JPH0353698A - Active silencer - Google Patents

Abstract

PURPOSE:To silence a sound even in a general open space by making a delay time in a delay circuit equal to a time obtained from a physical distance between an acoustoelectric conversion means and an electroacoustic conversion means divided by a sound wave propagation speed so as to silence the sound due to the sound wave interference at an observing point. CONSTITUTION:A sound wave generated from a sound source 1 is sounded from a speaker (electroacoustic conversion means) 6 through a delay circuit 3, an inverting circuit 4 and an amplifier 5 via a microphone (acoustoelectric conversion means) 2. When a sound wave is delayed by L1/c at a delay circuit 3 (L1 is a distance between a microphone 2 and a speaker 6 and (c) is a sound velocity), the sound wave from the sound source 1 and (c) is sound wave from the speaker 6 are interfered with each other and almost silenced together at a location of the speaker 6 because the sound waves are nearly of the same sound pressure and of the inverted phase. Thus, the silencing at an open space is attained with the simple device.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an active noise reduction device 1f, and particularly to an active noise reduction device 1f suitable for muffling sounds from one direction.

[Conventional technology]

Conventionally, noise prevention measures have been to reduce vibration and noise at the sound source, and on the other hand, there have been soundproofing techniques such as pasting sound-absorbing material on the station wall 1c to prevent intruding sound.However, these methods Passive silencing devices require improvement in terms of size, versatility, etc.

On the other hand, active silencing devices, in other words, suppress the noise propagating from the sound source and reduce the same sound pressure. There is a method that generates sound of opposite phase and attempts to cancel the sound by sonic interference.For example, there is a method described in Japanese Patent Application Laid-Open No. 61-296592. This study aims to elucidate a model of an electronic silencing system that makes it possible to eliminate unsteady noise generated in propagation paths such as pipes, and to construct an electronic silencing system based on this model.

[Problem to be solved by the invention]

The above-mentioned conventional technology is a system that employs a noise source that is restricted within a pipe or the like as a model. The present invention aims to improve this model and thus provide a device that can muffle noise not only in pipes but also in open spaces in general.

[Means to solve the problem]

The present invention includes a stage for detecting a propagating sound wave, which is installed on the sound source side, a delay means for inputting and delaying an electrical signal from the sound-to-electricity converting means and outputting the delayed signal, and phase inversion of the output of the delay means. This is achieved by a phase inversion means that is installed between the observation points, and an electric-to-sound conversion means that receives an electric signal from the phase inversion means, converts it into an f-wave, and outputs it. This method uses electricity/sound fyS. The sound waves generated by the means are
(It is effective as an inexpensive system when there is no feedback to the electrical conversion means or it can be almost ignored).

In addition, if it is necessary to consider feedback of the sound waves generated by the electricity/sound conversion means to the sound/1-air conversion means, the first sound/electricity conversion means and the 4-air/air conversion means, This is achieved by a control means for converting and outputting a signal from the first sound/air conversion means, and a second sound/electricity conversion means.

[Effect]

The sound-to-electricity conversion means converts the sound wave into an intense signal, the delay means delays the signal according to the distance from the sound-to-electricity conversion means to the electricity-to-sound conversion means, the calculation time and temperature of the circuit, etc. The phase inverting means inverts the delayed signal and converts the electrical
The sound converting means converts the inverted signal into sound waves. The sound waves obtained in this way have substantially the same sound pressure and substantially opposite phase to the source sound waves at the installation position of the electric/sound converting means, and the sound waves interfere with each other and are substantially muffled.

The above system does not take into account that the sound waves emitted from the electricity/sound conversion means are fed back to the sound/electricity conversion means, so the sound/electricity conversion means and the electricity/sound conversion means are highly directional. It is necessary to use it.

In another system, the sound-to-sound conversion means converts the sound waves into electrical signals, the control means converts the sound waves, and the sound-to-sound conversion means converts the sound waves into electrical signals. The second sound-to-electricity conversion means measures the interference wave between the source sound wave and the sound wave obtained as described above, and feeds back the result to the control means. The control means controls the signal to the air filling/sound converting means so that the interference wave received from the second sound/electrical converting means becomes zero.

〔Example〕

Hereinafter, one embodiment of the present invention will be described according to the drawings. FIG. 1 is a schematic diagram showing an apparatus as an embodiment of the present invention.・Electrical conversion means) 2, delay circuit 3. It passes through an inverting circuit 4, 7 and an amplifier 5, and generates a sound wave from a speaker (electricity/sound conversion means) 6. At this time, if the distance between the microphone 2 and the speaker 6 is Ll, and the speed of sound is C, then if the delay circuit 3 is delayed by "'C L, / c",
At the set position tjtl of the speaker 6, the sound waves from the sound source 1 and the sound waves from the speaker 6 have approximately the same sound pressure. They have substantially opposite phases and cancel each other out.

FIG. 3 is an explanatory diagram showing the relationship between time and sound pressure at the positions of the sound source 1 and the speaker 6 in the apparatus of FIG. 1.

FIG. 3(a) shows the relationship between time and sound pressure at the sound source.

At the microphone position, this wave arrives with a delay equal to the distance between the sound source and the microphone divided by the speed of sound. The delay circuit converts the electrical signal into L. /c delay, the inverting circuit inverts the signal, and after adjusting the level with an amplifier, a sound wave is generated from a speaker. Figure 3 (
b) represents the relationship between time and sound pressure at the speaker position at this time. At this time, the sound wave that reaches the speaker setting position from the sound source arrives with a delay of approximately L+/c from the microphone position, so the sound wave from the sound source and the sound wave generated from the speaker have approximately the same sound pressure and approximately opposite phase. As can be seen, these interference waves are close to zero (FIG. 5(C)).

In this embodiment, feedback of the sound from the speaker to the microphone is taken into consideration, and changes in the speed of sound due to the calculation time and temperature of the circuit are not taken into account. microphone. This is fine if both speakers are highly directional, the computation time for the round path can be ignored, and the speed of sound is approximately constant.
The speed of sound is C(
1), the delay in the delay circuit is (L+/cα)
1 α}, a system with even better performance can be constructed.

In this way, the present system provides an inexpensive and compact silencer.

FIG. 2 is a schematic diagram showing another embodiment of the present invention. In the figure, sound waves emitted from a sound source 1 are transmitted through a microphone (sound/electrical conversion means) 2 to a control circuit 7 and an amplifier. 5, and a sound wave is generated from the subika (air/sound conversion means) 6. The sound waves generated from the speaker 6 enter the second microphone 8 together with the sound waves generated from the sound source 1 . The control circuit 7 performs control so that the sound coming from the second microphone 8 is zero C.

FIG. 4 is a model of the apparatus of FIG. P is microphone 2
where G is the propagation characteristic of the sound wave from microphone 2 to microphone 8, G is the propagation characteristic of the sound wave from speaker 6 to microphone 2, G is the propagation characteristic of the sound wave from speaker 6 to microphone 8, M is the sound pressure to voltage conversion characteristic of the microphone 8, S is the voltage to sound pressure conversion characteristic of the speaker 6, E is the control characteristic of the control circuit 7, V1 is the voltage converted by the microphone 2, ■! is the voltage converted by the control circuit 7, ■ is the voltage converted by the control circuit 7, and is the microphone 8 1c
Therefore, it is considered as the converted voltage.

In contrast to such a model, the control characteristic E of the control circuit 7
I'm looking for you.

? Here, V. ．． V. ．． V. are respectively expressed by the following equations.

VI=M(P”(nSVt)
・=(1)V,=EV,
...(2) Vm = M
(GP” (QSVl)
- (5) ■, In order to set = 0, G P 0 Cn SV @ = O
..." (4) must hold. At this time, from (1) . (2) . (4), the control characteristic E is E = 8-' (- G-'Gl + Gl )-
1M-1 (5) Since S and M can be considered known, E is G-1 from (5).
fart. 0 determined from Gt, (1) (2) . (3
) YoQ G-1 at. a, is v,, VB- Vs
'jr. You can see what you can get by measuring.

As described above, it is possible to determine the control characteristic E by measuring v,, V■v and performing a predetermined calculation, and the sound pressure-to-voltage conversion characteristic of the microphone. It is possible to construct a high-precision muffling device that also takes into consideration the alpha-sound pressure characteristics of the speaker and the propagation characteristics of sound waves.

Figures 5(a) and 5(b) are perspective views showing an example of a device in which the circuits shown in Figure 1 are integrated.Since the overall configuration is simple, it is preferable to use an integrated type. However, the microphone section, calculation section, and part of the speaker may be separate.

FIG. 5(c) is a perspective view showing an example of a device in which the circuits shown in FIG. 2 are integrated. Compared to No. 5 (a) and (b), a microphone portion forming a feeder back is added.

Generally, in an open space, the sound source does not necessarily come from only one direction as in a pipe. In such a case,
As shown in FIG. 6, by preparing a plurality of devices and arranging them so that the sound pressure is the lowest at the observation point, an efficient noise reduction effect can be obtained.0 [Effects of the Invention] As explained above, One of the advantages of the present invention is that it is possible to muffle noise in an open space with a relatively simple installation. The other invention is a high-precision muffling device that takes into account the feedback from the speaker to the microphone, and also takes into consideration the sound pressure to volume pressure conversion characteristics of the microphone, the voltage to sound pressure conversion characteristics of the speaker, and the propagation characteristics of sound waves. This has the effect that it can be configured.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a schematic configuration of one embodiment of the present invention, FIG. 2 is a block diagram showing a schematic configuration of another embodiment of the present invention, and FIG. 5 is a sound source position in the embodiment of FIG. Figure 4 is a model diagram that focuses on the characteristics of each element of the embodiment shown in Figure 2, and Figure 5 is a diagram showing the phase characteristics of the sound pressure at the speaker position and the result of interference between the two sound pressures. Embodiment 8 of the Invention FIG. 6 is a slanted diagram showing a device in which the constituent circuits are integrated, and FIG. 6 is an explanatory diagram showing a mode in which a plurality of active silencing devices according to the present invention are used. Explanation of symbols 1... Sound source 3... Delay circuit 5... Amplifier 2.8... Microphone 4... Phase inversion circuit 6... Speaker panel 1 Figure 42 Figure y1'5 Figure 4 Figure Congee 5 On-ha W-r,, On-ha/V-,,,, On-51#- /'t, Ha,・1 On-Ki r・Ichinohe\ノ'1 5-Izu On-no-Ko L

Claims (1)

[Claims] 1. In an active sound damping device that generates sound waves with the same sound pressure and opposite phase to the propagating sound waves traveling from the sound source to the observation point, and mutes the sound at the observation point by the interference of the sound waves, the sound source side a sound-to-electricity conversion means installed in the , which detects a propagating sound wave, converts it into an electric signal, and outputs it; a delay means, which inputs the electric signal from the sound-to-electricity conversion means, delays it and outputs it; and the delay means. and an electric-sound converting means installed on the observation point side and receiving an electrical signal from the phase inverting means and converting it into a sound wave and outputting it, the delay means By making the delay amount equal to the amount of time obtained by dividing the physical distance between the sound-to-electrical conversion means and the electric-to-sound conversion means by the propagation speed of the sound wave, the sound can be suppressed by sound wave interference at the observation point. An active silencer characterized by performing the following. 2. In the active noise reduction device according to claim 1, the amount of delay in the delay means is calculated by dividing the physical distance between the sound-to-electricity conversion means and the electricity-to-sound conversion means by the propagation speed of the sound wave. An active silencing device characterized in that the amount of time obtained is equal to the amount obtained by subtracting the total value of the time required for the operation of each of the means. 3. In the active silencer according to claim 1 or 2,
An active silencing device characterized by comprising a correction means for correcting the propagation velocity of a sound wave, which determines the amount of delay in the delay means, based on ambient temperature. 4. In an active sound muffling device that generates a sound wave of the same sound pressure with an opposite phase to the propagating sound wave traveling from the sound source to the observation point, and muffling the sound at the observation point by the interference of the sound waves, the device is installed on the sound source side and is installed on the sound source side. a first sound-to-electricity conversion means (2) that detects and converts it into an electric signal and outputs it;
A control means (7) which receives, controls and outputs the electrical signal from the sound-to-electricity conversion means (2), and a control means (7) which is installed on the observation point side and which receives the output signal from the control means (7) and converts it into a sound wave. An electricity/sound conversion means (6) that converts and outputs the sound, and a second sound installed on the observation point side that detects the sound wave from the electricity/sound conversion means (6), converts it into an electrical signal, and outputs it. - electrical conversion means (8), the control characteristic in the control means (7) is the sound pressure-voltage conversion characteristic M of the first sound-to-electrical conversion means (2), and the electrical-to-sound conversion means (6) Voltage-sound pressure conversion characteristic S, sound wave propagation characteristic G from the first sound-to-electricity conversion means (2) to the second sound-to-airflow conversion means (8), and the electricity-to-sound conversion a propagation characteristic G1 of a sound wave from the means (6) to the first sound-to-sound converting means (2), the above-mentioned electricity-to-sound converting means (6);
It is characterized in that the conversion output in the second sound-to-electric conversion means (8) is determined based on the propagation characteristic G2 of the sound wave from Active silencer. 5. In the active silencer according to claim 4, the propagation characteristic G of the sound wave from the first sound-to-electricity converting means (2) to the second sound-to-electricity converting means (8); Propagation characteristic G1 of a sound wave from the sound converting means (6) to the first sound-electrical converting means (2), the electric-sound converting means (6)
The propagation characteristic G2 of the sound wave from to the second sound-to-electric conversion means (8) is determined by the voltage V1 of the electric signal output from the first sound-to-electric conversion means (2), and the control means (7). voltage V2 of the electrical signal output from the second sound.
Voltage V3 of the electrical signal output from the electrical conversion means (8)
An active silencer characterized by determining: