JPH04217199A - Directional microphone assembly - Google Patents

Abstract

PURPOSE: To provide a housing for a simple microphone element which can be easily handled. CONSTITUTION: A directional microphone assembly is composed of a primary gradient microphone element 200 including a diaphragm in a housing 110 made of an elastic material such as an EPDM. The housing is provided with channels 113 and 114 for transmitting a sound pressure from each opening parts 111 and 112 to each face of the diaphragm and the microphone element. A seal for preventing the sound pressure of one channel from being leaked to the other is formed at the outer periphery of the housing. A distance between the opening parts is made relatively large for improving the sensitivity and directivity of the microphone. Also, a directional microphone assembly is inserted in the outer face of an acoustic inputting device or attached to the back of the outer face so that the opening parts of the housing can be positioned at the outer face of the acoustic inputting device. A housing structural body made of the elastic material forms a seal in a space with the face of the acoustic inputting device.

Description

[Detailed description of the invention]

0001

FIELD OF THE INVENTION This invention relates to directional microphones, and more particularly to structures having one or more microphone elements.

0002

BACKGROUND OF THE INVENTION Microphones with directional characteristics are useful in many applications. One well-known method of obtaining directivity is the use of first-order gradient (FOG) microphone elements. It has a movable diaphragm with a front and back face enclosed within a capsule. The capsule has openings on each side of the capsule to receive sound pressure, which interacts with the front and rear surfaces of the diaphragm.

[0003] In response to this interaction, an electrical signal is generated, which is proportional to the sound pressure difference between the two sides (front and back) of the diaphragm. Sound coming from directions such that the wavefronts of the sound waves arrive at the front and back surfaces of the diaphragm simultaneously are ignored. In this case, the instantaneous sound pressure on each side of the diaphragm is the same, so the sound pressure difference is zero.

[0004] Sound coming from different directions arrives at one side of the diaphragm, but it arrives at the other side on both sides (front and back).
is delayed by propagating the effective path distance "d" between. This delay causes directivity, but this delay also affects the frequency response characteristics for the following reasons. That is, it is because the path distance "d" corresponds to a different fraction of the wavelength at each of the different frequencies. Low frequency responsivity is low because sound waves with virtually the same phase arrive at both sides (front and back) of the diaphragm at the same time.

US Pat. No. 3,715,500 to Sessler et al., filed on February 6, 1973.
Published on the 1st, this is a technology called unidirectional microphone. Sessler et al. disclose that connecting FOG microphone elements and tubing effectively increases the separation distance between acoustic ports. Although increasing the separation distance improves the low frequency response of the microphone, it is quite cumbersome to assemble and attach the disclosed structure to modern audio input devices.

US Pat. No. 4,742,548, issued March 3, 1988 to Sessler et al.
This technology is called a unidirectional secondary gradient microphone. In this patent, to increase the effective acoustic path distance between the acoustic ports of FOG microphones,
Sensitivity is improved by housing the FOG microphone in a baffle. The baffle preferably has a square or circular plane. Although this structure is an improvement over previous technology, it does not address the problem of conveniently mounting the FOG microphone to the audio input device due to its large physical size and protrusion from the audio input device. .

A known microphone device called WM-46AAD201 is commercially available from National/Panasonic (Matsushita Electric Industrial Co., Ltd.).
cardioid polar
) has sensitivity characteristics. The FOG microphone element is enclosed within a rigid, two-piece plastic housing. This housing transfers sound waves to the FO inside the housing.
G has an opening on each side to receive the microphone.

[0008] The housing and the FOG microphone are bonded together by adhesive or other bonding material, so that each side of the FOG microphone is affected only by sound waves entering the appropriate opening in the housing. Unfortunately, the construction of such devices is cumbersome due to the use of adhesives and additional steps requiring curing time. Furthermore, if the application method is bad,
This will cause leakage, resulting in a change in the acoustic directivity characteristics.

One useful directional microphone assembly that uses a tube to couple the microphone element to the desired acoustic pickup point is shown in FIG. This diagram was created by Knowles Electronics.
electronics, Inc. ) Technical Bulletin, TB-2
“EB Directional Hearing Aid Microphone Application Note” in 1
This is a quote from. Unfortunately, no structural means are provided to support such an assembly within the acoustic input device, and the tube does not appear to be easily sealed to the device surface.

0010

Accordingly, it would be desirable to provide a housing for a microphone element of relatively simple construction that is easy to manufacture and install.

It is further desired that a microphone assembly be essentially non-protruding and easily attachable to an audio input device while retaining the improved functionality achieved by Sessler et al.

0012

SUMMARY OF THE INVENTION A directional microphone assembly is comprised of a microphone element enclosed within a housing that is made from a sound insulating and resilient material. The microphone element includes a diaphragm that operates under the influence of sound pressure applied to its opposite sides and produces an electrical signal that is proportional to the sound pressure difference.

The housing has a first acoustic propagation channel for transmitting sound pressure from a first opening in the housing to one side of the diaphragm. The housing also has a second acoustic propagation channel for transmitting sound pressure from a second opening in the housing to the other side of the diaphragm.

In one embodiment of the invention, the housing is made of ethylene propylene diene monomer (EPDM).
It is a rubber-like material with elasticity. This creates a good seal around the microphone element, so that sound pressure from one channel does not leak to the other. Furthermore, this rubber-like material for the housing also forms a seal against the surface of the audio input device in which it is housed.

In the same embodiment, the housing is formed from two identical parts, which are joined in the area of the microphone element. In this example,
The use of adhesive materials is unnecessary for the following reasons. That is, each identical housing part can be joined to the microphone element with sufficient friction to connect the entire structure.

A feature of the invention is that the directional microphone assembly is conveniently inserted into or mounted behind the exterior surface of the audio input device such that the channel openings thereof are located on one or more sides of the audio input device. It is possible.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Pressure Microphone A single port microphone is capable of sensing instantaneous sound pressure at its input acoustic port and produces an electrical output voltage signal corresponding to the magnitude of the sound pressure. Such microphones are known as "pressure microphones" and are typically configured as shown in FIG. Acoustic port 101 introduces sound into microphone 100 which is transmitted to diaphragm 1
03 to generate a voltage.

The opposite side of the diaphragm 103 is a sealed area whose volume affects the compliance of the diaphragm. A pressure microphone responds equally to sounds coming from all directions, so its sensitivity pattern is omnidirectional. FIG. 5 shows the omnidirectional sensitivity pattern in the far field of a pressure microphone along with some associated characteristics. The information in Figure 5 was compiled using the following data. Namely, Knowles Electronics
ics, Inc. ) Technical Bulletin (Tech
This is the "EB Directional Hearing Aid Microphone Application Note" in TB-21 (Bulletin).

Primary Gradient Microphone Gradient microphones measure differential pressure across one or more diaphragms to obtain directional polar sensitivity characteristics. FIG. 2 shows a first order gradient (FOG) microphone 200 having input acoustic ports 201 and 202 on opposite sides of a diaphragm 203. FIG. These acoustic ports are separated by an effective distance d. From one acoustic port 201 to the other acoustic port 20
2, the sound wave must propagate this distance around the FOG.

The movement of diaphragm 203 is converted into voltage as the output of the microphone. The magnitude of the output voltage of a FOG microphone is a function of the instantaneous sound pressure difference across the diaphragm 203. The smaller the distance d, the more FO
The output voltage from the G microphone is also reduced. On the other hand, the speed of sound in air at 21° C. is 344 m/s, so an f=2250 Hz audible signal has a wavelength of approximately 15.24 cm.

Therefore, even if the separation distance (effective distance) between the acoustic ports is small, the acoustic ports 201 and 20
Since the phase difference between the two is sufficient, the FOG microphone exhibits a bidirectional polar sensitivity pattern, as shown in FIG. In fact, this polar sensitivity pattern is hardly affected by frequency, as shown in Equation 2 below. Here, the polarity of the output voltage is determined by the particular side of the diaphragm that the wavefront of the propagating sound wave first impinges on. FOG microphones also do not respond to sounds coming from certain directions, known as nulls. The present invention takes advantage of these properties. A FOG microphone element suitable for use in the present invention is the WM-55A103 manufactured by the Panasonic Division of Matsushita Electric Industrial Co., Ltd.

The separation distance "d" between the acoustic ports on either side of diaphragm 203 can be varied. In the far field, the pressure gradient Δp has the following relationship with “d”.

[0023]

[Math 1]

θ=polar direction of the impinging wavefront with respect to the microphone principal axis. C=propagation velocity Equation 1 is simplified as follows for small values of kd.

[0025]

[Math 2]

FIG. 4 shows the sensitivity or frequency response [Equation 1] of the FOG microphone when the direction θ=0°. It is known that the frequency response and directivity pattern can be changed by changing the gradient microphone itself. For example, as shown in FIG.
2, acoustic resistance Ra can be introduced. Such resistance changes both the directivity pattern and the frequency response.

More generally, FOs operating in the far field
The directivity pattern D(θ) associated with the G microphone is
When kd<1, it is given by the following relational expression.

[0028]

[Math 3]

In Equation 3, ρ is the density of air, V is the volume of the acoustic region on the back side of the diaphragm, and Ca is
The acoustic compliance (analogous to capacitance) between the diaphragm and the acoustic resistance Ra. From Equation 3, the cardioid sensitivity is obtained when B is set equal to 1. That is, the time constant RaCa is the distance "d" of the sound wave.
is set equal to the time it takes to propagate. FIG. 5 shows such a cardioid pattern and other characteristics of this particular FOG microphone.

Another well-known directivity pattern is supercardioid. This is obtained by adjusting d, Ra, and V such that B is equal to the square root of 3. If the value of B is further increased to 3, a hypercardioid directivity pattern is obtained. Each of the microphone directivity patterns selected and illustrated in FIG. 5 has its own set of characteristics. For example, (1) the position (angle) of the null, and (2) the distance factor, which indicates how many times the effective distance one directional microphone can obtain from the pressure microphone to the acoustic source. and a multiplier indicating that the directional microphone has the same signal to random incident noise ratio, (3) front to rear sensitivity ratio, etc.

FIG. 6 shows a prior art arrangement detailed in US Pat. No. 4,742,548. A baffle 205 surrounds the FOG microphone 200,
This increases the distance that the acoustic signal wavefront must travel to go from one side of the FOG microphone to the other by the baffle. This distance "d" is a parameter that directly affects the sensitivity and frequency of the associated microphone, and sometimes also affects the polar sensitivity characteristics. Unfortunately, this baffle must be oriented perpendicular to the plane of the acoustic input device, and the baffle shape must be retracted during the design of the acoustic input device, thereby reducing design flexibility. ability is limited.

FIG. 7 shows a flat housing 110 for a FOG microphone element. This housing 1
10 effectively extends the distance "d" between the acoustic ports of the FOG microphone elements disposed therein. This rectangular block structure is vulcanized (hardened)
It is molded from rubber or other suitable resilient material and is used in place of the baffle 205 shown in FIG. One suitable material available on the market is ethylene propylene diene.
There is a monomer (EPDM).

The housing 110 of FIG. 7 is made from a sound insulating material that does not transmit sound pressure as effectively as air. However, the housing 110 has openings 111, 112 for introducing sound pressure, and the sound pressure introduced from these openings passes through sound propagation channels 113, 114, where the microphone element 200 (see FIG. 8) is arranged. It is accepted into the cavity where it is located. Microphone element 200 has a set of wires 116 that extend from the housing through self-sealing holes 115.

Housing 110 is sized to form a seal with microphone element 200 so that sound pressure in one channel does not leak around the microphone element to the other channel. Thus, by using an elastic material for the housing, there is no need to use a sealing adhesive, which is advantageous. FIG. 8 is a cross-sectional view of the microphone/housing assembly, showing housing 110, FOG
The mutual arrangement of microphone 200, channels 113, 114, and apertures 111, 112 is shown.

FIG. 9 shows a portion of housing 110, which is made from two such identical parts. The junction 117 of these two parts is shown in FIG. When the part of the housing shown in FIG. 9 is joined to another identical part, a cavity is formed in the area surrounded by surfaces 118, 119. This cavity is illustratively cylindrical and sized to form a seal with the particular microphone element used.

Since EPDM is an elastic material, there is no need to use an adhesive material. This is because each identical housing part can be joined to the microphone element with sufficient frictional force, so that the resulting assembly can be held securely.

Application The present invention can be attached and applied to any acoustic input device using a directional microphone. Typical examples of audio input devices include tape recorders or telephone handsets. FIG. 10 shows one example application of the invention within a teleconferencing device. The teleconference device 130 is
A loudspeaker 131 and four directional microphone assemblies (11
0-1, 110-2, 110-3, 110-4).

Each microphone element is placed within a housing as shown in FIG. This microphone array provides full room coverage, which is very useful for conference calling applications. Since typically only one person speaks at a time, background noise and reverberation are minimized by only activating one microphone at a time. Circuitry within teleconference device 130 compares the output signals from each directional microphone assembly to determine which microphone assembly is sending the strongest signal.

FIG. 11 shows a teleconference device 130
FIG. 2 is a front view of the microphone housing, showing the position of 110-1 as a representative example of the microphone housing. As is clear from Figure 11,
This device is superior in that it is flat and compactly packaged. Housing 110-1, 110-2,
Four pockets are molded into the outer surface of the teleconference device 130 for attaching the teleconference devices 110-3 and 110-4. Each pocket is designed to be slightly smaller than the corresponding housing, which frictionally holds the housing in place.

[0040] The housing is held as described above by utilizing the elastic properties of the housing 110, but such elastic properties of the housing are also utilized when sealing the microphone element. The directional microphone is configured to be inserted into or mounted behind the exterior surface of the teleconference device 130 with its channel opening located on the exterior surface of the device. In this way, the housing is arranged unobtrusively. Additionally, the rubber housing 110 forms a seal with the surface of the teleconferencing device.

FIG. 12 shows another application of the invention. Here, microphone housing 110 is placed along one side of telephone 120. The telephone has a loudspeaker 121. This loudspeaker allows hands-free operation and is also known as a speakerphone. Housing 110 includes a primary gradient microphone element as shown in FIG.

The distance between the openings of the housing 110 improves sensitivity and narrows the microphone beam width.
This selects to form a supercardioid polar sensitivity pattern. A pocket is molded into the exterior of the phone for attaching the housing 110. This pocket is made slightly smaller than the housing, so that the housing is held within the pocket by frictional forces. Acoustic transmission materials may also be used to conceal the openings in housing 110.

Although specific embodiments of the invention have been described above, it is clear that further modifications are possible within the scope of the invention. Examples of such modifications include, for example, the use of elastic materials other than EPDM in the manufacture of the housing;
Examples of variations include the use of non-molded housings, housing openings that are not circular, or openings that are not flush. Of course, the present invention
The invention is not limited to the above embodiments and their modifications. Furthermore, instead of using a single FOG microphone element, the use of two electrically interconnected pressure microphones is also contemplated.

All of these are included within the spirit of the present invention. Note that the reference numerals used in the claims are for easy understanding of the invention and should not be construed to limit the technical scope thereof.

[0045]

As described above, the present invention provides an excellent microphone element housing that has a simple structure and is easy to manufacture and install.

[Brief explanation of the drawing]

FIG. 1 shows a pressure microphone element with omnidirectional polar sensitivity characteristics.

FIG. 2 shows a first order gradient microphone element as used in the present invention.

FIG. 3 shows a primary gradient microphone element with a restriction on one of its acoustic ports.

FIG. 4 is a diagram showing the frequency response of the microphone shown in FIG. 2;

5 is a table showing the characteristics associated with the microphone of FIG. 3 for different values of B; FIG.

FIG. 6 shows a secondary gradient microphone with improved sensitivity due to the use of baffles according to the prior art.

FIG. 7 is a perspective view of a preferred structure housing a primary gradient microphone element.

FIG. 8 is a plan view of the housing of FIG. 10;

FIG. 9 is a perspective view of the structure of FIG. 7;

FIG. 10 is a top view of a teleconference device using a primary gradient microphone according to the invention.

11 is a front view of the teleconference device of FIG. 10. FIG.

FIG. 12 is a perspective view of a loudspeaker telephone using a primary gradient microphone according to the present invention.

[Explanation of symbols]

100 Microphone 101 Acoustic port 103 Diaphragm 110 (110-1 to 110-4) Microphone housing (microphone assembly) 111 Opening 112 Opening 113 Channel 114 Channel 115 (self-sealing) hole 116 Wire 117 Joint (area) 118 Surface 119 Surface 120 Telephone 121 Loudspeaker 130 Teleconference device 131 Loudspeaker 200 Microphone (element) 201 Acoustic port 202 Acoustic port 203 Diaphragm 205 Baffle 300 Microphone 301 Acoustic port 302 Acoustic port 303 Diaphragm

Claims (7)

[Claims] 1. A directional microphone assembly having a microphone element (200) enclosed within a resilient housing (110), wherein the microphone element (200) has a diaphragm (203).
), the diaphragm has a function of responding to a sound pressure difference between the two sides of the diaphragm and generating an electric signal proportional to the sound pressure difference, and the housing (110) having elasticity includes: (1) a housing (110); The first opening (111
) to one side of the diaphragm (203); (2) a second opening (112) in the housing to one side of the diaphragm (203);
3), and the housing is formed from a sound insulating material, thereby making the first and second
directional microphone assembly, characterized in that the channels (113, 114) have the function of increasing the path distance (d) between the opposite sides of the microphone element (200), improving the sensitivity and directivity of the microphone. . 2. The resilient housing (110) holds the microphone element (200), and
A directional microphone assembly according to claim 1, characterized in that the microphone element (200) forms a continuous seal around its outer periphery so as not to transmit the sound pressure of one channel to the other. 3. The resilient housing (110) is formed from a set of identical structures, these structures comprising:
The area where the microphone element (200) is held (
3. The directional microphone assembly of claim 2, wherein each structure has one channel and one aperture molded into the structure. 4. The resilient housing (110) is made of ethylene propylene diene monomer (EPDM).
) The directional microphone assembly according to claim 2, wherein the directional microphone assembly comprises: 5. A directional microphone assembly having an attached acoustic input device having an exterior surface, the directional microphone assembly having an attached acoustic input device inserted into or positioned immediately after the exterior surface of the acoustic input device; Directivity according to claim 2, characterized in that it has a function of forming an acoustic input device having a flat outer shape with improved microphone sensitivity and directivity by forming a seal between the input device and the input device. Microphone assembly. 6. The directional microphone assembly of claim 5, wherein the acoustic input device comprises a telephone (120). 7. Directional microphone assembly according to claim 5, characterized in that the acoustic input device comprises a teleconferencing device (130).