i.e., a cutoff frequency below 20Hz), an omnidirectional microphone with a rising frequency response, or a unidirectional microphone with a cardioid polar directivity.

[0041] FIG. 10 shows another detailed view of the sub-casing 220 of the microphone subassembly 204 according to one embodiment. The movable cover 400 is placed over the port hole 228b. In one example, the cover 400 can correspond to an adhesive tape or other suitable material. Similar to the function of the post 304 in FIG. 5, the cover 400 can function as a sealing mechanism and seal the port hole 228b. In another example, the cover 400 can slide relative to the port hole 228b. The first guide rail and the second guide rail can be axially spaced apart from each other and disposed on the top side of the sub-casing 220. The cover 400 can slide along the first guide rail and the second guide rail to vary the level of coverage of the port hole 228b from 0% to 100%. The port hole 228b can be fully open when the cover 400 is moved away from the port hole 228b. Conversely, the port hole 228b can be fully closed or covered by the cover 400. The cover 400 may also be positioned in any number of positions relative to the port hole 228b such that the port hole 228b is uncovered, partially covered, or completely covered.

[0042] As described above, an external audio signal reaches both the underside of the diaphragm 102 (e.g., via the first audio port 228a and the first acoustic path 230) and the top side of the diaphragm 102 (e.g., via the second acoustic opening 237b and the port hole 228b) through the second audio port 228b. Longer wavelengths and lower frequency sound waves pass through smaller openings more easily. Thus, depending on the size of the port hole 228b, the cover 400 can be placed in different positions relative to the port hole 228b to provide omnidirectional microphones with different frequency responses without significantly changing the overall design of the microphone subassembly 204 and the microphone assembly 300. For example, when the cover 400 is not installed or is positioned to leave the second audio port 228b of the assembly 300 substantially open, the assembly 300 functions as an omnidirectional microphone with a rising frequency response as shown in the waveform 402 of the plot shown in FIG. 7. When the cover 400 completely covers the port hole 228b, the microphone assembly 300 operates as an omnidirectional microphone with a flat frequency response as shown in waveform 404 of the plot shown in Figure 7. When the cover 400 partially covers the second audio port 228b, the microphone assembly 300 functions as an omnidirectional microphone with a rising frequency response as shown in waveform 403 of the plot whose cutoff frequency is between waveforms 402 and 404 shown in Figure 7.

[0043] It is recognized that the first acoustic resistive element 310a and the second acoustic resistive element 310b may also be implemented on the microphone assembly 300 regardless of whether the cover 400 is provided. The first acoustic resistive element 310a and the second acoustic resistive element 310b may simply be provided to prevent the ingress of foreign objects and moisture. While the implementation of the first acoustic resistive element 310a and the second acoustic resistive element 310b is provided, if the cover 400 is not used, the microphone assembly 300 operates as a unidirectional microphone with a cardioid directional pattern as long as the acoustic resistance value of the second acoustic resistive element 310b satisfies the aforementioned mathematical relationship.

[0044] FIG. 11A shows a top view of the subcasing 220 and port holes 228b of the microphone subassembly 204. FIG. 11B shows another top view of the subcasing 220 and port holes 228b. In this case, the port holes 228b may be formed as a plurality of holes 420 exhibiting a desired pattern. One or more of the plurality of holes 420 may be sealed (or covered) to provide a gradually adjustable cutoff frequency. For example, this embodiment may enable the assembly 300 to provide an omnidirectional microphone with a variable frequency response without significantly changing the overall design of the microphone subassembly 204. It is recognized that the number of holes 420 may vary based on the desired criteria of a particular implementation.

[0045] Although exemplary embodiments have been described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the words used herein are words of description rather than limitation, and it will be understood that various changes may be made without departing from the spirit and scope of the invention. Moreover, features of various implementing embodiments may be combined to form further embodiments of the invention.

Claims

1. 1. A microphone assembly comprising: A housing and a first printed circuit board (PCB); 1. A microphone subassembly comprising: A subcasing; a microelectromechanical system (MEMS) transducer disposed within the subcasing; a second PCB supporting the MEMS transducer; the microphone subassembly including: Equipped with the second PCB defines a first audio port located directly below the MEMS transducer; the first PCB defines a first acoustic path disposed below the second PCB and the MEMS transducer and axially aligned with the first audio port; the housing defines a first acoustic opening disposed beneath the first acoustic path to allow an audio input signal to pass through the first audio port to an underside of the MEMS transducer; the housing defines a second acoustic opening spaced a distance of 3 to 30 mm from the first acoustic opening; The microphone assembly.

2. The microphone assembly of claim 1 , wherein the first acoustic opening and the second acoustic opening are disposed on a same surface of the housing.

3. The microphone assembly of claim 1 , wherein the first acoustic opening and the second acoustic opening are located on different surfaces of the housing.

4. 10. The microphone assembly of claim 1, further comprising a first acoustic resistor disposed about the first acoustic opening and a second acoustic resistor disposed about the second acoustic opening.

5. The microphone assembly of claim 1 , wherein the sub-casing defines at least one port hole disposed on a top side thereof.

6. The microphone assembly of claim 5 , wherein the at least one port hole comprises a plurality of port holes spaced apart from one another on a top side of the subcasing.

7. The microphone assembly of claim 5 , wherein the housing includes a post disposed over the at least one port hole to seal the sub-casing.

8. The microphone assembly of claim 7 , wherein the post extends from the top side of the sub-casing to an underside of the top side of the housing.

9. The microphone assembly of claim 5 , further comprising a cover disposed on a top side of the sub-casing.

10. 10. The microphone assembly of claim 9, wherein the cover slides against the at least one port hole to provide multiple frequency responses for the assembly.

11. 1. A microphone assembly comprising: A housing and a first printed circuit board (PCB); Post and 1. A microphone subassembly comprising: A subcasing; a microelectromechanical system (MEMS) transducer disposed within the subcasing for receiving an audio input signal; At least one port hole disposed on an upper side of the subcasing; the microphone subassembly including: Equipped with the post is disposed over the at least one port hole to seal the subcasing; The microphone assembly.

12. The microphone assembly of claim 11 , further comprising a second PCB that supports the MEMS transducer and defines a first audio port.

13. the first PCB defines a first acoustic path disposed beneath the second PCB and the MEMS transducer; the housing defines a first acoustic opening disposed beneath the first acoustic path and the first audio port to allow the audio input signal to pass through the first audio port to an underside of the MEMS transducer; 13. A microphone assembly as claimed in claim 12.

14. The microphone assembly of claim 13 , wherein the housing defines a second acoustic opening that allows the audio input signal to pass to a top side of the MEMS transducer.

15. 15. The microphone assembly of claim 14, wherein the second acoustic opening is located at a distance of 3 to 30 mm from the first acoustic opening to increase sensitivity of the MEMS transducer and minimize a difference in sound pressure amplitude of the audio input signal at the first acoustic opening and the second acoustic opening.

16. The microphone assembly of claim 14 , wherein the first acoustic opening and the second acoustic opening are disposed on a same surface of the housing.

17. The microphone assembly of claim 14 , wherein the first acoustic opening and the second acoustic opening are located on different surfaces of the housing.

18. The microphone assembly of claim 11 , wherein the post extends from the top side of the sub-casing to an underside of the top side of the housing.

19. 1. A microphone assembly comprising: A housing and a first printed circuit board (PCB); 1. A microphone subassembly comprising: A subcasing; a microelectromechanical system (MEMS) transducer disposed within the subcasing for receiving an audio input signal; At least one port hole disposed on an upper side of the subcasing; a cover disposed over the at least one port hole and movable about the at least one port hole to provide a plurality of frequency responses based on a position of the cover relative to the at least one port hole; the microphone subassembly including: The microphone assembly.

20. 20. The microphone assembly of claim 19, wherein the cover slides against the at least one port hole to provide the multiple frequency responses.

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