JPH05210391A - Muffler - Google Patents

Abstract

PURPOSE:To suppress the generation of howling on the conditions of generating howling although setting the sound pressure level of acoustic waves transmitted from a speaker at a high level so as to normally muffle even the acoustic waves at the high sound pressure level as well. CONSTITUTION:A microphone 1 is provided to detect acoustic waves in a sound field. A speaker 2 is provided to transmit acoustic waves into the sound field. A signal generating circuit 3 is provided to generate a driving signal to the speaker 2 based on the output signal of the microphone 1. Further, this signal generating circuit 3 is provided with an inverted amplifier circuit 31 to invert the phase of the output signal from the microphone 1 and an AGC circuit 32 to reduce an amplification factor when the level of the output signal from the microphone 1 exceeds a prescribed threshold value. Then, the acoustic waves transmitted from the speaker 2 are muffled by being interferred by acoustic waves in the sound field.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention detects a sound wave in a sound field by a microphone and drives a speaker by a drive signal generated based on an output signal of the microphone, and converts the sound wave sent from the speaker into a sound wave in the sound field. The present invention relates to a muffling device that muffles sound waves in a sound field by causing interference.

[0002]

2. Description of the Related Art Conventionally, as shown in FIG.
A sound wave (especially noise) propagating through the inside of the speaker 1 is detected by the microphone 1, and the speaker 2 is driven by the drive signal generated by the signal generation circuit 3 based on the output signal of the microphone 1.
There is known a silencer called an active type which drives a and 2b. The signal generation circuit 3 includes an inverting amplification circuit 31 having a constant amplification degree, and the microphone 1
Drive signal having a phase opposite to that of the output signal is generated. Therefore, if the distance between the microphone 1 and the speakers 2a, 2b is set appropriately, the phase of the sound waves transmitted from the speakers 2a, 2b is made opposite to the phase of the sound waves propagating in the duct 4. The sound waves around the speakers 2a and 2b can be silenced by the interference between the sound waves.

[0003]

By the way, in the above structure, since the loop of the microphone 1-signal generation circuit 3-speakers 2a, 2b-microphone 1 is formed, the amplification factor of this loop is 1. If larger and positive feedback occurs, howling will occur.

Generally, if the level of the drive signal is set so that the sound wave in the duct 4 can be canceled out, the amplification degree becomes larger than 1. Therefore, when positive feedback occurs, a housing is generated. Here, the phase of the sound wave detected by the microphone 1 is the signal generation circuit 3
Therefore, if the phases of the sound waves sent from the speakers 2a and 2b are reversed when detected by the microphone 1, positive feedback will occur in the loop. Such a phenomenon occurs depending on the positional relationship between the microphone 1 and the speakers 2a and 2b, the reflection in the duct 4, the wavelength of the sound wave to be silenced, and the like.

For example, a microphone 1 and a speaker 2
When the distance between a and 2b is relatively small, the wavelength of the low-frequency component is long, so the phase of the sound wave is rarely inverted in the space between the speakers 2a and 2b and the microphone 1, but the high-frequency component. Since the wavelength becomes shorter, the phase inversion easily occurs. Further, when the duct 4 is a ventilation duct for ventilation and the noise of the ventilation fan is to be silenced, the wavelength of the sound wave may change depending on the velocity of the air flow, which may cause positive feedback.

To solve such a problem, it is conceivable to set the amplification degree of the above loop to such an extent that howling does not occur. That is, it is conceivable to set the amplification degree of the inverting amplifier circuit 31 to be small or to move the speakers 2a and 2b away from the microphone 1. However, when the amplification degree of the inverting amplification circuit 31 is set small, the amplification degree cannot be set to a level that can sufficiently muffle the sound waves transmitted from the speakers 2a and 2b, and the muffling effect is reduced. Further, when the speakers 2a and 2b are arranged at positions apart from the microphone 1, the sound waves detected by the microphone 1 and the speakers 2a and 2b are
The difference between the sound wave from the sound wave and the sound wave to be interfered becomes large, and the phase relationship cannot be predicted. That is, there is a problem in that the relationship of opposite phases cannot be obtained and the silencing effect is reduced.

SUMMARY OF THE INVENTION The present invention is intended to solve the above-mentioned problems, and by controlling the amplification degree of the signal generating circuit according to the level of the output signal of the microphone, it is usually possible to obtain a sufficient silencing effect. It is an object of the present invention to provide a muffling device that suppresses howling by limiting the amplification degree in a situation where howling occurs even though the amplification degree is set to a large value.

[0008]

According to the present invention, a microphone for detecting a sound wave in a sound field, a speaker for sending a sound wave in the sound field, and a speaker for amplifying an output signal of the microphone and changing a phase thereof are driven. It is premised on a muffling device that includes a signal generation circuit that generates a signal and that muffles a sound wave transmitted from a speaker by interfering with a sound wave in a sound field.

According to a first aspect of the present invention, in order to achieve the above object, a signal generation circuit includes an amplification section for amplifying an output signal of a microphone, a phase inverting section for inverting a phase of an output signal of the microphone, and an output signal of the microphone. And an amplification degree control section for reducing the amplification degree of the amplification section when the level exceeds a predetermined threshold value. In the second aspect, the frequency characteristic control unit for controlling the frequency characteristic of the drive signal is added to the signal generation circuit.

According to a third aspect of the present invention, the signal generating circuit is provided with a phase changing section for giving fluctuation to the phase of the drive signal. According to another aspect of the present invention, the signal generation circuit is formed by an amplification unit that amplifies the output signal of the microphone, a phase inversion unit that inverts the phase of the output signal of the microphone, a microphone, a signal generation circuit, a speaker, and a sound field. A howling detector that detects howling in the loop,
The amplification control section reduces the amplification degree of the amplification section when the howling detection section detects the occurrence of howling.

According to a fifth aspect of the present invention, the signal generation circuit has an amplification section that amplifies the output signal of the microphone, a phase inversion section that inverts the phase of the output signal of the microphone, and an amplification degree variation that gives fluctuations to the amplification degree of the amplification section. It has a section.

[0012]

According to the structure of claim 1, when the level of the output signal of the microphone exceeds a predetermined threshold value, the amplification degree of the signal generating circuit is reduced. Therefore, the threshold value is set to a level at which howling occurs. If this happens, howling will occur and the amplification will be reduced, and the conditions for howling will not be satisfied.As a result, it will be possible to suppress the howling while still being able to sufficiently muffle the sound in normal times. Of.

According to the structure of claim 2, since the frequency characteristic control unit for controlling the frequency characteristic of the drive signal is provided,
The sound waves in a specific frequency range can be effectively silenced, the amplification degree of the signal generation circuit can be set to be large, and the volume of sound to be mute can be increased. According to the configuration of claim 3, since the phase varying unit that gives fluctuations to the phase of the drive signal is provided, it is possible to prevent the phase condition that causes howling from being satisfied steadily, resulting in howling. It is possible to suppress the occurrence of. That is, the amplification degree of the signal generating circuit can be set to be large, and the volume of the sound can be increased.

According to the structure of claim 4, when the howling detector detects the howling, the amplification degree is reduced. Therefore, only when the howling occurs, the amplification degree is reduced and the occurrence of the howling is suppressed. Therefore, the degree of amplification can be set to a large value at all times, and the volume of sound to be erased is increased. According to the configuration of claim 5, since the amplification degree of the signal generating circuit is constantly changed, it is possible to control so that the condition is not satisfied immediately after the howling occurrence condition is satisfied, and as a result, Howling can be suppressed while ensuring a sufficient volume.

[0015]

First Embodiment As shown in FIG. 1, a microphone 1 for detecting a sound wave in a sound field, a speaker 2 for sending a sound wave in the sound field, and a speaker 2 based on an output signal of the microphone 1.
And a signal generation circuit 3 for generating a drive signal for driving the. The sound field has a higher sound deadening effect in a limited space such as in the duct 4 than in an open space.

The signal generating circuit 3 is an inverting amplifier circuit 31 which also serves as an amplifier and a phase inverter, and an amplification degree controller A.
And a GC circuit 32. The AGC circuit 32 is
As shown in FIG. 2, a circuit for feedback controlling the inverting amplifier circuit 31 so as to adjust the amplification degree of the inverting amplifier circuit 31 according to the level (amplitude voltage) of the output signal of the microphone 1 input to the inverting amplifier circuit 31. Is. That is,
The amplitude voltage of the output signal of the microphone 1 is the first threshold value V ₁
Until the gain reaches a constant value G
_When the amplitude voltage exceeds ₀ , and the amplitude voltage exceeds the first threshold value V ₁ , the amplification degree is decreased at a constant decrease rate as the amplitude voltage increases. Further, when the second threshold value V ₂ is exceeded, the rate of decrease of the amplification degree is increased.

However, if the amplification level G ₀ when the amplitude voltage of the output signal of the microphone 1 is equal to or lower than the first threshold value V ₁ is set to the extent that howling does not occur, the amplitude voltage of the output signal of the microphone 1 is set. However, when howling exceeds the first threshold value V ₁ and howling is likely to occur, the amplification degree decreases, and thus howling can be suppressed. Further, when the amplitude voltage exceeds the second threshold value V ₂ , the reduction rate of the amplification degree is further increased and the howling is surely prevented.

[0018]

Second Embodiment In this embodiment, as shown in FIG. 3, in order to correct the frequency characteristic in the loop of the microphone 1-signal generation circuit 3-speaker 2-microphone 1, the frequency characteristic control is performed by the signal generation circuit 3. A filter circuit 33 as a part is provided. The filter circuit 33 is inserted between the inverting amplifier circuit 31 and the speaker 2.

For example, a low pass filter having a frequency response as shown in FIG. 4 can be used as the filter circuit 33. By using the filter circuit 33 having such characteristics, the amplification degree of the high frequency component in the loop can be suppressed. That is, as described in the section “Problems to be Solved by the Invention”, since a high frequency component has a higher probability of causing howling, the use of a filter circuit 33 having such characteristics has an effect of suppressing howling. Is even higher. In other words, for the low frequency component, the amplification degree of the loop can be increased, so that it is possible to enhance the silencing effect with respect to the noise having a large sound pressure level of the low frequency component.

In the above embodiment, the inverting amplifier circuit 31 is used.
Although the filter circuit 33 is inserted between the speaker 2 and the speaker 2, the filter circuit 33 may be inserted in the output section or the input section of the AGC circuit 32. Further, the frequency response of the filter circuit 33 is not necessarily limited to the above-mentioned characteristics, and may be set appropriately according to the purpose.

[0021]

Third Embodiment In this embodiment, as shown in FIG. 5, a phase fluctuation circuit 34, which is a phase fluctuation unit that gives fluctuations to the phase of the output signal of the microphone 1, is provided between the inverting amplifier circuit 31 and the speaker 2. It is inserted. That is, the phase variation circuit 34 gives fluctuations to the phase of the signal obtained by inverting the phase of the output signal of the microphone 1 by the inverting amplifier circuit 31 (the phase is different by 180 degrees). For example, if the width of the phase fluctuation is ± α (<180) degrees, the drive signal to the speaker 2 is a signal that is out of phase with the output signal of the microphone 1 by (180 ± α) degrees. Such a phase fluctuation circuit 34 can be configured by using, for example, a delay circuit and a switch element. By turning the switch element on and off at indefinite intervals, the delay of the signal by the delay circuit is indefinite. It only has to occur at intervals.

According to the above configuration, even if the phase relationship between the output signal of the microphone 1 and the drive signal to the speaker 2 satisfies the condition of howling at a specific time, the phase relationship immediately changes thereafter. As a result, the howling occurrence condition is not satisfied, and as a result, howling occurrence can be suppressed. That is, it is possible to suppress howling while increasing the amplification level of the loop to increase the volume of the sound.

In the above embodiment, the inverting amplifier circuit 31 is used.
Although the phase fluctuation circuit 34 is inserted between the speaker 2 and the speaker 2, the phase fluctuation circuit 34 may be inserted in the output section or the input section of the AGC circuit 32.

[0024]

Fourth Embodiment In the present embodiment, as shown in FIG. 6, a frequency detection circuit 35 as a howling detection unit is provided in the signal generation circuit 3.
And the AGC circuit 3 as an amplification degree control unit when a signal of a predetermined frequency is detected by the frequency detection circuit 35.
By controlling 2, the amplification degree of the loop is lowered. Therefore, as the AGC circuit 32, a circuit in which the amplification degree of the inverting amplification circuit 31 is switched between two levels before and after howling is used. Frequency detection circuit 35
For example, a PLL circuit or the like can be used.

When the howling occurs, it is normal to oscillate at a single frequency, and therefore the occurrence of the howling can be detected by the frequency detection circuit 35. When the howling occurs, the amplification degree of the loop is changed. By lowering it, howling is suppressed. According to this configuration, even if the howling occurs, it can be stopped immediately, so that the amplification degree of the loop can be made large and the volume of the sound can be made large.

[0026]

[Fifth Embodiment] In this embodiment, as shown in FIG.
Instead of the circuit 32, an amplification degree changing circuit 3 which is an amplification degree changing section
6 is provided, and the amplification degree variation circuit 36 is configured to change the amplification degree of the inverting amplification circuit 31 with time as shown in FIG. That is, the amplification degree changing circuit 36 is used for the inverting amplification circuit 3 when howling occurs.
When the amplification degree of 1 is Gs, the amplification degree Gs is changed within a predetermined range (Ga <Gs <Gb) over time. For example, in FIG. 8, the amplification degree is periodically changed, and control is performed so that the time variation of the amplification degree is sawtooth.

According to this structure, even if howling is generated due to the increase in amplification of the loop, the amplification is decreased at the next moment and the howling condition is not satisfied, so that howling is not generated. It can be suppressed. Further, since the amplification degree Gb larger than the amplification degree Gs at the time of howling temporarily occurs is obtained, the mute volume becomes relatively large.

In the above configuration, since the sound volume to be silenced changes with the change of the amplification degree, a sound wave to be silenced causes a breathing phenomenon. However, the sound wave after the silence is changed by 1 / f fluctuation. If the amplification degree varying circuit 36 is configured, the discomfort caused by the breathing phenomenon after muffling is alleviated. In each of the above embodiments, the phase inverting unit is realized by the inverting amplifier 31, but the connection to the speaker 2 may be reversed in polarity to function as the phase inverting unit. Further, in each of the above embodiments, the internal processing in the signal generation circuit 3 is performed by an analog signal, but by configuring the signal generation circuit 3 using a DSP (digital signal processor) or the like, processing is performed by a digital signal. It is also possible.

[0029]

As described above, according to the configuration of claim 1, when the level of the output signal of the microphone exceeds a predetermined threshold value, the amplification degree of the signal generating circuit is reduced, so that howling occurs. If a threshold is set for the level of, when the howling occurs, the amplification degree is reduced and the howling generation condition is no longer satisfied. There is an advantage that the occurrence can be suppressed.

According to the structure of claim 2, since the frequency characteristic control section for controlling the frequency characteristic of the drive signal is provided,
The sound waves in a specific frequency range can be effectively silenced, and the amplification degree of the signal generating circuit can be set to be large, and the volume of sound to be silenced can be increased. According to the configuration of claim 3, since the phase varying unit that gives fluctuations to the phase of the drive signal is provided, it is possible to prevent the phase condition that causes howling from being satisfied steadily, resulting in howling. It is possible to suppress the occurrence of. That is, there is an effect that the amplification degree of the signal generation circuit can be set to be large and the volume of the sound can be increased.

According to the structure of claim 4, when the howling detecting section detects the howling, the amplification degree is reduced. Therefore, only when the howling occurs, the amplification degree is reduced and the occurrence of the howling is suppressed. Therefore, there is an advantage in that the amplification degree can be set to a large value at all times, and the volume of the sound is increased. Claim 5
According to the configuration, since the amplification of the signal generation circuit is constantly changed, it is possible to control so that the condition is not satisfied immediately after the howling occurrence condition is satisfied, and as a result, sufficient muffling is achieved. Howling can be suppressed while the amount can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram illustrating a first embodiment.

FIG. 2 is an operation explanatory diagram showing an operation of the AGC circuit used in the first embodiment.

FIG. 3 is a schematic configuration diagram showing a second embodiment.

FIG. 4 is an operation explanatory diagram showing characteristics of the filter circuit used in the second embodiment.

FIG. 5 is a schematic configuration diagram showing a third embodiment.

FIG. 6 is a schematic configuration diagram showing a fourth embodiment.

FIG. 7 is a schematic configuration diagram showing a fifth embodiment.

FIG. 8 is an operation explanatory diagram showing an operation of the amplification degree varying circuit used in the fifth embodiment.

FIG. 9 is a schematic configuration diagram showing a conventional example.

[Explanation of symbols]

 1 Microphone 2 Speaker 3 Signal generation circuit 31 Inversion amplification circuit 32 AGC circuit 33 Filter circuit 34 Phase fluctuation circuit 35 Frequency detection circuit 36 Amplification degree fluctuation circuit

Front page continued (72) Inventor Takashi Mori 1-8-1 Kaga, Itabashi-ku, Tokyo Inside Noguchi Research Institute Nishiwaki Research Institute Co., Ltd. (72) Inventor Masao 2-4-2 Shirokane, Minato-ku, Tokyo 3-227

Claims (5)

[Claims] 1. A microphone for detecting a sound wave in a sound field, a speaker for sending a sound wave in the sound field, and a signal generation circuit for amplifying an output signal of the microphone and generating a drive signal to the speaker whose phase is changed. In a muffling device that includes a speaker and silences a sound wave transmitted from a speaker by interfering with a sound wave in a sound field, a signal generation circuit inverts the phase of the output signal of the microphone and an amplification unit that amplifies the output signal of the microphone. A phase inversion unit,
A muffling device comprising: an amplification degree control section that reduces the amplification degree of the amplification section when the level of the output signal of the microphone exceeds a predetermined threshold value. 2. The silencer according to claim 1, wherein a frequency characteristic control unit for controlling the frequency characteristic of the drive signal is added to the signal generating circuit. 3. The silencer according to claim 1, wherein the signal generating circuit is further provided with a phase changing section for giving fluctuation to the phase of the drive signal. 4. A microphone for detecting a sound wave in a sound field, a speaker for sending a sound wave in the sound field, and a signal generation circuit for amplifying an output signal of the microphone and generating a drive signal to the speaker whose phase is changed. In a muffling device that includes a speaker and silences a sound wave transmitted from a speaker by interfering with a sound wave in a sound field, a signal generation circuit inverts the phase of the output signal of the microphone and an amplification unit that amplifies the output signal of the microphone. A phase inversion unit,
A howling detection section that detects the occurrence of howling in a loop formed by a microphone, a signal generation circuit, a speaker, and a sound field, and reduces the amplification degree of an amplification section when the howling detection section detects the occurrence of howling. A silencer comprising an amplification degree control unit. 5. A microphone for detecting a sound wave in a sound field, a speaker for sending a sound wave in the sound field, and a signal generation circuit for amplifying an output signal of the microphone and generating a drive signal to the speaker whose phase is changed. In a muffling device that includes a speaker and silences a sound wave transmitted from a speaker by interfering with a sound wave in a sound field, a signal generation circuit inverts the phase of the output signal of the microphone and an amplification unit that amplifies the output signal of the microphone. A phase inversion unit,
A muffling device comprising: an amplification degree varying section that gives fluctuations to the amplification degree of the amplification section.