JPH0546189A - Noise controller - Google Patents

Abstract

PURPOSE:To improve the sound elimination effect for the noise from a noise generation source as to the noise controller which eliminates the noise by using a speaker. CONSTITUTION:The noise controller has an electric signal-to-sound wave converter 2 which outputs a sound wave having the opposite phase from and the same sound pressure with the noise of the noise generation source 1 and a sound wave-to-electric signal converter 3 which feeds the result of the sound elimination back; and plural speakers 2 are arranged symmetrically and concentrically at the periphery of the tail pipe 5 of a muffler 4 and the opening parts of the speakers 2 are set in the same direction with the exhaust port of the tail pipe 5.

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 muffling device such as a muffler has been used to reduce noise generated from an internal combustion engine, etc., but improvements have been desired from the viewpoint 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 frequency characteristic or stability of the active noise control device itself is not sufficient, 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 the result of noise being detected by a noise source microphone installed upstream of the duct, and a signal processing circuit outputting a signal of opposite phase and equal sound pressure to the noise from a speaker installed downstream of the duct, and the result being silenced. This is a so-called two-microphone / one-speaker type active noise control device in which a feedback system and a feed-forward system for detecting and feeding back the noise by a microphone for a sound deadening point are combined.

[0005]

However, when the noise source is an automobile engine, even if a speaker is provided around the tail pipe of the muffler to muffle the noise emitted from the muffler, the muffling effect is unevenly distributed. Depending on the situation, there was a problem that the desired noise reduction effect could not be obtained. Therefore, in view of the above problems, it is an object of the present invention to provide a noise control device capable of elucidating the cause of uneven distribution of the silencing effect and improving the silencing effect.

[0006]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention uses an electric signal / sound wave converter to output a sound wave having a sound pressure opposite to that of noise from a noise source. In a noise control device for silencing the noise, electric signal / sound wave converters are symmetrically arranged on a concentric circle around the noise discharge port, and the opening of the electric signal / sound wave converter is the same as the discharge port. Turn in the direction.

[0007]

According to the noise control device of the present invention, a plurality of speakers are arranged symmetrically on a concentric circle around the noise outlet, and the openings of the speakers are oriented in the same direction as the exhaust outlet. The interference between the noise from the tail pipe and the noise reduction from the speaker is symmetrical with respect to the tail pipe, and the noise reduction effect is improved without uneven distribution.

[0008]

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 vicinity of the discharge port 3 of a transmission path (for example, a muffler) that transmits noise from a noise generation source such as an automobile engine, and eliminates noise from the noise generation source 1. The speaker 2 which outputs the compensating sound wave to the sound deadening point P (in the figure) and the sound deadening point P
A microphone 30 that is arranged in the vicinity and captures the result of eliminating the noise from the noise source 1 with the sound wave from the speaker 2.
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,
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
0, the transfer characteristic simulating means 106 for simulating transfer characteristics of the system leading to the differential signal calculation means 5 to be described later via an amplifier 103, A / D converter 104 (Hd · H _M) equal to the transfer characteristic (Hd1), a microphone Difference signal calculating means 1 for calculating the difference signal between the output of 30 and the output of the transfer characteristic simulating means 106.
07 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).
According to this noise control device, the noise signal from the noise source 1
_N, and its transfer characteristic up to the microphone 30 is H
_NOISE , the compensation signal of the adaptive filtering means 105 is S _C , the transfer characteristic from the adaptive filtering 105 to the microphone 30 through the speaker is Hd, and the microphone 30 to the difference signal calculating means 10
When the transfer characteristic up to 7 is H _M and Hd1 = Hd · H _M , the signal S _M output from the microphone 30 is S _M =
S _N · H _NOISE + S _C · Hd, and the difference signal S _R, which is the calculation result in the difference signal calculation unit 5, is S _R = S _M · H _M
-S _C · Hd1 = (S _N · H _NOISE + S _C · Hd-S _{C
· Hd) · H M = S} N · H NOIS E · H M , and the only noise becomes computing the signal when detected by the microphone 30. The output S _E of the A / D converter 104 is given as a control signal for changing the adaptive filtering coefficient of the adaptive filtering means 105. The adaptive filtering means 105 changes the coefficient so that this control signal becomes zero, and S _E = S _M · H _M
Therefore, when S _E = 0, S _M = 0. Therefore, the difference signal S _R from the difference signal calculation unit 107 is input to the adaptive filtering unit 105 as the control signal, and the output S _E of the A / D converter 104 is input as the control signal, whereby the adaptive filtering unit 105 is input. Is S _E = O
The adaptive filtering means 105 calculates the compensation signal S _{C so} that

FIG. 2 is a diagram showing the structure of the speaker in the noise control device according to the embodiment of the present invention. This figure (a) is a cross-sectional view of the loudspeaker arrangement. It is intended to muffle the noise of the exhaust gas emitted from the engine to the atmosphere intermittently at a pressure and temperature within a certain range, so as to muffle the exhaust manifold from the exhaust manifold. A muffler 4 which is provided in advance and which has a durable sound absorbing material, for example, of a resonance type or an expansion type, and which is complicatedly combined with the above in order to consume acoustic energy with a resistance as low as possible, and a muffler 4 The tail pipe 5 is provided on the discharge side of the muffler 4 for discharging the exhaust gas to the atmosphere after muffling by the muffler 4, and is attached around the tail pipe 5, and its opening is directed in the same direction as the exhaust port of the tail pipe 5. The two speakers 2 symmetrically arranged with respect to the tail pipe 5 are built in, the end surface on the muffler 4 side is closed, and the end surface on the opposite side is slightly narrowed to open. And Kabokkusu 6, one end thereof is coupled to the opening side of the speaker box 6, its other end is opened,
And a muffler cutter 7 extending beyond the exhaust port of the tail pipe 5. The speaker box 6 may be provided with a hole 8 for exposing the tail pipe 5 so that heat can be released. The hole 8 is for exposing the tail pipe to the outside, that is, for bringing the tail pipe into contact with the outside air, and a wall is formed on the side surface of the hole 8 to make the speaker 2
Sound waves from the outside are not emitted to the outside through the hole 8.

This figure (b) is a front view seen from the muffler cutter side, and this figure (c) is a perspective view. As shown in these figures, the speaker box 6 and the muffler cutter 7 are the tail pipe 5 and the support shown in the figure. It is fixed by the part 9. Next, the operation of the arrangement of the present speaker will be described. The exhaust gas silenced by the muffler 4 is emitted from the tail pipe 5, and the noise caused by this exhaust gas is the main part of the noise generated by the automobile. It has been found that even if the speaker 2 is arranged to superimpose a sound deadening sound wave on the noise emitted from the tail pipe 5 in order to eliminate this noise by the noise control device shown in FIG. 1, the sound deadening effect is unevenly distributed depending on the place. .. Further, the reason why the sound deadening effect is unevenly distributed is that the sound waves from the speaker 2 and the tail pipe 5 are diffused as spherical waves, respectively, so that the interference effect that causes the sound deadening occurs when the tail pipe 5 is asymmetric.

Therefore, according to the present invention, since the two speakers are arranged symmetrically with respect to the tail pipe 5, it is possible to prevent uneven muffling effect. Further, the sound waves of opposite-phase equal sound pressure from the speaker 2 are effectively overlapped with the noise emitted from the tail pipe 5 before being diffused as a spherical wave guided by the muffler cutter 7, so that the sound deadening effect is improved.

FIG. 3 is a diagram showing an arrangement of speakers in the noise control device according to the embodiment of the present invention. This figure shows the arrangement of the speakers as seen from the side of the tail pipe 5, and the four speakers 2 are arranged in 90 ° rotational symmetry with respect to the tail pipe 5. In the case of two symmetrical speakers, if the observation point (listening position) is symmetrical with respect to the two speakers 2A and 2B (see FIG. 3), the muffling effect is great, but for example, the two speakers 2A and 2B. Since it is asymmetrical with respect to the direction in which (see FIG. 3) is aligned (the axial direction connecting the speakers 2A and 2B), the above-described sound deadening effect is reduced when the observation point is this asymmetrical point. In the present embodiment, the other speakers 2C and 2D are provided and the speakers 2C and 2D are arranged symmetrically with respect to the direction in which the speakers 2A and 2B are arranged, so that the above-described muffling effect can be improved. That is, in the case of only the two speakers 2A and 2B, the difference in the sound deadening effect becomes large depending on the observation point, so that the range of the observation point having the sound deadening effect becomes narrow, but by providing the speakers 2C and 2D, this defect is compensated. Therefore, the difference in the sound deadening effect due to the difference in the observation points becomes small, and the range of the observation points having the sound deadening effect can be expanded. Therefore, in general, it is preferable that a large number of speakers are symmetrically arranged on the concentric circle around the tail pipe 5 so that the sound deadening effect can be uniformly obtained at any position of the observation points. The noise control device on which the present invention is based is not limited to the embodiment shown in FIG. 1. For example, noise from the noise source 1 is extracted from a part of a muffler, which is its transmission path, and delayed. There are various methods such as those that create a noise compensation signal using a device, etc.,
Either may be used.

[0014]

As described above, according to the present invention, a plurality of speakers are symmetrically arranged on the concentric circle around the tail pipe of the muffler, and the opening of the speaker is directed in the same direction as the exhaust port of the tail pipe. As a result, uneven distribution of the silencing effect can be prevented and the silencing effect can be improved.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a noise control device on which the present invention is based.

FIG. 2 is a diagram showing an arrangement of speakers in the noise control device according to the embodiment of the present invention.

FIG. 3 is a diagram showing another speaker arrangement in the noise control device according to the embodiment of the present invention.

[Explanation of symbols]

 1 ... Noise generation source 2 ... Electric signal / sound wave converter 3 ... Sound wave / electric signal converter 4 ... Muffler 5 ... Tail pipe 6 ... Speaker box 7 ... Muffler cutter

Claims (1)

[Claims] 1. Using an electric signal / sound wave converter (2),
In a noise control device that silences noise from a noise source (1) by outputting sound waves having an anti-phase equal sound pressure, in a concentric circle around the noise discharge port (3), electric power is symmetrically generated. A noise control device, characterized in that a signal / sound wave converter (2) is arranged, and an opening of the electric signal / sound wave converter (2) is directed in the same direction as the discharge port (3).