JP2893756B2 - Microphone device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Industrial Field of the Invention The present invention uses a pair of microphone units, and based on the outputs of these microphone units, a first and a second.
And a microphone device for obtaining a signal of a channel of

B. Summary of the Invention The present invention uses a pair of omnidirectional microphone units, the diaphragms of these microphone units are arranged on the same plane, and the output from these microphone units is subjected to predetermined signal processing to perform a first signal processing. By obtaining the signal of the second channel, sufficient vibration isolation can be performed with a simple configuration, and good characteristics can be realized as a stereo microphone device, miniaturization of the device itself and simplification of manufacture can be achieved. And a microphone device.

C. Prior Art Conventionally, there has been proposed a stereo microphone device configured to discriminate and detect a sound wave incident from the front left and a sound wave incident from the front right to obtain an audio signal constituting stereophonic sound.

As such a microphone device, there is one configured using a pair of microphone units having a single directivity. As shown in FIG. 8, this microphone device has a pair of first and second microphone units M _A and M each having unidirectionality as shown by hatching in FIG.
_B is arranged such that the directional axes P _A and P _B have certain angles θ _L and θ _R with respect to the central axis. In this microphone device, the first microphone unit M _A
The output of more is obtained from the output terminal L as the main detection signal of the sound waves incident from the left front, the transmitted sound wave output from the second microphone unit M _B is incident from the right front as primarily detected signal Obtained from the output terminal R.

Further, as shown in Figure 7 which is a combination of the second microphone unit M _S having a first microphone unit M _M and bidirectivity having unidirectional as indicated by oblique lines respectively in FIG. 7 An MS (midside) type stereo microphone device has been proposed. The microphone device MS method, the directional axes P _M of the first microphone unit M _M directivity axis P _S of the second microphone unit M _S is arranged so as to be perpendicular to each other.

Incidentally, at the output of the second microphone unit M _S, the output when it detects a sound wave which enters from the output and right at the time of detecting the sound waves incident from the left, it has a signal of opposite phases , the output in detecting the sound waves incident from the left have been made to the first microphone unit M _M output the same phase in this example.

Then, in this microphone device, the sum signal output and is added by the adder 101 the output of the first microphone M _M and the second microphone unit M _S is obtained from the output terminal L as the first signal. Also, in the microphone unit, the output of the second microphone unit M _S from the output of the first microphone unit M _M is subtractors
The difference signal subtracted by 102 is obtained from the output terminal R as a second signal.

The first signal thus obtained is a signal mainly detecting the sound wave incident from the front left, and the second signal is a signal mainly detecting the sound wave incident from the front right. It has become. That is, these first and second signals, a same directional and directional axes is detected so as to form a reverse angle to each other with respect to the directional axes P _M of the first microphone unit M _M Corresponding to the output signal.

D. Problems to be Solved by the Invention By the way, since the microphone device as described above uses a unidirectional microphone unit, it is difficult to reduce the size of the device itself.

In other words, the microphone unit includes a diaphragm vibrated by the collected sound. However, as shown in FIG. 8, in the unidirectional microphone unit 103, the directional axis P is perpendicular to the diaphragm 104. It has become. As shown in FIG. 8, the diaphragm 104 has a disk-like shape having a diameter Φ equal to or greater than a certain length in order to realize sufficient sound collection sensitivity and frequency characteristics of the microphone unit 103. Is formed. Diameter of this diaphragm Φ
Is approximately 5 mm or more in electret condenser type microphone units. further,
In the unidirectional microphone unit 103, the length l in the direction of the directing axis P of the support plate 105 that supports the diaphragm 104 cannot be less than a certain length in order to achieve a predetermined directivity.

Therefore, the unidirectional microphone unit 103
Is housed in the housing 106.
As shown in FIG. 9, when the center of the left and right directional axes P _A and P _B is the front side, the thickness t of the housing 106 cannot be smaller than the diameter of the diaphragm. Also, this microphone device
The width and depth of the housing 106 cannot be less than a certain length.

When a microphone device as described above is incorporated in a recording device such as a tape recorder or a video tape recorder, a space for accommodating the microphone device is required, and it is difficult to reduce the size of the device.

In addition, the microphone unit constituting the above-described microphone device obtains directivity by the phase difference of sound waves incident on two sound terminals of the front sound hole and the back sound hole of the microphone unit, and thus the microphone unit can be freely used. It is necessary to dispose it close to the sound field, and it is necessary to consider acoustically the mounting structure of the housing and the microphone unit, which makes designing and manufacturing difficult.

And, as described above, the microphone device configured by using the unidirectional microphone unit easily detects mechanical vibration as noise. That is, noise due to vibration has many low frequency components, and in this low frequency band, a unidirectional microphone unit is more sensitive to vibration than a omnidirectional microphone unit. Here, assuming that the vibration acceleration is α and the output of noise due to vibration is E _V , the vibration sensitivity S _V is represented by S _V = E _V / α. Moreover, the sound pressure of p, when an output obtained by detecting the sound pressure and E _P, sound pressure sensitivity S _P is represented by S _P = E _P / p. And the ratio S _V / S _{P of} vibration sensitivity and sound pressure sensitivity
Is S _V / S _P = m (1 + jkda) / s (1 + jkda-e- ^jkd )
It can be shown by the first equation. In this first formula, m is the effective mass of the diaphragm of the microphone unit, s is the effective area of the diaphragm, and k is the ratio of the angular frequency and the speed of sound to be detected (angular frequency / sound speed). , D is the acoustic effective distance between the two acoustic terminals (front and rear sound holes) of the microphone unit, and a is a coefficient determined by the directivity of the microphone unit. a = ∞, a = 1 for unidirectionality, and a = 0 for bidirectionality. When a = ∞, S _V / S _P = m / s (2)

Then, the the first formula, the S _V / S _P unidirectional microphone unit is as shown in FIG. 5 in r _1, S _V / S _P omnidirectional microphone unit, the R _{2 in} Fig. 5
It becomes as shown in. As is clear from FIG. 5, since the S _V / S _P of the unidirectional microphone unit is larger than the S _V / S _{P of the} omnidirectional microphone unit, the unidirectional microphone unit is It can be seen that the microphone unit is more sensitive to vibration than the omnidirectional microphone unit.

Thus, a unidirectional microphone unit is
When mounted on a portable recording device such as a tape recorder or video tape recorder, it is necessary to provide an anti-vibration mechanism so that vibration is not transmitted to this microphone unit. It is difficult to simplify the configuration.

Therefore, the present invention has been proposed in view of the above situation, and can be used as a stereo microphone device, and can be reduced in size and simplified in configuration.
It is an object of the present invention to provide a microphone device that is easy to design and manufacture, has good vibration resistance, and can simplify a vibration isolation mechanism when attached to another device.

E. Means for Solving the Problems In order to solve the above problems and achieve the above objects, a microphone device according to the present invention includes a pair of omnidirectional microphone units, and these microphone units are arranged on the same plane. The output from the first microphone unit is subtracted from the output from the second microphone unit that has been subjected to predetermined signal processing to obtain a signal of the first channel, and the signal from the second microphone unit is obtained. The output of the first microphone unit, which has been subjected to predetermined signal processing, is subtracted from the output to obtain a second channel signal.

F. Operation In the microphone device according to the present invention, signals of the first and second channels are obtained based on outputs from a pair of omnidirectional microphone units. These first and second
Channel signals can be used as left and right channel signals.

G. Examples Hereinafter, specific examples of the present invention will be described with reference to the drawings.

As shown in FIG. 1, the microphone device according to the present invention includes a pair of first and second microphone units M ₁ and M ₁ .
_{It has two} . The first and second microphone units M ₁ and M ₂ are omni-directional microphone units, and are arranged at a fixed distance D from each other as shown in FIG.

Then, the first microphone unit M ₁ is output from the microphone unit M ₁ The first obtained by detecting the acoustic waves is input to the first non-inverting input terminal of the subtracter 1. The output from the _first microphone unit M ₁ is input to the inverting input terminal of the second subtractor 3 via the first delay circuit 2.

On the other hand, the second microphone unit M ₂ is output from the second microphone unit M ₂ obtained by detecting the acoustic waves is input to the non-inverting input terminal of the second subtractor 3.
The output from the _second microphone unit M2 is input to the inverting input terminal of the first subtractor 1 via the second delay circuit 4.

Then, a signal of the first channel is obtained through the output terminal 5 of the first subtractor 1, and a signal of the second channel is obtained through the output terminal 6 of the second subtractor 3.

Here, sound pressure sensitivity SP ₁ of the first channel _{signal, SP 1 = S 1 -S 2} e -j (kDcosθ + φ) represented by ... third equation. In the third equation, S ₁ is the sound pressure sensitivity of the first microphone unit M ₁ , S ₂ is the sound pressure sensitivity of the second microphone unit M ₂ , and D is the first and second microphone units. Is the incident angle of the sound wave to the first and second microphone units as shown in FIG. 1, and φ is the delay amount in the second delay circuit 4 as the phase delay angle of the sound. Value.

In this microphone device, the sound pressure sensitivity S ₁ of the _first microphone unit M ₁ and the second microphone unit
M2 and sound pressure sensitivity S ₂ of equal, the phase delay angle phi phi = kD
Then, in the frequency band of kD <1, the third equation is approximated as SP ₁ ≒ jkDS ₁ (Cos θ + 1)... The sound pressure sensitivity expressed by the fourth equation is
As shown by P ₁ in FIG. 2, the first microphone unit M ₁ and the second line connecting the microphone unit M ₂ and directional axes, a single of the first microphone unit M ₁ a front side It corresponds to directivity.

Similarly, the sound pressure sensitivity SP of the signal of the second channel
₂ is represented by SP ₂ = S ₂ −S ₁ e− ^{j (kDcos θ + φ)} ... In the fifth equation, φ is a value indicating the amount of delay in the first delay circuit 2 as a phase delay angle of sound. Then, the fifth equation is approximated as in the third equation as follows: SP ₂ ≒ jkDS ₁ (1-Cos θ)... The sound pressure sensitivity represented by the sixth equation is
As indicated by P ₂ in FIG. 2, the axis connecting the first microphone unit M ₁ and the second microphone unit M ₂ and directional axes, a single of the second microphone unit M ₂ and the front side It corresponds to directivity.

As described above, since the signals of the first and second channels obtained in this microphone device have unidirectionality with the opposite sides facing the front, this microphone device is used as a stereo microphone device. be able to.

Since the frequency characteristics of the signals of the first and second channels have a slope indicated by, for example, 6 dB / Oct, the frequency characteristics are corrected by using a predetermined frequency characteristic correction circuit as necessary. Is corrected to be used as a left channel signal and a right channel signal.

In the microphone device according to the present invention configured as described above, the first and second microphone units are provided.
Since M ₁ and M ₂ have omnidirectionality, the microphone units M ₁ and M ₂ are supported such that the directions of the diaphragms 8 a and 8 b of the microphone units M ₁ and M ₂ are the directions shown in FIGS. 3 to 5. It can be arranged to be supported by the member 7. That is, the first and second microphone units M ₁ and M ₂ are arranged such that the diaphragms 8a and 8b are on the same plane as shown in FIG. In this microphone device, the first and second microphone units M ₁ and M ₂ are arranged at desired positions according to the shape and structure of a device main body such as a tape recorder or a video tape recorder to which the microphone device is attached. be able to.

Then, as shown in FIG. 3, the microphone device is configured such that each of the diaphragms 8a and 8b is parallel to a line connecting the first and second microphone units M ₁ and M ₂ and these microphone units M ₁ and M ₂ are connected to each other. Since the microphone units are arranged, the thickness T of the microphone device can be substantially equal to the thickness of the microphone units M ₁ and M _{2 in} the direction orthogonal to the diaphragms 8a and 8b, as shown in FIG. The thickness of the device can be reduced. In addition,
The thickness of the omnidirectional microphone unit can be approximately 2 mm or less.

Further, as shown in FIG. 4, the microphone device is arranged such that the first and second microphone units M ₁ and M ₂ are arranged so that the respective diaphragms 8 a and 8 b are in the same direction as each other, and are integrally formed. When it is configured to be supported by the support member 9 that is configured in a structured manner, detection of mechanical vibration as noise can be further reduced. That is, in this case,
Vibrations of the diaphragms 8a and 8b due to mechanical vibration applied from the outside of the apparatus have the same frequency and the same phase. First
If the effective areal densities m / s of the diaphragms 8a and 8b of the second microphone units M ₁ and M ₂ are made equal to each other, the vibration sensitivity of the omnidirectional microphone unit becomes _V = since (m / s) is S _P · · · seventh equation, vibration sensitivity S _V1 of the first channel _{signal, S V1 = (m / s} ) (S 1 -S 2 e -jφ ) ... can be expressed by the following equation (8). The ratio S _V1 / S _{P1 (0) of the} vibration sensitivity S _V1 and the sound pressure sensitivity S _{P1 (0)} on the front side when θ = 0.
Is S _V1 / S _{P1 (0)} = m (S ₁ −S2e− ^jφ ) / s (S1−S2e
^{−j (kD + φ)} )... And first and second microphone units
Assuming that the sound pressure sensitivities S ₁ and S ₂ of M ₁ and M ₂ are equal to each other, the ninth equation is as follows: S _V1 / S _{P1 (0)} = m (1−e− ^jφ ) / s (1−e
^{−j (kD + φ)} )...

Here, if the phase delay angle φ is φ = kD, the vibration sensitivity
S _V1 and sound pressure sensitivity S _{P1 (0)} ratio of S _V1 / S _{P1 (0),} in the low frequency band of kD <1, from the equation (10), in FIG. 5
As shown by r0, this is lower than that of a unidirectional microphone unit or an omnidirectional microphone unit.

Therefore, when this microphone device is attached to a device main body such as a tape recorder or a video tape recorder, it can be supported by a simple supporting mechanism that does not require much anti-vibration characteristics. This microphone device is particularly suitable for use in devices such as portable tape recorders and video tape recorders, and can simplify the configuration of devices using this microphone device.

H. Effects of the Invention As described above, in the microphone device according to the present invention, signals of the first and second channels are obtained based on outputs from a pair of omnidirectional microphone units. Since these first and second channel signals can be used as left and right channel signals, this microphone device is used as a stereo microphone device.

The omnidirectional microphone unit constituting the microphone device is easier to design and manufacture than the unidirectional microphone unit, so that the microphone device itself is easier to design and manufacture.

Further, in this microphone device, since a pair of omnidirectional microphone units are arranged on the same plane, the size and thickness of the device using the microphone device itself can be reduced.

Furthermore, the omnidirectional microphone unit has higher vibration resistance than the unidirectional microphone unit,
When attaching the microphone device to another device, the vibration isolating mechanism that supports the microphone device can be simplified.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a microphone device according to the present invention, and FIG. 2 is a graph showing directional characteristics of the microphone device. FIG. 3 is a schematic diagram showing directions of diaphragms of a microphone unit which is a main part of the microphone device, and shows a state where the respective diaphragms are arranged on the same plane. FIG. 4 is a sectional view showing a configuration for obtaining good vibration resistance in the microphone device. FIG. 5 is a graph showing the ratio of vibration sensitivity to sound pressure sensitivity in the microphone device, the unidirectional microphone unit, and the omnidirectional microphone unit. FIG. 6 is a plan view showing a conventional microphone device,
FIG. 7 is a plan view showing another example of the conventional microphone device, FIG. 8 is a side sectional view showing a unidirectional microphone unit constituting the conventional microphone device, and FIG. FIG. 2 is a perspective view showing the microphone device of FIG. M ₁ first microphone unit M ₂ second microphone unit 1 first subtractor 2 first delay circuit 3 second subtractor 4 second delay circuit

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-59-64994 (JP, A) JP-A-60-22897 (JP, A) JP-A-55-91292 (JP, A) 87121 (JP, U) Japanese Utility Model Application 57-109687 (JP, U) Japanese Utility Model Application 57-181186 (JP, U) (58) Fields investigated (Int. Cl. ⁶ , DB name) H04R 3/00 320 H04R 1/40 320 H04R 5/027

Claims (2)

(57) [Claims] 1. A microphone device comprising: a pair of omnidirectional microphone units; wherein the diaphragms of the pair of microphone units are arranged so as to be in the same direction on the same plane, and a predetermined signal is output from an output from the first microphone unit. A first channel signal is obtained by subtracting the output from the processed second microphone unit to obtain a signal of the first channel, and performing the predetermined signal processing from the output from the second microphone unit. A microphone device configured to obtain a signal of the second channel by subtracting the output of the microphone. 2. The microphone device according to claim 1, wherein said predetermined signal processing is a phase delay processing.