JPH09179565A - Noise reducing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the level of resonance sounds even under a circumstance in which a noise detecting means and a speaker can not be arranged adjacently by arranging the noise detecting means of a plane perpendicular to the progressing direction of standing waves forming sympathetic sounds and arranging a speaker on the same plane as the above plane while direction the output plane of the speaker to the standing waves. SOLUTION: This noise reducing device is constituted of a noise detecting means 1, a speaker 2 and a power amplifier 3 arranged between them. The noise detecting means 1 is arranged on a cross-section 6 with which the sides of standing waves 5 forming the resonance sounds to be generated in an objective space to be silenced 4 is cut perpendicularly to the progressing direction of the standing waves 5. The speaker 2 is arranged on one wall plane of the objective space to silenced 4 with which the cross-section 6 on which the noise detecting means 1 is arranged is intersected while the output plane of the speaker is directed to the sides of the standing waves 5. Since the noise detecting means 1 and the speaker 2 are both arranged on the plane perpendicular to the progressing direction of the standing waves 5, the reducing of the level of the resonance sounds is made possible even under the circumstance in which the noise detecting means 1 and the speaker 2 can be arranged adjacently.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a noise reducing apparatus for reducing the level of a resonance sound, which is a noise, by an active noise reduction system, and particularly, an analog type noise system in which a feedback system is constituted only by a power amplifier without phase correction. Reducing device

[0002]

2. Description of the Related Art An active noise reduction method is known as a noise level reduction measure. This active muffling method is basically a method in which noise emitted by a noise source collected by a microphone, which is a noise detection means, is emitted from a speaker in a phase opposite to that of the noise emitted from the speaker toward the noise source. Since the propagation state of sound changes depending on factors such as the case, when the microphone and the speaker are arranged at a long interval, it is necessary to correct the phase in the feedback system in consideration of environmental conditions.

This phase correction is normally performed by digital processing (for example, Japanese Utility Model Laid-Open No. 4-69253), but if an analog processing is attempted to do the same thing, the configuration becomes very complicated and the processing time increases significantly. However, followability becomes a problem (for example, US Pat. No. 4,153,815). Therefore, there has been proposed an analog noise reduction device in which a microphone and a speaker are arranged close to each other so that a change in environmental conditions can be ignored and a feedback system is composed of only a power amplifier (for example, US Pat. No. 4,527,282). According to this method, the noise reduction device can be configured inexpensively and easily.

On the other hand, a resonance sound that is often experienced when the frequency of noise is low is known as a squealing sound. Regarding the reduction of the level of the resonance sound, it is necessary to form the resonance sound when detecting the resonance sound. Since the antinode of the standing wave is the easiest to detect, a method has been proposed in which a speaker and a vibration detecting means facing the speaker are provided at the antinode position of the standing wave as a measure for reducing vehicle interior noise (the above-mentioned actual Kaihei). 4-69253).
Specifically, as is clear from the embodiment, the proposed system is a system in which a speaker is arranged on one belly and a vibration detecting means is arranged on the other belly in a secondary resonance having two bellies. is there.

[0005]

However, in the above-mentioned conventionally proposed analog system, it is necessary to dispose the microphone and the speaker in close proximity to each other, and therefore the situation of the existence space of the resonance sound to be silenced. When it becomes difficult to dispose the microphone and the speaker close to each other, it may not be possible to obtain a predetermined noise reduction effect.

Further, since the sound wave is a longitudinal wave, the level and phase of each wave differ in the traveling direction of the standing wave. That is, in the method disclosed in Japanese Utility Model Laid-Open No. 4-69253, which has been conventionally proposed for reducing the level of the resonance sound, the speaker and the vibration detecting means are set at different antinode positions, so that a phase difference occurs between them. However, it is difficult to align the phases between the two due to the configuration, and this is a method that allows the existence of a phase difference in principle.

Therefore, the concept of this conventional method cannot be applied to the analog method which is the object of the present invention, which does not require the phase correction. The present invention was created to solve such a conventional problem, and an object thereof is to reduce the level of resonance sound even in a situation where the noise detection means and the speaker cannot be arranged in close proximity to each other. The purpose of the present invention is to provide a noise reduction device of the type.

[0008]

In order to achieve the above object, the noise reduction device of the present invention has the following configuration. The noise reduction device according to claim 1 emits a noise having a phase opposite to that of the resonance sound, which is the noise detected by the noise detection means, toward the sound deadening target space in which the resonance sound exists, and the noise in the sound deadening target space is emitted. In the noise reduction device to reduce the level,
The noise detecting means is arranged on a plane perpendicular to the traveling direction of the standing wave forming the resonance sound, and the speaker directs its output surface to the standing wave on the same plane as the surface on which the noise detecting means is arranged. It is characterized by being arranged.

According to a second aspect of the present invention, there is provided the noise reduction device according to the first aspect, wherein the noise detection means is arranged such that the antinode of the standing wave forming the resonance sound is perpendicular to the traveling direction of the standing wave. The speaker is characterized in that it is arranged on the cross section cut into two, and the output surface of the speaker is arranged on the same plane as the cross section where the noise detecting means is arranged, with the output surface facing the antinode of the standing wave.

According to a third aspect of the present invention, there is provided the noise reduction device according to the first or second aspect, wherein the noise detection means is arranged at a position close to the traveling axis of the standing wave. Characterize. The noise reduction device according to claim 4 is
The noise reduction device according to any one of claims 1 to 3, wherein the speaker is set on one wall surface that partitions the sound deadening target space.

(Operation) Next, the operation of the noise reducing device of the present invention constructed as described above will be described. In the noise reduction device according to the first aspect, both the noise detection means and the speaker are arranged on a plane perpendicular to the traveling direction of the standing wave. Sound waves
Since it is a longitudinal wave, on a plane perpendicular to the traveling direction of the standing wave,
The sound pressure is the same at any position, and the phase is the same. Therefore, even in a situation where the noise detecting means and the speaker cannot be arranged close to each other, the level of the resonance sound can be reduced without the need for phase correction.

Particularly, as in the noise reducing device according to the second aspect, the noise detecting means and the speaker are both arranged on a cross section obtained by cutting the antinode of the standing wave perpendicularly to the traveling direction of the standing wave. The maximum noise level reduction effect can be obtained. If the noise detection means is arranged at a position close to the traveling axis of the standing wave, as in the noise reduction device according to claim 3, that position is a noise that enters from the outside apart from the partition wall of the sound deadening target space. Since it is at a position where noise is less likely to be detected, unnecessary sound can be prevented from being output from the speaker.

Further, since the noise detecting means and the speaker can be arranged on the same phase plane, it becomes possible to widen the arrangement interval between the two. Specifically, as in the noise reducing device according to claim 4, The speaker can be set on one wall surface that partitions the noise reduction target space, regardless of the position of the noise detection means.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram of a noise reduction device according to a first embodiment of the present invention. In FIG. 1, the noise reduction device of the present invention comprises a noise detection means 3, a speaker 2 and a power amplifier 3 provided between them.

The noise detecting means 1 has a cross-section 6 obtained by cutting an antinode of a standing wave 5 forming a resonance sound generated in the sound-deadening space 4 perpendicularly to the traveling direction of the standing wave 5 (left-right direction in the drawing). It is located at. In the illustrated example, the noise detection means 1 uses the standing wave 5
It is located close to the position of the traveling axis of. The arrangement method is, for example, hanging from the ceiling or fixing to a stand arranged on the floor in the same way as when the camera is supported by three legs.

A microphone, a piezoelectric element or the like can be used as the noise detecting means 1. Which one to use is determined according to the usage environment. For example, since a microphone easily adheres to dust, it is preferable to use a piezoelectric element in such an environment. The speaker 2 is arranged on one wall surface of the noise reduction target space 4 where the cross section 6 where the noise detection means 1 is arranged intersects with its output surface facing the antinode of the standing wave 5.

The power amplifier 3 inversely amplifies the resonance sound, which is the noise detected by the noise detecting means 1, for example, and causes the speaker 2 to output the noise at a high level. In the first embodiment, the sound deadening target space 4 is a closed space that does not have a noise source inside, such as a room of a building or a passenger compartment, and a standing wave 5 that forms a resonance sound due to noise entering from the outside is used. It envisions a possible space.

There are various types of standing waves generated in the sound deadening target space 4, as shown in FIG. 2, for example. FIG.
FIG. 4 is an explanatory diagram of a standing wave generated in a rectangular sound deadening target space. In FIG. 2, resonances in the horizontal and vertical directions are shown, and other resonances such as diagonal directions are omitted. However, as shown in the figure, the standing wave of the resonance has one antinode and one antinode. Two two
There are the following, etc.

Which resonance sound is most likely to be generated is determined by the noise frequency and the spatial shape. What kind of standing wave is generated in which direction is determined in advance by the spatial shape data of the sound deadening target space 4. It can be obtained by the finite element method. FIG. 1 shows a case of secondary resonance in the lateral direction. In the first embodiment, the noise detecting means 1 and the speaker 2 are arranged at one of the two antinode positions obtained by the finite element method. Therefore, it can be similarly applied to the case of the first resonance with one antinode.

Next, FIG. 3 is an explanatory diagram of the characteristics of the standing wave. In FIG. 3, since the sound wave is a longitudinal wave, a1, a2, a are on the surface in the Y-axis direction perpendicular to the X-axis which is the traveling direction of the standing wave.
The same sound pressure and the same phase at any position such as 3, a4, a5, .... Although the illustrated example is the antinode position of the maximum sound pressure, this relationship is the same even at a position deviating from the antinode position, and no special phase correction between the noise detection means 1 and the speaker 2 is necessary. .

Therefore, since it is not necessary to perform phase correction,
As shown in FIG. 1, the noise detection means 1 is arranged near the traveling axis of the standing wave 5, and the speaker 2 is arranged on the wall surface of the noise target space 4, that is, even if they are arranged apart from each other, noise is generated. It is possible to reduce the level of the barrel resonance sound. In particular, in the noise reduction target space 4 where noise enters from the outside, when the noise detection means 1 is close to the window position, external noise is also easily picked up, and as a result, unnecessary sound may be transmitted from the speaker 2. In such an environment, it is necessary to arrange the noise detecting means 1 at a position away from the window position.

In the first embodiment, since the noise detecting means 1 can be arranged near the traveling axis of the standing wave 5, the influence of external noise can be prevented and the level of the resonance sound can be effectively reduced. Next, FIG. 4 is a configuration diagram of a noise reduction device according to a second embodiment of the present invention. In FIG. 4, in the second embodiment, there is a noise source 8 in the silencing target space 7, and the noise source 8
The case where the resonance sound generated in the sound deadening target space 7 is reduced by the noise generated by is shown.

Even if the noise reduction target space 7 has the noise source 8 inside, the mode of the resonance sound generated can be similarly obtained by the finite element method. In the illustrated example, the resonance is the same secondary secondary resonance as in the first embodiment, and the noise detection means 1
And the speaker 2 are arranged in the same manner as in the first embodiment. In the illustrated example, the noise source 8 is, for example, an industrial power generator, and the noise reduction target space 7 is defined by a housing that is a noise shield surrounding the noise source 8. Also in this case, the noise detecting means 1 may be arranged as far away from the wall as possible.

FIG. 5 is a measurement diagram showing the silencing effect of the noise reduction device according to the second embodiment of the present invention. In FIG. 5, the horizontal axis represents frequency (Hz) and the vertical axis represents noise level.
The measurement position is a position 7 m outside the sound deadening target space 7. The frequency ranges from 60 Hz to 1 kHz or more, but in the case of active mute OFF in which the noise detection means 1 and the speaker 2 are not activated, as shown by the dotted line, 80
At Hz, a high level resonance sound equivalent to a high frequency noise level is generated.

In such a sound deadening space 7, noise is detected by the noise detecting means 1, the noise is inverted and amplified by the power amplifier 3, and the output of the power amplifier 3 is manually adjusted to an output that does not cause howling. When the sound is given to the speaker 2, that is, when the active mute is ON, as shown by the solid line, 80H
The noise level of the z resonance is reduced by approximately 10 dB. This indicates that the noise level of the resonance sound of 80 Hz was similarly reduced in the sound deadening target space 7.

As described above, in detecting the resonance sound, the antinode of the standing wave is most easily detected. Therefore, in the present embodiment, the noise detecting means and the speaker are arranged at the antinode position. The placement position does not necessarily have to be the belly position,
It is clear from the above explanation that if efficiency is neglected, it can be said that basically anything other than clauses can be used.

As the power amplifier, an inverting amplifier is usually used, but when an in-phase amplifier is used, the speaker side may be phase-inverted and transmitted.

[0028]

As described above, in the noise reducing device according to the first aspect, since the noise detecting means and the speaker are both arranged on the plane perpendicular to the traveling direction of the standing wave, the noise is reduced. Even in a situation where the detecting means and the speaker cannot be arranged close to each other, the level of the resonance sound can be reduced without the need for phase correction.

Particularly, as in the noise reducing device according to the second aspect, the noise detecting means and the speaker are both arranged on a cross section obtained by cutting the antinode of the standing wave perpendicularly to the traveling direction of the standing wave. The maximum noise level reduction effect can be obtained. If the noise detecting means is arranged at a position close to the traveling axis of the standing wave, as in the noise reducing device according to claim 3, it is less likely to detect noise that is noise that intrudes from the outside. You can prevent unwanted sounds from being sent out.

Since the noise detecting means and the speaker can be arranged on the same phase plane, it is possible to widen the arrangement interval between them, and more specifically, as in the noise reducing device according to claim 4, The speaker can be set on one wall surface that partitions the noise reduction target space, regardless of the position of the noise detection means.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a noise reduction device according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of a standing wave generated in a sound deadening target space of a rectangular parallelepiped.

FIG. 3 is an explanatory diagram of characteristics of a standing wave.

FIG. 4 is a configuration diagram of a noise reduction device according to a second embodiment of the present invention.

FIG. 5 is a measurement diagram showing a silencing effect of the noise reduction device according to the second embodiment of the present invention.

[Explanation of symbols]

 1 noise detection means 2 speaker 3 power amplifier 4, 7 noise suppression space 5 standing wave 6 vertical plane 8 noise source

Claims (4)

[Claims] 1. A sound having a phase opposite to that of a resonance sound which is a noise detected by a noise detecting means (1) is emitted from a speaker (2) toward a sound deadening target space (4, 7) in which the resonance sound exists, and the sound is emitted. In the noise reduction device for reducing the noise level in the silencing target space (4, 7), the noise detection means (1) is a surface (a plane perpendicular to the traveling direction of the standing wave (5) forming the resonance sound. 6) and the speaker (2) is arranged such that its output surface faces the standing wave (5) on the same surface as the surface (6) on which the noise detecting means (1) is arranged. A noise reduction device characterized by being provided. 2. The noise reduction device according to claim 1, wherein the noise detecting means (1) makes an antinode of a standing wave (5) forming the resonance sound perpendicular to a traveling direction of the standing wave. The speaker (2) is arranged on the cut section (6), and the output surface of the speaker (2) is on the same plane as the section (6) where the noise detecting means (1) is arranged. A noise reduction device, which is arranged toward the belly. 3. The noise reduction device according to claim 1 or 2, wherein the noise detection means (1) is arranged at a position close to the traveling axis of the standing wave (5). Noise reduction device. 4. The noise reduction device according to claim 1, wherein the speaker (2) is set on one wall surface that partitions a sound deadening target space. Reduction device.