WO2000002419A1

WO2000002419A1 - External microphone protective membrane

Info

Publication number: WO2000002419A1
Application number: PCT/US1999/013445
Authority: WO
Inventors: William R. Williams; David Q. Dobras; Patrick A. Mavrakis; David L. Luger
Original assignee: Resound Corporation
Priority date: 1998-07-01
Filing date: 1999-06-16
Publication date: 2000-01-13
Also published as: AU4567099A

Abstract

A sound capturing device that minimizes interference by ambient wind and water is provided. The device includes (a) a housing (10) having walls that have at least one aperture (52, 54) that is in acoustic communication with the environment external to the housing, and wherein each aperture has an exterior port, (b) a microphone (26) that is positioned in the housing; and a replaceable protective material (62, 64) that covers the exterior port of each aperture and that is exposed to the environment, wherein the protective material comprises (i) a porous, hydrophobic membrane having a sufficiently small pore size to prevent the accumulation of moisture in and the entrance of water through the hydrophobic membrane, and (ii) an air flow attenuating membrane having an effective thickness to reduce the turbulence of ambient wind impinging upon the exterior port. The sound capturing system can be a two way communications device, a hearing aid, a telephone headset, a multimedia headset, or other communication device.

Description

EXTERNAL MICROPHONE PROTECTIVE MEMBRANE

BACKGROUND OF THE INVENTION

Field of the Invention

The invention relates to a sound capturing system, such as for a hearing aid, a two-way communication device, or a multimedia device, and more particularly, the invention relates to a sound capturing system for capturing the speech sounds of the user that includes a windproof and waterproof microphone assembly.

Brief Description of the Related Art

Some users require devices such as voice pickups that provide a high quality capture of sound, for example, of the user's speech, and that are compact, discreet and convenient. For example, U.S. Secret Service agents assigned to covertly protect individuals require two way communications systems that are unobtrusive and allow them to clearly communicate with remote locations. Such an application requires a sound pickup that an agent can wear which is both discreet and accurate, particularly in situations such as a crowded room where ambient sound levels are high. Conventional two way communications systems used in such applications typically have boom-mounted or lapel-mounted microphones. Boom-mounted microphones are difficult to conceal, and lapel- mounted microphones and other conventional microphones mounted remotely from the user's mouth often suffer from a relatively low signal-to-noise ratio, especially in noisy environments. Traditionally, microphone elements are mounted on the inside of the housings of sound capturing systems; and if a seal is used, it is placed on the inside surface of the housing. A small opening, either a hole or a slot, then protrudes through the housing and is exposed to the outside environment. In many designs, the surface tension of the water causes the water to "skin" over the port, and block the audio path to the microphone.

Prior art wind/breath screens for microphones are exemplified by Das et. al., U.S. Patent 4,570,746 which describes a screen that includes a rigid perforated structure for enclosing a microphone which is physically isolated from the rigid perforated structure by a surrounding pad of air there-between and a compliant support member. In addition, a porous layer (e.g., latex foam) is utilized to enclose the rigid perforated structure thereby creating a pad of dead air between the microphone and the porous layer. The element described in the patent is a close-talking element, one of a class of elements known as pressure- difference or pressure-gradient microphones. Simply put, the pressure-difference element has two spaced-apart sound ports into the microphone capsule, one leading to the front of the diaphragm and the other leading to the back. When a sound arrives from a distance, the front and back pressures are nearly identical and the pressures cancel, so there is little output signal from the microphone. However, when the source of sound is close to the microphone, there is a difference in the pressure because the ports are separated. Sound pressure is proportional to the inverse of distance, which creates this close-talking effect. Prior art screens which were applied directly against the outside of the housing as discussed by Das et. al. upset the equality since amplitude and phase must both be equal and subsequently the cancellation effect is reduced or eliminated. Das et. al. determined that by spacing the screen away from the element with a rigid perforated support, the sound would be less disturbed by the presence of the screen and would properly enter the two ports in the microphone capsule contained within the "pad of air". Essentially, the Das et. al. device requires an air space between the screen and the sound ports of the microphone element or the screen will not work.

Thus, the types of screens described in Das et al., are necessarily relatively large in order to enclose the required pad of air. Therefore, there exists a need for a small, compact screen which provides protection against wind noise and moisture.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in greater detail with reference to the preferred embodiments illustrated in the accompanying drawings, in which like elements bear like reference numerals, and wherein:

FIG. 1 is a partially exploded perspective view of a sound capturing device according to the present invention; FIG. 2 A and 2B are perspective cut away views of the microphone housing;

FIG. 3 is a partial cut away of the microphone housing showing the protective membrane essentially completely covering the aperture of the external port; FIGS. 4, 6, 8 and 10 are frequency response graphs; and

FIGS. 5, 7, and 9 are polar graphs of the frequency response of an embodiment of the invention worn in a user's right ear, looking down upon the user where 0 degrees indicates a forward direction, i.e., the direction in which the user is facing. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention relates to a sound capturing system having a microphone with a windproof and waterproof membrane that eliminates the ability of water to easily block a microphone port. In particular, in one embodiment of the invention an external breathable membrane seal is wrapped around the front and back ports of a noise canceling or directional microphone. In a preferred embodiment, the membrane is configured as a "band-aid" strip that can be easily removed and replaced. There are no features around the front or back microphone ports to allow the surface tension of the water to skin over and block the port. The water will tend to roll off of the port opening as there is nothing remarkable on the outside of the seal at the microphone port opening for the water to "skin over" and obstruct. Accordingly, in one aspect, the invention is directed to a sound capturing device that minimizes interference by ambient wind and water that includes: a housing having walls that have at least one aperture that is in acoustic communication with the environment external to the housing, and wherein each aperture has an exterior port; a microphone that is positioned in the housing; and a protective material that covers the exterior port of each aperture and that is exposed to the environment, wherein the protective material comprises (a) a porous, hydrophobic membrane having a sufficiently small pore size to prevent the accumulation of moisture in and the entrance of water through the porous hydrophobic membrane, and (b) an air flow attenuating membrane having an effective thickness to reduce the turbulence of ambient wind impinging upon the exterior port.

In another aspect, the invention is directed to a sound capturing device that suppresses the effects of wind and water disturbances that includes: a housing having walls that have at least two apertures that are in acoustic communication with the environment that is external of the housing wherein each aperture has an exterior port; a microphone capsule or element that is positioned in the housing, wherein the capsule or element has at least two openings that are connected to corresponding apertures; a protective material that covers the exterior port of each aperture, wherein the protective material comprises (a) a porous, hydrophobic membrane having a sufficiently small pore size to prevent the accumulation of moisture in and the entrance of water through the hydrophobic membrane, and (b) an air flow attenuating membrane having an effective thickness to reduce the turbulence of ambient wind impinging upon the exterior port.

In the inventive sound capturing device the protective membrane and preferably the porous, hydrophobic inner layer membrane thereof is directly against the microphone ports. The hydrophobic wind screen is adhered directly to the microphone housing and directly covers the external sound ports. A microphone capsule or element is contained within the housing preferably with two ports and is a pressure-difference element. The microphone preferably uses differential acoustic phase delays to develop a directional characteristic to the microphone sensitivity, in addition to having the rapid decrease in sensitivity with distance of a close-talking microphone, as described in U.S. Patent Application

Serial Number entitled "Ear Level Noise Rejection Voice Pickup

Method and Apparatus", filed June 30, 1998, bearing docket number 022577-405, which is incorporated herein by reference. Direct attachment of the protective membrane over the ports avoids the problems of reduction or elimination of the cancellation, causing a loss of the falloff rate, and the loss of the directional characteristic associated with prior art devices. The inventive microphone does not employ a "pad of air" between the external environment and the microphone ports as is required by the prior art, thereby producing a smaller, more compact and lighter assembly providing a water tight seal at the exterior port.

The invention will be described using a sound capturing system that includes a microphone housing having ports that pick up sounds and allows the sound to be transmitted by the system back to a remote location or processed for use by a hearing impaired user. It is understood that the invention is applicable to communication devices in general that employ microphones, particularly those devices which are used in situations where environmental conditions, e.g., high wind and moisture levels, will adversely affect conventional microphones that are not equipped with the inventive protective membrane. As used herein, the terms "microphone element" and "microphone capsule" are meant to be equivalent.

A sound capturing system 10 for capturing sound from a user, as shown in the exploded perspective view of FIG. 1, includes a body 12, and microphone 26. Body 12 includes a cable 20 for electrical connection to a communication device such as a telephone, multimedia device, or other transmitting and/or receiving device. The communication device to which the sound capturing system 10 is connected by the cable 20 may be a fixed device or a portable device which may be worn on the person. Although the invention has been illustrated with a cable 20 for connection to external electronics, the cable may be omitted for certain devices and a wireless link may be used. Alternatively, for a hearing aid device, the electronics may be entirely contained within the body 12. The body 12 includes a case portion 22 containing appropriate sound receiving and processing circuitry for a particular application. For example, the case portion 22 may contain a sound processing circuit, receiver and battery. The case portion 22 is configured to be received and concealed behind the ear of the user. An ear hook portion 24 of the body 12 extends from the case portion 22 and curves over the ear of the user. The ear hook portion 24 supports the body 12 securely on the user's ear. When the sound capturing system 10 according to the present invention is used as a communications device or hearing aid, a microphone 26 may be mounted on an upper surface of the ear hook portion 24. The microphone 26 picks up sounds and allows the sound to be transmitted by the sound delivery system back to a remote location or processed for use by the hearing impaired user.

A preferred sound capture system including microphones that are suitable for the present invention is described in the above cited patent application entitled "Ear Level Noise Rejection Voice Pickup Method and Apparatus" . Specifically, the sound capture system comprises a voice pickup device that is highly discreet, and which capture a user's speech with a high sound quality and a relatively large signal-to-ambient noise ratio. In an exemplary embodiment of the sound capture system, a standard miniature pressure gradient type microphone element is provided and mounted very close to the side of the user's head, preferably near the user's ear. The microphone element is oriented so that its direction of maximum sensitivity is parallel to the side of the user's head, and pointing as much as possible toward the user's mouth. In this fashion, the microphone element picks up the user's speech sounds as the sounds diffract and travel along the side of the user's face and head, to the microphone element. In another embodiment, a miniature pressure gradient type microphone element is provided with low pass networks formed using acoustic resistances at front and rear ports of the microphone, instead of delay networks. These resistances are matched by design with air volumes in the element, so that the resistances and the air volumes together act as acoustic low-pass networks that provide directional sound pickup properties that vary with frequency. These directional properties further enhance the noise-rejection capability of the microphone element.

Referring to FIG. 1, the microphone housing 26 includes front port 52 and back port 54 which are covered by protective membranes 62 and 64, respectively. The ports can have any cross-sectional configuration, e.g. , rectangular or circular. Typically, each port is circular with a diameter of about 25 mils to 50 mils and preferably about 35 to 40 mils.

A preferred device 60 for attaching the protective membranes onto the exterior surface of the microphone housing comprises a laminated structure comprising liner 66 having adhesive material (not shown) on its perimeter around protective membranes 62 and 64, as depicted in FIG. 1. As is apparent, the external surface of the housing in the proximity of the ports has a smooth convex contour. In this fashion the "band-aid" strip can be wrapped around the housing continuously without creating any significant crevices between the external surface of the housing and the inner layer of the protective membrane through which moisture can enter. The "band-aid" strip can be readily removed and replaced if it becomes worn or soiled.

Another method of attaching the protective membrane is to configure the protective membrane as a cap with an interior contour that matches the outer contour of the microphone housing. In this fashion, the cap of the protective membrane can be placed over the housing. The bottom perimeter of the cap may include a miniature draw cord, elastic band or metal clip to secure the cap.

Each of the protective membranes 62 and 64 of the band-aid strip that is in contact with ports 52 and 64, respectively, preferably comprises a bilayer laminate. The inner layer which faces the port is preferably a hydrophobic, porous material such as a fluorocarbon polymer having a pore size of about 2 μm to 4 μm and preferably about 2.5 μm to 3.5 μm. The thickness of the inner layer typically ranges from about 1 mil to 3 mils and more preferably from about 1.5 mils to 2.5 mils. A preferred material is a 2 mil thick polytetrafluoroethylene (TEFLON) having a pore size of about 3 μm. The inner layer is attached to an outer layer that is exposed to the environment and which is preferably a polymeric material that reduces the turbulent flow of wind as it reaches the port. The thickness of the polymeric material typically ranges from about 6 mils to 12 mils and preferably 8 mils to 10 mils. A preferred material is a 9 mils thick water resistant, non-woven polyester. A preferred bilayer laminate suitable for covering the ports is available as GORE-TEX ALL WEATHER VENTS from W.L. Gore & Assoc, Inc., Elkton, MD. The bilayer laminate is attached to the external surface of the microphone housing 26 with adhesive that is approximately 2.5 mils to 5.5 mils thick. As shown in FIG. 3, adhesive layer 66 binds the inner layer to the external housing but the adhesive layer should not extend over the port since the adhesive blocks the sound transmissive pores in the protective membrane and thus block the port. Preferably, the surface of the inner layer which is facing the port apertures covers the port apertures with essentially little or no gap space between the external surface of the microphone housing around the port and the inner layer of the laminate, as shown in FIG. 3. Essentially, the surface of the inner layer that covers the aperture is flush with the external surface of the microphone housing around the aperture.

For physical protection, the band-aid strip is preferably positioned into a recess on the external surface of the plastic housing. If this recess were planar, water could easily fill up the recess and block the port. Since the protective membrane of the band-aid strip wraps around a corner of the housing surface, the possibility for water to fill up the recess is reduced; the water simply rolls off and leaves the audio port unobstructed. If the protective membrane was placed on the inside of the housing, a small drop of water could easily block the port hole as in conventional designs, since the ports are small and water tends to be pulled in and held by capillary forces. This water blockage problem could also be solved by using a planar protective membrane on the outside of the microphone port, as long as the protective membrane was not placed into a recess. Not putting the protective membrane in a recess in many instances is impractical due to the lack of protection afforded the protective membrane and the tendency for the exposed edges to peel up. Also, it could allow water to bypass the membrane at the edges that will then wick into the port opening and block the ports.

FIGS. 2 A and 2B depict microphone housing 26 containing microphone capsule 86 which includes microphone components and circuitry (not shown) therein. The microphone capsule has ports 92 and 94 which are attachable to suspension elements 82 and 84, respectively. The suspension elements are made of flexible, resilient material, e.g., natural or silicone rubber, and they serve to support the microphone capsule inside the housing and at the same time acoustically and vibrationally isolate it from housing vibrations. Each suspension has a flange structure at the distal end which is configured to fit into grooves along the inner wall of the housing. FIG. 2B shows the microphone capsule/suspension element assembly as positioned inside the interior chamber 80. As is apparent, in capturing a user's speech sound waves will travel through the protective membrane and directly into the microphone through capsule ports 92 and 94 via housing ports 52 and 54, respectively. Interior chamber 80 is not in acoustic communication with the capsule ports and/or housing ports. Indeed, instead of being filled with air the interior chamber can be filled with a solid material, however, in this latter case, the microphone element would be subject to higher levels of vibrational disturbance. The interior chamber 80 serves only to isolate the microphone capsules from those vibrations.

The wind noise performance of the above described sound delivery system equipped with the protective membrane attached to a two external port microphone was evaluated in a 20 mph wind. Experimental data demonstrated that the wind noise was clearly and significantly reduced, and the wind noise was essentially eliminated in certain positions relative to the wind stream. Received speech intelligibility was dramatically improved with the protective membrane. Measurements were also made to evaluate the performance of the microphone acoustic system, with and without the protective membrane, in both wet and dry conditions. For these tests, the measured output signal came directly from the microphone element, with no equalization to flatten the response. The test was intended for measuring changes due to the membrane. Frequency responses were measured with a flat-frequency acoustic drive signal at 1 -meter directly in front of the "head". The "head" was a KEMAR mannequin, so the measured responses included all head and torso effects as well. The earpiece was placed on the right ear of the mannequin for these tests. This microphone system was designed for a telecommunications application where the frequency band being transmitted extends from 300 Hz to 3 kHz, so response deviations outside of this frequency band were not important FIG. 4 shows the frequency response of the microphone system, without the protective membrane in place. The bass rolloff shown in this graph can be eliminated by electronically equalizing the microphone amplifier, however, this correction was not done in the units tested.

FIG. 5 shows the polar plots, i.e., directionality characteristics of this same configuration. The polar data was taken at four octave-separated frequencies of 500 Hz, 1 kHz, 2 kHz and 4 kHz. All measurements had an accuracy of +2.5dB and were only reproducible down to about 250 Hz. Thus, any deviations within these tolerances are not significant.

FIGS. 6 and 7 are the frequency response and polar plots, respectively, for the same system but with the membrane protective "band-aid" strip in place. The membrane covered both microphone ports. For this test the protective membrane was dry. As is apparent, except for a slight decrease in sensitivity above 5 kHz, there is essentially no adverse effect on the microphone's performance. FIGS. 8 and 9 show the microphone's performance after thoroughly drenching the protective membrane with water spray. Visual inspection of the protective membrane revealed no water accumulation and comparison of the data to those in FIGS. 6 and 7 confirmed that there was no acoustic degradation. Finally, FIG. 10 is a frequency response graph comparing the curves from FIGS. 4, 6, and 8. A slight high frequency performance change is visible above the frequency band of interest when adding the protective membrane, but otherwise, there are no significant changes caused by the membrane material, whether wet or dry.

While the invention has been described in detail with reference to the preferred embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made and equivalents employed, without departing from the present invention.

Claims

Claims:

1. A sound capturing device that minimizes interference by ambient wind and water comprising: a housing having walls that have at least one aperture that is in acoustic communication with the environment external to the housing, and wherein each aperture has an exterior port; a microphone that is positioned in the housing; and a protective material that covers the exterior port of each aperture and that is exposed to the environment, wherein the protective material comprises (a) a porous, hydrophobic membrane having a sufficiently small pore size to prevent the accumulation of moisture in and the entrance water through the porous hydrophobic membrane, and (b) an air flow attenuating membrane having an effective thickness to reduce the turbulence of ambient wind impinging upon the exterior port.

2. The sound capturing device of claim 1 wherein the protective material has a non-planar outer surface.

3. The sound capturing device of claim 2 wherein the housing has an external surface adjacent each port which is convex.

4. The sound capturing device of claim 1 wherein the exterior wall surface adjacent each of the hole is non-planar.

5. The sound capturing device of claim 4 wherein the housing has an external surface adjacent each port which is convex.

6. The sound capturing device of claim 1 wherein the porous, hydrophobic membrane has a pore size that ranges from about 2 microns to 4 microns.

7. The sound capturing device of claim 1 wherein the porous, hydrophobic membrane comprises a fluorocarbon polymer.

8. The sound capturing device of claim 1 wherein the porous, hydrophobic membrane comprises polytetrafluoroethylene.

9. The sound capturing device of claim 1 wherein the porous, hydrophobic membrane faces and covers the external port of each aperture.

10. The sound capturing device of claim 1 wherein the air flow attenuating membrane comprises polyester.

11. The sound capturing device of claim 1 wherein the microphone is acoustically and vibrationally isolated in the housing.

12. The sound capturing device of claim 1 wherein the microphone is supported in the housing by a resilient material.

13. The sound capturing device of claim 1 wherein the housing comprises two oppositely located apertures.

14. A sound capturing device that suppresses the effects of wind and water disturbances comprising: a housing having walls that have at least two apertures that are in acoustic communication with the environment that is external of the housing with the at least two apertures, designated the first, second apertures and so on, with two of the apertures being located at opposite sides of the housing, wherein each aperture has an exterior port; a microphone capsule that is positioned in the housing, wherein the capsule has a first opening that is connected to the first aperture and a second opening that is connected to the second aperture; and a protective material that covers the exterior port of each aperture, wherein the protective material comprises (a) a porous, hydrophobic membrane having a sufficiently small pore size to prevent the accumulation of moisture in and the entrance of water through the porous, hydrophobic membrane, and (b) an air flow attenuating membrane having an effective thickness to reduce the turbulence of ambient wind impinging upon the exterior port.

15. The sound capturing device of claim 14 wherein the protective material has a non-planar outer surface.

16. The sound capturing device of claim 15 wherein the housing has an external surface adjacent each port which is convex.

17. The sound capturing device of claim 14 wherein exterior wall surface adjacent each of the hole is non-planar.

18. The sound capturing device of claim 17 wherein the housing has an external surface adjacent each port which is convex.

19. The sound capturing device of claim 14 wherein the porous, hydrophobic membrane has a pore size that ranges from about 2 microns to 4 microns.

20. The sound capturing device of claim 14 wherein the porous, hydrophobic membrane comprises a fluorocarbon polymer.

21. The sound capturing device of claim 14 wherein the porous, hydrophobic membrane comprises polytetrafluoroethylene.

22. The sound capturing device of claim 14 wherein the porous, hydrophobic membrane faces and covers the external port of each aperture.

23. The sound capturing device of claim 14 wherein the air flow attenuating membrane comprises polyester.

24. The sound capturing device of claim 14 wherein the microphone is acoustically and vibrationally isolated in the housing.

25. The sound capturing device of claim 14 wherein the first opening is connected to the first aperture by a first tubular member made of a resilient material and the second opening is connected to the second aperture by a second tubular member made of a resilient material.

26. The sound capturing device of claim 14 wherein housing comprises two oppositely located apertures.

27. The sound capturing device of claim 14 wherein the protective material comprises a fluorocarbon polymer layer.

28. A sound capturing device that minimizes interference by ambient wind and water comprising: a housing having walls that have at least one aperture that is in acoustic communication with the environment external to the housing, and wherein each aperture has an exterior port; a microphone that is positioned in the housing; and a protective material that covers the exterior port of the aperture and forms a water tight seal at the exterior port.

29. The sound capturing device of claim 28 wherein the protective material comprises a porous, hydrophobic membrane having a sufficiently small pore size to prevent the accumulation of moisture in and the entrance water through the porous hydrophobic membrane.

30. The sound capturing device of claim 28 wherein the protective membrane comprises an air flow attenuating membrane having an effective thickness to reduce the turbulence of ambient wind impinging upon said exterior port.