JPH0763199B2 - Electro-acoustic transducer - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electroacoustic transducer that uses a plurality of microphone elements to obtain a directional characteristic in a specific direction and in a donut shape.

[Conventional technology]

Such devices can be used for large round table meetings, round-table discussions, or
In a similar meeting or roundtable discussion with the other party via the communication line, the voice of each participant is collected and amplified, then it is output from the speaker such as the ceiling, or the other party's voice is sent via the communication line. Is used for transmitting the voice of each participant to the other side while uttering the same from the same speaker. Conventionally, it is used in U.S. Pat. No. 4,311,874 and a separate application filed by the applicant. (Japanese Patent Application No. 58-197521) and the like have been proposed.

That is, in the former, several tens of omnidirectional microphones are arranged in a straight line to obtain omnidirectional in the horizontal plane and donut-shaped directional characteristics in the vertical plane, and in the latter, the center of the circle is obtained. In addition to placing one microphone element on the circumference of the circle, four microphone elements are placed at equal intervals on the circumference of the circle to give a relative gain of 4 to the center microphone element output, while A directional characteristic on a donut is obtained by adding a relative gain of 1 and a phase inversion to the microphone element output and then adding these outputs.

[Problems to be solved by the invention]

However, in the former case, the number of microphones is large, and accordingly, the number of peripheral devices such as amplifiers is also increased, gain adjustment is troublesome, and it becomes difficult to provide equal characteristics to each microphone. In the latter case, the gain difference between the central microphone system and the circumferential microphone system is 4: 1, the gain fluctuation of the central microphone system has a large effect, and the directional characteristics are generally unstable. Is causing problems.

The present invention has an object to fundamentally solve the above-mentioned drawbacks, and provides an electroacoustic transducer having a small number of microphone elements (hereinafter, elements) and stable directional characteristics.

[Means for solving problems]

Therefore, the present invention is configured by the following means.

That is, the first invention is that at least three peripheral microphone elements arranged in a circle at equal intervals and having the same distance from the speaker arranged on the central axis of the circle, and peripheral microphones arranged at the center of the circle. A central microphone element that produces an output signal that is in phase with the generated signal;
A circuit that gives a relative gain of 1 to the output of the central microphone element, and a circuit that gives a relative gain of 1 / n and relative phase inversion to the output of the microphone elements, where n is the number of peripheral microphone elements. And an adder for adding the outputs of these circuits.

According to a second aspect of the invention, at least three peripheral microphone elements arranged at equal intervals in a circle and having the same distance from the speaker arranged on the center axis of the circle, and arranged at the center of the circle and on the center axis of the circle. One central microphone element whose distance from the placed speaker is equal to the distance from the speaker to the microphone on the circumference, a circuit that gives a relative gain of 1 to the output of the central microphone element, and the number of peripheral microphone elements are set. It is provided with a circuit that gives a relative gain of 1 / n and a relative phase inversion to the output of each microphone element when n, and an adder that adds the outputs of these circuits.

The third invention is to provide at least three elements arranged on the circumference of the inner circle at equal intervals, and a circumference of the outer circle concentric with the inner circle and having a diameter larger than that of the inner circle. At least three elements arranged at equal intervals above, a circuit that gives a relative gain of 1 / m to the output of each of these elements when the number of elements in the inner circle is m, and an element in the outer circle When the number is n, it is composed of a circuit which gives a relative gain of 1 / n and a relative phase inversion to the outputs of these elements, and an adder which adds the outputs of these circuits.

[Work]

Therefore, the outputs of the respective elements are combined by the adder in a predetermined ratio and phase relationship, and a donut-shaped directional characteristic whose main directional direction is a direction along a plane including the circumference is obtained.

〔Example〕

Hereinafter, the details of the present invention will be described with reference to the drawings illustrating examples.

Figure 1 is a block diagram corresponding to the first invention, the placing one element 1 ₀ in the center of the circle, the circle on the n-number of elements 1 ₁ to 1 _n of the circle indicated by the dotted line place the equal intervals by the relative angle of each other 360 ° / n, the output of the element 1 ₀ through the amplifier 2 _0, through each amplifier 2 ₁ to 2 _n is the output of the element 1 ₁ to 1 _n, the adder while you are added in 3, is provided with a speaker 5 above the vertical and elements 1 ₀ to the plane including the circumference, drive the speaker 5 through the amplification system output of the adder 3 is diagram omitted It is supposed to do.

Figure 2 is a diagram for explaining the operation principle of the configuration of FIG. 1 generally element 1 ₀ and the element 1 ₁ to 1 _n the distance is d, the source point S and the element 1 by the speaker 5 R ₀ is the distance from ₀ ,
The vertical distance between the sound source point S and the plane including the circumference is r ₁ , and the sound source point S
A straight line connecting the element 1 ₀ and the element 1 ₁ the distance between the elements 1 _i on the circumference on the plane containing r _i, the circumference and, elements 1 ₀ and the source point S
The angle between the straight line connecting the right under the theta, and a straight line connecting the element 1 ₀ and the source point S, the angle between the plane containing the circumferential phi, elements 1 _1
If the number of 1 _n is n, the following equation is obtained.

In thisゝ, the gain of the amplifier 2 ₀ was relatively 1 to amplifiers 2 ₁ to 2 _n, contrary to the gain of relatively amplifier 2 ₁ to 2 _n and 1 / n, and input and output amplifier 2 ₀ between the
Assuming that to perform relatively phase inversion, the ratio of the combined output voltage E of the adder 3, and the output voltage E ₀ of the element 1 ₀ is indicated by the following equation.

However, k is a wavelength constant determined by the wavelength of the acoustic wave emitted from the sound source point S.

Also, if (d / r ₀ ) << 1 and k · d << 1, the following equation is obtained.

on the other hand, Therefore, the following equation is obtained.

Therefore, it is irrelevant to θ, is omnidirectional in the direction of the plane including the circumference, and has directivity in the direction orthogonal to this plane. Directional characteristics are obtained, for example, d = 6 cm, r = 1 m,
When n = 3, the acoustic frequencies from the sound source point S are 0.5, 1, 2,
Depending on each 3KH _Z, exhibits directivity characteristic shown in FIG. 4 to FIG. 7.

3 to 7, φ is the same as φ in FIG. 2, the outermost circle is 0 dB, and the inner circle is -10d.
B and the innermost circle show the pickup capacity of -20 dB.

Was Isuzu and, when the acoustic frequency decreases, as shown in FIG. 4 of 0.5KH _z, φ = desensitization of ± 90 ° direction is relatively decreased, which is of about 13 dB, as is this countermeasure it may be assumed to be incident by the same phase relative to _{1 0,} 1 1 ~1 _n acoustic waves the elements from the source point S.

Figure 8 is a sectional side view for the case of equal distance between the source point S and the element 1 _0, 1 ₁ to 1 _n, after which the same relationship as FIG. 1, the device 1 ₀ circumference distance d ₀ from the plane in the opposite direction to the source point S comprising spaced apart, the d ₀ Be determined as an acoustic wave each element from the source point S 1 _0, 1 ₁
Injects to ~ 1 _n with the same phase.

Therefore, under the same conditions as described above and when d ₀ = 1.3 mm, the directional characteristics obtained by calculation are as shown in FIG. 9, and there is a large decrease in sensitivity in the φ = + 90 ° direction.
A little heart-shaped donut-shaped directional pattern is obtained with little sensitivity reduction in the -90 ° direction.

Further, instead of the relationship of FIG. 8, as shown in FIG.
1 Insert the delay circuit 4 to the output side of the _0, when the speed of sound by C
If a delay equivalent to d ₀ / C is given, the directional characteristic of FIG. 11 can be obtained.

FIG. 12 is a block diagram corresponding to the second invention, the inward circle on the circumference indicated by a small circle of a dotted line, the element 6 ₁ to 6 _m of the number of elements m
Are equidistantly arranged at a relative angle of 360 ° / m, and the element 1 with the number n of elements is placed on the circumference of the outer circle that is concentric with the circle and has a diameter larger than the inner circle. ₁ to 1 _n are arranged in the same manner, and the outputs of the elements ₁ to 1 _n are amplified.
7 _{1 to} 7 _n are applied to the adder 4, and the outputs of the elements 6 _{1 to} 6 _m are applied to the adder 4 via amplifiers 8 ₁ to 8 _m .
The respective gains of the amplifiers 8 ₁ to 8 _m and 7 _{1 to} 7 _n are relatively defined as 1 / m and 1 / n, and in the amplifiers 7 _{1 to} 7 _n , the output phase with respect to the input is set to the amplifier 8 ₁ It is supposed to be inverted relative to ~ 8 _m .

Therefore, if the arrangement of the elements 1 ₁ to 1 _n, 6 ₁ to 6 _m and the same plane, the same results as in FIG. 1 is obtained, the number of elements of the center side than the first figure single If the influence of the characteristic deviation of each element is reduced and m = n instead of one, the amplifier 7 ₁
To _7-n, 8 ₁ to 8 gain of _m is equal, these becomes capable of using the same.

The phase inversion, since the wiring polarity of the input or output may be the opposite, in particular on the design and fabrication of the amplifier with it without paying special attention, the amplifier 2 ₀ or 8 ₁ to 8 _m
The same applies when phase inversion is performed on the side.

The same applies to the method shown in FIG. 8 or 10 with respect to FIG.

Therefore, if the arrangement plane of each element is set parallel to the table such as a conference table and the speaker 5 is provided in the direction of φ = ± 90 °,
The sound emitted from the speaker 5 does not appear in the output of the adder 3 and the howling is prevented, and the sound from the surrounding direction is picked up well due to the non-directionality.

However, if the arrangement plane of each element is set at the same height as the head of the speaker, it is suitable for picking up the sound, and noise such as tapping sound generated on the tabletop is not picked up and the signal-to-noise ratio is improved. improves.

An effect equivalent to this can be obtained not only by the directional characteristics shown in FIG. 9, but also by using unidirectional elements and arranging these elements facing upward.

In addition, in order to give a predetermined gain and phase inversion to the output of each element, not only setting the gain and input / output phase of the amplifier, but also inserting an attenuator or a phase inversion circuit. Of course, even if these functions are put together into the adder 4, the element output on the central or inner side and the element output on the outer side are added to each unit and common to each addition output. A gain setting circuit and a phase inverting circuit may be inserted and further addition may be performed.

Also, the number of elements on the circumference may be at least three for the purpose of evenly picking up sound from each direction, and each element may be a single element that converts sound into an electric signal, or a completed element. It suffices to use a microphone or the like as a product, and various modifications are possible, such as arranging these in individual pieces or accommodating them in the same housing.

〔The invention's effect〕

As is apparent from the above description, according to the present invention, the number of elements on the circumference is small, the gain difference between the microphone system on the center side and the microphone system on the circumference is reduced, and a stable donut-shaped directional characteristic is obtained. Therefore, a loudspeaking conference or a round-table discussion with a microphone and a speaker can be realized without using howling, without using a voice switch or VODAS, and a remarkable effect on sound collection for such an application can be obtained.

[Brief description of drawings]

FIG. 1 shows an embodiment of the present invention, FIG. 1 is a configuration diagram corresponding to the first invention, FIG. 2 is a diagram for explaining the principle, FIGS. 3 to 7 are diagrams showing directional characteristics, and FIG. Is a side view showing another embodiment, FIG. 9 is a diagram showing a directional characteristic according to FIG. 8, FIG. 10 is a configuration diagram showing another embodiment, and FIG. 11 is a diagram showing a directional characteristic according to FIG. FIG. 12 is a block diagram corresponding to the second invention. _{1 0, 1 1 ~1 n,} 1 n2, 1 i, 2 1 ~2 n1 ...... element (microphone _{element), 2 0, 2 1 ~2} n, 7 1 ~7 n2, 8 1 ~8 n1 ...... Amplifier, 3 ...
Adder.

Claims (3)

[Claims] 1. At least three peripheral microphone elements arranged in a circle at equal intervals and having the same distance from a speaker arranged on the central axis of the circle, and a central microphone element arranged at the center of the circle. A delay circuit connected to the central microphone for correcting the phase of the central microphone output signal so as to be the same as the phase of the signal generated from the peripheral microphones; and a circuit for giving a relative gain of 1 to the output of the central microphone element. A circuit for giving a relative gain of 1 / n and a relative phase inversion to the microphone element output, where n is the number of the peripheral microphone elements, and an adder for adding the respective outputs of these circuits. An electroacoustic transducer comprising: 2. At least three peripheral microphone elements arranged in a circle at equal intervals and having the same distance from a speaker arranged on the center axis of the circle, and arranged at the center of the circle and at the center of the circle. One central microphone element whose distance from the speaker arranged on the axis is equal to the distance from the speaker to a peripheral microphone; a circuit that gives a relative gain of 1 to the output of the central microphone element; and the number of peripheral microphone elements. Where n is n, a circuit for giving a relative gain of 1 / n to each microphone element output and a relative phase inversion, and an adder for adding the respective outputs of these circuits are provided. Electro-acoustic transducer. 3. At least three microphone elements arranged on the circumference of the inner circle at equal intervals, and on the circumference of an outer circle concentric with the inner circle and having a diameter larger than the inner circle. At least three microphone elements arranged at equal intervals, a circuit that gives a relative gain of 1 / m to each microphone element output when the number of microphone elements in the inner circle is m, and the outer circle A circuit that gives a relative gain of 1 / n and a relative phase inversion to the output of each microphone element, where n is the number of the microphone elements, and an adder that adds the outputs of these circuits. An electroacoustic transducer characterized by the above.