JPH05232974A - Noise control device - Google Patents

Abstract

PURPOSE:To attain the optimum control of sound pressure reproducing capacity of an actuator in accordance with its driven state by arranging a pipe allowing a reproduced sound from a speaker to pass and a space whose size is changed in accordance with the frequency of noise in an acoustic impedance buffer space. CONSTITUTION:Noise is eliminated by a tail pipe 101 and the actuator arranged on the post stage of a muffler in an automobile. In the actuator, an enclosure 3 closes the rear part of a speaker 2 for forming a reproduced sound for offsetting noise. In front of the speaker 2, a space (volume V1) is formed by a wall 4-1 and a space (V2) is formed by a wall 4-2. A door 4-4 is arranged in a wall 4-3 in common to both the spaces. Pipes 5 are arranged on the outside of the wall 4-1 opposed to the speaker 2. A wall 10 forms an acoustic impedance buffer on the post stage of the pipe 5. The opening/closing of the door 4 is controlled by the rotational frequency of an internal combustion engine.

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, the present invention relates to an actuator composed of a speaker according to a driving state when the noise control device is mounted on an automobile. The objective is to optimally control the sound pressure reproduction capability.

[0002]

2. Description of the Related Art Conventionally, as such a technique, there has been a noise control device described in JP-A-63-311396. This is a feed-forward system that detects noise with a microphone for noise source supplementation installed upstream of the duct and outputs a signal of opposite phase and equal sound pressure to this noise from a speaker installed downstream of the duct, and the result of the muffling. Is a so-called two-microphone / one-speaker type active noise control device in which a feedback system that detects a noise by a microphone for a muffling point is minimized. In this device, an adaptive filter that forms a compensating sound of opposite phase and equal sound pressure as a signal processing circuit is a DSP (Digital Signal Processor), and is composed of a FIR (Finite Impulse Response) filter.

By the way, conventionally, a passive muffler such as a muffler has been used to reduce noise generated from an internal combustion engine of an automobile or the like, but improvement has been desired from the viewpoint of size, muffling characteristics and the like. Therefore, it is required to reduce noises from the internal combustion engine or the like by using the noise control device to reduce the burden on the muffler or the like and further reduce the noise.

FIG. 10 is a diagram showing an actuator used for conventional noise control. As shown in this figure (a),
The tail pipe 101 and the actuator 1 which are installed in the latter stage of the muffler are installed side by side to eliminate noise. As shown in the front cross-sectional view (b) viewed from B of this figure (a), the openings of the actuator 1 and the tail pipe 101 are arranged. The actuator 1 is provided with an acoustic impedance buffer in the space formed by the wall 10 in front of the speaker 2 enclosed in the enclosure 3. The reason for providing this acoustic impedance is to prevent the acoustic impedance in the enclosure 3 from being higher than that to the outside, which causes a large mismatch in acoustic impedance and reduces the radiation efficiency in low frequency reproduction.
Further, the wall on the side farther from the tail pipe 101 is provided with an inclination as shown in the drawing in order to match the directivity in high frequency reproduction with that of the tail pipe 101.

[0005]

However, when the actuator 1 is applied to an automobile or the like, the frequency of noise generated from the internal combustion engine changes when the rotational speed of the internal combustion engine changes, but the frequency characteristic of the actuator 1 is fixed. Therefore, there is a problem that the performance of the noise control device cannot be sufficiently exerted depending on the operating condition.

Therefore, in view of the above problems, it is an object of the present invention to provide a noise control device capable of efficiently controlling the frequency of noise in which the characteristics of an actuator composed of a speaker change depending on the operating state.

[0007]

In order to solve the above problems, the present invention provides a noise control device comprising an actuator having a space for an acoustic impedance buffer in front of a speaker sealed in an enclosure. The space for use is provided with a tube through which the reproduced sound of the speaker passes and a space whose size changes according to the frequency of the noise. The area of the tube through which the reproduced sound of the speaker of the actuator passes may be changed according to the frequency of the noise. The length of the tube through which the reproduced sound of the speaker of the actuator passes may be changed according to the frequency of the noise. A noise control device including an actuator having a space for an acoustic impedance buffer in front of a speaker sealed in an enclosure is provided with a phase inversion port in an enclosure on the same plane as the speaker, and the phase inversion port is provided when the frequency of noise is low. May be opened. A branch pipe that guides the reproduced sound of the speaker from the space for the acoustic impedance buffer is provided at a position symmetrical to the actuator with respect to the tail pipe that discharges the exhaust gas of the internal combustion engine. The reproduced sound may pass through the branch pipe. The space for the acoustic impedance buffer may change according to the frequency of noise. In a noise control device that corrects the spatial transfer characteristics from the speaker to the muffling point, reproduces noise, and optimally controls so that the error signal of the muffling is minimized, in the noise control device that is based on the information on the rotational speed of the internal combustion engine, The resonance frequency, the radiation efficiency, and the directivity of the actuator having the space for the acoustic impedance buffer in the front may be controlled to correct the change in the spatial transfer characteristic due to the control.

[0008]

According to the noise control device of the present invention, by providing the space for the acoustic impedance buffer with the tube for passing the reproduced sound of the speaker and the space whose size changes according to the frequency of the noise, The resonance frequency of the actuator can be changed according to the frequency of noise. By changing the area of the tube through which the reproduced sound of the actuator speaker is passed according to the frequency of noise, and by changing the length of the tube through which the reproduced sound of the actuator speaker is passed according to the frequency of noise, The resonance frequency of the actuator can be changed according to the frequency of noise. In a noise control device including an actuator having a space for acoustic impedance buffer in front of a speaker sealed in an enclosure, a phase inversion port is provided in an enclosure on the same plane as the speaker, and the phase inversion port is provided when the noise frequency is low. The sound pressure in the low range can be enhanced by opening the. A branch pipe that guides the reproduced sound of the speaker from the space for the acoustic impedance buffer is provided at a position symmetrical to the actuator with respect to the tail pipe that discharges the exhaust gas of the internal combustion engine. As the reproduced sound passes through the branch pipe,
The directivity in the high range can be improved. Radiation efficiency can be improved by changing the space for the acoustic impedance buffer according to the frequency of noise. The above actuator control is performed in conjunction with a noise control device that corrects the spatial transfer characteristics from the speaker to the muffling point, reproduces noise, and optimally controls so that the error signal for muffling is minimized. From this information, the resonance frequency, the radiation efficiency, and the directivity of the actuator having the space for the acoustic impedance buffer in front of the speaker sealed in the enclosure are controlled, and the change in the spatial transfer characteristic due to this is corrected.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram for explaining general characteristics of an actuator which is a premise of the present invention. An actuator 1 shown in this figure includes a speaker 2 that forms a reproduced sound that cancels noise, an enclosure 3 that seals the rear of the speaker 2, and a wall 4 that forms a space of a predetermined size in front of the speaker 2. , And a tube 5 provided in a part of the wall 4.

When the volume of the space surrounded by the wall 4 is V, the length of the tube 5 is L, and the area is S, the resonance frequency F of the sound in this space can be expressed by the following equation. F = C / 2π · {(S / (L · V)} ^1/2 (1) where C is the speed of sound, so the parameters S, L,
When V is fixed, the resonance frequency formed by the actuator 1 is fixed. Therefore, as will be described below, in the present invention, these parameters are variously changed according to the change in the noise frequency.

FIG. 2 is a diagram showing an actuator for controlling the size of the space in front of the speaker according to the first embodiment of the present invention. As shown in this figure (a), the actuator 1 has a speaker 2 that forms a reproduced sound that cancels noise, an enclosure 3 that seals the rear of the speaker 2, and a space (volume V1) in front of the speaker 2. Wall 4-1 to be formed and wall 4-2 forming a space (volume V2)
A wall 4-3 common to both spaces, a door 4-4 provided in the wall 4-3, a pipe 5 provided outside the wall 4-1 facing the speaker 2, and the pipe 5 And a wall 10 forming an acoustic impedance buffer. In this figure (a), the door 4-4 is in an open state. In this figure (b), the door 4-4 is in a closed state. As described above, the acoustic impedance is provided in order to prevent the acoustic impedance inside the enclosure 3 from being higher than the outside so that the acoustic impedance mismatch becomes large and the radiation efficiency in the low frequency reproduction is lowered. Further, the reason that the wall on the side away from the tail pipe 101 is provided with an inclination as shown is to make the directivity in high frequency reproduction match that of the tail pipe 101.

FIG. 3 is a diagram showing frequency characteristics of the actuator of FIG. As shown in this figure (a), MODE1 is defined as the rotational speed of the internal combustion engine lower than N1 and MODE2 is defined as N1 or higher.
As a result, the door 4-4 of the actuator 1 is changed from open to closed at the rotation speed N1. As shown in this figure (b), the parameters S and L in the equation (1) are constant, and the parameter V is V1 +.
As the resonance frequency F changes from the low frequency to the high frequency by changing from V2 to V1, the frequency characteristic of the actuator 1 changes from MODE1 to MODE2. The door 4-4 is opened / closed by a command from the control unit described later.

FIG. 4 is a view showing a modification of the actuator 1 according to the first embodiment of FIG. In the actuator 1 shown in this figure, the space (volume V2) formed by the wall 4-2 and the wall 4-3 in FIG. 2 is further divided into volumes V3, V4, and V5 by the walls 4-6 and 4-7. A door 4-8, a door 4-9, and a door 4-10 are provided in the wall 4-3 for each space. The doors 4-8, 4-9, and 4-10 are controlled to be opened / closed by the rotation speed of the internal combustion engine as described above, and the frequency characteristics of the actuator 1 are smoothly switched, which contributes to a reduction in discomfort.

FIG. 5 is a diagram showing an actuator for controlling the opening area and length of a tube provided in a part of the space in front of the speaker according to the second embodiment of the present invention.
As shown in this figure (a), in a wall 4-1 for forming a space (area) in front of the speaker 2, a wall facing the speaker 2 has a tube 5-1 and a tube 5-having the same length. 2 and a door 5-3 is provided on the pipe 5-2. If the door 5-3 is opened when the noise frequency is increased, the opening area of the pipe is increased, and thus the resonance frequency is increased from the above (1). Further, as shown in this figure (b), tubes 5-5 and 5-6 having different lengths are provided on the opposing wall of the speaker 2, and
A door 5-7 is provided at -5, and a door 5-8 is provided at the pipe 5-6. When the noise frequency is low, the door 5-8 is opened, and when it is high, the door 5-6 is opened. Therefore, according to the above formula (1), the resonance frequency increases as the tube length decreases.

The above description has been made on an example using resonance. The improvement of the frequency characteristic based on another principle will be described below. FIG. 6 is a diagram showing an actuator for controlling a phase inversion port on the same surface as a speaker according to a third embodiment of the present invention. As shown in the figure, a phase inversion port 6-1 is provided on the same surface as the speaker 2 sealed in the enclosure 3, and a door 6-2 is attached to the phase inversion port 6-1.
A wall 10 for forming an acoustic impedance buffer is provided in front of the speaker 2. Phase inversion port 6
-1 contributes to the improvement of enhancing the sound pressure in the low range. Therefore, when the noise frequency increases, the door 6-2 is closed.

FIG. 7 is a diagram showing an actuator for controlling the passage for responding to the directivity of high frequency noise according to the fourth embodiment of the present invention. As shown in this figure (a), the tail pipe 1 provided downstream of the main muffler 100 for reducing the noise of the exhaust gas from the engine.
In the actuator 1 provided near 01, an acoustic impedance buffer is formed, and the tail pipe 10
1 is provided with a branch pipe 7-1 through which the reproduced sound from the speaker 2 is passed. This figure seen from the direction of arrow A (b)
As shown in FIG. 3, the opening of the branch pipe 7-1 is the tail pipe 1
01 is symmetrical to the opening 8-1 in the front space of the speaker 2. If the noise frequency increases, this figure (a)
As shown in, the door 7-2 provided in the branch pipe 7-1 is combined with the reproduced sound from the opening 8-1 and the directivity of the combined reproduced sound is the same as the directivity of the tail pipe 101. Like For this reason, the control efficiency of noise with high directivity in the high frequency range is improved.

FIG. 8 is a diagram showing an actuator 1 for controlling the size of the space of the acoustic impedance buffer according to the fifth embodiment of the present invention. As shown in the figure, a space surrounded by a wall 11 is provided next to a space surrounded by a wall 10, and a door 12 is provided on a boundary wall. When the noise frequency is low, the door 12 is opened to improve the radiation efficiency in the low range. Therefore, noise control in the low range is improved. FIG. 9 is a diagram showing a noise control device when an actuator for controlling the space in front of the speaker is used as a sixth embodiment of the present invention. The noise control device shown in this figure
A microphone 200 installed near the opening of the actuator 1 and the tail pipe 101, for capturing the sound remaining after the noise is superimposed by the erasing sound, and the microphone 2
Low pass filter 201 for removing the high frequency component of the signal from 00 and an A / D converter 202 for converting the analog signal from the low pass filter 201 into a digital signal.
(Analog to Digital Converter) and A / D on one side
Adder 2 to which the digital signal from the converter 202 is input
03, an adaptive filter 204 for inputting the output signal of the adder 203, and a space transfer characteristic (Hd1) from the speaker 2 to the microphone 200 when the door 4-4 of the actuator 1 is opened. A / D converter 2
A space transfer characteristic (Hd2) from the speaker 2 to the microphone 200 when the door 4-4 of the actuator 1 is closed, similarly to the first space transfer simulation unit 205 for correcting the signal from 02. The second minimization unit spatial transfer simulation unit 206 that corrects the signal from the A / D converter 202 to simulate, and the first and second second minimization unit spatial transfer simulation units 205 and 206. The switch 207 for switching the output signal and the space transfer characteristics (Hd1, Hd2)
In consideration of the above, the minimization unit 208 that generates the filter coefficient of the adaptive filter 204 to minimize the residual sound from the A / D converter 202, and the speaker when the door 4-4 of the actuator 1 is opened. 2 to the microphone 200, the first waveform reproduction space transfer simulation unit 209 that corrects the signal from the adaptive filter 204 to simulate the space transfer characteristic (Hd1), and the door 4-4 of the actuator 1 are closed. The second waveform reproduction spatial transfer simulation unit 210 that corrects the signal from the adaptive filter 204 in order to simulate the spatial transfer characteristic (Hd2) from the speaker 2 to the microphone 200 at the time of the first and second The output signals of the waveform reproduction spatial transfer simulation units 208 and 209 are selected, and the selected signal is given to the other input of the adder 203 to the adaptive filter 204. A switch 211 to form a noise reproduction signal, D / A converter 212 which converts the digital signal of the adaptive filter 204 to an analog signal (Digital
to analog converter), a low-pass filter 213 that removes high-frequency components from the D / A converter 212, and a power amplifier 214 that amplifies the signal from the low-pass filter 213 and supplies the amplified signal to the speaker 2. , The switch 2
And a microcomputer 215 for controlling opening / closing of the doors 07 and 211 and opening / closing of the door 4-4 according to the rotation speed of the internal combustion engine. The dashed line in the figure shows the DSP (Digital Signal Process).
or)). In this figure, the actuator 1 of the first embodiment is used.
The actuator 1 shown in Examples 3 and 4 may be used. Thus, the actuator 1 has the adaptive filter 2
04, etc. can be integrated together to cope with the frequency of noise that changes with the operating state.

[0018]

As described above, according to the present invention, the resonance frequency, the radiation efficiency, and the directivity of the actuator are controlled, and the changes in the space transfer characteristics due to the control are corrected, so that the change in the operating state can be prevented. With this, it is possible to efficiently control the noise whose frequency changes.

[Brief description of drawings]

FIG. 1 is a diagram for explaining general characteristics of an actuator which is a premise of the present invention.

FIG. 2 is a diagram showing an actuator for controlling the size of the space in front of the speaker according to the first embodiment of the present invention.

FIG. 3 is a diagram showing frequency characteristics of the actuator of FIG.

FIG. 4 is a diagram showing a modification of the actuator 1 according to the first embodiment of FIG.

FIG. 5 is a diagram showing an actuator for controlling an opening area and a length of a tube provided in a part of a space in front of a speaker according to a second embodiment of the present invention.

FIG. 6 is a diagram showing an actuator for controlling a phase inversion port on the same plane as a speaker according to a third embodiment of the present invention.

FIG. 7 is a diagram showing an actuator for controlling a passage for responding to a directivity of high frequency noise according to a fourth embodiment of the present invention.

FIG. 8 is a diagram showing an actuator 1 for controlling the size of a space of an acoustic impedance buffer according to a fifth embodiment of the present invention.

FIG. 9 is a diagram showing a noise control device when an actuator for controlling a space in front of a speaker is used as a sixth embodiment of the present invention.

FIG. 10 is a diagram showing an actuator used for conventional noise control.

[Explanation of symbols]

1 ... Actuator 2 ... Speaker 3 ... Enclosure 4, 4-1, 4-2, 4-3, 4-6, 4-7, 10 ...
Walls 4-4, 4-8, 4-9, 5-3, 5-8, 6-2, 7
-2, 12 ... Door 5 ... Pipe 6-1 ... Phase inversion port 101 ... Tail pipe

Claims (7)

[Claims] 1. A noise control device comprising an actuator (1) having a space for acoustic impedance buffer in front of a speaker (2) sealed in an enclosure (3), comprising: A noise control device comprising a pipe (5) for passing a reproduced sound of a speaker (2) and a space whose size changes according to the frequency of noise in the space. 2. The noise control device according to claim 1, wherein the area of the pipe (5) through which the reproduced sound of the speaker (2) of the actuator (1) passes is changed according to the frequency of noise. 3. The noise control device according to claim 1, wherein the length of the tube (5) through which the reproduced sound of the speaker (2) of the actuator (1) passes is changed according to the frequency of the noise. 4. A noise control device comprising an actuator (1) having a space for acoustic impedance buffer in front of a speaker (2) sealed in an enclosure (3), the speaker (2) of the actuator (1) and The phase inversion port (6-1) is provided in the enclosure (3) on the same plane, and the phase inversion port (6-1) is provided when the noise frequency is low.
A noise control device characterized in that 1) is opened. 5. A branch for guiding a reproduced sound of a speaker (2) from a space for an acoustic impedance buffer so that the tail pipe (101) for discharging exhaust gas of an internal combustion engine is positioned symmetrically with the actuator (1). The noise control device according to claim 4, wherein a pipe (7-1) is provided, and the reproduced sound of the speaker (2) passes through the branch pipe (7-1) when the frequency of noise is high. 6. The noise control device according to claim 4, wherein the space for the acoustic impedance buffer changes according to the frequency of the noise. 7. A noise control device for optimally controlling a space transfer characteristic from a speaker (2) to a sound deadening point to reproduce noise and minimize an error signal of the sound deadening, based on information on the number of revolutions of an internal combustion engine. , Resonance frequency, radiation efficiency and directivity of an actuator (1) having a space for acoustic impedance buffer in front of a speaker (2) sealed in an enclosure (3) are controlled, and a change in space transfer characteristic due to this is corrected. Claims 1, 2, 3, 4, 5,
Or the noise control device according to any one of 6 above.