JPH0657079B2 - Phase switching sound pickup device with multiple pairs of microphone outputs - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a sound pickup device configured by combining a plurality of pairs of unidirectional microphones used in a voice communication conference or the like.

(Prior Art) A microphone for a voice communication conference is placed in the center of the conference table to collect the voices of callers located around the conference table, and its sound collection characteristics are high in the horizontal direction on the outer periphery of the microphone. In addition to the sensitivity, it is desirable to reduce the vertical sensitivity of the microphone as much as possible in order to avoid the influence of the reflected sound from the ceiling or the conference table surface.

As a prior art example for realizing a sound collecting device having such characteristics, there is one in which two bidirectional microphones are used and their directional axes are shifted by 90 degrees and combined.

FIG. 2 is a diagram for explaining the configuration and the operation thereof according to the conventional technique. First, in FIG. 2a, reference numeral 1 denotes a microphone having bidirectional characteristics, which has directional characteristics with sensitivity as shown by a dotted line in the figure. In addition, the signs of + and-in the figure are
For the sound from the front and back of the microphone,
It shows that a relative phase difference of electrical signal outputs occurs by 180 degrees.

When one of the bidirectional microphones 1 is used, the sensitivity is zero for sound waves coming from directions B and B'which are different by 90 degrees with respect to the directivity axis A-A '. Is zero.

FIG. 2b shows the 9th microphone of the first microphone in which the sensitivity becomes zero.
A second bidirectional microphone whose directional axis is set in the 0 degree direction is arranged, and the outputs of these two microphones are added to each other, so that 90 ° with respect to the directional axis of the first microphone.
FIG. 7 is a diagram showing a horizontal bidirectional characteristic in an explanatory view of a method for obtaining sensitivity even with respect to a sound input in a degree direction. Ie 2
Add the outputs of the two bidirectional microphones 1 and 2,
If you combine that output as the microphone output,
The directional characteristic is a pattern of cos θ + sin θ shown by the solid line, and for acoustic input from the direction Y−Y ′ of θ = 135 ° and 315 °, the angle is the same as in the case shown in FIG. 2a. The difference is that the directional characteristics have zero sensitivity.

(Problems to be Solved by the Invention) However, even in the method of arranging two bidirectional microphones at a right angle as described above, there is a dead angle direction where the sensitivity becomes zero, and therefore the acoustic signal from this direction is collected. There was a problem that it was impossible to make a sound.

An object of the present invention is to solve the above-mentioned problems and to provide a sound pickup device capable of picking up sound with high sensitivity by constantly changing the directivity with respect to the change of the position of the sound source.

(Means for Solving the Problems) The present invention includes a plurality of pairs of unidirectional microphones arranged radially and a plurality of differential amplifiers corresponding to each pair of the unidirectional microphones. In a sound device, a phase for selectively connecting the output side of one microphone and the output side of the other microphone for each pair of unidirectional microphones and selectively connecting to the + input side or − input side of the differential amplifier. Based on the switching device, the comparator that compares the output levels of both microphones, and the output side of the microphone with the larger output level to the differential amplifier + input side, based on the comparison result from this comparator, the other side And a controller for controlling the phase switch so that the output side of the microphone is connected to the-input side of the differential amplifier.

(Operation) When a sound is generated from the sound source, each microphone captures the sound. Then, in each pair of microphones, the outputs of both microphones are compared by the comparator, and the controller controls the phase switching device based on the comparison result, and the switching device makes the output side of the microphone with the larger output differential. Connect to the + input side of the amplifier and connect the output side of the other microphone to the-input side of the differential amplifier. As a result, the phase of the microphone output of each pair is switched to a direction closer to the sound source, whereby a combined pattern is formed in a direction closest to the sound source. When the position of the sound source changes, the phase of the pair of microphones changes accordingly, and the synthesis pattern also changes in the direction closest to the sound source.

(Embodiment) FIG. 1 is a block diagram of an embodiment of the present invention. In FIG. 1, 1a, 1b, 2a and 2b are unidirectional microphones, respectively, which are arranged at equal intervals on the same circumference and whose directional axes point outward in the normal direction to the circumference. It is arranged. The arrow of each microphone in the figure indicates the pointing direction. 11, 12 are comparators, 2
Reference numerals 1 and 22 are controllers, 31 and 32 are phase inversion switches, 41 and 42 are differential amplifiers, 50 is an adder, and 60 is an electrical output terminal of the present microphone device.

In FIG. 1, first, the operation when the sound pressure is input from the direction of Z1 which is the directivity direction (direction in which the sensitivity increases) of the microphone 1a will be described.

With respect to the sound input from the Z1 direction, the output level of the microphone with respect to the input sound pressure of the microphone 1a paired with the microphone 1a is compared by the comparator 11. In this case, the directional axis is arranged in the Z1 direction with respect to the input sound pressure. It is determined that the output level of the existing microphone 1a is high. The determination result controls the phase inversion switch 31 by the controller 21. At this time, the phase inversion switch 31 is set so that the output of the microphone 1a is connected to the plus side of the differential amplifier 41.

The output of each microphone pair 2a and 2b is input sound pressure from the same direction with respect to the microphones.
It becomes equal when compared in 2. At this time, the control signal from the controller 22 to the phase inversion switch 32 is set so as to hold the state immediately before, but when the output of each microphone is input to the differential amplifier 42, the amplitude is constant and the phase is constant. Are added 180 degrees apart, the electrical output from the differential amplifier 42 is theoretically zero.

When a noise source is present vertically above and below the plane on which the microphones are arranged, the microphone pair 1a, 1b is included for the same reason as the operation of the microphone pair 2a, 2b. , The phases of the electrical outputs from the respective pairs of microphones are inverted by 180 degrees in the differential amplifiers 41 and 42 and added, so that the output becomes zero.

Therefore, only the electrical output corresponding to the acoustic signal from the Z1 direction output from the differential amplifiers 41 and 42 is input to the adder 50, and the electrical output signal of the microphone 1a is input to the output terminal 60 of the adder 50. Taken out.

Next, consider the case where an acoustic signal is input from the Z2 direction. In this case, the microphone pair 1 described above
Since the arrangements of a, 1b and 2a, 2b are equivalent to when they are shifted by 90 degrees, the above operation is directly applied.

Finally, the operation when an acoustic signal is input from the central direction Z3 of the microphones 1a and 2a will be described. Also in this case, the minimum output levels of the microphone pairs 1a and 1b and 2a and 2b are compared by the comparators 11 and 12, as in the above-described operation. That is, for the sound input from the Z3 direction, the microphones 1a and 2
It is determined that the output of a is large, and the differential amplifiers 41 and 4 are
The outputs of the microphones 1a and 2a are input to the positive side of 2. As a result, the value of (the sum of the output levels of the microphones 1a and 2a)-(the sum of the output levels of the microphones 1b and 2b) is extracted from the adder 50 as the output of the microphone with respect to the acoustic input from the Z3 direction. Becomes This operation is the same regardless of which direction the sound input direction is on the outer circumference of the microphone, and thus there is no blind spot with respect to the sound input direction.

Next, in order to clarify the effectiveness of the existence of the comparators 11 and 12 and the phase inversion switches 31 and 32, the operation without the comparators and the phase inversion switches 31 and 32 will be described.

In this case, the output of the microphone 1a is connected to the positive side of the differential amplifier 41 and the output of the microphone 2a is connected to the negative side of the differential amplifier 42 with respect to the input sound pressure from the Z3 direction, and it is simple. Microphones 1a and 2 for
Considering the case where the input sound pressure level to a is the same,
Since electric signals having the same amplitude and different phases by 180 degrees are input to the adder 50, the electric output of the microphone device becomes zero, and desired normal operation cannot be performed with respect to the acoustic input from the Z3 direction. This operating state corresponds to the case of the input sound pressure condition from the Y direction shown in FIG.

From the above operation reason, it is understood that the comparator, the phase inversion switch, and the controller that controls them are essential device functions for configuring the microphone and realizing the desired characteristics.

In addition, in the embodiment of the present invention, the case where two pairs of microphones are combined is described. However, when a microphone having a sharp directional characteristic is used, in order to cover the entire circumferential direction,
It is necessary to increase the number of microphones, and in this case, the same number of comparators, controllers, phase inversion switches, and differential amplifiers as the number of microphones should be prepared. Also in this case, the principle and procedure of operation are the same as described above.

Next, regarding the unidirectional microphone of the primary gradient type, the level change characteristics due to the angle change in the horizontal plane are
The result obtained by the number of microphones used is the third
Shown in the figure. From this figure, it can be seen that in the case of four lines, the amount of decrease of 3 dB at 90-degree intervals is 6 〃, 60 〃 1.2 dB is 8 〃, 45 〃 0.6 dB 〃.

As a result, by selecting the number of unidirectional microphones to be used according to the number of callers, etc., it is possible to absorb the radiated sound from the horizontal direction of the arrayed surface while reducing the level change. A donut-oriented microphone can be provided, which reduces the output level against indoor noise from the vertical direction of the microphone surface, while reducing the acoustic coupling amount by arranging the sound-receiving speaker in the vertical direction of the microphone surface. , And has an advantage that a sound pickup device capable of suppressing howling can be provided.

In the present embodiment, the case where the microphones are arranged on the circumference has been shown, but it is possible to take an arbitrary arrangement such as an ellipse or a square according to the arrangement of the conference callers, and by doing so, The function and effect of the sound pickup device is not lost.

As described above, according to the present invention, in each pair of microphones, the outputs of both microphones are compared, and the one with the larger output is connected to the + input side of the differential amplifier.
The synthetic pattern of each microphone output can be formed in the direction closest to the sound source, and the direction can be switched as the position of the sound source changes. Therefore, there is an effect that the directivity can be changed for a sound source whose input direction is not constant and high-sensitivity sound collection can be performed.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2a is a horizontal directional characteristic diagram of a conventional bidirectional microphone, and FIG. 2b is a combination of two bidirectional microphones arranged at right angles. FIG. 3 is a directional characteristic diagram, and FIG. 3 is a level change characteristic diagram in the horizontal plane direction with the number of microphones according to the present invention. 1, 2 ... Bidirectional microphones 1a, 1b, 2a, 2
b ... Unidirectional microphone, 11, 12 ... Comparator, 21, 22 ... Controller, 31, 32 ... Phase inversion switch, 41, 42 ... Differential amplifier, 50 ... Adder, 6
0 ... Output terminal.

Claims (1)

[Claims] 1. A sound collecting device comprising a plurality of pairs of unidirectional microphones arranged radially and a plurality of differential amplifiers corresponding to each pair of the unidirectional microphones, wherein the unidirectional microphone is provided. For each pair of sex microphones, a phase switch that switches between the output side of one microphone and the output side of the other microphone and is selectively connected to the + input side or − input side of the differential amplifier, and both microphones. The output side of the microphone with the larger output level is connected to the + input side of the differential amplifier, and the output side of the other microphone is connected based on the comparison result from this comparator. A phase switching sound pickup device for a plurality of pairs of microphone outputs, comprising: a controller that controls the phase switching device so as to be connected to the minus input side of the differential amplifier.