JPH0539712A - Noise control device - Google Patents

Abstract

PURPOSE:To improve an elimination effect on noise coming from a noise generation source, in relation to a noise control device for eliminating noise by means of a speaker. CONSTITUTION:In a noise control device for eliminating noise by outputting sound wave having antiphase against/iso-sound pressure to those of a noise lowing from a noise generation source by means of an electrical signal/sound wave switch 2, a resonant box 201 to agree with resonance frequency of noise discharged from the discharging port 3 of noise is provided in the electrical signal/sound wave switch 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a noise control device for canceling noise by using a speaker, and in particular, it is an object of the present invention to improve the effect of silencing noise from a noise source.

[0002]

2. Description of the Related Art Conventionally, a passive muffler such as a muffler has been used to generate the muffler from an internal combustion engine or the like, but improvement has been desired from the viewpoints of size and muffling characteristics. On the other hand, conventionally, there has been proposed an active noise control device that cancels noise by outputting from a speaker a compensating sound having an opposite phase and equal sound pressure to the noise generated from a sound source.

By the way, the active noise control device itself is not sufficient in frequency characteristics, stability, etc., and its practical application has been delayed. As a result of the recent development of signal processing technology using digital circuits and expansion of the frequency range that can be handled, many practical noise control devices have been proposed (for example, Japanese Patent Laid-Open No. 63-311396).

This is detected by a noise source microphone installed upstream of the duct, and a signal processing circuit outputs a signal of opposite phase to the noise and equal sound pressure from a speaker installed downstream of the duct to mute the silenced result. A so-called two-microphone that combines a feed-forward system with a feedback system that detects and feeds back with a point microphone.
This is a one-speaker active noise control device.

[0005]

However, in the conventional noise control device, when the noise source is an automobile engine, in order to eliminate the noise emitted from the muffler, the muffler is placed as close as possible to the tail pipe. However, if the noise level from the tail pipe is high, the level of noise reduction from the speaker must be increased, and the capacity of the speaker must be increased.

Therefore, in view of the above problems, it is an object of the present invention to provide a noise control device capable of increasing and suppressing the capacity of the speaker when the noise level increases.

[0007]

In order to solve the above-mentioned problems, the present invention uses an electric signal / sound wave converter to output a sound wave having a phase opposite to that of the noise from the noise generating source. Thus, in the noise control device that eliminates the noise, the speaker that is the electric signal / sound wave converter is provided with the resonance box that matches the resonance frequency of the noise emitted from the noise outlet.

Further, when the noise source (1) is an automobile engine, an enclosure surrounding the resonance box of the electric signal / sound wave converter and the rear of the electric signal / sound wave converter (2) is provided. It was installed in the car trunk room. The trunk room may be the enclosure.

[0009]

According to the noise control device of the present invention, since the speaker is provided with the resonance box that matches the resonance frequency of the noise, the noise can be eliminated with a small output. Further, by installing the resonance box in the luggage compartment, the cavity of the resonance box can be made large, and it is possible to match the low resonance frequency. Furthermore, the speaker enclosure can also increase the sound pressure by utilizing the space in the luggage compartment. Therefore, noise can be eliminated with a small output.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing an embodiment of a noise control device which is a premise of the present invention. The noise control device of this figure is provided in the peripheral portion of the discharge port 3 of a transmission path (for example, a muffler) that transmits noise from a noise generation source 1 such as an automobile engine,
A speaker 2 that outputs a compensating sound wave for eliminating noise from the noise generating source 1 to an erasing point P (in the figure), and a speaker 2 arranged near the erasing point P to emit noise from the noise generating source 1
Microphone 3 that captures the result of erasing with sound waves from
0, an amplifier 101 for driving the speaker 2, a D / A (Digital To Analog) converter 102 for converting a digital signal into an analog signal and outputting the analog signal to the amplifier 101,
Amplifier 10 for amplifying the output signal of the microphone 30
3 and an A / D (Analog To Digital) converter 1 for converting the output of the amplifier 103 from an analog signal to a digital signal
04 and the calculation result of the difference signal calculating means 107 described later, and the output signal of the microphone 30 is minimized by the least square method to calculate the compensation signal to calculate the D / A converter 1.
02 to the adaptive filtering means 105 and the compensation signal of the adaptive filtering means 105 are input, and the adaptive filtering means 105 outputs D / A converter 1
02, amplifier 101, speaker 2, microphone 3,
A transfer characteristic simulating means 106 for simulating transfer characteristics of the system leading to the differential signal calculation means 107 to be described later via an amplifier 103, A / D converter 104 (Hd · H _M) equal to the transfer characteristic (Hd1), microphone 2 Difference signal calculating means 10 for calculating a difference signal between the output and the output of the transfer characteristic simulating means 106.
Including 7 and.

Here, the adaptive filtering means 10
5, transfer characteristic simulation means 106 and difference signal calculation means 107
Is a DSP (Digital Signal Processor). Book
According to the noise control device, the noise signal of the noise source 1_N
And its transfer characteristic up to the microphone 30 is H
_NOISEAnd the compensation signal of the adaptive filtering means 105.
Issue S_CAnd from adaptive filtering 105
Hd is the transfer characteristic from the microphone 2 to the microphone 30.
Further, from the microphone 30 to the difference signal calculation means 10
Transfer characteristics up to 7 are H_MAnd Hd1 = Hd · H_MTo
And the signal S output from the microphone 30_MIs S_M=
S_N・ H_NOISE+ S_C・ Hd, the difference signal calculation unit 10
Difference signal S which is the calculation result in_EIs S_E= S_M・ H
_M-S_C・ Hd1 = (S_N・ H_NOISE+ S_C・ Hd-S
_C・ Hd) ・ H_M= S_N・ H _NOISE・ H_MBecomes noise
Calculate the signal when only the microphone 30 detects
The Rukoto. Also, the adaptive filtering means 105
As a control signal to change the adaptive filter coefficient of
Is the output S of the A / D converter 104_EIs given. Adaptive
The filtering means 105 makes this control signal zero.
Is to change the coefficient, and S_E= S_M・ H_MAnd
Therefore, S_E= O when S_M= O. Therefore the difference signal
Difference signal S from means 107_RIs used as the control signal
It is input to the filtering means 105 and A is used as a control signal.
Output S of the / D converter 104_ESuitable by entering
In the adaptive filtering means 105, S_E= O
And the adaptive filtering means 105_CPlayed
Calculated and output.

FIG. 2 is a diagram showing a resonance box and an enclosure of a speaker in a noise control device according to an embodiment of the present invention. This figure (a) is a cross-sectional view of a loudspeaker arrangement, in which a long exhaust pipe 110 extending from an exhaust manifold is used as a means for silencing the noise of exhaust gas emitted from the engine to the atmosphere intermittently at a certain range of pressure and temperature. Muffler 4, which is provided at the end of the muffler and which has a durable sound absorbing material, for example, of the resonance type or the expansion type, and has a complicated combination with the above in order to consume the acoustic energy with a resistance as low as possible. 4, a tail pipe 200 for discharging exhaust gas to the atmosphere after muffling by the muffler 4, and a pipe portion 20 arranged in parallel with the tail pipe 200.
1a and a resonance box 201 composed of a cavity 201b on the front surface of the speaker 2, and an enclosure 202 surrounding the rear of the speaker 2.

FIG. 3B is a front view of the tail pipe 200 as seen from the exhaust port 3 side, and the resonance box 201 and the enclosure 202 may be manufactured as one body, and this integrated body is shown in the figure. It may be fixed to the muffler 4 by the support portion 111. The frequency range of the noise from the muffler 4 is usually in the range of 100 to 500 Hz, and the muffler 4 has an inherent frequency characteristic, that is, a specific frequency peak, depending on its type, and therefore the frequency characteristic of the muffling from the speaker 2 is the frequency peak. If they match, noise can be eliminated with a small output of the speaker 2.

In the resonance box 201, a hole is formed in a part of the cavity 201b having a size smaller than the wavelength, and
Since 01a is the attached resonator, increasing the volume of the cavity lowers the resonance frequency, increasing the opening area of the hole increases the resonance frequency, and increasing the length of the tube decreases the resonance frequency. Therefore, it is possible to match the frequency peak of the muffler 4.

The enclosure 202 surrounds and surrounds the sound radiated from the back surface of the speaker 2 so as not to mix with the sound radiated from the front surface. FIG. 3 is a diagram showing a resonance box and an enclosure of a speaker in a noise control device according to another embodiment of the present invention. As shown in this figure (a), the cavity 20 of the resonance box 201 of the speaker 2
1b and the enclosure 202 are provided in a luggage compartment 203 which is a luggage compartment of an automobile, and a pipe portion 201a extends in a duct shape and is arranged in parallel with the tail pipe 200. This figure (b) is a partial perspective view seen from the rear part of the automobile, and the resonance box and the like of the speaker 2 are installed in one corner of the trunk room on the muffler side. According to this embodiment, the resonance box 20
It is possible to increase the volume of the hollow portion 201b of No. 1, and
Since 01a can be lengthened, it is advantageous when the resonance frequency needs to be lowered. Further, the volume surrounded by the enclosure 202 can be increased, the speaker 2 can be easily driven, and a large sound pressure can be obtained with a small output.

FIG. 4 is a diagram showing a resonance box and an enclosure of a speaker in a noise control device according to another embodiment of the present invention. As shown in this figure (a), the speaker 2 is installed so as to face the opening of the floor of the trunk room 203, and the cavity 201b and the pipe 201a connected to this opening are installed outside the trunk room 203. The enclosure 202 of the speaker 2 is the trunk room 20.
It is composed of the wall of the vehicle body forming part 3. This figure (b) is a partial perspective view seen from the rear part of the automobile, and the speaker 2 is installed in one corner of the trunk room on the muffler side.

According to this embodiment, the volume of the enclosure 202 becomes the same as the volume of the trunk room 203 and becomes wider, so that the speaker 2 can be driven more easily and a large sound pressure can be obtained with a small output. The noise control device which is the premise of the present invention is not limited to the embodiment shown in FIG. 1, and for example, the noise from the noise source 1 is extracted from a part of the muffler, which is its transmission path, and the delay device is extracted. There are various methods such as a method of creating a noise compensation signal using the above, and any method may be used.

[0018]

As described above, according to the present invention, the speaker is provided with the resonance box that matches the resonance frequency of the noise emitted from the tail pipe of the muffler, and the resonance box is provided in the trunk room to reduce the volume of the cavity. As the capacity increases, it becomes possible to match low resonance frequencies. Also, since the volume of the speaker enclosure can be increased, the sound pressure can be increased accordingly, and the noise can be eliminated with a small output.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a noise control device that is a premise of the present invention.

FIG. 2 is a diagram showing a resonance box and an enclosure of a speaker in the noise control device according to the embodiment of the present invention.

FIG. 3 is a diagram showing a resonance box and an enclosure of a speaker in a noise control device according to another embodiment of the present invention.

FIG. 4 is a diagram showing a resonance box and an enclosure of a speaker in a noise control device according to another embodiment of the present invention.

[Explanation of symbols]

 1 ... Noise control device 2 ... Speaker 3 ... Microphone 4 ... Muffler 200 ... Tail pipe 201 ... Resonance box 202 ... Enclosure 203 ... Trunk room

Claims (3)

[Claims] 1. A noise control device for eliminating a noise from a noise source (1) by outputting a sound wave having an opposite phase and equal sound pressure with an electric signal / sound wave converter (2). In the noise control device, the electric signal / sound wave converter (2) is provided with a resonance box (201) that matches a resonance frequency of noise emitted from the noise outlet (3). .. 2. The noise source (1) is an automobile engine, and the resonance box (201) of the electric signal / sound wave converter (2) and the rear side of the electric signal / sound wave converter (2) are provided. A noise control device according to claim 1, characterized in that the surrounding enclosure (202) is provided in the trunk (203) of the vehicle. 3. The noise control device according to claim 1, wherein the trunk room (203) serves as the enclosure (202).