JPS63135100A - Howling preventing equipment - Google Patents

Abstract

PURPOSE:To block the generation of howling by inserting a phase fluctuation circuit and a variable gain amplifier circuit controlled by an output of a control signal generating circuit in a system forming an acoustic loop. CONSTITUTION:A microphone 1 collecting mainly the voice of the sound source aud a microphone 7 collecting mainly speaker sound are used in an acoustic equipment having sound collection and reproducing system and the quantity of the signal level inputted to both is compared to control the variable gain amplifier circuit. Thus, the stable variable gain control is attained independently of the quantity of sound volume level in the sound field. Moreover, the phase fluctuation circuit 5 is provided to give a slow fluctuation to the phase of the sound wave radiated from the speaker thereby preventing the resonance of the sound wave only having a specific wavelength in the sound field, then no howling is caused and the output of the maximum sound volume level outputted by the accoustic equipment is obtained in the range where the feedback loop gain does not exceed the unity.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a howling prevention device that allows an acoustic device including a microphone, an amplifier, and a speaker to obtain the maximum volume output without causing howling.

Sound amplification is originally intended to amplify sounds that are difficult to hear and accurately convey the sound.
There are times when you want to improve the clarity, but if you carelessly raise the loudspeaker volume, oscillation due to howling will occur, which could lead to a fatal defect in the loudspeaker system. There is.

Therefore, as a method for preventing howling, various methods have been proposed in the past to suppress the amount of feedback of speaker sound to the microphone.

For example, (1) Use a microphone that is directional to the sound source and bring it as close to the sound source as possible to increase the ratio of direct sound to indirect sound. (2) Use speakers with sharp directivity to suppress positive feedback of indirect sounds.

(3) Limiting the vicinity of the peak value of the transmission frequency characteristic using an equalizer. (4) Shift the phase. (5) Give frequency fluctuation. (6) Change the switch so that the speaker sound does not enter the microphone. There are other methods.

However, even when these methods are adopted, (1
) and (2) cannot be applied to moving sound sources. (
3) There are many howling frequencies other than the peak value.

Regarding (4), the influence of phase shift is not uniform depending on frequency, sound pressure level, reflection, etc. (5) On the contrary, howling may be more likely to occur. (6) has limited uses. For reasons such as this, within the range where howling does not occur,
It is difficult to create an acoustic system that can consistently produce maximum volume.

Therefore, when we closely observe howling occurs, we find that (
b) Oscillation phenomenon occurs even when the speaker is not producing sound. (B)
When the degree of amplification is increased...the Uring rises steeply. (
C) The frequency waveform of howling is close to a pure tone.

) Frequencies that have a harmonic relationship with the oscillation frequency tend to oscillate. (e) When the microphone is moved away from the speaker on the radiation line, howling with almost the same oscillation frequency can be seen at multiple locations. (f) Induced by the position of the reflecting object. (g) The oscillation state continues. (b) The oscillation state may disappear spontaneously. (S) Small-level oscillations appear and disappear. ) If high-level audio is applied to the microphone during oscillation, the noise will temporarily disappear. ) When howling occurs, if an audio signal with a level as high as the oscillation level is applied, the howling will be masked by the audio signal.

Phenomena such as these are observed.

Considering these phenomena, we find that there are electrical factors such as the amplification of the loudspeaker, the frequency characteristics, voltage characteristics, phase characteristics, and noise of the various electrical components used in this device, and the propagation through the air. It can be seen that no-ring is easily induced due to the synergistic effect of the physical factors of the sound waves, such as the speed, phase, reflection, interference, and diffraction of the sound waves.

As mentioned above, the present invention focuses on the fact that the various phenomena that cause howling to occur consist of electrical factors and physical factors of sound waves, and realizes an effective howling prevention device. That's what I got.

The present invention provides a first microphone that mainly picks up direct sound from a sound source and a second microphone that mainly picks up speaker sound, so that the signal level input to the first microphone and the second microphone By detecting the level difference between the signal levels input to the audio signal line and controlling the amplification degree of the variable gain amplifier circuit inserted into the audio signal line, the gain of the acoustic feedback loop is prevented from exceeding 1, and the gain of the speaker By giving a gradual phase fluctuation to the amplified sound emitted by the speaker, so that the first microphone in the acoustic feedback loop receives a sound wave with a specific wavelength due to reflection or interference, , to prevent continuous and repeated synchronized input.

Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a block diagram of one embodiment of the present invention.

In the figure, 1 is a first microphone, 2 is a preamplifier, 3 is a power amplifier, and 4 is a speaker. The first microphone 1, preamplifier 2, power amplifier 3, and speaker 4 constitute a public address system. ing.

Reference numeral 5 denotes a phase fluctuation circuit, which is connected to the preamplifier 2 and applies phase fluctuation to the signal output from the preamplifier 2. A variable gain amplifier circuit 6 controls the gain of the output of the phase fluctuation circuit 5 and supplies it to the power amplifier 3. 7 is the second
A microphone 8 is a preamplifier connected to a second microphone 7, and the second microphone 7 mainly picks up the sound from the speaker 4. 9 is a first rectifier circuit, 10 is a second rectifier circuit, the first rectifier circuit 9 rectifies the output of the preamplifier 2, and the second rectifier circuit 10 rectifies the output of the preamplifier 8, respectively. 11 is an addition circuit, 12 is a level comparison circuit,
The adder circuit 11 obtains the summed output of the outputs of the first rectifier circuit 9 and the second rectifier circuit 10, and the level comparator circuit 12
is a level comparison circuit that outputs a high level output when the output level of the first rectifier circuit 9 is smaller than the output level of the second rectifier circuit 10. 13 is a first gate circuit; 14 is an integration circuit; the first gate circuit 13 supplies the addition output of the addition circuit 11 to the integration circuit 14; On the other hand, the first gate circuit 13 is controlled intermittently by the output of the level comparison circuit 12. Reference numeral 15 denotes a control current generating circuit, which supplies a control current to the variable gain amplifier circuit 6 according to the integrated output of the integrating circuit 14. A second gate circuit 16 controls the discharge of the integrating circuit 14.

Reference numeral 17 denotes a logic signal generation circuit, which receives the outputs of the adder circuit 11 and the level comparison circuit 12 and controls the second gate circuit 16 on and off. A portion 18 surrounded by a dotted line constitutes a control signal generation circuit.

The portion 19 surrounded by the dashed line constitutes the howling prevention device according to the present invention.

In the howling prevention device 19 configured in this way, the first microphone 1, the preamplifier 2, the phase fluctuation circuit 5, the variable gain amplifier circuit 6, the power amplifier 3, and the speaker 4 are configured to listen to the sound input from the first microphone l. A feedback loop is formed in which the signal is emitted by the speaker 4, and the sound wave emitted by the speaker 4 is input again to the first microphone l, and further, the input signals of the first microphone 1 and the second microphone 7 are The first rectifier circuit 9 and the second rectifier circuit 10 rectify the signal and add it to the control signal generation circuit 18, and the gain of the variable gain amplifier circuit 6 inserted into the audio signal line is controlled according to the output of the control signal generation circuit 18. Configure an automatic gain control circuit.

First, the functions of the first microphone 1 and the second microphone 7 will be explained. The first microphone 1, which mainly picks up the sound source of the sound, and the second microphone 7, which mainly picks up the speaker sound, determine the relative level between the sound level of the sound source and the volume level emitted from the speaker 4. By setting it up so that it can be compared with
Even if the volume level of the emitted sound is small or large, the level difference can be accurately detected. Therefore, the feedback loop gain can be accurately controlled. In addition, the first microphone l and the second
If the microphone 7 is made movable as one unit, the first microphone l and the second microphone integrated with the speaker 4 can be moved.
Due to the distance relationship with the microphone 7, a level difference occurs between the input signal level detected by the first microphone l and the input signal level detected by the second microphone 7. By detecting this level difference, the gain of the variable gain amplifier circuit 6 inserted into the audio signal line can be controlled.

Next, the function of the phase fluctuation circuit 5 will be explained. The phase fluctuation circuit 5 is inserted into the audio signal line in the acoustic feedback loop, and determines the maximum phase deviation angle of the audio signal that passes through the phase fluctuation circuit 5 to cause phase fluctuation, for example. The phase of the audio signal is fluctuated by setting the sweep period to 180°, for example, about 0.5 seconds, but this phase fluctuation causes an audible difference when the audio signal is emitted from the speaker 4. It's to the point where you can't even feel it.

Here, the situation in which howling occurs will be analyzed.

When howling occurs, it often increases until it reaches a saturation point, but the above-mentioned (a), (ni), and (7)
, as seen in the Q sword, excavations that do not reach the saturation point often appear. In addition, as seen in Kura, ni), (e), and (e), due to the acoustic conditions unique to the sound field, including feedback loops, sound waves of specific wavelengths resonate due to reflection and interference. It is thought that the howling generated in the reproduction system increases as these oscillations and resonances work together synergistically. Generally, the transmission characteristics of an acoustic system rarely have completely flat characteristics over a wide band. Sound fields and acoustic devices that have sound collection and reproduction systems have variations in transmission frequency characteristics. However,
When the amplification degree of the audio device is gradually increased, the entire frequency spectrum included in the audio signal transmission band is not equally amplified, and a particular frequency spectrum that is particularly emphasized quickly exceeds the loop gain l. Excavation and resonance. If you further increase the amplification of the audio equipment, the second, third,
...and countless oscillation frequency spectra appear. On the other hand, when the transmission energy changes, the reflectance of the sound wave and the voltage-phase characteristics of the electrical system change, and this causes the resonance spectrum of the sound wave to fluctuate and howling to appear and disappear. ), (male, ←), and Quri can be seen as examples.

Based on the above analysis results, the present invention automatically controls the gain of the feedback loop by using a combination of the first microphone 1 and the second microphone 7, and also uses the phase fluctuation circuit 5 to control the sound field. The control signal generating circuit 18 is constructed to prevent resonance of a specific frequency in the control signal generating circuit 18. Next, the operation of the control signal generating circuit 18 will be explained. When a sound is emitted from a sound source, this sound is! 1 microphone l and the second microphone 7, but the first
The microphone 1 is installed so that it can easily pick up the direct sound mainly from the sound source, and the second microphone 7 is installed so that it can easily pick up the sound mainly from the speaker, so the input level of the first microphone 1 is , which is higher than the input level of the second microphone 7. Therefore, the audio signal level at which the output of the first microphone l is input to the first rectifier circuit 9 via the preamplifier 2 is the same as the level at which the output of the second microphone 7 is input to the second rectifier circuit via the preamplifier 8. This is higher than the audio signal level input to IO. Since the rectified output output by the first rectifier circuit 9 is larger than the rectified output of the second rectifier circuit 10, the level comparison circuit 12H does not have a low level, and the gate circuit 1
3 is non-conductive. Therefore, no input signal is supplied to the integrating circuit 14. Since the control current generating circuit 15 does not receive multiple outputs as the integrating circuit 14 does, it does not output a control current. The sound from the sound source input to the IT microphone l is input to the phase fluctuation circuit 5 via the preamplifier 2, subjected to phase fluctuation by the phase fluctuation circuit 5, and input to the variable gain amplifier circuit 6. Since the variable gain amplifier circuit 6 receives no more control current than the control current generation circuit 15, only the output of the phase fluctuation circuit 5 is outputted to the power amplifier 3. The audio signal power-amplified by the power amplifier 3 is emitted by the speaker 4. .

On the other hand, the sound waves emitted by the speaker 4 are feedback-backed and input to the first microphone 1 and the second microphone 7 by an acoustic feedback loop. If the input level of the first microphone l is lower than the input level of the second microphone 7, the first microphone l
Contrary to the case where the input level of the second microphone 7 is higher than the input level of the second microphone 7, the rectified output of the first rectifier circuit 9 is smaller than the rectified output of the second rectifier circuit 10. becomes high level, and the gate circuit 13 becomes conductive. Further, the rectified output of the first rectifying circuit 9,
The rectified outputs of the second rectifier circuit 10 are summed by an adder circuit 11, and then applied to an integrator circuit 14 via a gate circuit 13, where they are accumulated. The output of the integrating circuit 14 is applied to a control current generating circuit 15, and the control current generating circuit 15 generates a control current according to the output of the integrating circuit 14. The variable gain amplifier circuit 6 is attenuated and controlled in accordance with the control flow generated by the control current generation circuit 15. The signal input to the first microphone l is input to the phase fluctuation circuit 5 via the preamplifier 2, and after being given phase fluctuation by the phase fluctuation circuit 5, it is input to the variable gain amplifier circuit 6, and the signal is input to the variable gain amplifier circuit 6. The signal applied to the amplifier circuit 6 is controlled according to the output level of the control signal generation circuit 18.
controls the variable gain amplifier circuit 6 so that the feedback loop gain does not exceed 1. Variable gain amplifier circuit 6
The output of is supplied to a power amplifier 3, and the signal power-amplified by the power amplifier 3 is emitted by a speaker 4.

The logic signal generation circuit 17 detects that the output of the adder circuit 11 is at a predetermined level or higher and is increasing with a steep rise, and the output of the level comparison circuit 12 is at a low level. Sometimes it outputs a high level signal. The second gate circuit 16 becomes conductive when the output of the logic signal generating circuit 17 is at a high level, and controls the discharging of the integrating circuit 14.

FIGS. 2 and 3 show howling prevention device 1 according to the present invention.
FIG. 9 is a block diagram of an embodiment of the present invention when the system 9 is applied to a two-way loudspeaker telephone, a multi-channel simultaneous broadcasting device, and the like. The same reference numerals are given to the same main parts as in FIG. 1, and the explanation thereof will be omitted.

In FIG. 2, a first microphone 1, a preamplifier 2,
The power amplifier 3, the speaker 4, and the howling prevention device 19 constitute a transmission transmission circuit, and the microphone 20 and the amplifier 2
1. The speaker 22 constitutes a reception transmission circuit. By considering the speaker 4 and the microphone 20 as an acoustic coupler, the portion 23 surrounded by the two-dot chain line can be considered equivalent to the howling prevention device 19 described in FIG.
The first microphone 1, the preamplifier 2, the anti-knolling device 23, the amplifier 21, and the speaker 22 constitute an acoustic feedback loop.

FIG. 3 shows an embodiment in which the anti-knolling device 19 shown in FIG. 2 is inserted in the receiving and transmitting circuit.

As described above, the present invention provides an acoustic device having a sound collection and reproduction system, which uses a microphone that mainly collects the sound of the sound source and a microphone that mainly collects the sound of the speaker.
Since the variable gain amplifier circuit is controlled by comparing the magnitude of the signal level input to the other side, stable variable gain control can be performed without being affected by the volume level in the sound field. In addition, by imparting gentle phase fluctuations to the sound waves emitted from the speakers, we prevent only sound waves with a specific wavelength from resonating in the sound field, so feedback loop gain can be increased without causing howling. As long as the value does not exceed 1, an output at the maximum volume level that the audio device can output can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of a circuit of a public address system equipped with a no-no-ring prevention device according to the present invention. FIGS. 2 and 3 show other embodiments including the circuit shown in FIG. 1. 1... 1st microphone, 2, 8...
Preamplifier, 3... Power amplifier, 4...
・Speaker, 5... Phase fluctuation circuit, 6...
...Variable gain amplifier circuit, 7...Second microphone, 9...First rectifier circuit, 10...
Second rectifier circuit, 11...Addition circuit, 12...
...Level comparison circuit, 13...First gate circuit, 14...Integrator circuit, 15...Control current generation circuit, 16...Second Gate circuit, 17
...Logic signal generation circuit, 18 ... Control signal generation circuit, 19.23 ... No-wring prevention device, 20 ... Microphone, 21 ...・・・
...Amplifier, 22...Speaker.

Claims (2)

[Claims] (1) Sound collection consisting of a microphone, amplifier, and speaker;
A device for preventing howling occurring in a reproduction system, comprising: a first microphone that mainly collects direct sound from a sound source; a phase fluctuation circuit and a variable gain amplification circuit inserted between the first microphone and a speaker; and a speaker sound. a second microphone that mainly picks up sound, a first rectifier circuit that rectifies the output of the first microphone, a second rectifier circuit that rectifies the output of the second microphone, and the outputs of the first and second rectifier circuits. By inserting the above-mentioned phase fluctuation circuit and the above-mentioned variable gain amplifier circuit controlled by the output of the above-mentioned control signal generation circuit into a system that is composed of a control signal generation circuit that generates a control signal and creates an acoustic loop. , a howling prevention device characterized in that it prevents howling from occurring. (2) In the above control signal generation circuit, an adder circuit that adds the output of the first rectifier circuit and the output of the second rectifier circuit, and a level that compares the output level of the first rectifier circuit and the output level of the second rectifier circuit. a comparator circuit, a first gate circuit that performs intermittent control based on the output of the level comparator circuit, an integrator circuit connected to the adder circuit via the first gate circuit, and a The control signal generation circuit is configured by a second gate circuit that controls the discharge of the integration circuit accordingly, and a control current generation circuit that generates a control current based on the output of the integration circuit. Howling prevention device according to scope 1.