JP2017098707A - Flat directional microphone - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a microphone capable of securing flat directivity within a practical band.SOLUTION: The microphone comprises: a unit pair U which includes two microphone units Ma and Mb having bi-directionality and in which the microphone units Ma and Mb are disposed in such a manner that orientation axes are orthogonal to each other; and a phase difference demultiplexer which outputs signals from the unit pair U to a hot-side terminal and a cold-side terminal in such a manner that a phase difference at 90 degrees can be obtained. The phase difference demultiplexer consists of a multistage shift circuit configured by connecting in series a plurality of shifters. For the shifters, frequencies in which the input/output phase difference becomes 90 degrees are different.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an improvement of a flat directional microphone having a flat directivity that is wide in the horizontal direction and narrow in the vertical direction.

For example, when a speaker moves in a horizontal direction, such as a conference or lecture, or in a state where a wide sound field is formed in a horizontal direction, such as an orchestra, the horizontal direction is wide and the vertical direction A flat directional microphone having a flat directivity that is very narrow is suitable.
Such flat directional microphones are disclosed in, for example, Patent Document 1 and Non-Patent Document 1.

According to the microphone disclosed in Patent Document 1, two ribbon microphone units having bidirectionality are used, and these ribbon microphone units are arranged in a state in which the directional axes intersect each other by 90 degrees. The output of the ribbon microphone unit is electrically connected in series, and the output added by the series connection is provided as an audio signal via a 90-degree phase shift circuit.
As a result, a flat directional microphone having a three-dimensional donut-shaped directional characteristic that is wide in the horizontal direction and narrow in the vertical direction can be obtained.

  Incidentally, the 90-degree phase shift circuit used in the flat directional microphone disclosed in Patent Document 1 is configured by a combination of a coil and a capacitor. Therefore, according to the phase shift circuit described above, the phase shift characteristic of 90 degrees within the voice band is obtained only at one point of the resonance frequency determined by the combination of the coil and the capacitor, and in a region other than the resonance frequency, A phase shift characteristic of 90 degrees cannot be obtained.

Therefore, according to the microphone disclosed in Patent Document 1, it is possible to obtain an ideal flat directivity that is wide in the horizontal direction and narrow in the vertical direction at only one point of the above-described resonance frequency, and deviates from this specific resonance frequency. In the frequency band, an ideal flat directivity cannot be obtained.
In other words, there is a technical problem that it is difficult to ensure flat directivity within the entire range of a practical band that collects a human voice.

On the other hand, according to the microphone KEM970 disclosed in Non-Patent Document 1, a large-scale microphone array composed of a large number of microphone units is used, and this microphone array and a signal processing circuit using DSP (Digital Signal Processing) are accompanied. .
Therefore, according to the microphone KEM970, since a large-scale microphone array is necessary and a signal processing circuit using a DSP is accompanied, the size is inevitably increased, and an increase in cost cannot be avoided.

US Pat. No. 2,539,671

MICROTECH GEFELL Microphone KEM970 introduction article Internet <URL: http://www.microtechgefell.de/index.php/en/microphones/livesound-a-installation/table-a-ceiling-microphones/439-kem870> [Heisei Search on November 13, 2015]

The present invention has been made paying attention to the technical problems described above, and can ensure flat directivity at least in a practical band that targets at least a human voice. It is an object to provide a microphone.
In addition, it is an object of the present invention to provide a flat directional microphone that can be reduced in price and size without using a signal processing circuit such as a large-scale microphone array or DSP.

  A flat directional microphone according to the present invention, which has been made to solve the above-described problems, includes two microphone units having bi-directionality, and a pair of units arranged so that the directional axes of the microphone units are orthogonal to each other. Each of the signals from the unit pair is output to the hot side terminal and the cold side terminal so as to obtain a phase difference of 90 degrees, and the phase difference wave It is characterized by comprising a multistage transfer circuit in which a plurality of transferers having different frequencies at which the input / output phase difference is 90 degrees are connected in series.

  In this case, in a preferred embodiment, the multistage between the one microphone constituting the unit pair and the hot side terminal and between the other microphone constituting the unit pair and the cold side terminal. A configuration provided with each transfer circuit is adopted.

  The microphone constituting the unit pair used in the flat directional microphone according to the present invention is preferably a combination of a condenser microphone unit or a combination of a ribbon type microphone.

  Further, a preferred form of the transfer device constituting the multi-stage transfer circuit includes a first resistor and a second resistor, one end of which is commonly connected to the inverting input terminal of the operational amplifier, and one end of the non-inverting input terminal of the operational amplifier. Are connected in common, and the other ends of the first resistor and the third resistor are connected in common to form the input terminal of the transfer device, and the output terminal of the operational amplifier is transferred The other end of the capacitor is grounded, and the other end of the second resistor is connected to the output terminal of the operational amplifier.

  In this case, it is desirable that the first resistor, the second resistor, and the third resistor have the same resistance value.

  According to another preferable embodiment of the transfer device constituting the multistage transfer circuit, an active element that generates signals in opposite phases at the second terminal and the third terminal by a signal supplied to the first terminal, A first resistor and a second resistor having one end commonly connected to the second terminal; a third resistor having a first end commonly connected to the third terminal of the active element; and a capacitor. The other ends of the three resistors are connected between the DC power sources, the first terminal of the active element constitutes the input terminal of the transfer device, and the other ends of the second resistor and the capacitor are connected in common. The output terminal of the transfer device is configured.

  In this case, it is preferable that the first resistor and the third resistor have the same resistance value.

The flat directional microphone according to the present invention includes two microphone units having bi-directionality, and a unit pair arranged so that each directional axis is orthogonal to each other, and each signal from the unit pair is about 90 degrees. A phase difference wave detector is provided to output to the hot side terminal and the cold side terminal so as to obtain a phase difference.
Therefore, as disclosed in Non-Patent Document 1, it is possible to provide a flat directional microphone that can be reduced in price and reduced without using a signal processing circuit such as a large-scale microphone array or DSP. It becomes.

Further, the phase difference wave filter is constituted by a multistage transfer circuit in which a plurality of transfer devices having different frequencies at which the input / output phase difference is 90 degrees are connected in series. Therefore, as an overall characteristic of the phase difference wave detector, each audio signal from the unit pair can be output with a phase difference of approximately 90 degrees within the practical whole band.
Thereby, it is possible to provide a microphone that can ensure a substantially flat directivity within the practical band described above.

It is an external view including the directional characteristics of the flat directional microphone according to the present invention. It is the circuit block diagram which showed the example of the microphone unit pair and the 1st phase difference wave transducer. It is the characteristic view which showed the state of the phase shift by the phase difference wave device shown in FIG. 2 is a polar pattern showing horizontal directivity characteristics of the microphone shown in FIG. It is the characteristic view which similarly showed the directivity frequency response of the horizontal direction. 2 is a polar pattern showing the vertical directivity characteristics of the microphone shown in FIG. It is the characteristic view which similarly showed the directivity frequency response of the perpendicular direction. It is the circuit block diagram which showed the example of the microphone unit pair and the 2nd phase difference wave transducer.

A flat directional microphone according to the present invention will be described based on an embodiment shown in a drawing using a condenser microphone unit.
As shown in FIG. 1A, the basic configuration of the flat directional microphone 1 according to the present invention includes two condenser microphone units Ma and Mb having bidirectionality, and the directional axis of the condenser microphone unit Ma is The condenser microphone unit Mb is oriented in the left-right direction. That is, the directivity axes of the condenser microphone units Ma and Mb are arranged so as to be orthogonal to each other in the horizontal plane, thereby constituting a unit pair U.

The unit pair U by the condenser microphone units Ma and Mb is arranged in a guard mesh 2a that constitutes the upper half of the microphone case 2. And in the metal case 2b which comprises the lower half part of the microphone case 2, the circuit board in which the microphone amplifier containing the impedance converter mentioned later and the phase difference wave device are mounted is accommodated.
Thus, a flat directional microphone 1 (hereinafter also referred to as a microphone main body 1) is configured.

As shown by the polar pattern at the top of FIG. 1A, the horizontal directivity of the condenser microphone units Ma and Mb alone is the front-rear bidirectional directivity Da indicated by the solid line and the horizontal direction indicated by the broken line. It will have bi-directionality Db.
The directivity in the vertical direction has a relatively narrow characteristic as depicted by the solid line Dc with the unit pair U in the center in FIG.

FIG. 2 shows a first circuit configuration for signal processing the outputs of the microphone units Ma and Mb constituting the unit pair U described above.
The microphone units Ma and Mb used in this embodiment are electret condenser microphone units. The thin film electrodes on the diaphragm side of the microphone units Ma and Mb, for example, are connected to a reference potential point (ground), and the fixed electrodes facing the diaphragm are connected to the microphone amplifiers Aa and Ab including the impedance conversion circuit. It is connected.

  In the circuit configuration shown in FIG. 2, a multistage transfer circuit Pa in which three transfer devices are connected in series is connected to the output terminal of the microphone amplifier Aa. Each phase shifter includes operational amplifiers OP1, OP2, and OP3, and the output terminal of the third-stage transporter is connected to the terminal pin P2 (hot output terminal) of the output connector arranged in the microphone body 1. Has been.

A multistage transfer circuit Pb in which two transfer devices are connected in series is connected to the output terminal of the microphone amplifier Ab. Each phase shifter is provided with operational amplifiers OP4 and OP5, respectively, and the output terminal of the second stage transfer device is connected to the terminal pin P3 (cold side output terminal) of the output connector arranged in the microphone body 1. Has been.
The terminal pin P1 of the output connector is connected to a reference potential point (ground) of the microphone body 1.

Each transfer device formed using an operational amplifier has the same circuit configuration. For example, in a transfer device using the operational amplifier OP1, a first resistor R1 and a second resistor R2 whose one ends are commonly connected to the inverting input terminal of the operational amplifier OP1, and one end of the non-inverting input terminal of the operational amplifier OP1. Are connected in common with a third resistor R3 and a capacitor C1. The other ends of the first resistor R1 and the third resistor R3 are connected in common to form the input terminal of the transfer device, and the output terminal of the operational amplifier OP1 forms the output terminal of the transfer device, and The other end of the capacitor C1 is grounded, and the other end of the second resistor R2 is connected to the output terminal of the operational amplifier OP1.
As described above, the circuit configuration of the other transporters shown in FIG. 2 is the same, and therefore, the reference numerals corresponding to the first to third resistors provided in the other transporters are omitted in the drawing. Yes.

The above-described transporter is also called an all-pass circuit or an all-pass filter, and it is desirable that the resistance values of the first to third resistors R1, R2, and R3 are set to the same value (= R). . The frequency f at which the phase difference between the input and output of the transporter at this time is 90 degrees is as follows. However, the capacitance of the capacitor C1 is C.
f = 1 / 2πCR (Formula 1)
That is, the frequency f at which the input / output phase difference of the single transfer unit is 90 degrees is only one point obtained by the above-described equation 1.

Therefore, in the embodiment shown in FIG. 2, the transfer devices connected in series are set so that the frequencies f at which the input / output phase difference is 90 degrees are different from each other.
For this purpose, the resistance values of the first to third resistors R1, R2, and R3 provided in each transfer device are set to the same value (= 10 KΩ), and the values of the capacitors (C1 to C5) are set. By appropriately selecting, the frequencies f at which the input / output phase differences of the individual transfer devices are 90 degrees are made different from each other.

In the circuit configuration shown in FIG. 2, the condenser microphone units Ma and Mb are connected to each other via a ground, and three condensers are connected in series to the condenser microphone unit Ma via a microphone amplifier Aa. A connected multistage transfer circuit Pa is connected. Similarly, a multi-stage transfer circuit Pb in which two transfer devices are connected in series via a microphone amplifier Ab is connected to the condenser microphone unit Mb.
Therefore, it can be regarded that a phase difference wave filter composed of a series circuit of multistage transfer circuits Pa and Pb is inserted between the condenser microphone units Ma and Mb between the hot side terminal P2 and the cold side terminal P3. it can.

Here, in the configuration shown in FIG. 2, the following values are adopted as examples of the capacities of the capacitors C1 to C5 provided in each transfer device.
C1 = 27 nF, C2 = 22 nF, C3 = 2.2 nF, C4 = 20 nF, C5 = 8 nF

FIG. 3 shows the overall characteristics of the phase difference wave filter when the capacitors C1 to C5 having the values described above are used. That is, according to this characteristic, the phase difference is approximately 90 degrees over a range of about 100 Hz to 5 KHz, which indicates the phase characteristic between the hot side terminal P2 and the cold side terminal P3. Yes.
This has a characteristic that the phase difference is almost 90 degrees within the entire range of a practical band for collecting a human voice.

Returning to FIG. 1A, if the sensitivity of the microphone unit Ma having the directional axis in the front-rear direction is K, the output signal is expressed as K cos θ, and the sensitivity of the microphone unit Mb having the directional axis in the left-right direction is the same. Then, the output signal can be expressed as Ksin θ. When the unit Mb has a phase difference of 90 degrees with respect to the unit Ma, the combined components of the two signals are as follows. However, j shows a complex number.
K (cos θ + jsin θ) (Formula 2)

したがって、２つの双指向性ユニットＭａ，Ｍｂの信号間の位相差が９０度となる帯域においては、図１（Ｂ）および（Ｃ）に示すように、ドーナツ形の指向性Ｄｘを得ることができるものとなる。なお、図１（Ｃ）はマイクロホンと指向特性の斜視図である。
すなわち、図１（Ｂ）の上部にポーラパターンで示したように、水平方向には３６０度に感度を有する無指向性になされ、垂直方向にはユニット対Ｕを中央にして実線Ｄｃで描いたように、比較的狭い指向特性を有する扁平な指向特性を有するマイクロホンを得ることができる。
したがって、この実施の形態によると、前記した偏平な指向特性は図３に基づいて説明したように、約１００Ｈｚ〜５ＫＨｚの範囲にわたって得ることができる。 Since the absolute value of K (cos θ + jsin θ) shown in Equation 2 is constant, this can be expressed as Equation 1 below.

Therefore, in the band where the phase difference between the signals of the two bidirectional units Ma and Mb is 90 degrees, a donut-shaped directivity Dx can be obtained as shown in FIGS. It will be possible. FIG. 1C is a perspective view of a microphone and directivity characteristics.
That is, as shown by the polar pattern at the top of FIG. 1B, the horizontal direction is omnidirectional with a sensitivity of 360 degrees, and the vertical direction is drawn with a solid line Dc with the unit pair U at the center. Thus, a microphone having a flat directional characteristic having a relatively narrow directional characteristic can be obtained.
Therefore, according to this embodiment, the flat directivity described above can be obtained over a range of about 100 Hz to 5 KHz as described with reference to FIG.

4 to 7 show the polar patterns of the flat directional microphones having the respective configurations shown in FIGS. 1 to 3 and the phase shift characteristics, and the measured values of the frequency response characteristics.
FIG. 4 shows the directivity in the horizontal direction of the microphone in a polar pattern, and it can be understood that the directivity in the horizontal direction is almost omnidirectional.
FIG. 5 shows frequency response characteristics in the horizontal direction, where a is 0 degree with respect to the sound source, b is 90 degrees, and c is 180 degrees. As can be understood from the characteristics shown in FIG. 5, in a practical sound collection range of about 100 Hz to 5 KHz, characteristics with uniform frequency responses can be obtained in any of the front, side and back surfaces in the horizontal direction.

FIG. 6 shows the directivity in the vertical direction of the microphone in a polar pattern. According to this, it can be understood that the sensitivity is high on the front and back surfaces and the sensitivity is low in the vertical direction. That is, when the horizontal directivity shown in FIG. 4 is included, it can be understood that the microphone has a donut-shaped directivity in a three-dimensional manner.
FIG. 7 shows frequency response characteristics in the vertical direction, where d is 0 degrees with respect to the sound source, e is 90 degrees, and f is 180 degrees. As can be understood from the characteristics shown in FIG. 7, in a practical sound collection range of about 100 Hz to 5 KHz, characteristics with uniform frequency responses can be obtained on the front and back in the horizontal direction.

  In the embodiment shown in FIG. 2, a multi-stage transfer circuit Pa using a three-stage transfer device is connected to the above-described bidirectional unit Ma, and a two-stage transfer device is connected to the bidirectional unit Mb. The multi-stage transfer circuit Pb is connected to form a phase difference wave detector using a fifth-order all-pass filter. By increasing the order of the filter (the number of stages of the transfer device), flat directivity can be obtained. Bandwidth can be expanded.

Further, for example, only the multistage transfer circuit Pa connected to the bidirectional unit Ma side constitutes a 90-degree phase difference wave transmitter, and the output from the microphone amplifier Ab is directly connected to the terminal pin P3 on the bidirectional unit Mb side. Even if the configuration is such that the output is made to the (cold side output terminal), a microphone having a flat directional characteristic can be obtained similarly.
This constitutes a 90-degree phase difference wave device only in the multistage transfer circuit Pb connected to the bidirectional unit Mb side, and the output from the microphone amplifier Aa is directly connected to the terminal pin P2 on the bidirectional unit Ma side. The same applies to the configuration in which the output is made to the (hot side output terminal).

FIG. 8 shows a second circuit configuration for signal processing the outputs of the microphone units Ma and Mb.
In the circuit configuration shown in FIG. 8, the multistage transfer circuit Pa is connected to the output terminal of the microphone amplifier Aa connected to the microphone unit Ma, and the output terminal of the final stage transfer device is arranged in the microphone body 1. Connected to the terminal pin P2 (hot output terminal) of the output connector. Similarly, the multistage transfer circuit Pb is connected to the output terminal of the microphone amplifier Ab connected to the microphone unit Mb, and the output terminal of the final stage transfer device is the terminal pin P3 of the output connector arranged in the microphone body 1. (Cold side output terminal). The terminal pin P1 of the output connector is connected to a reference potential point (ground) of the microphone body 1.

Each of the transporters in this embodiment is an active element, that is, a bipolar transistor, which generates signals in opposite phases to a collector as a second terminal and an emitter as a third terminal by a signal supplied to a base as a first terminal Are formed respectively.
For example, in a transfer device using the first transistor T1, the first resistor 11 and the second resistor 12 having one end connected in common to the collector of the transistor T1, and the one end connected in common to the emitter of the transistor T1. A third resistor R13 and a capacitor C11 are provided. The other ends of the first resistor R11 and the third resistor R13 are connected between a DC power source (Vcc-ground), and the base of the transistor constitutes an input terminal of the transfer device, and the second resistor The other end portions of R12 and capacitor C11 are commonly connected to constitute the output terminal of the transfer device.

In this case, it is desirable that the resistance values of the first resistor R11 and the third resistor R13 are set to the same value in the above-described transfer device.
Base bias resistors R14 and R15 are connected in series between the DC power supply (Vcc and ground), and the midpoint of the connection is connected to the base of the transistor T1, and a DC bias is applied to the base of the transistor T1. .
Note that the circuit configuration of the other transfer devices using the transistors T2 to T4 shown in FIG. 8 is the same, and therefore, the description of the reference numerals corresponding to the resistors and capacitors provided in the other transfer devices is omitted in the drawing. doing.

In the above-described transfer device, the frequency f at which the input / output phase difference of the transfer device becomes 90 degrees depends on the value of the resistor R12 having one end connected to the collector and emitter of the transistor T1 and the capacitance of the capacitor C11. It is determined. This performs the same function as the transfer device using the operational amplifier shown in FIG.
Therefore, by changing the combination of the value of the resistor R12 and the capacitance of the capacitor C11 according to each transfer device, each transfer device having different frequencies f at which the input / output phase difference is 90 degrees is obtained. Can do.

And between the hot side terminal P2 and the cold side terminal P3, the phase difference wave filter by the multistage transfer circuit Pa and Pb which connected the several transfer device in series with the condenser microphone units Ma and Mb is inserted. Can be considered. Therefore, in the circuit configuration shown in FIG. 8 as well, as in the example shown in FIG. 3 already described, within the practical band range, the above-described hot side terminal P2 and cold side terminal P3 are connected. It is possible to provide a phase characteristic in which the phase difference is approximately 90 degrees.
Therefore, even if the circuit configuration shown in FIG. 8 is used, a flat directional microphone that exhibits omnidirectional sensitivity at 360 degrees in the horizontal direction and relatively narrow directivity characteristics in the vertical direction is provided. Can do.

In addition, although bipolar transistors are used for the respective transporters shown in FIG. 8, the same operational effects can be obtained even if unipolar transistors such as FETs are used.
In the embodiment described above, a combination of a condenser microphone unit is used as the two microphone units having bidirectionality. However, a combination of a ribbon type microphone can be suitably used instead of the condenser microphone unit. can do.

1 Flat directional microphone (microphone body)
2 Microphone Case 2a Guard Mesh 2b Metal Case Aa, Ab Microphone Amplifier C1-C5 Capacitor C11 Capacitor Ma, MB Condenser Microphone Unit OP1-OP5 Operational Amplifier Pa, Pb Multistage Transfer Circuit (Phase Difference Waver)
P1 terminal pin (ground)
P2 terminal pin (hot side output terminal)
P3 terminal pin (cold side output terminal)
R1-R3 resistors R11-R15 resistors T1-T4 active elements (transistors)
U unit pair

Claims (7)

A unit pair including two microphone units having bi-directionality, the microphone units being arranged so that the directivity axes of the microphone units are orthogonal to each other;
Each signal from the unit pair is provided with a phase difference wave detector for outputting to the hot side terminal and the cold side terminal so as to obtain a phase difference of 90 degrees, respectively.
The phase difference wave filter is a flat directional microphone characterized by comprising a multi-stage transfer circuit in which a plurality of transfer devices having different frequencies at which the input / output phase difference is 90 degrees are connected in series.   The multi-stage transfer circuit is provided between one microphone constituting the unit pair and the hot side terminal and between the other microphone constituting the unit pair and the cold side terminal, respectively. The flat directional microphone according to claim 1, wherein:   The flat directional microphone according to claim 1 or 2, wherein the microphone constituting the unit pair is a combination of a condenser microphone unit or a combination of a ribbon type microphone. The transfer device includes a first resistor and a second resistor having one end commonly connected to an inverting input terminal of the operational amplifier, and a third resistor and a capacitor having one end commonly connected to the non-inverting input terminal of the operational amplifier. Is provided,
The other ends of the first resistor and the third resistor are connected in common to form the input terminal of the transfer device, the output terminal of the operational amplifier forms the output terminal of the transfer device, and the other end of the capacitor The flat directivity according to any one of claims 1 to 3, wherein the portion is grounded and the other end of the second resistor is connected to an output terminal of the operational amplifier. Microphone.   The flat directional microphone according to claim 4, wherein the first resistor, the second resistor, and the third resistor have the same resistance value. The transfer device has one end connected in common to an active element that generates signals having opposite phases to the second terminal and the third terminal according to a signal supplied to the first terminal, and the second terminal of the active element. A first resistor and a second resistor; a third resistor and a capacitor having one end commonly connected to the third terminal of the active element;
The other ends of the first resistor and the third resistor are connected between DC power supplies, the first terminal of the active element constitutes an input terminal of the transfer device, and the other ends of the second resistor and the capacitor 5. The flat directional microphone according to claim 4, wherein the parts are connected in common to constitute an output terminal of the transfer device.   The flat directional microphone according to claim 6, wherein the first resistor and the third resistor have the same resistance value.

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