PATENT DOCUMENT

Publication Number: US-11310591-B2
Application Number: US-202016880825-A
Country: US
Kind Code: B2

Title: Vented acoustic transducers, and related methods and systems

Abstract:
An electronic device has an acoustic transducer with an acoustic diaphragm. The diaphragm has opposed first and second major surfaces. A front volume is positioned adjacent the first major surface. A back volume is positioned adjacent the second major surface. An elongated channel defines a barometric vent and extends from a first end fluidly coupled with the front volume to a second end fluidly coupled with the back volume, fluidly coupling the front volume with the back volume. The elongated channel may have a high aspect ratio (L/D), providing the vent with a substantial air mass. The elongated channel may be segmented to define a higher-order filter. For example, a segmented channel can have a cascade of repeating acoustic-mass and acoustic-compliance units, providing the barometric vent with additional degrees-of-freedom for tuning.

Claims:
We currently claim: 
     
       1. An electronic device, comprising:
 an acoustic transducer element having an acoustic diaphragm, wherein the diaphragm has opposed first and second major surfaces; 
 a front volume positioned adjacent the first major surface of the diaphragm; 
 a back volume positioned adjacent the second major surface of the diaphragm; 
 a substrate coupled with the acoustic transducer element; and 
 a segmented channel defining a barometric vent fluidly coupling the front volume with the back volume, wherein the segmented channel has a plurality of duct portions and a plurality of chamber portions, wherein the segmented channel extends from a first end fluidly coupled with the front volume to a second end fluidly coupled with the back volume, and wherein a portion of the segmented channel extends through the substrate. 
 
     
     
       2. The electronic device according to  claim 1 , wherein the barometric vent is configured to equalize pressure between the front volume and the back volume. 
     
     
       3. The electronic device according to  claim 1 , wherein each duct portion extends from one of the chamber portions to an adjacent chamber portion, providing a contraction in cross-sectional area from each respective chamber portion into the corresponding duct portion and an expansion in cross-sectional area from the respective duct portion to the corresponding adjacent chamber portion. 
     
     
       4. The electronic device according to  claim 1 , wherein the substrate defines an acoustic port opening to the front volume. 
     
     
       5. The electronic device according to  claim 4 , wherein the substrate is a first substrate and the electronic device further comprises:
 a second substrate, the first substrate mounted to the second substrate; 
 an integrated circuit device mounted to the second substrate, the integrated circuit device and the acoustic transducer element electrically coupled with each other, wherein the second substrate comprises an electrical output connection coupled with the integrated circuit device; and 
 a recessed lid overlying the acoustic transducer element, the first substrate, and the integrated circuit device. 
 
     
     
       6. The electronic device according to  claim 4 , wherein the substrate further defines the segmented channel, the segmented channel having a plurality of duct portions and a plurality of chamber portions, wherein each duct portion extends from one of the chamber portions to an adjacent chamber portion, providing a contraction in cross-sectional area from each respective chamber portion into the corresponding duct portion and an expansion in cross-sectional area from the respective duct portion to the corresponding adjacent chamber portion. 
     
     
       7. The electronic device according to  claim 6 , wherein a region of the segmented channel opens to the acoustic port. 
     
     
       8. The electronic device according to  claim 6 , wherein a region of the segmented channel opens to the front volume. 
     
     
       9. The electronic device according to  claim 4 , wherein the substrate comprises a plurality of juxtaposed layers and an aperture extends through the plurality of layers to define the acoustic port. 
     
     
       10. The electronic device according to  claim 9 , wherein at least one of the layers defines a corresponding portion of the segmented channel having a duct portion and a corresponding chamber portion, the duct portion having a cross-sectional area substantially smaller than a corresponding cross-sectional area of the chamber portion. 
     
     
       11. The electronic device according to  claim 10 , wherein the segmented channel comprises a plurality of comparatively narrow duct portions juxtaposed with a corresponding plurality of comparatively wider chamber portions, the segmented channel defining at least one convolution among the duct portions and the chamber portions. 
     
     
       12. The electronic device according to  claim 10 , wherein the at least one of the layers comprises a first layer and a second layer, wherein each respective portion of the segmented channel defined by the first layer and each respective portion of the segmented channel defined by the second layer are fluidly coupled together, defining a respective convolution in the segmented channel. 
     
     
       13. The electronic device according to  claim 12 , wherein the substrate further comprises an intermediate layer of material separating the first layer and the second layer from each other, the intermediate layer defining an aperture fluidly coupling the segment of the segmented channel defined by the first layer with the segment of the segmented channel defined by the second layer. 
     
     
       14. The electronic device according to  claim 4 , wherein the substrate comprises a first layer and a second layer, the second layer positioned between the first layer and the acoustic diaphragm, wherein the second layer comprises a sacrificial material susceptible to etching and an etch-stop defining a boundary of a recess extending through the sacrificial material, wherein the recess defines a corresponding portion of the segmented channel. 
     
     
       15. The electronic device according to  claim 4 , wherein the first end of the segmented channel is positioned adjacent the acoustic port, the front volume, or both, and the second end of the segmented channel is positioned adjacent the back volume. 
     
     
       16. The electronic device according to  claim 1 , wherein the portion of the segmented channel that extends through the substrate has a duct portion and a corresponding chamber portion, wherein the duct portion has a first end that opens to the front volume and a second end that opens to the corresponding chamber portion. 
     
     
       17. The electronic device according to  claim 16 , wherein the acoustic transducer element is coupled with the substrate and defines an aperture aligned with the segmented channel, wherein the aperture opens to the back volume, fluidly coupling the front volume with the back volume. 
     
     
       18. The electronic device according to  claim 1 , wherein the acoustic transducer element further comprises a backplate and an insulator, wherein the insulator is positioned between the diaphragm and the backplate. 
     
     
       19. An electro-acoustic device, comprising:
 a movable diaphragm, wherein the diaphragm has opposed first and second major surfaces; and 
 a substrate coupled with the movable diaphragm, wherein the substrate defines an acoustic port acoustically coupled with the first major surface of the diaphragm and a segmented passageway extending from a first end fluidly coupled with the acoustic port to a second end fluidly coupled with a region adjacent the second major surface of the diaphragm, the segmented passageway defining a barometric vent coupling the acoustic port with the region adjacent the second major surface of the diaphragm, wherein the segmented passageway has a plurality of duct regions juxtaposed with a corresponding plurality of chamber regions. 
 
     
     
       20. The electro-acoustic device according to  claim 19 , wherein the substrate comprises a plurality of juxtaposed layers and an opening extends through the plurality of layers to define the acoustic port. 
     
     
       21. The electro-acoustic device according to  claim 20 , wherein the at least one of the layers comprises a first layer and a second layer, the first layer defining a corresponding first channel and the second layer defining a corresponding second channel, the first channel and the second channel fluidly coupled with each other to define a convolution in the segmented passageway. 
     
     
       22. The electro-acoustic device according to  claim 19 , wherein each respective duct region has a cross-sectional area substantially smaller than a corresponding cross-sectional area of an adjacent chamber region. 
     
     
       23. An electro-acoustic device, comprising:
 a diaphragm having opposed first and second major surfaces; 
 a front volume adjacent the first major surface of the diaphragm; 
 a back volume adjacent the second major surface of the diaphragm; 
 a substrate coupled with the diaphragm; and 
 a segmented channel in the substrate, wherein the segmented channel defines a barometric vent fluidly coupling the front volume with the back volume, and wherein the segmented channel has a plurality of acoustic-mass units and a corresponding plurality of acoustic-compliance units. 
 
     
     
       24. The electro-acoustic device of  claim 23 , wherein the segmented channel has a plurality of segments, each segment having one or more acoustic-mass units that extend between each pair of adjacent acoustic-compliance units. 
     
     
       25. The electro-acoustic device of  claim 23 , wherein each acoustic-compliance unit has an open internal volume that is larger than an open internal volume of an adjacent acoustic-mass unit.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from and benefit of U.S. Patent Application No. 62/853,626, filed May 28, 2019, the contents of which are hereby incorporated in their entirety for all purposes. 
    
    
     FIELD 
     This application and the subject matter disclosed herein (collectively referred to as the “disclosure”), generally concern vented acoustic transducers, and related methods and systems. More particularly, but not exclusively, vent arrangements configured to exhibit a complex acoustic impedance are described in relation to a variety of electro-acoustic transducers and electronic devices incorporating such transducers. Examples of electro-acoustic transducers include loudspeaker transducers, and microphone transducers, including by way of example, MEMs microphone transducers. 
     BACKGROUND INFORMATION 
     In general, sound (sometimes also referred to as an “acoustic signal”) constitutes a vibration that propagates through a carrier medium, such as, for example, a gas, a liquid, or a solid. An electro-acoustic transducer, in turn, is a device configured to convert incoming sound to an electrical signal, or vice-versa. 
     Over the course of its useful life, an electro-acoustic transducer may be exposed to a variety of ambient pressures, e.g., barometric pressures. For example, an electronic device having an electro-acoustic transducer may be operated by a user at different elevations (e.g., from around sea level to high alpine environments) or even under water (e.g., when participating in a water sport, like swimming, surfing, rafting, wake boarding, etc.). Such variation in ambient pressure can induce movement of the transducer&#39;s diaphragm, affecting an output of the transducer. And, above a given threshold or rate of change, such movement can even damage the transducer. 
     More specifically, a large pressure gradient applied across a conventional acoustic diaphragm can bias the diaphragm to an outermost (or innermost) position of displacement. When biased by an external load, operation of the acoustic transducer, whether configured as a loudspeaker or a microphone, can be negatively affected, or the transducer can be altogether rendered inoperable. Examples of negative effects include acoustic distortion or lower-than-normal amplitude (e.g., emitted or detected loudness). 
     SUMMARY 
     Disclosed acoustic transducers include a diaphragm and a vent to equalize pressure across the diaphragm. More particularly, but not exclusively, certain disclosed venting arrangements permit equalization of barometric pressures (e.g., low-frequency variation or slow rate-of-change in pressure) across the diaphragm, while inhibiting pressure equalization under higher-frequency variations in pressure (e.g., in an audible bandwidth). 
     Disclosed vents define a passageway having a complex acoustic impedance. Some passageways with a complex acoustic impedance have a high aspect ratio (e.g., a length-to-effective-diameter ratio between about 1,000 and about 32,000, or a ratio of length-to-cross-sectional-area between about 1×10 8  and about 2×10 9 ), providing the passageway with a large acoustic mass and causing the vent to behave as an acoustic inductor. Other of passageways having a complex acoustic impedance described in detail below are segmented, defining a plurality of acoustic-mass units juxtaposed with a corresponding plurality of acoustic-compliance units. As described more fully below, an acoustic-mass unit can be arranged as a comparatively narrow duct, and an acoustic-compliance unit can be arranged as a comparatively larger duct, or chamber. 
     Disclosed vents can substantially reduce so-called “leak noise” or “leakage noise.” Leakage noise can arise, generally, when the diaphragm is excited by a flow of air (or other acoustic medium) through a vent, particularly when the flow excites the diaphragm within a desired bandwidth (e.g., a human-audible band). Such leakage noise may arise, for example, when a vent behaves primarily as an acoustic resistor. In contrast to a resistive vent, a vent as described herein can damp flow through the vent when exposed to pressure variations (or sound) in a desired frequency band (e.g., between about 20 Hz and about 20 kHz), and yet can permit flow under low-frequency or slow variations in pressure (e.g., as with changes barometric pressure). 
     Consequently, disclosed venting arrangements can reduce leak noise, a significant contributor to in-band noise power, while still providing a passage to equalize pressures across a diaphragm. Thus, transducers incorporating disclosed venting arrangements can provide improved signal-to-noise signals compared to transducers incorporating a predominantly resistive venting arrangement. 
     Further, by equalizing pressures across the diaphragm, disclosed venting arrangements can reduce or eliminate external biasing forces applied to the diaphragm by changes in ambient pressures. Moreover, reduced biasing forces can permit the transducer to provide lower acoustic distortion and can allow the diaphragm to move through full-stroke excursions over a wide range of ambient pressures. Thus, acoustic transducers incorporating disclosed venting arrangements can provide improved emitted or detected loudness over a wide range of ambient pressures. 
     In accordance with an aspect, an electronic device has an acoustic transducer element having an acoustic diaphragm. The diaphragm has opposed first and second major surfaces. A front volume is positioned adjacent the first major surface of the diaphragm, and a back volume is positioned adjacent the second major surface of the diaphragm. An “elongated channel” defines a barometric vent fluidly coupling the front volume with the back volume. The elongated channel extends from a first end fluidly coupled with the front volume to a second end fluidly coupled with the back volume. According to an aspect, the elongated channel can be a “segmented channel” that is segmented into a plurality of acoustic-mass units juxtaposed with a corresponding plurality of acoustic-compliance units. In another aspect, the elongated channel circuitously extends from the first end to the second end. 
     The barometric vent can be configured to equalize pressure between the front volume and the back volume. Some disclosed electro-acoustic devices also include a substrate coupled with the acoustic transducer element. The substrate can define an acoustic port opening to the front volume. In an aspect, the substrate further defines the barometric vent. 
     In some aspects, the substrate is a first substrate, and the electro-acoustic device can include a second substrate. For example, the first substrate can be mounted to the second substrate. The electro-acoustic device can further include an integrated circuit device mounted to the second substrate. The integrated circuit device and the acoustic transducer element can be electrically coupled with each other. The second substrate can include an electrical output connection coupled with the integrated circuit device. The electro-acoustic device can also have a recessed lid overlying the acoustic transducer element, the first substrate, and the integrated circuit device. 
     The barometric vent can open to the acoustic port, the front volume, or both. 
     A disclosed substrate can include a plurality of juxtaposed layers. An aperture can extend through the plurality of layers to define the acoustic port. At least one of the layers can define a corresponding segment of a sinuous passage. The sinuous passage can fluidly couple the front volume with the back volume, defining the elongated channel. The sinuous passage can include at least one convolution. 
     A first layer of a disclosed substrate can define a corresponding first segment of the sinuous passage and the second layer can define a corresponding second segment of the sinuous passage. The substrate can also include an intermediate layer of material separating the first layer and the second layer from each other. The intermediate layer can define an aperture fluidly coupling the first segment of the sinuous passage with the second segment of the sinuous passage, defining a convolution in the sinuous passage. 
     As noted above, a disclosed substrate can have a first layer and a second layer. The second layer can be positioned between the first layer and the acoustic diaphragm. The second layer can include a sacrificial insulator susceptible to etching. The second layer can also include an etch-stop defining a boundary of a recess that extends through the sacrificial insulator. The recess can define a corresponding portion of the elongated channel. 
     In an aspect, the elongated channel can extend from a position adjacent the acoustic port, the front volume, or both, to a position adjacent the back volume. 
     The substrate can define a tortuous segment of the barometric vent. The tortuous segment can open to the front volume. The acoustic transducer element can be mountably coupled with the substrate and can define an aperture aligned with the tortuous segment of the barometric vent. The aperture can open to the back volume, fluidly coupling the barometric vent (and thus the front volume) with the back volume through the acoustic transducer element. 
     A disclosed acoustic transducer element can include a back plate and an insulator positioned between the diaphragm and the backplate. 
     A disclosed acoustic transducer element can include a first back plate and a corresponding first insulator positioned between the first back plate and the diaphragm. The acoustic transducer element can also include a second back plate and a corresponding second insulator positioned between the second back plate and the diaphragm. The diaphragm can be positioned between the first back plate and the second back plate. 
     A disclosed acoustic transducer element can include a first diaphragm and a second diaphragm. The acoustic transducer element can also include a back plate, a first insulator positioned between the back plate and the first diaphragm, and a second insulator positioned between the second diaphragm and the back plate. For example, the back plate can be positioned between the first diaphragm and the second diaphragm. 
     A disclosed diaphragm can include a piezoelectric actuator. An acoustic transducer element can include a first substrate defining a corresponding open port. The piezoelectric actuator can be mounted to the first substrate and extend over the open port of the first substrate. The acoustic transducer element can be mounted to a second substrate defining a corresponding acoustic port with the open port aligned with the acoustic port, and the piezoelectric actuator extending across the aligned open port and acoustic port, defining a boundary therebetween. 
     In accordance with another aspect, an electronic device includes an acoustic transducer element having a movable diaphragm. The diaphragm has opposed first and second major surfaces, and the acoustic transducer element defines an aperture positioned adjacent the movable diaphragm. A substrate couples with the acoustic transducer element. The substrate defines an acoustic port open to the acoustic transducer element. An elongated passageway extends from a first end fluidly coupled with the acoustic port to a second end fluidly coupled with the aperture, defining a barometric vent coupling the acoustic port with the aperture. 
     The substrate can include a plurality of juxtaposed layers and an opening can extend through the plurality of layers to define the acoustic port. At least one of the layers can define a corresponding channel defining a segment of the passageway. The passageway can include a tortuous passageway having at least one convolution. 
     The at least one of the layers can include a first layer and a second layer. The first layer can define a corresponding first channel and the second layer can define a corresponding second channel. The first channel and the second channel can be fluidly coupled with each other, defining a convolution in the elongated passageway. 
     The plurality of juxtaposed layers can include a first layer and a second layer. The second layer can be positioned between the first layer and the acoustic transducer element. The second layer can include a sacrificial insulator susceptible to etching and an etch-stop defining a boundary of a channel extending through the sacrificial insulator. The channel can define a corresponding portion of the elongated passageway. 
     The acoustic transducer element can include a back plate and an insulator positioned between the diaphragm and the backplate. 
     The acoustic transducer element can include a first back plate and a corresponding first insulator positioned between the first back plate and the diaphragm. The acoustic transducer element can include a second back plate and a corresponding second insulator positioned between the second back plate and the diaphragm. The diaphragm can be positioned between the first back plate and the second back plate. 
     The diaphragm of the acoustic transducer element can be a first diaphragm. The acoustic transducer element can also include a back plate and a first insulator positioned between the back plate and the first diaphragm. The acoustic transducer element can also include a second diaphragm and a second insulator positioned between the second diaphragm and the back plate. The back plate can be positioned between the first diaphragm and the second diaphragm. 
     The diaphragm of the acoustic transducer element can include a piezoelectric actuator. The diaphragm can be mounted to the substrate and the piezoelectric actuator can extend over the acoustic port. 
     Also disclosed are associated computing environments that can incorporate described technologies. 
     The foregoing and other features and advantages will become more apparent from the following detailed description, which proceeds with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Referring to the drawings, wherein like numerals refer to like parts throughout the several views and this specification, aspects of presently disclosed principles are illustrated by way of example, and not by way of limitation. 
         FIG. 1  illustrates a cross-sectional view taken through a package for an acoustic transducer, e.g., a MEMS microphone transducer. 
         FIG. 2  schematically illustrates a cross-sectional view taken through a package for an acoustic transducer having an acoustically resistive barometric vent.  FIG. 2  is annotated with an electrical analog of an acoustic pathway through the package. 
         FIG. 3  shows a plot comparing contribution of several noise sources to total acoustic noise for a packaged transducer as in  FIG. 2 . 
         FIG. 4  schematically illustrates a cross-sectional view taken through a package for an acoustic transducer having a barometric vent that exhibits a complex acoustic impedance.  FIG. 4  is annotated with an electrical analog of an acoustic pathway through the package. 
         FIG. 5  shows a plot comparing contribution of several noise sources to total acoustic noise for a packaged transducer as in  FIG. 4 . 
         FIG. 6  illustrates an isometric view of a substrate defining a high-aspect-ratio barometric vent, sectioned along line A-A in  FIG. 7 . 
         FIG. 7  illustrates a plan view of the substrate shown in  FIG. 6  from above. 
         FIG. 8  illustrates a plan view, from above, of an acoustic transducer having an acoustic transducer element mounted to a substrate as in  FIGS. 6 and 7 . 
         FIG. 9  shows an exploded, cross-sectional view of an acoustic transducer as in  FIG. 8 , sectioned as along line A-A in  FIG. 7 . 
         FIG. 10  shows an exploded, cross-sectional view of another acoustic transducer, sectioned as along line A-A in  FIG. 7 . 
         FIG. 11  shows an exploded, cross-sectional view of still another acoustic transducer, sectioned as along line A-A in  FIG. 7 . 
         FIG. 12  shows an exploded, cross-sectional view of yet another acoustic transducer, sectioned as along line A-A in  FIG. 7 . 
         FIG. 13  shows an exploded, cross-sectional view of a packaged microphone transducer having a package substrate incorporating high-aspect ratio barometric vent, sectioned as along line A-A in  FIG. 7 . 
         FIG. 14  shows an exploded, cross-sectional view of a packaged microphone transducer having a package substrate incorporating a high-aspect ratio barometric vent structured within, sectioned as along line A-A in  FIG. 7 . 
         FIG. 15  shows a plot of filter response for several a high-aspect-ratio (second-order) barometric vents defined by a substrate (e.g.,  FIGS. 6 through 12 ) for an acoustic transducer. 
         FIG. 16  shows a plot of filter response for several high-aspect-ratio barometric vents defined by a substrate (e.g.,  FIGS. 13 and 14 ) for a package for an acoustic transducer. 
         FIGS. 17A and 17B  show a perspective view of a portion of a segmented channel defining a barometric vent. 
         FIG. 17C  shows a two-dimensional projection of the segmented channel shown in  FIGS. 17A and 17B  onto a plane. 
         FIG. 18  shows an electrical-circuit analog to an acoustic filter defined by a segmented channel that defines a barometric vent. 
         FIG. 19  shows a perspective view of a segmented channel defined by a cascade of six repeating duct and chamber units. 
         FIG. 20  shows a two-dimensional projection of the segmented channel shown in  FIG. 19 . 
         FIG. 21A  shows a plot demonstrating low-frequency roll off for several different orders of acoustic filter, each defined by a respective segmented channel having a corresponding cascade of repeating duct and chamber units.  FIG. 21B  shows variation in low-frequency roll off for several segmented channels having similar cascades of repeating duct and chamber units, albeit with different dimensions for each cascade. 
         FIGS. 22A and 22B  show respective plots of frequency and phase response for a microphone vented with different segmented channels. 
         FIG. 23  shows a perspective view of a segmented channel having a cascade of repeating duct and chamber units. 
         FIG. 24  shows a two-dimensional projection of the segmented channel shown in  FIG. 23 . 
         FIG. 25  shows a perspective view of another segmented channel having a cascade of repeating duct and chamber units. 
         FIG. 26  shows a two-dimensional projection of the segmented channel shown in  FIG. 25 . 
         FIG. 27  shows a block diagram of a computing environment suitable to implement disclosed technologies. 
     
    
    
     DETAILED DESCRIPTION 
     The following describes various principles concerning vented acoustic transducers and transducer packages, and related methods and systems, by way of reference to specific features. For example, certain principles pertain to barometric vents for transducer elements, and other principles pertain to barometric vents for transducer packages. More particularly but not exclusively, certain aspects pertain to vents that have complex acoustic impedance to equalize barometric pressure across acoustic diaphragms. Vents described in context of specific configurations are just particular examples of contemplated vent arrangements chosen as being convenient illustrative examples of disclosed principles. Nonetheless, one or more of the disclosed principles can be incorporated in various other arrangements of acoustic transducers, modules, and systems to achieve any of a variety of corresponding system characteristics. 
     Thus, vented acoustic transducers, modules, and systems (and associated techniques) having attributes that are different from those specific examples discussed herein can embody one or more presently disclosed principles, and can be used in applications not described herein in detail. Accordingly, such alternative embodiments can also fall within the scope of this disclosure. 
     I. Overview 
     A loudspeaker can emit an acoustic signal in a carrier medium by vibrating or moving an acoustic diaphragm to induce, or otherwise inducing, a pressure variation or other vibration in the carrier medium. For example, an electromagnetic loudspeaker arranged as a direct radiator can induce a time-varying magnetic flux in a coil (e.g., a wire wrapped around a bobbin) attached to a diaphragm. The coil can be exposed to a magnetic field, e.g., a magnetic field of a permanent magnet, and a resultant force as between the magnetic flux emanated from the coil and the magnetic field(s) can urge the coil, and thus the diaphragm, into motion. 
     Conversely, a microphone transducer can be configured to convert an incoming acoustic signal to, for example, an electrical signal. An acoustic diaphragm of a microphone transducer, e.g., a MEMs microphone transducer, can vibrate, move, or otherwise respond to a pressure variation received through a surrounding or adjacent carrier medium. Movement of the diaphragm can induce a corresponding response in an electrical component. For example, movement of a diaphragm in a capacitive MEMs microphone can alter a capacitance of the device, inducing an observable, time-varying voltage signal in an electrical circuit. As another example, movement of a piezoelectric diaphragm can generate a time-varying electrical signal by virtue of a piezoelectric response to the movement. A time-varying electrical response generated with either type of microphone transducer can be converted to a machine-readable form (e.g., digitized) for subsequent processing. 
     Thus, an electro-acoustic transducer (sometimes simply referred to as an “acoustic transducer”) in the form of a loudspeaker can convert an incoming signal (e.g., an electrical signal) to sound, while an acoustic transducer in the form of a microphone can convert incoming sound to an electrical (or other) signal. As used herein, the term “audio signal” can refer to an electrical response (e.g., an analog or a digital signal) carrying audio information or data that can be converted to sound or that has been converted from sound. 
     An acoustic transducer can be mounted to a substrate (or chassis) and covered or enclosed by a housing (or lid) to define an enclosed acoustic chamber partially bounded by the diaphragm. With such an arrangement, the diaphragm can induce an acoustic response in the chamber as the diaphragm emits or receives sound energy. 
     Referring now to  FIGS. 1, 2 and 4 , component packages, e.g., for microphone transducers, are illustrated and briefly described. In  FIG. 1 , the component package  100  has a substrate  102  defining a first major surface  104  and an opposed second major surface  106 . The substrate  102  also defines at least one aperture  101   a  extending through the substrate from the first major surface  104  to the second major surface  106 , defining a sound-entry opening  101  (sometimes also referred to as an acoustic port) through the substrate  102 . A microphone transducer  103  is mountably coupled with the substrate  102  on the first major surface  104  and has a sound-responsive diaphragm (e.g., as in  FIGS. 2 and 4 ) acoustically coupled with the sound-entry opening  101  defined by the substrate, permitting sound to enter a front volume bounded in part by the microphone transducer. A lid  109 , mounted to the substrate  102 , overlies the microphone transducer  103  and defines a back volume  112 . 
     A pressure gradient between the front volume  110  and the back volume  112  can apply a biasing force to the diaphragm. Some disclosed electro-acoustic devices  103  and transducer elements  107  are barometrically vented, e.g., to equalize barometric pressure on opposed sides of the diaphragm. As an alternative, some transducer packages  100  are barometrically vented, e.g., to equalize barometric pressure on opposed sides of the diaphragm. 
     Such vented transducers and packages can mitigate or eliminate movement of the diaphragm arising from variations in ambient pressure, and thus can mitigate or eliminate effects of changes in ambient pressure on transducer output. Moreover, vented transducers and packages can mitigate or eliminate a likelihood of damage to the transducer by virtue of changes in ambient pressure. 
     In some respects, concepts disclosed herein generally concern vented acoustic transducers and related methods and systems. Some disclosed concepts pertain to components configured to equalize a static or a low-frequency pressure differential across an acoustic diaphragm. As an example, some disclosed transducers and packages have a vent arrangement configured to exhibit a complex acoustic impedance. Some vents incorporate an elongated, tortuous passage fluidly coupling a front volume of a transducer with a back volume of the transducer, providing a compact arrangement for a vent having complex acoustic impedance that may be quite long compared to the vent&#39;s cross-section or even the transducer&#39;s or package&#39;s overall dimensions. Other vents incorporate a segmented passage having a plurality of acoustic-mass-units juxtaposed with a corresponding plurality of acoustic-compliance-units, providing a higher-order filter. 
     Referring again to  FIG. 1 , a microphone transducer  103  can have a sound-responsive element  107 , sometimes also referred to as an “acoustic transducer element.” The illustrated transducer  105  also includes a substrate  105  supporting the acoustic transducer element, e.g., on which the acoustic transducer element is formed during manufacture. The substrate  105  defines a sound-entry opening  105   a  that permits sound waves to enter the acoustic-transducer element, e.g., from the sound entry opening  101  of the package substrate  102 . 
     Many configurations of acoustic transducer elements are possible, several of which are described below by way of example. For example, the microphone transducer  103  may include, for example, a micro-electro-mechanical system (MEMS) microphone. A flexible diaphragm spaced apart from a capacitive back plate provides one arrangement of an acoustic transducer element for a MEMS microphone, as described more fully below. It is contemplated, however, that microphone transducer can be any type of electro-acoustic transducer operable to convert sound into an electrical output signal, such as, for example, a piezoelectric microphone, a dynamic microphone or an electret microphone. 
     In the schematic illustrations of MEMS microphones in  FIGS. 2 and 4 , each sound-responsive element  207 ,  307  includes a corresponding diaphragm  220 ,  320  and a backplate  222 ,  322  mountably coupled with a substrate  205 ,  305 . Each diaphragm is spaced apart from the corresponding backplate by a spacer, defining a respective gap positioned between the diaphragm and the backplate. In  FIGS. 2 and 4 , each respective acoustic diaphragm  220 ,  320  can define a boundary between a front volume  210 ,  310  and a back volume  212 ,  312 . As sound enters a front volume, corresponding pressure gradients form between the front volume  210 ,  310  and the back volume  212 ,  312 , perturbing the respective diaphragm  220 ,  320 . As a diaphragm moves relative to the corresponding back plate due to sound, capacitance of the acoustic transducer element changes in correspondence with sound pressure level. The variations in capacitance can be observed to generate an electrical signal corresponding to variations in sound pressure level. That electrical signal or one derived from it (e.g., after processing to digitize, or to remove noise or echo) is sometimes referred to in the art as an audio signal. 
     As noted above, the front volume  210 ,  310  and the corresponding back volume  212 ,  312  can be fluidly coupled with each other, e.g., to equalize pressure between the back volume and the front volume. For example, the diaphragm  220  can be perforated, as depicted schematically in  FIG. 2 . Such a perforation can define an acoustically resistive vent fluidly coupling the front volume with the back volume. Nonetheless, an acoustically resistive vent can give rise to a substantial level of so-called “leak noise,” as when the diaphragm is excited by a flow of air through the vent driven by pressure variations having a frequency within a desired frequency band (e.g., human-audible band). 
     As an alternative, shown schematically for example in  FIG. 4 , a vent with a complex acoustic impedance can substantially reduce leakage noise ( FIG. 5 ). In contrast to a resistive vent, a vent with complex acoustic impedance can damp flow through the vent when exposed to pressure variations (or sound) in the desired frequency band, and yet can permit flow under low-frequency variations in pressure (e.g., as with changes barometric pressure). Although  FIG. 4  schematically illustrates a vent with a complex acoustic impedance across the diaphragm  320 ,  FIG. 4  should not necessarily be interpreted as requiring the vent to extend through the diaphragm, though that may be an option in some arrangements. 
     In other arrangements, a vent with complex acoustic impedance can extend through structure adjacent the diaphragm rather than the diaphragm itself, fluidly coupling the front volume  310  with the back volume  312 . For example, an elongated channel can extend from the front volume  310  to the back volume  312 , fluidly coupling them together and defining a vent with a complex acoustic impedance. An elongated channel as disclosed herein can provide sufficient air mass to impede airflow through the vent when exposed to pressure variations above a threshold frequency. In some aspects, the elongated channel can be defined by a high-aspect-ratio passageway, and in other aspects, the elongated channel can be segmented to provide a higher-order filter. 
     Nonetheless, providing a high-aspect-ratio vent in a confined volume, e.g., in an electro-acoustic transducer or other electronic device, presents certain difficulties and is not straightforward. For example, a length of such a vent may be several orders of magnitude larger than an acoustic-transducer device&#39;s nominal dimensions or several orders of magnitude larger than an acoustic-transducer package&#39;s nominal dimensions. 
     As shown in  FIG. 6 , however, a tortuous channel  610  can define a high-aspect-ratio barometric vent suitable to be incorporated in a transducer component  103  (e.g., within the substrate  105 ) or a transducer package  100  (e.g., within the substrate  102 ). Alternatively, a plurality of mass and compliance units as in  FIGS. 17A through 17C  can be assembled together to define a segmented channel that provides a higher-order roll-off than the tortuous channel  610 . With disclosed vents having complex acoustic impedance, low-frequency pressure variations, such as for example, due to weather changes, changes in a user&#39;s elevation, or pressurization of a passenger cabin on an airplane, can be equalized between the front volume  110  and the back volume  112 . Such a vent can significantly reduce noise in an audible frequency band arising by virtue of leakage through the barometric vent. 
     Further details of disclosed principles are set forth below. Section II describes principles pertaining generally to microphone packages. Section III describes principles pertaining to substrates that define tortuous channels suitable to provide a barometric vent with complex acoustic impedance. Section IV describes principles pertaining to vented microphone transducers and vented packages for microphone transducers. Section V describes several attributes of improved performance attainable by incorporating disclosed venting arrangements. And, Section VI describes principles related to a general purpose computing environment that can implement disclosed technologies. 
     As used herein, the terms “sinuous,” “tortuous,” “circuitous,” and “serpentine” are used synonymously and intended to connote structure that may be, but is not necessarily, curved, straight, ordered, disordered, spiraled, or laced or intertwined with, within, or through other structure. 
     II. Microphone Packages 
     Referring again to  FIG. 1 , the microphone transducer  103  can be mounted on or otherwise be operatively coupled with another substrate  102 , e.g., a package-level substrate and/or an interconnect substrate. The microphone package  100  can also include a lid  109  overlying the acoustic transducer  103 . The lid  109  can be recessed, defining a chamber, or back volume  112 , for the transducer  103 . 
     In  FIG. 1 , the package substrate  102  defines a sound entry region  101  acoustically coupled with the sound-entry opening  105   a  defined by the substrate  105  of the microphone package  103 . The sound-entry region  101  may be a single aperture or may be defined by a plurality of apertures  101   a  defining a perforated region of the substrate  102 . In either arrangement, the sound entry region  101  is acoustically, and in many instances fluidly, coupled with the sensitive region of the sound-responsive element  107  of the microphone transducer  103 . An unoccupied, open chamber bounded by the substrate  102 , the substrate  105 , and the sensitive region of the microphone transducer  103  is sometimes referred to in the art as a “front volume.” 
     The acoustic port  105   a  through the microphone substrate  105  can be the same size and shape as the sound-entry region  101  of the microphone package  100 , or the acoustic port  105   a    150  can be larger or smaller, or otherwise shaped differently, than the sound-entry region  101 . 
     A typical package level substrate  102  can have a thickness measuring between about 0.250 mm and about 0.65 mm, e.g., between about 0.300 mm and about 0.600, or between about 0.400 mm and about 0.500 mm. That typical substrate  102 , when viewed from above as in  FIG. 7  (e.g., in a plane orthogonal to the direction of “thickness”), can have an ordinate dimension measure about 4.000 mm by about 3.500 mm. For example, in selected aspects, each in-plane ordinate dimension can measure between about 2.500 mm and about 6.000 mm, such as, for example, between about 3.000 mm and about 5.000, or between about 3.300 mm and about 4.100 mm. 
     Each aperture  101   a  defining a sound-entry region  101  through the substrate  102  can be a non-plated through via having a diameter measuring between about 50 μm and about 200 μm, such as, for example, between about 75 μm and about 150 μm, e.g., between about 90 μm and about 110 μm. The sound-entry region  101  can have a characteristic dimension, e.g., a hydraulic diameter in selected aspects, measuring between about 1.000 mm and about 3.000 mm, such as, for example, between about 1.200 mm and about 2.400 mm, e.g., between about 1.4 mm and about 2.2 mm. Naturally, other configurations and dimensions for a sound-entry region  101  are possible. The dimensions listed above have been chosen as being representative of one particular configuration of the many configurations contemplated by this disclosure. 
     The sound-entry region  101 , and each respective aperture  101   a , has a corresponding characteristic dimension. Flow or acoustic characteristics of an aperture may vary with a selected characteristic dimension of the aperture. In some instances, a characteristic dimension of a given structure can be defined in a manner to enable, e.g., acoustic or flow comparisons of structures having different shapes. For example, a characteristic dimension of a circle can be a diameter of the circle. On the other hand, a characteristic dimension of a square can be length of the side of the square, or a ratio of an area of the square to a perimeter of the square. Such a ratio is sometimes referred to in the art as a hydraulic diameter. For a circle, the ratio reduces to the diameter of the circle. 
     Referring still to  FIG. 1 , the microphone package has an integrated circuit device  115  (e.g., an application-specific integrated circuit, or ASIC) mounted to the package substrate  102 . A bond wire  113  electrically couples the integrated circuit device with the acoustic transducer element  107 . For a capacitive MEMS microphone, the ASIC  115  can include circuitry to impose a charge on the acoustic transducer element  107 , and as the diaphragm (not shown in  FIG. 1 ) deforms, the ASIC can observe changes in voltage arising from the deformation of the diaphragm (e.g., changes in capacitance). The voltage variations can correspond to sound waves that induce the deflections in the diaphragm. 
     The package substrate  102  can have an electrical output connection (not shown) coupled with the integrated circuit device  115 . As well, the package substrate  102  can have an electrical trace or other electrical coupler that extends from the contact to another region defined by the substrate (e.g., a second, external electrical contact). Consequently, the package substrate  102  can electrically couple an external portion of an electrical circuit with the ASIC  115 . 
     The package  100  can be mounted to and electrically coupled with an interconnect substrate (not shown). In general, an interconnect substrate can include a plurality of electrical conductors configured to convey an electrical signal, or a power or a ground signal, from one interconnection location (e.g., a solder pad) to another interconnection location (e.g., another solder pad). For example, a packaged component, e.g., the packaged microphone transducer  100  can be soldered or otherwise electrically coupled with one or more interconnection locations defined by an interconnect substrate. 
     The interconnect substrate can electrically couple the packaged component  100  with one or more other components (e.g., a memory device, a processing unit, a power supply) physically separate from the packaged component. In addition to the microphone transducer, one or more other components can electrically couple with the electrical conductors in the interconnect substrate, electrically coupling the microphone package with such other component. Examples of the other component can include a processing unit, a sensor of various types, and/or other functional and/or computational units of a computing environment or other electronic device. 
     In an aspect, the interconnect substrate (not shown) can be a laminated substrate having one or more layers of electrical conductors juxtaposed with alternating layers of dielectric or electrically insulative material, e.g., FR4 or a polyimide substrate. Some interconnect substrates are flexible, e.g., pliable or bendable within certain limits without damage to the electrical conductors or delamination of the juxtaposed layers. The electrical conductors of a flexible circuit board may be formed of an alloy of copper, and the intervening layers separating conductive layers may be formed, for example, from polyimide or another suitable material. Such a flexible circuit board is sometimes referred to in the art as “flex circuit” or “flex.” As well, the flex can be perforated or otherwise define one or more through-hole apertures. 
     Although not illustrated, the microphone package  100  can define a plurality of exposed electrical contacts configured to be soldered or otherwise electrically connected with a corresponding interconnection location defined by the interconnect substrate. In an aspect, the electrical contacts are exposed on a same side of the transducer package  100  as the sound-entry region  101  (e.g., the bottom side  106 ). The interconnect substrate can define an aperture or other gas-permeable region (not shown) configured to permit an acoustic signal to pass therethrough in an acoustically transparent manner, or with a selected measure of damping, acoustically coupling an ambient environment with the sensitive region of the microphone transducer  103  through the interconnect substrate. In an alternative arrangement, the electrical contacts are exposed on the top side  104  of the substrate  102 . 
     III. Substrates with Tortuous, Sinuous or Serpentine Channels 
       FIG. 6  schematically illustrates a high-aspect ratio channel  610  defined by a substrate  600 . The substrate  600  in  FIG. 6  can be representative of either substrate shown in  FIG. 1 , e.g., a transducer substrate  105  or a package level substrate  102 . 
     Referring still to  FIG. 6 , the substrate  600  can define an inlet  612  to the tortuous channel  610 . Whether the vent is incorporated at the component level or at the package level, the inlet  612  can fluidly couple with the front volume  110 . For example, when the vent  610  is incorporated in the transducer substrate  105 , the inlet  612  to the vent  610  can fluidly couple with the acoustic port  105   a  at a position adjacent the acoustic transducer element  107 . Alternatively, when the vent  610  is incorporated in the package substrate  102 , the vent can fluidly couple with the front volume  110  at a position adjacent the sound-entry region  101 . 
     In either configuration, the channel  610  can extend predominantly circumferentially around an opening  614  through the substrate  600 . For example, the channel  610  can steadily spiral around and radially outward of the opening  614 . Alternatively, as shown in  FIG. 6 , the channel  610  can extend from the inlet  612  circumferentially around the substrate aperture  614  at a substantially constant radial position, and step or otherwise extend outward in a predominantly radial direction at a position  613  near the inlet  612 . The circuitous passage  610  can continue to extend around the aperture  614  at each successive radial position until the channel  610  has a desired path length from the inlet  612 . A terminal portion  616  of the channel  610  can define an outlet region from the channel at a position laterally or radially outward of the aperture  614  defined by the substrate  600 . In  FIG. 6 , the terminal portion  616  of the channel defines a substantially circular outlet fluidly coupled with the channel. Although not shown in  FIG. 6 , the terminal portion  616  of the channel  610  can extend to and open from an outer periphery  618  of the substrate  600 , directly coupling the channel with the transducer&#39;s back volume (e.g., back volume  112  in  FIG. 1 ). 
       FIG. 6  schematically depicts a volume  620  occupied by a device that is supported by or mounted to the substrate  600 . In  FIG. 6 , the volume  620  can represent an acoustic transducer element (e.g., acoustic transducer element  107  in  FIG. 1 ) of an acoustic transducer, or the volume  620  can represent an acoustic transducer (e.g., MEMS microphone  103  in  FIG. 1 ) mounted to a package substrate (e.g., substrate  102  in  FIG. 1 ). In either case, the device represented by the volume  620  can define an aperture  622  extending from the terminal portion  616  of the channel  610  to a back volume and through the device represented by the volume. 
     In yet another arrangement, as when an overall dimension of the substrate  600  exceeds an overall dimension of the device represented by the volume  620 , the terminal portion  616  of the channel can extend to a region (not shown) of the substrate positioned laterally outward of the volume  620 . Such a channel can directly couple the front volume with the back volume of the transducer, without requiring the vent to extend through the transducer or other structure. 
     Referring still to  FIG. 6 , the substrate  600  can have a base layer  602  formed of silicon (Si) or another suitable substrate material. An insulator layer  604  can overlie the base layer and be formed of silicon dioxide (SiO 2 ) or polyimide, or another suitable insulator. An aperture  614  can extend through the plurality of layers of the substrate. The insulator layer  604  can define a segment of the tortuous passage  610 . For example, the insulator layer  604  can be a sacrificial layer that has been selectively etched to define the channel  610  between walls  611  of remaining insulator. In an arrangement, the channel can be bounded by a lateral etch-stop material, such as, for example, silicon nitride (SiN). The etch-stop  615  ( FIG. 9 ) can define channel walls  611   a ,  611   b  ( FIGS. 6 and 9 ) as the sacrificial material can be selectively etched to remove material between the juxtaposed walls  615  of etch stop, defining a recess and forming a corresponding portion of the tortuous channel  610  extending around the aperture  614 . 
     High-aspect-ratio barometric vents can have a ratio of characteristic-length-to-characteristic-diameter (“L/D ratio”) of between about 1,000 and about 32,000, such as for example, between about 2,000 and about 16,000, or for example between about 4,000 and about 8,000. For example, a vent having a hydraulic diameter of 25 μm and an L/D ratio of 32,000 measures about 800 mm in length, while a vent having the same cross-section and an L/D ratio of 8,000 measures about 200 mm in length. Both vent examples have a length several orders of magnitude greater than an ordinate dimension of a package for a microphone transducer. 
     As yet another example, a substrate  105  for a microphone transducer  103  ( FIG. 1 ) can define a vent having a hydraulic diameter of about 5 μm and a passage length measuring about 80 mm, providing an L/D ratio of 16,000. As another example, a vent having a hydraulic diameter of 5 μm and a passage length measuring about 5 mm in length has an L/D ratio of 1,000. 
     In general, passage length for a vent can be measured longitudinally from a vent inlet to a vent outlet along a center line through the vent. A center line for a vent that has a cross-sectional shape that varies with longitudinal position can be defined by a curve that passes through the centroid of each cross-section defined by the vent from the inlet to the exhaust. An example of a characteristic diameter for a vent can be a hydraulic diameter (e.g., an area of a cross-section divided by a wetted perimeter of the cross-section) of the vent. 
     IV. Vented Microphone Transducers and Packages 
     Referring now to  FIGS. 7, 8, and 9 , a vented microphone transducer will be described using a high-aspect-ratio vent as an illustrative example of a vent with a complex acoustic impedance, though a segmented or other higher-order vent can be substituted for the high-aspect-ratio vent. The substrate  600  shown in  FIG. 7  defines a high-aspect ratio barometric vent  610  circuitously extending outward of an acoustic port  614 , generally as described above in relation to  FIG. 6 . As seen in  FIGS. 6 and 7 , the elongated barometric vent  610  can circuitously extend from a first end  612  fluidly coupled with the front volume  614  to a second end  616  fluidly coupled with a back volume of the transducer (e.g., through the aperture  622  in  FIG. 6 ). In  FIG. 8 , an acoustic-transducer element  800  is shown in a top-plan view mounted to the substrate  600  in overlying relation to the channel  610 . The exploded view in  FIG. 9  shows a side-elevation view of the substrate  600  and the acoustic-transducer element  800  in section, taken along Line A-A in  FIG. 7 . 
     As depicted in  FIG. 9 , the acoustic-transducer element  800  has a single back plate  810  separated from the acoustic diaphragm  802  by an insulator layer  804 . The back plate  810  has a plurality of layers, including a conductive layer (e.g., polysilicon) and an insulator layer (e.g., SiN). The diaphragm can be formed of silicon (Si), polysilicon, silicon nitride (SiN), or another material suitable to form a deflectable diaphragm for use in a capacitive microphone transducer. 
     As shown in  FIGS. 8 and 9 , the backplate  810  defines a plurality of apertures  812  fluidly and acoustically coupling a backside  803  of the diaphragm  802  with a back volume, e.g., back volume  112  in  FIG. 1 . The insulator layer  804  defines an aperture  805  having an outer periphery (e.g., circumference) positioned outward of the apertured region of the back plate  810 . The aperture  805  defined by the insulator can be larger, smaller or a same size as the acoustic port  614  defined by the substrate. An outer peripheral region  806  of the diaphragm can be attached or bonded with the insulator layer  804  and can overlie and contact the walls  611  defining the tortuous channel  610 , closing off a distal edge (relative to the layer  602 ) of the channel  610 . The closed-off distal edge of the channel, in combination with the walls defined by the sacrificial layer  604  and the floor defined by the layer  602 , can define an enclosed circuitous passage extending from the inlet  612  to outlet  616  ( FIG. 7 ). 
       FIG. 10  depicts an alternative configuration for an acoustic transducer. In  FIG. 10 , the substrate is configured similarly to the substrate  600  described in relation to  FIGS. 7, 8, and 9 . And, the acoustic-transducer element  1000  can contact, attach with or mount to the substrate  600  in a fashion similar as described in relation to  FIGS. 7, 8 and 9  to enclose the channel  610  defined by the substrate  600 . 
     However, unlike the acoustic-transducer element  800  in  FIG. 9 , the acoustic-transducer element  1000  in  FIG. 10  has a diaphragm  1002  positioned between first and second opposed back plates  1008 ,  1010 . An insulator  10007 ,  1009  separates the diaphragm  1002  from each respective back plate  1008 ,  1010 . Each backplate  1008 ,  1010  can be formed in a manner similar to the back plate  810  in  FIG. 9 . Similarly, the diaphragm  1002  can be formed of materials similar to the diaphragm  802  in  FIG. 9 . As well, each back plate  1008 ,  1010  can define a corresponding plurality of apertures to fluidly and acoustically couple the diaphragm with the front volume and the back volume, respectively, of the diaphragm (e.g., front volume  110  and back volume  112  in  FIG. 1 ). 
       FIG. 11  depicts yet another alternative configuration for an acoustic transducer. In  FIG. 11 , the substrate  600  is configured similarly to the substrate described in relation to  FIGS. 7 through 10 . And, the acoustic-transducer element  1100  can contact, attach with or mount to the substrate  600  in a fashion similar as described in relation to  FIGS. 7 through 10  to enclose the channel  610  defined by the substrate  600 . 
     However, unlike the acoustic-transducer elements  800  and  1000  in  FIGS. 9 and 10 , the acoustic-transducer element  1100  in  FIG. 11  has a back plate  1100  positioned between first and second opposed diaphragms  1101 ,  1102 . An insulator  1107 ,  1109  separates each respective diaphragm  1101 ,  1102  from the back plate  1110 . The backplate  1110  can be formed in a manner similar to the back plates described above in relation to  FIGS. 9 and 10 . Similarly, each diaphragm  1101 ,  1102  can be formed of materials similar to the diaphragms  802 ,  1002  described above in relation to  FIGS. 9 and 10 . 
       FIG. 12  depicts still another alternative configuration for an acoustic transducer. In  FIG. 12 , the substrate  600  is configured similarly to the substrates described in relation to  FIGS. 7 through 11 . And, the acoustic-transducer element  1200  can contact, attach with or mount to the substrate  600  in a fashion similar as described in relation to  FIGS. 7 through 11  to enclose the channel  610  defined by the substrate. Although exploded views shown in  FIGS. 9, 10, 11 and 12 , it will be understood and appreciated that each respective acoustic transducer element  800 ,  1000 ,  1100  and  1200  contacts or otherwise is physically coupled with or supported by the substrate  600  shown in those drawings. 
     However, unlike the acoustic-transducer elements described above in relation to  FIGS. 9 through 11 , the diaphragm  1202  in  FIG. 12  is a piezoelectric actuator overlying and extending across the acoustic port  614  defined by the substrate  600 . In  FIG. 12 , the acoustic transducer element includes a first substrate  1201  defining a corresponding open port  1203 . The piezoelectric actuator  1202  is mounted to the first substrate and extends across the open port  1203  of the first substrate. The acoustic transducer element  1202  is mounted to a second substrate  600  defining the acoustic port  614 . When the acoustic transducer element  1200  and the second substrate  600  are assembled together, the open port of the acoustic transducer element is aligned with the acoustic port  614 , and the piezoelectric actuator  1202  extends across the aligned open port and acoustic port, defining a boundary therebetween. 
     The diaphragm  1202  can include a thin-film piezoelectric material, such as, for example, aluminum nitride (AlN) and aluminum scandium nitride (AlScN). Other suitable materials from which to form the piezoelectric diaphragm  1202  can include, for example, Pb(Zr, Ti)O 3  and other piezoelectric materials now known or hereafter developed. 
     A peripheral region of each acoustic-transducer element described above in relation to  FIGS. 9 through 12  can define a through-hole aperture  822  aligned with and overlying the outlet  616  from the tortuous vent. The aperture  822  can fluidly couple the vent outlet  616  with the back volume of the transducer, thus coupling the front volume (e.g., front volume  110  in  FIG. 1 ) with the back volume (e.g., back volume  112  in  FIG. 1 ) by way of the tortuous channel  616  and the aperture  822 . 
     The tortuous channels described above in relation to  FIGS. 9 through 12  represent high-aspect-ratio arrangements of vents having a complex acoustic impedance. The vents are formed in or by a substrate for a microphone transducer, e.g., a substrate  105  in  FIG. 1 . However, as noted above in relation to  FIG. 6 , a venting having a higher-order complex acoustic impedance can be formed in or by a transducer substrate. As well, package-level substrates, e.g., substrate  102  in  FIG. 1 , can also define high-aspect-ratio vent having a complex acoustic impedance, as well as higher-order vents of the type described more fully below.  FIGS. 13 and 14  depict two package-level substrates defining a vent with a complex acoustic impedance suitable for use in a package for an acoustic transducer. Although exploded views are shown in  FIGS. 13 and 14 , it will be understood and appreciated that each respective acoustic transducer  1302 ,  1402  contacts or otherwise is physically coupled with or supported by the corresponding substrate  1301 ,  1401  shown in those drawings. 
       FIG. 13  depicts an exploded view of a MEMs microphone transducer mounted to a package-level substrate defining a vent with a complex acoustic impedance embodied as a tortuous channel, similar to the arrangement shown in  FIG. 6 . The MEMs microphone transducer  1302  shown in  FIG. 13  can incorporate an acoustic-transducer element according to any of the arrangements described above in relation to  FIGS. 9 through 12 . As in  FIG. 6 , the substrate  1301  has an upper layer  1304  and a lower layer  1303 . The upper layer  1304  of the multi-layer substrate  1301  shown in  FIG. 13  has been selectively etched (or otherwise processed) to define a high-aspect ratio acoustic pathway  1307 . The microphone transducer  1302  can define an aperture  1310  fluidly coupling the outlet  1309  from the pathway  1307  to the back volume  1330  of the microphone. And, the pathway  1307  extends from an inlet  1306  to the outlet  1309 , fluidly coupling the acoustic port  1305  or other region of the front volume  1320  with the back volume  1330  of the microphone transducer  1302  by way of the pathway  1307  and the aperture  1310 . More particularly, the pathway  1307  can extend along an outwardly expanding spiral, e.g., a radius of curvature of the pathway can continuously increase with longitudinal position along the pathway moving from the inlet  1306  to the outlet  1309 . Alternatively, the pathway can extend circumferentially around the acoustic port  1305  with a substantially constant radius, and in a selected region of the substrate, the pathway can extend in a predominantly radial direction from one ring to an adjacently positioned, successively larger-radius ring. The channel  1307  can be defined between juxtaposed walls  1308 .  FIG. 6  and  FIG. 7  depict a high-aspect ratio vent  610  having such a sequence of successively larger-radius rings joined together by relatively short, radially extending segments  613 . As with the channel  610  in  FIG. 6 , the channel  1307  can extend to an outer periphery of the substrate or extend laterally outward of the MEMs component  1302 , directly coupling the front volume  1320  with the back volume  1330 . 
       FIG. 14  depicts an exploded view of a MEMs microphone transducer  1402  mounted to an alternative arrangement of a package-level substrate  1401  defining a high-aspect ratio vent  1410 . In  FIG. 14 , the substrate  1401  has four layers (though additional or fewer layers are possible), with alternating insulative layers  1404 ,  1406  being substantially continuous, and alternating sacrificial layers  1403 ,  1405  having been selectively etched (or otherwise processed) to define corresponding segments  1410 ,  1412  of a high-aspect ratio acoustic pathway. As with package-level substrates described above, the substrate  1401  in  FIG. 14  defines a sound entry region (or acoustic port)  1407 . An inlet  1411  to the vent fluidly couples with the acoustic port  1407 , providing a direct fluid coupling of a first sinuous segment  1410  of the vent with the front volume  1420 . The first sinuous segment  1410  extends through successively larger radius passages, similarly to the vent described above in relation to  FIG. 13 , until it meets a first outlet region  1414 . 
       FIG. 14  shows a substantially continuous layer  1406  overlying the first sinuous segment  1410 . The layer  1406  defines an aperture  1416 , or open via, aligned with the first outlet region  1414  of the first sinuous segment  1410 . The upper layer  1405  of the substrate  1401  defines a second sinuous segment  1412  of the barometric vent, and the aperture  1416  fluidly couples the first sinuous segment  1410  with the second sinuous segment  1412 . The second sinuous segment  1412  extends circumferentially around the acoustic port  1407  through successively smaller-radius passages until the second sinuous segment  1412  meets a second outlet region  1418 . The successively smaller-radius passages can be defined by a continuously decreasing-radius spiral or can have substantially constant radius segments, with adjacent segments joined together with a predominantly radially extending segment, as with the rings depicted in  FIG. 6 . In some arrangements, the layer  1406  can be omitted, providing a direct coupling between the first sinuous segment  1410  and the second sinuous segment  1412 . As with the acoustic transducer  1302  shown in  FIG. 13 , the acoustic transducer  1402  shown in  FIG. 14  can define a through-hole aperture  1419  fluidly coupling the second outlet region  1418  with the back volume  1430 . By including one or more convolutions (or other change in channel direction) as just described (e.g., a combination of an outwardly expanding segment  1410  with an inwardly contracting segment  1412 ), overall packing density of a high-aspect ratio vent can be further increased. 
     V. Performance Examples 
     An acoustic vent having an L/D ratio of between about 1,000 and about 32,000 has a large acoustic mass, as with high-aspect-ratio vents described above. Such a vent can thus damp flow through the vent when excited by pressure variations having a frequency above a threshold frequency, reducing leakage noise compared to leakage noise arising from a predominantly resistive acoustic vent. For example, vents having a complex acoustic impedance described herein can substantially reduce leakage noise at frequencies above a threshold of between about 30 Hz and about 150 Hz, such as, for example, above threshold frequencies between about 40 Hz and about 100 Hz, e.g., above threshold frequencies between about 50 Hz and about 80 Hz. Stated differently, such a vent can act as a low-pass filter, e.g., to airflow, having a cutoff frequency between about 30 Hz and about 150 Hz. 
     The plot in  FIG. 15  shows representative acoustic responses to component-level vents. The plot in  FIG. 16  shows representative acoustic responses to package-level vents. Both plots generally depict similar trends, e.g., as aspect ratio of a high-aspect ratio vent increases, resonant frequency of the barometric vent decreases, as does the magnitude of the resonance. 
     In a general sense, reducing the resonance peaks as much as possible is preferred, though that can drive aspect ratios toward or even above 32,000. Thus, volume available to route the high-aspect-ratio barometric vent may impose an upper threshold on feasible length for the vent. Nonetheless, compensation with a digital signal processor (DSP) may be possible when manufacturing tolerances can be controlled sufficiently that the resonance frequency is essentially the same across devices. Such a DSP can be embodied in software, firmware or hardware (e.g., an ASIC). A DSP processor may be a special purpose processor such as an application specific integrated circuit (ASIC), a general purpose microprocessor, a field-programmable gate array (FPGA), a digital signal controller, or a set of hardware logic structures (e.g., filters, arithmetic logic units, and dedicated state machines), and can be implemented in a general computing environment as described herein. 
     That being said, if a given venting arrangement exhibits a substantial resonance peak (e.g., as with the responses shown in  FIGS. 15 and 16  at lower aspect ratios), the structure may be physically more responsive to a infrasonic input or an input at or near the sonic fringe. As a consequence, a low frequency input like a foot fall, which does not have much perceptible “sound” associated with it, could, in theory, produce significant levels of low-frequency noise if it overlaps with a resonant peak in the vent response, which in turn can substantially increase a high output level by the transducer. Consequently, a user may hear an increased noise level without really being aware of a corresponding a physical stimulus driving the noise. Alternatively, compensation, e.g., compensation by a DSP, can remove some or all of the resonance arising from excitation at or below a sonic fringe. 
     Moreover, such enhanced sensitivities at or below the sonic fringe can be exploited to detect events, e.g., infrasonic events such as, for example, foot falls. By way of example, resonance arising from an external source can be detected by a microphone transducer, or circuitry that receives an audio signal from the transducer. Additionally, selected sources or classes of infrasonic activity can have unique spectral signatures. Accordingly, in some instances, the microphone or the system may be able to detect a presence of a infrasonic event, as well as to classify the event, e.g., in correspondence with a level of resonance, alone, or in relation to energy content in other bands. 
     VI. Vents Having Higher-Order Complex Acoustic Impedance 
     Referring now to  FIGS. 17A, 17B and 17C , another example of a vent with a complex acoustic impedance that has a second-order roll off is shown and described. The elongated channel  1700 , segmented as shown in  FIGS. 17A, 17B and 17C , can define a barometric vent between a front volume and a back volume of a MEMS microphone. In  FIG. 17A , the substrate walls defining the segmented channel  1700  are omitted to reveal the open internal volume of the segmented channel. Stated differently, the shaded regions of the segmented channel in  FIG. 17A  depict the open volume within the channel  1700  occupied by an acoustic medium (e.g., air). The segmented channel  1700  has chamber portions  1701   a ,  1701   b  and duct portions  1703   a ,  1703   b  juxtaposed with the chamber portions. Each duct portion has a substantially smaller cross-sectional area than a corresponding cross-sectional area of an adjacent chamber portion. For example, in  FIG. 17 a   , a cross-sectional area of the duct portions  1703   a ,  1703   b  in a y-z plane is substantially smaller than a cross-sectional area of the chamber portions  1701   a ,  1701   b  in a y-z plane. 
     The duct portion  1703   b  extends from one of the chamber portions  1701   a  to the adjacent chamber portion  1701   b , providing a contraction in cross-sectional area from the chamber portion  1701   a  into the duct portion  1703   b  and an expansion in cross-sectional area from the duct portion to the adjacent chamber portion  1701   b . Consequently, chamber portions of the segmented channel  1700  provide acoustic compliance to the segmented channel and the duct portions of the segmented channel provide acoustic mass to the segmented channel. In the following discussion, duct portions of segmented channels are referred to generally as mass units and chamber portions of segmented channels are referred to generally as compliance units. 
     In  FIG. 17B , the segmented channel  1700  is shown with shading removed to reveal internal fluid connections as among the compliance units  1701   a ,  1701   b  and mass units  1703   a ,  1703   b , while still showing the edges and corners of each unit.  FIG. 17C  shows a two-dimensional projection on the x-y plane of the passageway defined by the segmented channel  1700 . The mass unit  1703   a  extends from an open proximal end  1702  to an open distal end  1704 . The open proximal end  1702  of the mass unit  1703   a  μm fluidly couple with a front volume (not shown) or other acoustic chamber of a microphone transducer. The open distal end  1704  of the mass unit  1703   a  μm fluidly couple with the compliance unit  1701   a  through a selected face of the compliance unit, e.g., the proximal face  1705   a  ( FIG. 17A ) along the x-axis. 
     Similarly, the mass unit  1703   b  extends from an open proximal end to an open distal end. The open proximal end of the mass unit  1703   b  μm fluidly couple with the compliance unit  1701   a  through a selected face (e.g., the face positioned distally of the proximal face  1705   a  along the x-axis). The open distal end of the mass unit  1703   b  μm fluidly couple with the compliance unit  1701   b  through a selected face of the compliance unit, e.g., the proximal face  1705   b  ( FIG. 17A ). A selected face of the second compliance unit  1701   b  (e.g., the face positioned distally of the proximal face  1705   b  along the x-axis) can define an opening  1706 . The opening  1706  can be directly or indirectly fluidly coupled with a back-volume or other acoustic chamber of the microphone transducer. 
     Each compliance unit  1701   a ,  1701   b  has a comparatively larger open internal volume (e.g., cross-sectional area and length) compared with the open internal volume (e.g., cross-sectional area and length) of each respective mass unit  1703   a ,  1703   b . Although the dimensions of the compliance units  1701   a ,  1701   b  are shown as being the same in  FIG. 17A , the dimensions of each compliance unit  1701   a ,  1701   b  may be selected differently from each other to provide a desired overall tuning of the segmented channel  1700 . Similarly, the dimensions of the mass units  1703   a ,  1703   b  may be the same as or different from each other. 
     Accordingly, a segmented channel can provide relatively more degrees-of-freedom, and thus offers relatively more flexibility in tuning, as compared to a tortuous, high-aspect-ratio channel. For example, a length (e.g., along the x-axis in  FIGS. 17A, 17B and 17C ) and a cross-sectional area (e.g., in the y-z plane) of each mass unit  1703   a ,  1703   b  m be selected to achieve a desired acoustic mass within each segment. Moreover, viscous losses associated with each mass unit  1703   a ,  1703   b  μm be tuned by adjusting relative position in the y-z plane. And, although only a single mass unit  1703   a ,  1703   b  is shown for each segment of the channel  1700 , more than one mass unit can extend between adjacent compliance units (e.g., units  1701   a ,  1701   b ) to reduce the acoustic mass for a given segment, providing additional options to tailor a response of the segmented channel  1700 . One or more further segments, each having a corresponding mass unit and a corresponding compliance unit, can be added to the segmented channel  1700  shown in  FIGS. 17A, 17B and 17C . 
       FIG. 18  shows an analogous electric circuit  1800  representing a segmented channel having four cascaded mass and compliance units. In the electrical circuit  1800 , the resistive, inductive and capacitive elements R 1 , L 1 , and C 1  are analogous to the acoustic conductance, the acoustic compliance, and the acoustic mass, respectively, of the first segment ( 1701   a ,  1703   a ) of the channel  1700 . Similarly, the resistive, inductive and capacitive elements R 2 , L 2 , and C 2  are analogous to the acoustic conductance, the acoustic compliance, and the acoustic mass, respectively, of the second segment ( 1701   b ,  1703   b ) of the channel  1700 . 
     Referring still to  FIG. 18 , the elements R 3 , L 3 , and C 3  and R 4 , L 4 , and C 4  correspond, respectively, to a third segment (e.g., units  1901   c ,  1903   c  in  FIG. 19 ) and a fourth segment (e.g., units  1901   d ,  1903   d  in  FIG. 19 ) of mass and compliance units. Cascaded mass and compliance structures, as in  FIGS. 18 and 19 , can achieve a higher order roll off than that achieved by, for example, the two-segment channel  1700 . The roll-off order increases in correspondence to an increasing number of repeating mass/compliance units. 
     For example, the segmented channel  1900  shown in  FIGS. 19 and 20  includes a fifth cascade (e.g., units  1901   e ,  1903   e ) and a sixth cascade (e.g., units  1901   f ,  1903   f ) of mass and compliance units. As shown in  FIG. 21A , cascading the segments of mass and compliance units can reduce the cutoff frequency of the segmented barometric vent  1900 , e.g., compared to the segmented channel  1700 . Vent noise can be filtered out across higher frequencies on the noise spectrum using higher-order vents by achieving a steeper roll-off compared to that achieved by a high-aspect-ratio vent. Consequently, signal-to-noise ratio for a microphone can be improved using a higher-order vent. 
     For a given microphone back volume and a selected number of cascaded segments of mass and compliance units, dimensions of each mass and compliance unit can be tuned to achieve a desired roll off. For example, viscous losses through the high mass units can be tuned to adjust damping. More generally, each of the cascaded segments can be tuned to have a selected combination of acoustic mass and acoustic compliance (e.g., high/high, high/low, low/high, respectively) to achieve a desired cut-off frequency and corresponding microphone frequency response.  FIG. 21B  shows an example of variation in roll off for a different tunings of a given cascade of mass and compliance units. 
     In one illustrative example, dimensions of the segmented channel  1900  (having 6 segments) can be selectively tuned to provide selected roll-off frequencies when used to barometrically vent a back volume having a volume of 2.5 mm 3 . For example, the x-, y-, and z-dimensions of each compliance unit  1901   n  can be selected to be 400 μm, 500 μm, and 400 μm, respectively, and the x- and y-dimensions of each mass unit  1903   n  can be selected to be 60 μm, and 10 μm, respectively. The z-axis dimension, t, of each mass unit can be varied and a corresponding roll-off frequency determined. In this example, the z-axis dimension, t, varied from 20 μm to 50 μm in increments of 5 μm, and the resulting low-frequency roll-off occurred at 8 Hz, 12 Hz, 16 Hz, 23.5 Hz, and 32.5 Hz, respectively. 
     Referring now to  FIGS. 22A and 22B , representative frequency responses and phase responses, respectively, of a microphone back whose back volume is barometrically vented using different second-order, under-damped vents. Notably, the frequency response  2201  and phase response  2202  flatten over the audible bandwidth when the low-frequency roll-off falls below a lower-threshold frequency, e.g., 20 Hz. Moreover, phase mismatch common among conventional designs can be reduced or minimized using higher-order vents described herein. Although the responses shown in  FIGS. 22A and 22B  result from a second-order filter, the responses will also flatten with higher-order filters as shown in, for example,  FIG. 19 . 
     And, in some respects, an elongated, segmented channel can more readily be manufactured, packaged, and reliably tuned than a high-aspect ratio vent described above. For example, a segmented channel as described above can have an overall volume about one-tenth of that required for a high-aspect ratio vent as described above in relation to, for example,  FIG. 6 . As well, a segmented channel can provide more degrees-of-freedom for tuning the filtering provided by the channel. 
     Further, cascaded segments of a higher-order, segmented vent need not be combined along a single coordinate direction, as with the vent  1900  shown in  FIG. 19 . Rather, each successive segment of mass and compliance units can be added to a previous segment in any orientation subject to any physical constraints imposed by a given microphone or package. As well, the number of cascaded segments (e.g., the vent order) can be selected in accordance with each desired application. 
     For example, in  FIGS. 23 and 24 , the segmented vent  2300  is shown having six segments arranged in a U-shape parallel to an x-y plane. More specifically, a first segment has a compliance unit  2301   a  and a mass unit  2303   a . The mass unit  2303   a  has a major longitudinal axis extending in ay-axis direction from a proximal end (e.g., coupled with a front volume, not shown) to a distal end opening to an x-z face of the compliance unit  2301   a.    
     The second segment is oriented in a different direction, rotated 90-degrees about the z-axis. For example, the proximal end of the second segment&#39;s mass unit  2303   b  couples with a y-z face of the compliance unit  2301   a  and the mass unit  2303   b  extends in an x-axis direction to couple with a y-z face of the compliance unit  2301   b . The third segment (unit  2303   c  and  2301   c ) is oriented generally as the second segment. However, the fourth segment (mass unit  2303   d  and compliance unit  2301   d ) is rotated 90-degrees in a direction opposite the rotation of the second segment, providing the fourth segment with an orientation similar to that of the first segment (mass unit  2303   a  and compliance unit  2301   a ). And, the fifth segment (mass unit  2303   e  and compliance unit  2301   e ) is again rotated about a z-axis by another 90-degrees relative to the fourth segment, orienting the fifth segment at 180-degrees relative to the second segment. The sixth segment (mass unit  2303   f  and compliance unit  2301   f ) is oriented as the fifth segment, with a channel  2306  provided to couple the compliance unit  2301   f  with a back volume (not shown). 
       FIGS. 25 and 26  show yet another alternative arrangement of a segmented vent. In  FIGS. 25 and 26 , the segments are arranged to provide the vent  2500  with an L-shape parallel to an x-z plane. Still other arrangements are possible. For example, the sixth segment  2501   f ,  2503   f , shown in  FIG. 25  as extending in a z-axis direction from the prior segment can alternatively extend in a y-axis direction from that prior segment. 
     In general, such segmented vents can be made compact in one or more coordinate directions by adding successive segments in a different orientation compared to the prior segment. For example, as shown in  FIG. 23 , a vent defined by a segmented channel can loop back on itself, providing a desired number of segments (e.g., to achieve a desired higher-order filter) while not extending along a single coordinate direction. By including one or more convolutions (or other change in channel direction or orientation), overall packing density of a segmented channel vent can be further increased. 
     As well, vents with complex acoustic impedance, as described herein, can be positioned between the back volume and the front volume, over a MEMS device, or anywhere within a package, substrate or lid, with any selected compact orientation. For example, a segmented channel described in relation to any of  FIGS. 17A through 26  can be substituted for a high-aspect-ratio vent described above in relation to any of  FIGS. 1 through 16 . Similarly, a segmented channel can be manufactured using techniques described above in connection with high-aspect-ratio vents described above in relation to  FIGS. 1 through 16 . In the foregoing discussion, duct portions and chamber portions of segmented channels are described generally as being rectangular, prismatic structures within a Cartesian coordinate system. Nonetheless, duct portions and chamber portions are not so limited; they may have other regular or irregular three-dimensional shapes. Moreover, the wetted surfaces of those regular or irregular three-dimensional shapes may have a smooth or rough contour, e.g., the surfaces may be flat, curved, or undulating (e.g., smoothly or with discontinuous slopes), as may arise from a given manufacturing process. Nonetheless, nominal dimensions of each segment can be selected in a manner described above to achieve a desired overall tuning for the segmented channel. 
     VII. Computing Environments 
       FIG. 27  illustrates a generalized example of a suitable computing environment  2700  in which described technologies can be implemented. The computing environment  2700  is not intended to suggest any limitation as to scope of use or functionality of the technologies disclosed herein, as each technology may be implemented in diverse general-purpose or special-purpose computing environments. For example, each disclosed technology may be implemented with other computer system configurations, including wearable and/or handheld devices (e.g., a mobile-communications device, and more particularly but not exclusively, IPHONE®/IPAD®/HomePod™/AIRPODS® devices, available from Apple Inc. of Cupertino, Calif.), multiprocessor systems, microprocessor-based or programmable consumer electronics, embedded platforms, network computers, minicomputers, mainframe computers, smartphones, tablet computers, data centers, audio appliances, and the like. Each disclosed technology may also be practiced in distributed computing environments where tasks are performed by remote processing devices that are linked through a communications connection or network. In a distributed computing environment, program modules may be located in both local and remote memory storage devices. 
     The computing environment  2700  includes at least one central processing unit  2710  and a memory  2720 . In  FIG. 27 , this most basic configuration  2730  is included within a dashed line. The central processing unit  2710  executes computer-executable instructions and may be a real or a virtual processor. In a multi-processing system, or in a multi-core central processing unit, multiple processing units execute computer-executable instructions (e.g., threads) to increase processing speed and as such, multiple processors can run simultaneously, despite the processing unit  2710  being represented by a single functional block. A processing unit can include an application specific integrated circuit (ASIC), a general purpose microprocessor, a field-programmable gate array (FPGA), a digital signal controller, or a set of hardware logic structures arranged to process instructions. 
     The memory  2720  may be volatile memory (e.g., registers, cache, RAM), non-volatile memory (e.g., ROM, EEPROM, flash memory, etc.), or some combination of the two. The memory  2720  stores software  2780   a  that can, for example, implement one or more of the technologies described herein, when executed by a processor. 
     A computing environment may have additional features. For example, the computing environment  2700  includes storage  2740 , one or more input devices  2750 , one or more output devices  2760 , and one or more communication connections  2770 . An interconnection mechanism (not shown) such as a bus, a controller, or a network, interconnects the components of the computing environment  2700 . Typically, operating system software (not shown) provides an operating environment for other software executing in the computing environment  2700 , and coordinates activities of the components of the computing environment  2700 . 
     The store  2740  may be removable or non-removable, and can include selected forms of machine-readable media. In general machine-readable media includes magnetic disks, magnetic tapes or cassettes, non-volatile solid-state memory, CD-ROMs, CD-RWs, DVDs, magnetic tape, optical data storage devices, and carrier waves, or any other machine-readable medium which can be used to store information and which can be accessed within the computing environment  2700 . The storage  2740  can store instructions for the software  2780   b , which can implement technologies described herein. 
     The store  2740  can also be distributed over a network so that software instructions are stored and executed in a distributed fashion. In other aspects, some of these operations might be performed by specific hardware components that contain hardwired logic. Those operations might alternatively be performed by any combination of programmed data processing components and fixed hardwired circuit components. 
     The input device(s)  2750  may be any one or more of the following: a touch input device, such as a keyboard, keypad, mouse, pen, touchscreen, touch pad, or trackball; a voice input device, such as a microphone transducer, speech-recognition software and processors; a scanning device; or another device, that provides input to the computing environment  2700 . For audio, the input device(s)  2750  may include a microphone or other transducer (e.g., a sound card or similar device that accepts audio input in analog or digital form), or a computer-readable media reader that provides audio samples to the computing environment  2700 . 
     The output device(s)  2760  may be any one or more of a display, printer, loudspeaker transducer, DVD-writer, or another device that provides output from the computing environment  2700 . 
     The communication connection(s)  2770  enable communication over or through a communication medium (e.g., a connecting network) to another computing entity. A communication connection can include a transmitter and a receiver suitable for communicating over a local area network (LAN), a wide area network (WAN) connection, or both. LAN and WAN connections can be facilitated by a wired connection or a wireless connection. If a LAN or a WAN connection is wireless, the communication connection can include one or more antennas or antenna arrays. The communication medium conveys information such as computer-executable instructions, compressed graphics information, processed signal information (including processed audio signals), or other data in a modulated data signal. Examples of communication media for so-called wired connections include fiber-optic cables and copper wires. Communication media for wireless communications can include electromagnetic radiation within one or more selected frequency bands. 
     Machine-readable media are any available media that can be accessed within a computing environment  2700 . By way of example, and not limitation, with the computing environment  2700 , machine-readable media include memory  2720 , storage  2740 , communication media (not shown), and combinations of any of the above. Tangible machine-readable (or computer-readable) media exclude transitory signals. 
     As explained above, some disclosed principles can be embodied in a tangible, non-transitory machine-readable medium (such as microelectronic memory) having stored thereon instructions. The instructions can program one or more data processing components (generically referred to here as a “processor”) to perform a processing operations described above, including estimating, computing, calculating, measuring, adjusting, sensing, measuring, filtering, addition, subtraction, inversion, comparisons, and decision making (such as by the control unit  52 ). In other aspects, some of these operations (of a machine process) might be performed by specific electronic hardware components that contain hardwired logic (e.g., dedicated digital filter blocks). Those operations might alternatively be performed by any combination of programmed data processing components and fixed hardwired circuit components. 
     VII. Other Embodiments and Examples 
     The previous description is provided to enable a person skilled in the art to make or use the disclosed principles. Arrangements other than those described above in detail are contemplated based on the principles disclosed herein, together with any attendant changes in configurations of the respective apparatus or changes in order of method acts described herein, without departing from the spirit or scope of this disclosure. Various modifications to the examples described herein will be readily apparent to those skilled in the art. 
     For example, an electronic device can have an acoustic transducer element having an acoustic diaphragm. The diaphragm can have opposed first and second major surfaces. A front volume can be positioned adjacent the first major surface of the diaphragm. A back volume can be positioned adjacent the second major surface of the diaphragm. A substrate can be coupled with the acoustic transducer element, and a segmented channel can define a barometric vent fluidly coupling the front volume with the back volume. The segmented channel can extend from a first end fluidly coupled with the front volume to a second end fluidly coupled with the back volume, and a portion of the segmented channel can extend through the substrate. 
     In an example, the barometric vent can be configured to equalize pressure between the front volume and the back volume. 
     The segmented channel can have, for example, a plurality of duct portions and a plurality of chamber portions. Each duct portion can extend from one of the chamber portions to an adjacent chamber portion, providing a contraction in cross-sectional area from each respective chamber portion into the corresponding duct portion and an expansion in cross-sectional area from the respective duct portion to the corresponding adjacent chamber portion. 
     The substrate can define an acoustic port opening to the front volume. In an example, the substrate is a first substrate, and the electro-acoustic device can have a second substrate. The first substrate can be mounted to the second substrate. The electro-acoustic device can also have an integrated circuit device mounted to the second substrate. The integrated circuit device and the acoustic transducer element can be electrically coupled with each other. The second substrate can have an electrical output connection coupled with the integrated circuit device. The electro-acoustic device can also include a recessed lid overlying the acoustic transducer element, the first substrate, and the integrated circuit device. 
     In another example, the substrate also defines the segmented channel. Further, the segmented channel can have a plurality of duct portions and a plurality of chamber portions. Each duct portion can extend from one of the chamber portions to an adjacent chamber portion, providing a contraction in cross-sectional area from each respective chamber portion into the corresponding duct portion and an expansion in cross-sectional area from the respective duct portion to the corresponding adjacent chamber portion. 
     In an example, a region of the segmented channel can open to the acoustic port. The substrate can have a plurality of juxtaposed layers and an aperture can extend through the plurality of layers to define the acoustic port. In another example, a region of the segmented channel opens to the front volume. 
     At least one of the layers can define a corresponding portion of the segmented channel having a duct portion and a corresponding chamber portion. The duct portion can have a cross-sectional area substantially smaller than a corresponding cross-sectional area of the chamber portion. 
     The segmented channel can have a plurality of comparatively narrow duct portions juxtaposed with a corresponding plurality of comparatively wider chamber portions. The segmented channel can define at least one convolution among the duct portions and the chamber portions. 
     The at least one layer can include a first layer and a second layer. Each respective portion of the segmented channel defined by the first layer and each respective portion of the segmented channel defined by the second layer can be fluidly coupled together, defining a convolution in the segmented channel. Such a substrate, in another example, can include an intermediate layer of material separating the first layer and the second layer from each other. The intermediate layer can define an aperture fluidly coupling the segment of the segmented channel defined by the first layer with the segment of the segmented channel defined by the second layer. 
     In another example, the substrate has a first layer and a second layer. The second layer can be positioned between the first layer and the acoustic diaphragm. The second layer can have a sacrificial insulator susceptible to etching and an etch-stop defining a boundary of a recess extending through the sacrificial insulator. The recess can define a corresponding portion of the segmented channel. 
     According to an example, the first end of the segmented channel can be positioned adjacent the acoustic port, the front volume, or both, and the second end of the segmented channel can be positioned adjacent the back volume. 
     The portion of the segmented channel that extends through the substrate can have a duct portion and a corresponding chamber portion. The duct portion can have a first end that opens to the front volume and a second end that opens to the corresponding chamber portion. 
     The acoustic transducer element can be mountably coupled with the substrate and can define an aperture aligned with the segmented channel. For example, the aperture can open to the back volume, fluidly coupling the front volume with the back volume. 
     In an example, the acoustic transducer element has a back plate and an insulator. The insulator can be positioned between the diaphragm and the backplate. 
     In another example, the acoustic transducer element has a first back plate and a corresponding first insulator positioned between the first back plate and the diaphragm. The acoustic transducer element can also have a second back plate and a corresponding second insulator positioned between the second back plate and the diaphragm. The diaphragm can be positioned between the first back plate and the second back plate. 
     In another example, the diaphragm is a first diaphragm. The acoustic transducer element can have a back plate and a first insulator positioned between the back plate and the first diaphragm. The acoustic transducer element can also have a second diaphragm, and a second insulator positioned between the second diaphragm and the back plate. The back plate can be positioned between the first diaphragm and the second diaphragm. 
     In yet another example, the diaphragm can have a piezoelectric actuator and a substrate defining an open port. The diaphragm can be mounted to the substrate and the piezoelectric actuator can extend over the open port. 
     According to other examples, an electronic device can include an acoustic transducer element having a movable diaphragm. The diaphragm can have opposed first and second major surfaces, and the acoustic transducer element can define an aperture positioned adjacent the movable diaphragm. A substrate can be coupled with the acoustic transducer element. The substrate can define an acoustic port open to the acoustic transducer element and a segmented passageway extending from a first end fluidly coupled with the acoustic port to a second end fluidly coupled with the aperture, defining a barometric vent coupling the acoustic port with the aperture. 
     For example, the substrate can have a plurality of juxtaposed layers and an opening can extend through the plurality of layers to define the acoustic port. The at least one layer can be a first layer, and the substrate can have a second layer. The first layer can define a corresponding first channel and the second layer can define a corresponding second channel. The first channel and the second channel can be fluidly coupled with each other, defining a convolution in the segmented passageway. 
     The segmented passageway can have a plurality of duct regions juxtaposed with a corresponding plurality of chamber regions. Each respective duct region can have a cross-sectional area substantially smaller than a corresponding cross-sectional area of an adjacent chamber region. 
     Directions and other relative references (e.g., up, down, top, bottom, left, right, rearward, forward, etc.) may be used to facilitate discussion of the drawings and principles herein, but are not intended to be limiting. For example, certain terms may be used such as “up,” “down,”, “upper,” “lower,” “horizontal,” “vertical,” “left,” “right,” and the like. Such terms are used, where applicable, to provide some clarity of description when dealing with relative relationships, particularly with respect to the illustrated embodiments. Such terms are not, however, intended to imply absolute relationships, positions, and/or orientations. For example, with respect to an object, an “upper” surface can become a “lower” surface simply by turning the object over. Nevertheless, it is still the same surface and the object remains the same. As used herein, “and/or” means “and” or “or”, as well as “and” and “or.” Moreover, all patent and non-patent literature cited herein is hereby incorporated by reference in its entirety for all purposes. 
     And, those of ordinary skill in the art will appreciate that the exemplary embodiments disclosed herein can be adapted to various configurations and/or uses without departing from the disclosed principles. Applying the principles disclosed herein, it is possible to provide a wide variety of arrangements for high-aspect ratio, barometric vents to reduce leakage noise. For example, the principles described above in connection with any particular example can be combined with the principles described in connection with another example described herein. Thus, all structural and functional equivalents to the features and method acts of the various embodiments described throughout the disclosure that are known or later come to be known to those of ordinary skill in the art are intended to be encompassed by the principles described and the features and acts claimed herein. Accordingly, neither the claims nor this detailed description shall be construed in a limiting sense, and following a review of this disclosure, those of ordinary skill in the art will appreciate the wide variety of acoustic vents that can be devised using the various concepts described herein. 
     Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. No claim feature is to be construed under the provisions of 35 USC 112(f), unless the feature is expressly recited using the phrase “means for” or “step for”. 
     The appended claims are not intended to be limited to the arrangements shown herein, but are to be accorded the full scope consistent with the language of the claims, wherein reference to a feature in the singular, such as by use of the article “a” or “an” is not intended to mean “one and only one” unless specifically so stated, but rather “one or more”. Further, in view of the many possible embodiments to which the disclosed principles can be applied, we reserve the right to claim any and all combinations of features and technologies described herein as understood by a person of ordinary skill in the art, including the right to claim, for example, all that comes within the scope and spirit of the foregoing description, as well as the combinations recited, literally and equivalently, in any claims presented anytime throughout prosecution of this application or any application claiming benefit of or priority from this application, and more particularly but not exclusively in the claims appended hereto.

Metadata:
Filing Date: 20200521
Publication Date: 20220419
Grant Date: 20220419
Priority Date: 20190528
Inventors: HRUDEY, PETER C.
Crosby, Justin D.
HATIPOGLU, Gokhan
Assignee: APPLE INC
CPC Classifications: [{"code": "H04R31/00", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04R1/406", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04R2410/03", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04R1/2846", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04R1/245", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04R7/16", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04R1/2846", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04R2400/11", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04R19/005", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04R1/403", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04R2400/11", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04R1/403", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04R7/16", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04R1/2846", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 81127190