JP2006197407A - Loudspeaker system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a loudspeaker equipment capable of coping with generation of howling in a different frequency band due to variation in an audio environment, and protecting a loudspeaker from an abrupt howling. <P>SOLUTION: Howling detector 12 detects howling generation from an input signal. When howling occurs, it directs a tone control circuit 200 to suppress input signal at the generating frequency band. Moreover, the howling detector 12 detects the output signal level to a loudspeaker, and when detecting the signal with more than a predetermined level, it directs a switching circuit 8 to intercept the signal to it. The signal interception is canceled, when the tone control circuit 200 attenuates an input signal, further, the howling canceler 100 functions and the howling is suppressed. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a loudspeaker system that is installed in a lecture hall, a hall, or the like and suppresses howling and protects a speaker.

  In general, when a loudspeaker is used in a lecture hall, a hall, or the like, sound output from a speaker is input to a microphone again through an acoustic path having a certain transfer function. That is, a closed loop is formed by the path of microphone-amplifier-speaker-acoustic path-microphone. When the gain of the closed loop exceeds 1, the sound returned from the speaker to the microphone increases, and howling occurs.

  As a method for preventing this howling, there is a method in which an equalizer, a compressor (limiter), or the like is inserted into an amplification path from a microphone to a speaker and these are manually adjusted.

  In such a system, it is necessary to actually generate howling, manually detect the frequency at which howling is generated using a graphic equalizer or a parametric equalizer, and manually lower the volume level of the frequency. In such a method, not only does the adjustment time take much, but even after the adjustment, howling may occur if the positional relationship between the speaker and the microphone changes. Needed.

To solve such problems, a method has been proposed in which the peak frequency at which howling occurs is automatically detected, the equalizer is adjusted to automatically reduce the volume of the peak frequency when howling occurs, and a compressor is applied. ing. (For example, see Patent Document 1)
JP-A-6-46490

  However, the howling prevention processor described in Japanese Patent Laid-Open No. 2004-228561 is configured to generate howling by manually increasing a gain at the time of installation or the like, and to operate after measuring the frequency at which howling occurs. Therefore, there is a problem that it is impossible to cope with howling that occurs in a band different from the frequency at the time of measurement due to a change in the positional relationship between the speaker and the microphone or a change in the installation environment (for example, a change in temperature and humidity).

  In addition, the compressor starts compression when a signal exceeding the threshold level is input, and gradually decreases the output signal. Therefore, when the howling occurs suddenly due to changes in the sound field environment, the signal immediately decreases. In this case, an excessive signal is input to the speaker, which may damage the speaker.

  In view of the above circumstances, the present invention can cope with the occurrence of howling in different frequency bands due to changes in the sound field environment, and can protect a speaker even if howling occurs suddenly. The purpose is to provide.

  According to the first aspect of the present invention, there is provided an adjustment circuit for adjusting sound quality of an input signal from a microphone, a signal blocking means for turning on / off a signal output to a speaker, an input signal level from a microphone or an output signal to a speaker A howling detection means for detecting the level and detecting howling and its frequency is provided, and when detecting howling, the howling detecting means suppresses the level of the input signal to the adjustment circuit for the detected frequency band. The generation of howling is detected, and when a signal having a level higher than a predetermined level is output to the speaker, the signal blocking means is instructed to block the signal.

  In the present invention, there is provided a howling detection means for detecting a howling occurrence frequency by detecting an input signal level from a microphone. The frequency spectrum of the input signal is detected, and when it is determined that the signal level of a certain frequency has increased, it is determined that howling has occurred at that frequency. When howling is detected, the input signal level in the detected frequency band is suppressed. For example, the equalizer may be operated so as to attenuate the detected frequency band component, or the signal may be attenuated by an attenuator or a compressor. Further, equalization may be performed so that only the detected frequency band is attenuated. Further, the howling detection means also detects an output signal level to the speaker, and when a signal having a level higher than a predetermined level is output to the speaker, the switch is turned off to block the signal. The predetermined level is, for example, when an input of about ½ of the rated input of the speaker is made. As a result, the speaker can be protected even if howling occurs suddenly.

  According to a second aspect of the present invention, in the above invention, the howling detection unit instructs the signal blocking unit to release the blocking of the signal when occurrence of howling is not detected. .

  In the present invention, when a signal having a level higher than a predetermined level is input to the speaker, the switch is turned off to cut off the signal and suppress the input signal level in the detected frequency band, but howling is suppressed. Switch on. When howling occurs abruptly, a high level signal is input to the speaker and thus the signal is blocked. However, by suppressing the signal level in the detected frequency band, the input level of the speaker can be lowered. Therefore, the switch is turned on when howling is suppressed. As a result, the time for blocking the signal can be minimized.

  As described above, according to the present invention, howling is generated in different frequency bands due to changes in the sound field environment by detecting the frequency band of howling occurrence and suppressing the level of the detected frequency band at the time of howling occurrence. Can also respond.

  Also, when the input level of the speaker is detected and an input signal of a predetermined level or higher is detected, the switch is instantly turned off and the signal is cut off, so that the speaker can be protected even if a sudden howling occurs. It becomes possible.

  Hereinafter, a loudspeaker system according to an embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a block diagram of a loudspeaker system. As shown in the figure, this loudspeaker system includes a microphone 1 to which an audio signal is input, a microphone amplifier 2 that is a front-end amplifier, an A / D converter 3 that converts an output signal of the microphone amplifier 2 into a digital signal, A / Howling canceller 100 connected to the output terminal of D converter 3, sound quality adjusting circuit 200 for adjusting the output signal of howling canceller 100, switch circuit 8 connected to the output terminal of sound quality adjusting circuit 200, and output signal of switch circuit 8 D / A converter 9 that converts the signal into an analog audio signal, power amplifier 10 that amplifies the audio signal, speaker 11 that produces audio from the audio signal input from the power amplifier 10, and output signal and power of the A / D converter 3 Howling detector 1 to which the output signal of amplifier 10 is input Consists, microphone 1 and speaker 11 are disposed in the auditorium and halls like. The howling detector 12 can input both a digital signal and an analog signal. When an analog signal is input, A / D conversion can be performed internally for digital processing.

  The howling canceller 100 is configured to add an adder 4 inserted between the A / D converter 3 and the sound quality adjustment circuit 200, an adaptive filter 14 that inputs a signal to the adder 4, and a signal output from the sound quality adjustment circuit 200. A delay circuit 13 for supplying the adaptive filter 14 after time delay is provided.

  The sound quality adjustment circuit 200 includes an equalizer 5 connected to the output side of the adder 4, an attenuator 6 connected to the output of the equalizer 5, and a compressor 7 connected between the attenuator 6 and the switch circuit 8. .

  The audio signal input to the microphone 1 is converted to a digital signal by the A / D converter 3 through the front-end microphone amplifier 2 and input to the adder 4. The adder 4 subtracts the output signal of the adaptive filter 14 from the input signal from the microphone 1 and outputs the result. The output signal of the adder 4 is adjusted in sound quality by the equalizer 5 and input to the attenuator 6. The attenuator 6 attenuates the input signal and outputs a signal. The signal output from the attenuator 6 is input to the compressor 7. The compressor 7 attenuates by changing the ratio of the volume to the input signal when the input signal exceeds a predetermined level (threshold). The signal output from the compressor 7 is converted into an analog audio signal by the D / A converter 9 via the switch circuit 8 and is input to the speaker 11 after being amplified by the power amplifier 10. The speaker 11 generates sound from the input sound signal. Here, the sound produced from the speaker 11 is re-input to the microphone 1 as a feedback signal.

  In such a configuration, a closed loop is formed by the route of the microphone 1 -the sound quality adjustment circuit 200 -the speaker 11 -the microphone 1. When the gain of this closed loop exceeds 1, the sound that returns from the speaker to the microphone increases, resulting in howling.

  In the howling canceller 100, the audio signal input from the microphone 1 is propagated through the sound quality adjusting circuit 200, the speaker 11, and the microphone 1 by the delay circuit 13 and the adaptive filter 14, and is returned to the microphone 1 again. This simulates the transmission characteristics of a series of voice transmission paths until they are input as.

  The delay circuit 13 provides a time delay that estimates the time delay of the feedback signal that is fed back from the speaker 11 to the microphone 1. The signal output after being given a time delay by the delay circuit 13 is input to the adaptive filter 14.

  The adaptive filter 14 is a filter that simulates the transfer function of the acoustic feedback path, and filters the signal delayed by the delay circuit 13. The filtered output signal is output to the adder 4 as a simulation signal. The adder 4 subtracts the simulation signal from the input signal of the microphone 1.

  The howling canceller 100 provided with such an adaptive filter 14 uses the current residual signal, which is a signal obtained by subtracting the simulation signal from the input signal of the microphone 1, and the past residual signal output from the delay circuit 13. Originally, the filter coefficient is updated so that the simulated signal matches or approximates the feedback signal, so when a continuous sound of a certain frequency is input due to howling, the continuous sound is canceled over time. It is possible.

  Without the delay circuit 13, the signal input to the microphone 1 is input to the adder 4 and also input to the adaptive filter 14 without delay. Since the adaptive filter 14 updates the filter coefficient so as to reduce the residual signal, all signals input from the microphone are canceled by the output signal of the adaptive filter 14 in the adder 4 as the filter coefficient is updated. It becomes like this. For this reason, the delay circuit 13 is indispensable for canceling the feedback signal by the simulated signal while preventing cancellation of the sound source signal.

  The howling detector 12 constantly monitors the signal input from the microphone 1 and detects howling. Specifically, the howling detector 12 determines that howling has occurred when a specific frequency component of the input signal is input without being attenuated for a predetermined time or more. When it is determined that howling has occurred, the sound quality adjustment circuit 200 is instructed to suppress the input signal.

  In order to detect the frequency at which howling occurs, the howling detector 12 performs fast Fourier transform (hereinafter referred to as FFT) on the input signal. By detecting howling frequency, it is possible to suppress only that frequency band. Note that any method can be used as long as it can detect howling in a plurality of frequency bands without being limited to FFT. For example, a howling may be detected by dividing a signal into a plurality of frequency bands using a band-pass filter or the like.

  When detecting howling, the howling detector 12 instructs the equalizer 5 and the compressor 7 of the sound quality adjustment circuit 200 to suppress and output the input signal. When the frequency at which howling occurs as described above is detected, the equalizer 5 is instructed to suppress the amplitude level of the signal in that frequency band. Further, the howling detector 12 instructs the compressor 7 to perform a signal level suppression process of a predetermined compression rate with respect to an input signal having a predetermined amplitude level or higher. The equalizer 5 may control a plurality of frequency bands.

  FIG. 2 is a block diagram for explaining the equalizer 5 in detail. As shown in the figure, the equalizer 5 includes a low sound range equalizer 5a, a mid sound range equalizer 5b, and a high sound range equalizer 5c. Each equalizer can be further adjusted by dividing the frequency band into a plurality. Each equalizer is a parametric equalizer that can vary the adjustment frequency band. The low sound range equalizer 5a, the middle sound range equalizer 5b, and the high sound range equalizer 5c are connected to the howling detector 12, respectively. The howling detector 12 controls each equalizer so as to suppress the detected howling occurrence frequency. In addition, not only a parametric equalizer but a graphic equalizer may be used. Any equalizer may be used as long as the equalizer can divide and adjust the frequency band.

  At this time, the low sound range equalizer 5a, the mid sound range equalizer 5b, and the high sound range equalizer 5c may be instructed to suppress signals with different frequency bandwidths. For example, the low sound range equalizer 5a is suppressed in a wide frequency band, and the high sound range equalizer 5c is suppressed in a narrow frequency band. As a result, it is possible to suppress a signal due to howling without deteriorating sound quality.

  The equalizer is not limited to the three-band equalizer as shown in this example, and the equalizer may be further divided into a plurality of bands. For example, it may be divided into four bands, a low sound range, a low mid sound range, a mid sound range, and a high sound range.

  The howling detector 12 also detects the output signal level to the speaker 11. When howling occurs, a high-level signal with a constant frequency is input, and a higher voltage than that during normal use is input to the speaker 11, which may damage the speaker. Therefore, when a signal of a predetermined level or higher is input to the speaker 11, the switch circuit 8 is instructed to cut off the signal. Thereafter, the attenuator 6 is operated to instruct the switch circuit 8 to connect a signal after suppressing the signal level. The attenuator 6 adjusts the input signal level to ½. As a result, when the switch circuit 8 is connected, the attenuator is connected while suppressing the input signal, so that the speaker can be protected.

  The output signal level to the speaker detected by the howling detector 12 is not limited to the output signal level of the power amplifier 10 as shown in FIG. The output signal level of the D / A converter 9 or the output signal level of the compressor 7 may be used. The signal level between the sound quality adjustment circuit 200 and the speaker 11 may be detected.

  Further, the switch circuit 8 is not limited to the example connected between the compressor 7 and the D / A converter 9 as shown in FIG. It may be connected between the D / A converter 9 and the power amplifier 10, or may be connected between the power amplifier 10 and the speaker 11. What is necessary is just to connect to either between the sound quality adjustment circuit 200 and the speaker 11.

  Next, the operation of the howling detector 12 will be described in detail. FIG. 3 is a flowchart showing how the howling detector 12 operates. This operation is started when an input signal is detected. First, an input signal is captured (s1), FFT is performed, and a frequency spectrum is detected. Thereafter, it is determined whether howling has occurred (s2). When a specific frequency component is detected as a high level signal of a predetermined level or higher, it is determined that howling has occurred. When it is determined that no howling has occurred, the operation is terminated (s2 → END).

  When the occurrence of howling is detected, the output signal level to the speaker 11 is detected, and it is determined whether there is an output signal level equal to or higher than a predetermined threshold (s3). The predetermined threshold is set to 1/2 of the rated input of the speaker, for example. When the output signal level to the speaker 11 exceeds a predetermined level, the switch circuit 8 is instructed to cut off the signal (s4), and then the attenuator 6 of the sound quality adjustment circuit 200 is operated to input signal level. Is adjusted to 1/2 (s5). The adjustment amount is not limited to ½ and may be set to any amount.

  Thereafter, the sound quality adjustment circuit 200 is instructed to suppress the input signal (s6). Even if howling occurs, if the output signal level to the speaker 11 is below a predetermined level, the sound quality adjustment circuit 200 is instructed without blocking the signal (s3 → s6). Since the sound quality adjustment circuit 200 includes the equalizer 5 and the compressor 7 as described above, the sound quality adjustment circuit 200 instructs to suppress the signal according to the detected howling.

  Thereafter, it is determined whether howling has occurred (s7). If howling still occurs, the signal suppression process is repeated (s7 → s3). If it is determined that no howling has occurred, the switch circuit 8 is instructed to be connected (s8). However, if the switch circuit 8 is already connected, this process is omitted.

  Thereafter, the frequency characteristic of the equalizer 5 is returned to a flat state, the compression by the compressor 7 is released, and the signal suppression by the attenuator 6 is released (s9). These release processes may be performed by gradually reducing the suppression level over time.

  As described above, the loudspeaker system of the present invention detects howling from the input signal, and when howling occurs, suppresses the input signal for the generated frequency band, thereby different frequency bands due to changes in the sound field environment. It is possible to deal with the occurrence of howling at the site.

  Also, when the output signal level to the speaker is detected and the input exceeds the predetermined level, the signal is cut off and the signal is suppressed by the attenuator, so that the speaker can be protected even if howling occurs suddenly. It becomes possible.

Block diagram of the loudspeaker system of the present invention Block diagram explaining the equalizer in detail Flow chart showing howling detector

Explanation of symbols

1-microphone 2-microphone amplifier 3-A / D converter 4-adder 5-equalizer 5a-low range equalizer 5b-mid range equalizer 5c-high range equalizer 6-attenuator 7-compressor 8-switch circuit 9-D / A Converter 10-Power amplifier 11-Speaker 12-Howling detector 13-Delay circuit 14-Adaptive filter 100-Howling canceller 200-Sound quality adjustment circuit

Claims (2)

An adjustment circuit for adjusting the sound quality of an input signal from the microphone, a signal blocking means for turning on / off a signal output to the speaker, an input signal level from the microphone or an output signal level to the speaker, detecting howling and Including howling detection means for detecting the frequency,
The howling detection means, when detecting the occurrence of howling, instructs the adjustment circuit to suppress the level of the input signal for the detected frequency band,
A loudspeaker system characterized by detecting occurrence of howling and instructing the signal blocking means to block a signal when a signal having a level higher than a predetermined level is output to a speaker.   2. The loudspeaker system according to claim 1, wherein the howling detection unit instructs the signal blocking unit to release blocking of a signal when occurrence of howling is not detected. 3.

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