US3835263A

US3835263A - Microphone assembly operable in directional and non-directional modes

Info

Publication number: US3835263A
Application number: US00329673A
Authority: US
Inventors: M Killion
Original assignee: Industrial Research Products Inc
Current assignee: Knowles Electronics LLC
Priority date: 1973-02-05
Filing date: 1973-02-05
Publication date: 1974-09-10
Anticipated expiration: 1991-09-10
Also published as: DK149294C; ATA820273A; FR2216745B1; NL167832C; FR2216745A1; NL167832B; JPS49107723A; NL7317130A; DE2400666A1; DE2400666B2; AT332465B; CH587594A5; AU6048473A; GB1430200A; CA991738A; JPS5317444B2; DK149294B

Abstract

A microphone assembly being selectively operable in directional and non-directional modes; and, having similar response characteristics relative to frequency whether operating in one or the other mode.

Description

United States Patent 1191 1111 3,835,263 Killion 1 Sept. 10, 1974 MICROPHONE ASSEMBLY OPERABLE IN DIRECTIONAL AND NON-DIRECTIONAL [5 6] References Cited MODES UNITED STATES PATENTS [75] Inventor: Mead Clifford Killion, Elk Grove 3,770,911 11/1973 Knowles 179/107 S Village, lll.

. Primary Examiner-Ralph D. Blakeslee [73] Asslgnee. Industrial Research Products, Inc., Attorney, Agent, or Firm wilfred S. stone; Leo J Elk Grove Village, Ill. Aubel [22] Filed: Feb. 5, 1973 211 App]. No.: 329,673 [57] ABSTRACT A microphone assembly being selectively operable in directional and non-directional modes; and, having to [58] Field of Search..... 181/23; 179/107 FD, 107 s, w er peratmg m one e er 179/107 E, 107 H 15 Claims, 9 Drawing Figures PATENIEDSEPIOIW 3835 263 sum-1 nrg- I k vgi. J 10 Response in DB BACKGROUND OF THE INVENTION Various types of hearing aids are known which have non-directional or omni-directional response characteristics; and, other types of hearing aids are known which have directional response characteristics. Still other prior art hearing aids are known which can be utilized either as directional hearing aids or as nondirectional hearing aids by suitable modification of the structure. However, such other prior art hearing aids, which can be used either as directional or nondirectional devices have the marked disadvantage that when the aid is used as a non-directional aid, it 'will have a given response characteristic relative to frequency and when the aid is used as a directional device, it will have an entirely different response characteristic relative to frequency. For example, curve or response line A of FIG. 3 shows a typical response of a nondirectional device wherein the lower frequency portion of the curve is relatively flat and then drops off at the higher frequencies. Curve B shows the frequency response characteristics of a directional device wherein the frequency response rises from a low value as a relatively straight line to a maximum level and then drops off at the higher frequencies.

Accordingly, it is a principal object of the present invention to provide a microphone assembly particularly for use with hearing aids which assembly can be operated either in a directional or a non-directional mode, but which has essentially the same response characteristics relative to the frequency for sound arriving from the preferred direction whether it is operated in a directional or non-directional mode.

DESCRIPTION OF THE DRAWINGS FIG. 1 is an isometric view, partly cut away, of one embodiment of the inventive microphone assembly in accordance with the invention;

FIG. 2 is an isometric view of the microphone assembly positioned inversely or upside down relative to FIG. 1 to better show the closure element for the sound inlet;

FIG. 3 shows typical characteristic response curves of prior art directional and non-directional devices with the axis of ordinates indicating response in decibels and the axis of abscissas indicating frequency;

FIG. 4 shows another embodiment of the microphone assembly according to the invention mounted as in a behind-the-ear type hearing aid.

FIG. 5 is another embodiment of a microphone assembly in accordance with the invention;

FIG. 6 is another embodiment of a microphone assembly in accordance with the invention;

FIG. 7 is still another embodiment of a microphone assembly according to the invention; and,

FIGS. 8 and 9 are characteristic response curves useful in explaining the operation of the structure of FIGS. 5 and 6, with the axis of ordinates indicating response in decibels and the axis of abscissas indicating frequency.

DESCRIPTION OF THE INVENTION It should be understood at the outset that the present invention is generally applicable to head mounted hear- 2 ing aids, including the eye-glass mounted type, as indicated in FIGS. 1 and 2, and the behind-the-ear type such as shown in FIGS. 4 and 7.

FIG. 1 shows a microphone assembly 11 in accor- 5 dance with the invention mounted in the temple piece 12 of an eye-glass type hearing aid 10. The temple piece 12 includes a recess 13 formed therein in which a microphone capsule 15 is mounted on a suitable isolator pad 18 as is well known. The microphone capsule 15 includes an acoustically responsive diaphragm which is indicated by the dotted line 14, and a transducer assembly, not shown, which couples to the diaphragm. Both the diaphragm and the transducer are well known in the art. The recess 13 is formed in a rela tively inverted position; that is, the top of the recess may be integrally closed; and, sound openings or

sound inlets

17 and 19 may be formed in the bottom cover 16.

Sound inlets

17 and 19 are formed in spaced relation relative to the longitudinal axis of the temple piece 12 and hence, in a forward and aft direction relative to the wearer. I

' Sound inlets l7 and 19 are positioned to face downwardly for the purpose of permitting draining of the recess 13 to eliminate moisture or condensation from collecting therein, as well as to minimize-dust or dirt from entering the recess. The direction toward which the

sound inlets

17 and 19 face can be varied, the only restraint being that the inlets be aligned with the preferred direction of sound reception.

FIG. 2 shows an inverted view of FIG. 1 to better show the movable or slidable closure member 28 which selectively closes sound inlet 19, for purposes to be described.

The closure member 28 is slidably mounted on temple piece 12 and may be of any suitable type provided it is selectively adjustable to close and open the rear sound inlet 19. Other means, such as a plug, for covering or closing sound inlet 19 may be utilized in lieu of closure member 28.

As will be explained more fully, when sound inlet 19 is closed, the microphone assembly 11 operates as a pressure sensitive device having non-directional or omni-directional response. When sound inlet 19 is open, the microphone assembly 11 operates as a directional device having its most sensitive response to sound coming from a forward direction relative to the wearer; and, a minimum response to sound coming from some rearward direction relative to the wearer.

Referring both to FIGS. 1 and 2, microphone capsule 15 includes a first or front sound port 25 and a second or rear sound port 27.

Sound ports

25 and 27 convey sound to opposite sides of the diaphragm 14. The microphone capsule 15 could be of the type shown in, for example, US. Pat. No. 3,577,020 to Carlson et al., modified to have two inlet ports, which as mentioned above, communicate with opposite sides of the diaphragm 14.

One end of an elongated and sound conducting tube 21 connects to sound inlet 17 and the other end of the tube 21 connects to sound port 25. Tube 21 thus conducts or conveys the sound entering the sound inlet 17 directly to sound port 25 of microphone 15. The tube 21 has communication through an acoustical impedance 34 which may comprise an acoustical material mounted over the opening 33.

' The rear sound inlet 19 opens into an acoustical cavity 22 formed in the recess 13. In turn, the cavity 22 that is, as a pressure gradient microphone wherein the.

sound entering the two

spaced sound inlets

17 and 19 undergoes a phase shift to provide directional characteristics as explained in detail in US. Pat. application Ser. No. 273,943 titled Hearing Aid System filed on July 21, 1972, in the names of Hugh S. Knowles and Elmer V. Carlson and assigned to the same assignee as the present application, now US. Pat. No. 3,770,911.

Briefly sound coming from a given direction, say the frontal direction, or the left, as oriented in FIGS. 1 and 2 will be effective at sound inlet 17 to be coupled through tube 21 to sound port 25 of microphone capsule and the front side of diaphragm 14. At a discrete time period later, the same sound stimulus or bit of information will be effective at sound inlet 19 to be coupled through cavity 22 and the rear sound port 27 of microphone capsule 15 to the back or'rear side of the diaphragm 14. As in previous art, sound port 27 and microphone capsule 15 include an impedance element for providing a suitable phase shift or acoustical time delay to provide a directional response which is maximum in a frontal direction and minimal in a rearward direction.

Sound energy also couples from front sound inlet 17 through the parallel path comprising opening 33, passage 26, cavity 22 to rear sound port 27 and diaphragm 14. However, the relative acoustic impedances of the passageways between sound inlet 17 and acoustical element 34, and between sound inlet 19 and the acoustical element 34 are selected to be low relative to the acoustical impedance of the communication through acoustical element 34. Accordingly, the sound pressure at sound port 25 from sound entering inlet 17 is substantially unaffected by the presence of the element 34.

The converse is true for the effect of sound entering sound inlet 19. That is, element 34 effectively isolates or blocks sound entering sound inlet 19 from substantially affecting the sound pressure at port 25. In a similar manner, the sound pressure at port 27 is substantially unaffected by the presence of element 34.

Hence, in the directional mode of operation, the relative effect of sound entering sound inlet 17 and effective on the back side of the diaphragm 14 is minimal and, the effect of sound entering sound inlet 19 is maximal.

When the closure member 28 is moved to close or cover the rear sound inlet 19, the sound enters through front sound inlet 17 only; and, the microphone assembly 11 functions as a non directional or omnidirectional device.

In this non-directional mode of operation, sound enters front sound inlet 17 and passes normally through tube 21 and sound port 25 to the diaphragm 14. Sound which enters front sound inlet 17 also passes through opening 33, the acoustical impedance 34, passageway 26, cavity 22 and rear sound port 27 to be effective on the rear side of diaphragm 14. i

The value of the acoustical impedance in element 34 is chosen so that, in cooperation with cavity 22, it produces a phase shift or delay in the sound wave as it arrives at sound port 27 which is equivalent to the delay of the sound emanating from a forward direction in passing between

sound inlet

17 and 19 externally of capsule 15. Note that the cavity 22 provides essentially a rigidly closed tube which presents an acoustic reactance provided the dimensions of the cavity are small compared to the wavelength. For sound arriving from the frontal direction relative to the device, the differential sound pressure on diaphragm 14' is substantially similar whether the rear sound inlet 19 is open or closed. Note that sound arriving from an undesired direction will be relatively attenuated when inlet 19 is open. Thus, the inventive microphone assembly may be operated in either a directional or a non-directional mode without changing its frequency response characteristics for sound emanating from the front or desired direction. A principal feature of the invention is that if the microphone assembly of FIGS. 1 and 2 is operated in a directional mode, the response is substantially the curve, or line B of FIG. 3; and importantly, when the microphone assembly is operated in a non-directional mode, the response also follows the curve B.

FIG. 4 shows another embodiment of the inventive microphone capsule 35 mounted in a behind-the-ear type of hearing aid 36 within an acoustically transparent closure 40, which aid includes suitable amplifier means, receiver means, and battery; as labeled and well known in the art. The structure of the microphone assembly of FIG. 4 may be that as illustrated in FIGS. 5 or 6.

Refer now to FIG. 5. The microphone capsule 35 is also operable in a directional and non-directional mode and has similar frequency response characteristics whether operating in one or the other mode. Microphone capsule 35 comprises an assembly which in and of itself includes means for adjusting the directional and non-directional characteristics. The microphone capsule 35 can be mounted, for example, in an open recess of a hearing aid device as in FIG. 4, or it could be placed conveniently in a recess of an associated hearing aid housing such as in FIGS. 1 and 2, with the top cover 37 forming a part of the hearing aid housing.

The top cover 37 of the microphone capsule 35 has a short tube thereon which forms a front sound inlet 41 and a second short tube positioned in spaced relation to the first tube to form a rear sound inlet 43 therein. The tubes at

sound inlets

41 and 43 may be used as coupling tubes. Similarly, as mentioned above, the orientation of the microphone capsule 35 can be such that the

sound inlets

41 and 43 open downwardly or sidewardly, provided that a relatively fore and aft spacing exists between the

sound inlets

41 and 43 in order to obtain a response pattern with maximum directivity or sensitivity being in the desirable direction relative to the user or wearer.

For purposes of the following description, microphone capsule 35 will be considered to be mounted for operation in the orientation shown.

The microphone capsule 35 includes a suitable diaphragm 45 mounted to separate the microphone into a first sound cavity 47 and a second sound cavity 49. The first sound cavity 47 is contiguous with the front side or surface of the diaphragm 45 and cooperates with the front sound inlet 41. The second sound cavity 49 is contiguous with the back side of the diaphragm 45 and cooperates with the back or rear sound inlet 43. A removable plug 39 when inserted into inlet 43 prevents access of sound through sound inlet 43.

A bulkhead 51 is mounted to provide an acoustical seal between the upper and lower portions of the microphone assembly 35, except for an opening on its lower left side 53 which permits direct communication of sound inlet 41 to sound cavity 47.

An acoustical sealing flange or bulkhead 57 separates the space between the bulkhead and top 37 of microphone capsule 35 into essentially first or front chamber 54 and a second or rear chamber 56. A sound opening 59 is formed on flange 57 and a suitable acoustical impedance such as a cloth, screen material, a slit or porous material is positioned across or over opening 59. The diaphragm 45 is attached to any suitable transducer assembly, not shown, to energize the associated electronic circuitry as is well known in the art.

In operation, with the closure member 39 in its position shown in FIG. 5, the microphone capsule 35 functions as a directional microphone with maximum sensitivity or response to sound coming from a forward direction along a longitudinal line between

sound inlets

41 and 43. In this mode of operation, sound coming from the forward direction will enter the front sound inlet 41, and pass through to cavity 47 to be effective on the front side of the diaphragm 45. At a discrete time period later, the same bit of sound will enter the rear sound inlet 43 into cavity 56 and pass through sound port 55 into cavity 49 to be effective on the rear side of the diaphragm 45. Sound port 55 includes suitable acoustical impedance means to provide a phase shift or delay to sound passing therethrough thus providing a directional characteristic response. The relative acoustic impedances of the passageway between sound inlet 41 and acoustical element 59, and between sound inlet 43 and the acoustical element 59 are selected to be low relative to the acoustical impedance of the communication through acoustical element 59. Accordingly, the sound pressure in cavity 47 and on front of diaphragm 45 from sound entering sound inlet 41 is substantially unaffected by the presence of element 34. The converse is true for the effect of sound entering sound inlet 43. That is, element 59 effectively isolates or blocks sound entering sound inlet 43 from substantially affecting the sound pressure in cavity 47.

To operate the device of FIG. 5 in a non-directional mode, the closure member 39 is moved to close the rear sound inlet 43. In this mode of operation, sound is coupled to the diaphragm 45 only through sound inlet 41. Sound entering sound inlet 41 passes to front sound cavity 47 to be effective on the front side of the diaphragm 45. Sound entering front sound inlet 41 also passes through the acoustical impedance of sound opening 59 to rear chamber 56, through acoustical element 55, and rear cavity 49 to be effective on the back side of the diaphragm 45.

The opening 59 provides a relatively high acoustical impedance; hence, the phase shift provided by the acoustical impedance of opening 59 and chamber 56 can be selected to correspond to, or match, the phase shift of the sound moving externally of microphone capsule 35 between sound inlet 41 and sound inlet 43.

Stated differently, the impedance of opening 59 and the associated screen material is too high an impedance to significantly affect the sound pressure in chamber 56 while the sound inlet 43 is open. In the operating condition, where sound inlet 43 is closed however, the impedance provided by opening 59 and the associated screen material in combination with the impedance of chamber 56 provides the additional phase shift that the sound wave experiences in traveling from sound inlet 41 to sound inlet 43 in the free space externally of the microphone capsule.

'If chamber 56 is relatively large as compared to cavity 49, the performance of the microphone capsule 35 I is substantially the same as the microphones of FIGS. 1 and 2; that is, for sound arriving from the front there is minimal difference in the operating characteristics whether the microphone is operating in the directional or in the non-directional mode. If however, the chamber 56 is relatively small as compared to cavity 49, the transition fron one to the other mode will have an effect on the upper end of the frequency response characteristic. More specifically, in the latter case, the response of microphone capsule 35 is as shown in FIG. 8. That is, when microphone capsule 35 is operated in a directional mode, its performance is indicated by line D; and, its performance when it is operating in a nondirectional mode is given by the line N, which drops off at a lower frequency then line D.

Thus, as stated above, when the microphone capsule 35 is functioning in a non-directional mode with sound inlet 43 closed, the acoustical transmission in the path which may be traced from sound inlet 41, opening 59 and its acoustical resistance, chamber 56 and inlet port 55 to the back side of the diaphragm 45 substantially matches the frontally arriving sound entering through rear sound inlet 43, chamber 56 and rear sound port 55 when sound inlet 43 is open.

Another embodiment of the invention is shown in FIG. 6 wherein the microphone capsule is similar to the microphone capsule of FIG. 5. A principal modification of the structure of FIG. 6 with respect to that of FIG. 5 is that the closure means provided for closing the rear sound inlet 43A is different, and also the flange 57 and the included opening providing an acoustical impedance are eliminated. A further minor difference is that the sound inlets 41A and 43A do not include the associated short tubes. In FIG. 6, a pivotable vane 67 is mounted to be movable from a vertical position as indicated by the solid lines to a horizontal position as indicated by the dotted lines. Vane 67 can be adjustably positioned such as by suitable knob 69 to a vertical position to leave sound inlet 43A open, and to close or block sound from passing from front sound inlet 41A and chamber to sound port 55A. In this mode of operation, both sound inlets 41A and 43A are open and microphone 65 functions as a directional device as described above.

By adjustment of the knob 69, the vane 67 can be moved or positioned in its horizontal position or orientation to block sound from passing through rear sound inlet 43A. In this mode of operation, the microphone 65 functions as a non-directional device.

When vane 67 is in its horizontal position (labeled 67A), sound entering front sound inlet 41A passes through the passage or chamber 66 to the sound port 55A. Very little phase shift or time delay occurs in a passage such as this, which is not terminated so as to absorb appreciable energy. The total phase shift between the sound reaching the front of the diaphragm in cavity 47A and the rear of the diaphragm in cavity 49A is essentially that due to acoustical element over sound port 55A and cavity 49A. The result is some loss in the frontal sensitivity, but very little change in the frequency characteristic as illustrated in FIG. 9. In FIG. 9, the characteristic curve D is obtained with the microphone capsule 65 operating in a directional mode and characteristic curve N is obtained with the microphone capsule 65 operating in the non-directional mode. Curves D and N are similar in shape but represent different sensitivities. If the directional characteristic is a cardioid pattern this displacement operating in a nondirectional mode is approximately 6dB.

Still another embodiment of the invention is shown in FIGv 7 wherein a microphone capsule 75 is shown mounted in a suitable recess 77 in a behind-the-ear type hearing aid 70. The microphone capsule 75 inciudes a suitable diaphragm 86 similar to diaphragm 14 of FIG. 1. Capsule 75 is mounted on a suitable isolator pad 76. Recess 77 includesa cover or top 88 having a front sound inlet 79 and a rear sound inlet 81 formed thereon. A suitable closure member 84 is slidably movable toselectively open and close the rear sound inlet 81. The microphone 75 has a front sound port 83 communicating with one side of diaphragm 86 and a rear sound port 85 communicating with the other side of diaphragm 86, the latter port having a suitable acoustical impedance therein. a

An acoustical impedance member 91 is positioned in the space between the housing of the hearing aid and the microphone to thus divide the recess 77 into a frontal acoustical cavity 87 and a back acoustical cavity 89. Acoustical impedance 91 provides the same function as acoustical impedance 34 in FIG. 1. And, the operation of the device of FIG. 7 is basically the same as that described above for FIG. 1.

When the closure member 84 is in the position shown in FIG. 7, the device of FIG. 7 operates in a directional mode, and when the closure member 84 is moved to close rear sound inlet 81, the device of FIG. 7 operates in a non-directional mode.

The acoustical impedance 91 is selected, similarly as discussed above, to have minimal effect on the sound pressure in the two

cavities

87 and 89 when sound inlet 81 is open; and, to cooperate with cavity 89 to produce additional phase shift when sound inlet 81 is closed.

The structure of FIG. 7 conveniently permits making cavity 89 larger than that cavity 92 within microphone capsule 75 which latter cavity is located behind the acoustical element of sound port 85. The foregoing assures that there will be minimal difference in the sensitivity and frequency characteristic irrespective of the setting of closure 84.

While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

l. A microphone assembly selectively operable in directional and non-directional modes, comprising, in combination, diaphragm means positioned to have its front and back sides responsive to sound coupled thereto, at least two spaced sound inlets and at least two sound ports, means providing acoustical communication between said sound inlets and said sound ports, sound entering a first sound port being effective on the front side of said diaphragm, and sound entering a second sound port being effective on the back side of the diaphragm whereby said microphone assembly functions in a directional mode, means for selectively interrupting acoustical communication between the second sound inlet and the second sound port whereby said microphone assembly functions in a non-directional mode when communication between the second sound inlet and the second sound port is interrupted, and an acoustical communication path including an impedance means therein for controllably conveying sound from said first sound inlet to the second sound port to thereby obtain substantially the same response characteristics relative to frequency when the microphone assembly is operated in a directional as when it is operated in a non-directional mode.

2. A microphone assembly as in claim 1 further including an acoustical impedance positioned in said second sound port to provide an acoustical phase shift.

3. A microphone assembly as in claim 1 wherein the sound conveyed by said acoustical communication path to said second port and the other side of the diaphragm has minimal effect when said second sound inlet is open.

4. A microphone assembly as in claim 1 wherein adjustable vane means are provided for interrupting said acoustical communication.

5. A hearing aid microphone assembly selectively operable as a directional device and as a non-directional device comprising at least a pair of spaced sound inlets, a microphone having a diaphragm and at least two sound ports communicating to respectively opposite sides of a diaphragm, means for coupling sound from the first sound inlet to the first sound port, an acoustical communication path including an acoustical impedance means therein for controllably coupling sound from the first inlet to the second sound port, means coupling sound from the second sound inlet to the second sound port, and means for selectively closing and opening said second inlet to cause said hearing aid microphone assembly to function as a non-directional and a directional mode respectively, and the acoustical impedance of said acoustical communications path providing an acoustical match whereby said hearing aid microphone assembly develops substantially the same response characteristics relative to frequency whenit is functioning in a directional mode as when it is functioning in a non-directional mode.

6. A hearing aid as in claim 5 wherein said acoustical passage comprises an elongated tube having one end connected to a sound inlet of the housing and the other end connected to a first port of the microphone.

7. A microphone assembly comprising diaphragm means, first and second sound ports acoustically communicating with opposite sides of the diaphragm means, first and second sound inlets respectively communicating with the first and second ports, one of said sound inlets being selectively'openable and closeable to cause said microphone assembly to function as a directional and non-directional device respectively, and auxiliary acoustical communication path means including impedance means for enabling said microphone assembly to have substantially the same characteristic re- 9 sponse relative to frequency whether it is functioning as a directional or non-directional device.

8. A microphone assembly as in claim 1 wherein said microphone assembly is mountable on a head worn hearing aid and said openings are in a fore and aft relatively spaced relation, whereby by the maximum response sensitivity is in a direction toward the front of the wearer.

9. A microphone assembly as in claim 1 wherein the sound pressure level effective on the back side of the diaphragm from sound entering through one sound inlet is less than the pressure level effective on'the back side of the diaphragm from sound entering through the other sound inlet.

10. A microphone assembly as in claim 1 wherein the sound pressure level input from the second sound inlet to the second sound port is sufficiently high such that when there is acoustical communication therebetween, sound coupled from the first sound inlet to the second sound port has minimal effect.

11. A microphone assembly as in claim 1 comprising a housing, the diaphragm mounted in said housing to provide a front and back cavity, a bulkhead mounted in the housing to provide a distinct and separable sound communication paths between said sound inlets and said sound ports, an acoustical impedance in one of said paths and means including said bulkhead forming a chamber in said communication path and cooperating with said back cavity to effect the characteristic response of said assembly.

12. A microphone assembly as in claim 7 further including a chamber formed between said second sound opening and said second sound port, a cavity formed between said second sound port and said diaphragm means, said chamber being relatively small as compared to said cavity whereby the transistion from one mode to the other mode will have the effect of shifting the response characteristic at the upper end of the frequency range.

13. A microphone assembly as in claim 12 wherein the chamber is relatively large as compared to said cavity thereby providing a minimal difference in the operating characteristics whether the microphone is operating in the directional mode or in the non-directional mode.

14. A microphone assembly as in claim 7 including a first chamber between the front sound opening and the second sound port, vane means in said first chamber and operable to a first position for closing the rear sound opening to cause the microphone to operate in a non-directional mode, the vane means operable to a second position for closing the acoustical communication between the front sound opening and the rear sound port to cause the microphone to operate in a directional mode, a second chamber formed between the rear sound opening and the rear sound port when said vane means is in the second position whereby some loss in frontal sensitivity is realized when operating in a non-directional mode while the frequency response characteristic curves of the assembly for either mode remain substantially the same.

15. A hearing aid as in claim 5 wherein a first acoustical cavity is formed between said first sound opening and said first sound port, a second cavity is formed between said second sound opening and said second sound port, acoustical impedance means mounted between said sound cavities, and said microphone having an internal cavity formed behind the acoustical element of said sound port and assuring that the second cavity is substantially larger than the internal cavity thereby to assure that there is minimal difference in the sensitivity and frequency characteristics irrespective of the operating mode of the hearingaid.

Claims

1. A microphone assembly selectively operable in directional and non-directional modes, comprising, in combination, diaphragm means positioned to have its front and back sides responsive to sound coupled thereto, at least two spaced sound inlets and at least two sound ports, means providing acoustical communication between said sound inlets and said sound ports, sound entering a first sound port being effective on the front side of said diaphragm, and sound entering a second sound port being effective on the back side of the diaphragm whereby said microphone assembly functions in a directional mode, means for selectively interrupting acoustical communication between the second sound inlet and the second sound port whereby said microphone assembly functions in a non-directional mode when communication between the second sound inlet and the second sound port is interrupted, and an acoustical communication path including an impedance means therein for controllably conveying sound from said first sound inlet to the second sound port to thereby obtain substantially the same response characteristics relative to frequency when the microphone assembly is operated in a directional as when it is operated in a non-directional mode.

5. A hearing aid microphone assembly selectively operable as a directional device and as a non-directional device comprising at least a pair of spaced sound inlets, a microphone having a diaphragm and at least two sound ports communicating to respectively opposite sides of a diaphragm, means for coupling sound from the first sound inlet to the first sound port, an acoustical communication path including an acoustical impedance means therein for controllably coupling sound from the first inlet to the second sound port, means coupling sound from the second sound inlet to the second sound port, and means for selectively closing and opening said second inlet to cause said hearing aid microphone assembly to function as a non-directional and a directional mode respectively, and the acoustical impedance of said acoustical communications path providing an acoustical match whereby said hearing aid microphone assembly develops substantially the same response characteristics relative to frequency when it is functioning in a directional mode as when it is functioning in a non-directional mode.

7. A microphone assembly comprising diaphragm means, first and second sound ports acoustically communicating with opposite sides of the diaphragm means, first and second sound inlets respectively communicating with the first and second ports, one of said sound inlets being selectively openable and closeable to cause said microphone assembly to function as a directional and non-directional device respectively, and auxiliary acoustical communication path means including impedance means for enabling said microphone assembly to have substantially the same characteristic response relative to frequency whether it is functioning as a directional or non-directional device.

9. A microphone assembly as in claim 1 wherein the sound pressure level effective on the back side of the diaphragm from sound entering through one sound inlet is less than the pressure level effective on the back side of the diaphragm from sound entering through the other sound inlet.

15. A hearing aid as in claim 5 wherein a first acoustical cavity is formed between said first sound opening and said first sound port, a second cavity is formed between said second sound opening and said second sound port, acoustical impedance means mounted between said sound cavities, and said microphone having an internal cavity formed behind the acoustical element of said sound port and assuring that the second cavity is substantially larger than the internal cavity thereby to assure that there is minimal difference in the sensitivity and frequency characteristics irrespective of the operating mode of the hearing aid.