JP2006109340A - Acoustic system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent occurrence of an acoustic echo and howling with a configuration simpler than that of prior arts. <P>SOLUTION: A microphone M picks up voice of a talker, and an array speaker ASP emits the picked-up voice as an acoustic beam W. The emission directions at this time are directions of side wall faces WL1, WL2 other than a sound collection area A1 wherein the talker can reside. The acoustic beam W is reflected in the side wall faces WL1, WL2 and the reflected beams reach a listening area A2. The acoustic beam after reaching the listening area A2 is absorbed by an acoustic absorbing body B provided to a rear wall face. Since the acoustic beam emitted from the array speaker ASP is not picked up by the microphone M in this way, acoustic echo and howling seldom take place. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a technique for preventing acoustic echo and howling caused by so-called acoustic coupling.

  An acoustic echo or an oscillation phenomenon (howling) at a specific frequency may occur due to acoustic coupling between sound output from a speaker and sound collected by a microphone. Conventionally, various echo canceller techniques for solving this type of problem have been proposed. In a typical echo canceller technique, first, a transfer function (impulse response) by acoustic coupling is obtained, and a pseudo echo is generated from a received input signal using the transfer function as a filter coefficient. Next, only the echo signal is deleted by subtracting the already generated pseudo echo from the transmission output signal including the echo signal that wraps around due to acoustic coupling from the speaker to the microphone.

  In the above echo canceller technique, the transfer function is always considered to be constant, but the actual characteristics of the acoustic space vary depending on various factors. For example, it is known that the speed of sound changes according to a change in room temperature, but this changes the transfer function. Therefore, Patent Document 1 proposes a technique that can withstand the change of the transfer function by acoustically coupling the impulse response from the main speaker to the impulse response from the main speaker.

The typical echo canceller technique described above is a method of erasing an echo signal from a sound signal picked up by a microphone later, whereas the technique described in Patent Document 1 basically emits sound from a speaker. The idea is to control the acoustic coupling itself so that no echo is generated from the point of time. However, in order to realize this, complicated calculations such as obtaining an impulse response using an adaptive filter, for example, must be performed, and there is a problem that the configuration and processing of the echo canceller apparatus become complicated.
JP-A-5-007170

  The present invention has been made in view of such a background, and an object of the present invention is to prevent the occurrence of acoustic echoes and howling with a simpler configuration than conventional ones.

  In order to solve the above-described problem, the present invention provides a sound collection unit that collects sound and a sound collection unit that collects sound in a direction other than a direction toward a sound collection area where the sound collection unit may exist. There is provided an acoustic system including a sound emitting unit that emits the uttered sound as a directional sound wave and an acoustic reflector that reflects the directional sound wave emitted by the sound emitting unit toward a listening area. According to this acoustic system, the sound collected by the sound collecting means is radiated as a directional sound wave in a direction other than the direction toward the sound collecting area where the sound collecting means may exist. That is, since the directional sound wave is not collected by the sound collecting means, it is possible to suppress the occurrence of acoustic echo and howling.

  The present invention also provides a sound collecting means for collecting sound, a sound emitting means for emitting the sound collected by the sound collecting means as a directional sound wave, and a directional sound wave emitted by the sound emitting means. An acoustic reflector that reflects toward the listening area, a position detection unit that detects the position of the sound collection unit, and a direction other than the direction from the sound emission unit toward the position of the sound collection unit detected by the position detection unit And a control unit that emits the directional sound wave. According to this acoustic system, the sound collected by the sound collecting means is radiated as a directional sound wave in a direction other than the direction toward the position of the sound collecting means. That is, since the directional sound wave is not collected by the sound collecting means, it is possible to suppress the occurrence of acoustic echo and howling. Further, since the position of the sound collecting means is detected, even if the speaker moves around while carrying the sound collecting means or wearing the sound collecting means, the generation of acoustic echo and howling can be suppressed.

  In this invention, it comprises a second sound collecting means for collecting sound in the listening area, and a second position detecting means for detecting the position of the second sound collecting means, wherein the control means comprises the The directional sound wave is emitted from the sound emitting means in a direction other than the direction toward the position detected by the position detection means and in a direction other than the direction toward the position detected by the second position detection means. You may make it radiate | emit. According to this acoustic system, the directional sound wave is not picked up by the sound pickup means and is not picked up by the second sound pickup means. Therefore, it is possible to suppress the occurrence of acoustic echo and howling that may occur due to the acoustic coupling between the sound emitting means and the second sound collecting means.

  Moreover, in another preferable aspect, an acoustic sound absorber is provided, and the acoustic reflector directs a reflection surface in a direction in which the reflected directional sound wave reaches the acoustic sound absorber without passing through the sound collection area. Has been placed.

  In the best mode for carrying out the present invention, a so-called array speaker is used as the sound emitting means. An array speaker is a speaker system in which a plurality of speaker units are arranged in a row direction or a planar shape. In this array speaker, a sound wave (acoustic beam) having directivity can be emitted in a desired direction by appropriately controlling the delay time of the audio signal supplied to each speaker unit. That is, the greatest feature of the array speaker is that the direction of the acoustic beam can be freely changed without changing the direction of each speaker unit itself.

  Therefore, before entering the details of the embodiment, the principle of the array speaker will be briefly described. FIG. 1 is a diagram showing an electrical configuration of an array speaker ASP configured by two speaker units SP1 and SP2. In FIG. 1, the center axes Y1 and Y2 of the speaker units SP1 and SP2 are parallel to each other, and the cones (diaphragms) of the speaker units SP1 and SP2 are disposed at the same position in the direction of the center axes Y1 and Y2. It is assumed that Further, the interval between the central axis Y1 and the central axis Y2 is “a”, and the angles from the central axes Y1 and Y2 to the sound wave radiation directions Y11 and Y22 (hereinafter referred to as radiation angles) are “θ”. Assuming that the sound receiving point is sufficiently far away, the path difference between the sound wave radiated from the speaker unit SP1 in the radiation direction Y11 and the sound wave radiated from the speaker unit SP2 in the radiation direction Y22 is a · sin θ. Since the radiation angle θ is positive in the counterclockwise direction from the central axes Y1 and Y2 and negative in the clockwise direction, −180 ° ≦ θ ≦ 180 °.

  The audio signal is supplied from the input terminal Tin to the speaker units SP1 and SP2 via the delay circuits DL1 and DL2. Note that the “audio signal” in the present embodiment is a signal that represents sound in a waveform on the time axis. In the delay circuits DL1 and DL2, the audio signal is subjected to delay processing for delay times D1 and D2 (D2 ≧ D1). Therefore, a time difference (D2−D1) occurs between the sound wave emitted from the speaker unit SP1 and the sound wave emitted from the speaker unit SP2. In addition to the time difference between the two sound waves, there is a path difference between the radiation directions Y11 and Y22, so that the phase relationship between the two sound waves varies depending on the position of the listening area. For example, in a certain listening area, both sound waves are added in phase and the sound volume is doubled. Also, in a certain listening area, both sound waves are out of phase and cancel each other, and the sound volume becomes zero. Therefore, if the delay amount in each of the delay circuits DL1 and DL2 is appropriately controlled, the sound waves emitted from the array speaker ASP can have a desired directivity. Of course, the principle is the same even if the number of speaker units is increased. It should be noted that the sound wave can be given directivity even if the phase of the audio signal is shifted (phase shift) or the level is adjusted instead of the delay processing.

  In FIG. 1, the number of audio signal channels is one, but the number of channels may be increased. In addition, after performing the delay process with an appropriate delay amount on the audio signal of each channel, if the audio signal subjected to the delay process is added and radiated from each speaker unit, an acoustic beam for each channel is respectively obtained. It is possible to radiate in different directions.

Hereinafter, embodiments of the present invention will be described in detail.
(1) First Embodiment FIG. 2 is a plan view showing a configuration when the sound system according to the first embodiment is applied to a lecture hall. The microphone M, which is a sound collecting means, is carried by the speaker, attached to the clothes of the speaker, or supported by a microphone stand (not shown). The voice of the speaker is picked up by the microphone M, and the picked-up voice is emitted as an acoustic beam W from the array speaker ASP. The emitted acoustic beam W is reflected by the side wall surfaces WL1 and WL2 of the acoustic space (lecture hall) and reaches the listener. That is, the side wall surfaces WL1 and WL2 function as acoustic reflectors. The acoustic beam after reaching the listener is absorbed by the acoustic absorber B provided on the rear wall surface WL4.

  The sound collection area A1 shown in FIG. 2 is an area where the microphone M can exist. For example, if the speaker is allowed to speak while walking on the stage with a microphone, the occupied area of the stage corresponds to the sound collection area A1. When the microphone M is fixed by a microphone stand, the position where the microphone M is fixed is the sound collection area A1. On the other hand, the listening area A2 is an area where a listener can exist, and corresponds to, for example, a passenger seat area where the listener is seated. The array speaker ASP is provided along the front wall surface WL3 behind the speaker. Here, “behind the speaker” means a direction opposite to the direction toward the listening area A2 when viewed from the position of the sound collection area A1. It is assumed that sufficient intervals are secured among the array speaker ASP, the sound collection area A1, and the listening area A2.

  The array speaker ASP is composed of eight speaker units SP1 to SP8 arranged in a line in the horizontal direction. FIG. 3 is a block diagram showing the electrical configuration of the array speaker ASP and its peripheral devices. The audio signal is supplied from the main control unit CU to the speaker units SP1 to SP8 through the input terminal Tin, the delay circuits DL1 to DL8, and the level control circuits W1 to W8. The delay circuits DL1 to DL8 perform delay or phase shift (phase shift) of the input audio signal. The level control circuits W1 to W8 attenuate or amplify the level of the input audio signal. The operation parameters of the delay circuits DL1 to DL8 and the level control circuits W1 to W8 are set by control signals supplied from the main control unit CU. The control unit CU includes a CPU and various memories, and is connected to the operation unit UI. The operator of the acoustic system can designate operation parameters to be set in the delay circuits DL1 to DL8 and the level control circuits W1 to W8 by operating the operation unit UI. For example, if the delay time by the delay circuits DL1 to DL8 is appropriately set, the acoustic beam can be emitted from the array speaker ASP at an arbitrary radiation angle θ.

  The positional relationship among the sound collection area A1, the listening area A2, and the array speaker ASP can be specified in advance when the lecture hall is set up. Therefore, from this positional relationship, it is possible to obtain in advance what route the acoustic beam W travels in the lecture hall (acoustic space). In the example of FIG. 2, if the acoustic beam W is radiated from the array speaker ASP at the radiation angle θ1, the acoustic beam W travels in the direction of the side wall surface WL1, is reflected by the wall surface WL1, and then reaches the listening area A2. That is, it is possible to avoid the sound collection area A1 and allow the acoustic beam W to reach only the listening area A2. The acoustic beam W after reaching the listening area A2 is absorbed by the acoustic sound absorber B. The array speaker ASP may radiate not only the acoustic beam W directed toward the side wall surface WL1 but also the acoustic beam directed toward the side wall surface WL2, but the description is simplified in FIG. Therefore, illustration of the acoustic beam toward the side wall surface WL2 is omitted.

  According to the first embodiment described above, the acoustic beam W is radiated from the array speaker ASP in a direction other than the sound collection area A1, and the acoustic beam W is reflected by the wall surface of the acoustic space to reach the listening area A2. it can. That is, since the acoustic beam emitted from the array speaker ASP is not picked up by the microphone M, acoustic echo and howling hardly occur. Although the acoustic beam radiated from the array speaker ASP has a very strong directivity, some side lobes (leakage sound) are generated, and there is a possibility that the side lobes may reach the sound collection area A1. . However, the volume of the side lobe is very small and not so high as to cause echo or howling.

  In the first embodiment, the array speaker ASP is installed behind the speaker. However, the installation position as described above has the following advantages. First, since there is often a relatively large space behind the speaker, there is no need to bother to secure an installation space for the array speaker ASP. In addition, some conventional products have a speaker on the front of the speaker's podium (the surface facing the listening area), but the position of the speaker is relatively low, so the sound reaches the back of the listening area. It is pointed out that it is difficult. On the other hand, when the array speaker ASP is installed behind the speaker, the installation position is not subject to height restrictions so that the array speaker ASP can be installed at a relatively high position. It becomes easy to make the voice reach the whole area. Furthermore, in the first embodiment, the listening area is sandwiched between the array speaker ASP and the acoustic sound absorber B behind the speaker. For example, this is an acoustic system in which speakers are distributed on the ceiling. In comparison, since there is less acoustic reflection on the floor surface, there is an advantage that the SN ratio is improved.

(2) Second Embodiment In the first embodiment described above, the maximum range in which the speaker (microphone) can move is set as the sound collection area. However, when the size of the sound collection area is very large (for example, when the stage is wide), or when a sufficient interval cannot be secured between the sound collection area and the array speaker (for example, when the depth of the stage is narrow). Even if the acoustic beam is emitted in a direction other than the microphone, the radiation direction is extremely limited, and as a result, the acoustic beam may not reach the entire listening area. Therefore, in the second embodiment described below, the position of the speaker (microphone) is detected each time, and the radiation direction of the acoustic beam radiated from the array speaker is appropriately determined according to the detected position. In this way, even if the stage is wide or the depth of the stage is narrow, the acoustic beam can be made to reach the entire listening area while radiating in a direction other than the microphone.

  FIG. 4 is a plan view showing a configuration when the sound system according to the second embodiment is applied to a lecture hall. In FIG. 4, the same reference numerals are given to the same components as those in FIG. 1. Also in the second embodiment, as in the first embodiment, the voice of the speaker is picked up by the microphone M, and the picked up sound is radiated as an acoustic beam W from the array speaker ASP. The emitted acoustic beam W is reflected by the side walls WL1 and WL2 of the lecture hall and reaches the listening area A2. The acoustic beam after reaching the listening area A2 is absorbed by the acoustic sound absorber B provided on the rear wall surface WL4.

  The microphone M is attached with a transmitter S0 that transmits a radio signal having a specific frequency. On the other hand, the front wall surface WL3 is provided with receiving devices S1, S2, and S3 that receive the radio signal. These transmitting device S0 and receiving devices S1, S2, S3 are position detecting means for detecting the position of the microphone M. A radio signal is periodically transmitted from the transmitting device S0, and the receiving devices S1 to S3 receive it. At this time, the distance between the transmitting device S0 and the receiving device S1, the distance between the transmitting device S0 and the receiving device S2, and the distance between the transmitting device S0 and the receiving device S3 vary depending on the position of the microphone M. Therefore, the time when each of the receiving devices S1, S2, and S3 receives the radio signal transmitted from the transmitting device S0 at the same time is different. Using the time difference, the installation position interval of the receivers S1, S2, and S3, and the propagation speed of the radio signal in the air, the trigonometric method calculates the transmitter for the receivers S1, S2, and S3. The position of S0 can be specified.

  FIG. 5 is a block diagram showing an electrical configuration of the array speaker ASP and its peripheral devices in the second embodiment. The main control unit CU is connected to the receiving devices S1 to S3, and specifies the position of the transmitting device S0 by the above-described method using the difference in time when the receiving devices S1 to S3 receive the radio signal. When the position of the transmitting device S0 (the position of the microphone M) is specified, the main control unit CU calculates a radiation angle θ that can avoid the microphone M. And in order to implement | achieve this radiation | emission angle (theta), the main control part CU sets an appropriate operation parameter to the delay circuits DL1-DL8 and the level control circuits W1-W8. As a result, the acoustic beam W can be emitted from the array speaker ASP at a radiation angle θ that avoids the microphone M.

  In this way, by changing the radiation angle of the array speaker θ according to the position of the microphone M, when the speaker is on the right side (downward in the drawing) as shown in FIG. The acoustic beam W3 radiated from the speaker ASP at the radiation angle θ2 (θ2 <0) is reflected by the side wall surface WL1 and then reaches the listening area A2. In addition, the acoustic beam W2 radiated at the radiation angle θ3 (θ3> 0) reaches the listening area A2 after being reflected by the side wall surface WL2. Neither acoustic beam W2, W3 reaches the position of the microphone M. Therefore, acoustic echo and howling cannot occur.

  On the other hand, as shown in FIG. 6, when the speaker is on the left side (above the paper surface) toward the listening area, the acoustic beam emitted from the array speaker ASP at the radiation angle θ2 ′ (θ2 ′ <0). W3 ′ reaches the listening area A2 after being reflected by the side wall surface WL1. The acoustic beam W2 'emitted at the radiation angle θ3' (θ3 '> 0) is reflected by the side wall surface WL2 and then reaches the listening area A2. None of the acoustic beams W2 'and W3' reach the position of the microphone M. Therefore, acoustic echo and howling cannot occur.

The embodiment of the present invention described above may be modified as follows.
For example, in the case of a lecture such as a question-and-answer format, not only the speaker but also the listener may become the speaker. In such a case, if the acoustic beam reaches the microphone of the listener, acoustic echo and howling may occur. Therefore, this problem may be solved by applying a technique for changing the radiation direction of the acoustic beam according to the position of the microphone as described in the second embodiment. Specifically, as shown in FIG. 7, a transmitter S4 that transmits a radio signal of a specific frequency is attached to a microphone M1 (second sound pickup means) dedicated to the listener, Receiving devices S5 to S7 that receive radio signals are provided. A radio signal is periodically transmitted from the transmission device S4, and the reception devices S5 to S7 receive it. That is, the transmitting device S4 and the receiving devices S5 to S7 are second position detecting means for detecting the position of the microphone M1 in the listening area. The main control unit CU specifies not only the position of the transmitting device S0 (the position of the microphone M) but also the position of the transmitting device S4 (the position of the microphone M1) based on the same principle as described in the second embodiment. The radiation angle θ that can avoid the microphones M and M1 is calculated. Then, the main control unit CU sets appropriate operation parameters for the delay circuits DL1 to DL8 and the level control circuits W1 to W8, so that the array speaker ASP has a radiation angle θ that avoids the microphones M and M1. An acoustic beam is emitted. By doing so, neither of the acoustic beams W4 and W5 shown in FIG. 7 reaches the positions of the microphones M and M1.

  Moreover, as the acoustic reflector, the ceiling surface may be used instead of the wall surface of the acoustic space, or the floor surface may be used. Or you may make it use the beam reflection apparatus only for reflection. FIG. 8 is a perspective view showing an example of a beam reflecting apparatus 100 that can be applied to the first embodiment and the second embodiment. The beam reflecting device 100 includes, for example, a parabolic or semicircular reflector 10, a shaft 20 that extends vertically downward from a lower portion of the reflector 10, and a base 30 that supports the shaft 20. A motor 40 is built in the base 30, and the shaft 20 is rotated in the arrow b direction by the rotation of the motor 40. Since the shaft 20 and the reflector 10 are fixed, as the shaft 20 rotates, the reflector 10 also rotates so as to swing its head in the direction of the arrow c about the axial direction of the shaft 20. That is, the motor 40 functions as reflecting surface driving means that changes the direction of the reflector (reflecting surface). If the amount of rotation of the reflector 10 is appropriately adjusted, the reflector 10 can be directed in the direction of the listening area. For example, the amount of rotation of the reflector 10 may be specified by operating an operation knob provided on the beam reflecting device 100, or by operating an operation panel connected to the beam reflecting device 100 via a communication cable. May be specified. In response to this operation, the motor 40 rotates the shaft by a specified amount. Moreover, the reflector 10 can use not only the concave surface as a reflective surface but also the back surface (convex surface) as a reflective surface. When the acoustic beam is reflected by the concave surface, the acoustic beam travels toward the listening area while converging in the space. On the other hand, when reflected by the convex surface, the reflected acoustic beam travels while diffusing in the space, contrary to the concave surface. Such a diffuse reflection method is convenient when, for example, a large number of listeners are moving around at a party venue and the position of each listener cannot be specified. Further, a re-radiating body formed by connecting a large number of cylindrical, prismatic or honeycomb-shaped cavities may be used as the acoustic reflector of the present invention.

  The microphone position detection means is not limited to the above-described one, and any known position detection technique can be applied. The installation position of the array speaker ASP is not necessarily limited to the back of the speaker, and may be a ceiling surface above the speaker or a wall surface on the side of the speaker. Further, the array speaker is used as the sound emitting means. However, if the radiation angle θ can be determined in advance as in the first embodiment, a directional sound wave can be emitted instead of the array speaker. A simple directional speaker may be used. However, as in the second embodiment, when detecting the position of the speaker and changing the radiation angle θ of the directional sound wave in order to avoid the speaker, it is desirable to use an array speaker. Note that the delay circuits DL1 to DL8 and the level control circuits W1 to W8 can be configured by a DSP. In this case, the audio signal from the terminal Tin is A / D converted and then supplied to the DSP, and the signal from the DSP is D / A converted and then supplied to the speaker units SP1 to SP8.

It is a figure explaining the principle for an array speaker to radiate | emit an acoustic beam. It is a figure showing the whole composition at the time of applying the sound system concerning a 1st embodiment of the present invention to a lecture hall. It is a block diagram which shows the electrical structure of the array speaker and its peripheral device in 1st Embodiment. It is a figure which shows the whole structure at the time of applying the acoustic system which concerns on 2nd Embodiment of this invention to a lecture hall. It is a block diagram which shows the electrical structure of the array speaker and its peripheral device in 2nd Embodiment. It is a figure which shows the whole structure at the time of applying the acoustic system which concerns on 2nd Embodiment of this invention to a lecture hall. It is a figure which shows the modification in 2nd Embodiment. It is a perspective view which shows an example of the beam reflection apparatus applicable to 1st Embodiment and 2nd Embodiment.

Explanation of symbols

A1 ... Sound collecting area, A2 ... Listening area, M, M1 ... Microphone, ASP ... Array speaker, SP1-SP8 ... Speaker unit, W1-W8 ... Level control circuit, DL1 ~ DL8 ... delay circuit, CU ... main control unit, UI ... operation unit, WL1, WL2 ... side wall surface, B ... acoustic sound absorber, S0 ... transmitter, S1, S2 , S3... Receiving device.

Claims (4)

Sound collection means for collecting sound;
A sound emitting means for radiating the sound collected by the sound collecting means as a directional sound wave in a direction other than the direction toward the sound collecting area where the sound collecting means may exist;
An acoustic system comprising: an acoustic reflector that reflects a directional sound wave emitted by the sound emitting means toward a listening area. Sound collection means for collecting sound;
Sound emitting means for emitting the sound collected by the sound collecting means as a directional sound wave;
An acoustic reflector that reflects the directional sound wave emitted by the sound emitting means toward a listening area;
Position detecting means for detecting the position of the sound collecting means;
An acoustic system comprising: control means for radiating the directional sound wave in a direction other than the direction toward the position of the sound collecting means detected by the position detecting means from the sound emitting means. Second sound collection means for collecting sound in the listening area;
Second position detecting means for detecting the position of the second sound collecting means,
The control means is a direction other than a direction toward the position detected by the position detection means and a direction other than the direction toward the position detected by the second position detection means. The acoustic system according to claim 2, wherein the directional sound wave is radiated from a sound source. Equipped with an acoustic sound absorber,
The acoustic system according to claim 1, wherein the acoustic reflector is disposed with a reflecting surface facing in a direction in which the reflected directional sound wave reaches the acoustic sound absorber without passing through the sound collection area.

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