JPH08123433A - Active noise eliminating device - Google Patents

Abstract

PURPOSE: To obtain the active noise eliminating device which is conveniently carried and has superior noise elimination effects by arranging a sound sensor nearby the diaphragm surface of a speaker that generates a secondary sound, and integrating detected sound signal and generating the secondary sound based upon the integrated sound signal by the speaker. CONSTITUTION: This device is equipped with the speaker 41 which generates the secondary sound, the sound sensor 42 which is arranged nearby the diaphragm surface of the speaker 41, and an integrator 45 which integrates the sound signal detected by the sound sensor 42. This sound sensor 42 inputs a sound radiated from one surface of the diaphragm surface of the speaker 41 and a sound radiated from the other surface, and they are applied in mutually opposite phase relation to the sound sensor. Consequently, the sound sensor 42 outputs only the sound signal which representing a primary sound and the problem of howling is solved. Then the integrator 45 integrates the sound signal obtained from the sound sensor 42 and the secondary sound based upon the integrated sound signal is generated by the speaker 41 and superposed on the primary sound, so that they cancel each other.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
This primary sound is canceled based on the sound signal representing the next sound. 2
The present invention relates to an active muffling device that generates the next sound.

[0002]

2. Description of the Related Art In recent years, an active silencer has been used to eliminate noise generated by a noise source such as a refrigerator or an air conditioning duct (see Nikkei Mechanical 1992.2.3). An example of a conventional active silencer will be described with reference to FIG. FIG. 5 is a schematic configuration diagram showing an active silencer used to eliminate noise in an air conditioning duct.

This active silencer receives a sound sensor 12 for measuring noise, an error microphone 14 for measuring the noise left unerased, and a sound signal from these sound sensors 12, 14 for inputting noise canceling noise. It is composed of a controller 20 for generating a sound signal representing the next sound and a speaker 16 for generating the secondary sound. The noise generated by a noise source (not shown) propagates inside the air conditioning duct 10 in the direction indicated by the arrow A and is measured by the sound sensor 12. While the measured noise further advances to the position of the speaker 16, the sound signal measured by the sound sensor 12 passes through the microphone amplifier 21, the A / D converter 22, and the adder 23 built in the controller 20. And ADF (adaptive digital
Filter) 24, and the ADF 24 generates a sound signal representing a secondary sound having a sound pressure obtained by inverting the phase of the sound pressure of the sound represented by the input sound signal, based on the input sound signal. To be done.

Here, the noise measured by the sound sensor 12 changes due to the transfer characteristic of the sound field while traveling from the sound sensor 12 to the speaker 16. Therefore, the sound sensor 1
Even if a secondary sound in which the phase of the sound pressure of the noise measured in 2 is inverted is generated from the speaker 16, the noise does not completely disappear but a part remains. In order to completely eliminate the noise, the secondary sound emitted from the speaker 16 is a sound in which the phase of the sound pressure of the noise is inverted at the position where the speaker 16 is provided, that is, the position where the noise and the secondary sound are superposed. It must be a secondary sound with pressure. In addition, the transfer characteristic of the sound field is
It changes momentarily according to changes in the temperature / humidity of the sound field and the flow velocity, and also due to deterioration of the air conditioning duct. Therefore, the controller 20 is provided with a filter coefficient adjuster 25 for adjusting the filter coefficient of the ADF 24 according to the transfer characteristic. This filter coefficient adjuster 25
The sound signal of the error microphone 14 is transmitted to the microphone amplifier 26,
Based on this sound signal input via the A / D converter 27, the filter coefficient adjuster 25 constantly adjusts the filter coefficient of the ADF 24 so that the unerased sound becomes small.

Further, the input signal of the sound sensor 12 is output from the speaker 16 via the controller 20, and again,
A “howling phenomenon” may occur in which the sound sensor 12 is input, amplified, and output from the speaker 16. In order to prevent this “howling phenomenon”, the controller 20 is provided with a digital filter 28. In this digital filter 28, the sound sensor 12
A transfer characteristic of a sound field between the speaker 16 and the speaker 16 is electrically created. A sound signal sent to the speaker 16 is branched and input to the digital filter 28, a sound signal in which the above-mentioned transfer characteristic is added is generated, and is output to the adder 23. In the adder 23, the signal formed by the digital filter 28 is subtracted from the sound signal of the sound sensor 12.
This prevents the "howling phenomenon".

[0006]

The conventional active silencer described above needs to be constructed so that the secondary sound generated from the speaker 16 is not input to the sensor microphone 12 as much as possible. 1
2 are arranged at positions separated from each other. Therefore, the conventional active silencer is limited to fixed equipment and is not portable. That is, in the conventional active silencer, when the sound sensor 12 and the speaker 16 are brought close enough to each other so that they can be housed in one housing for convenience of carrying, an extremely loud secondary sound, which is about the same as the noise, is emitted together with the noise. Since it is input to the sensor 12, it becomes extremely difficult to cancel the secondary sound and extract a signal of only noise, and the silencing effect is significantly reduced.

In view of the above circumstances, the present invention is convenient to carry,
Moreover, it is an object of the present invention to provide an active muffling device having excellent muffling effect.

[0008]

SUMMARY OF THE INVENTION To achieve the above object, an active silencer of the present invention detects a primary sound generated by a primary sound source to obtain a sound signal, and based on the sound signal,
In an active muffling apparatus that generates a secondary sound that cancels a secondary sound, a speaker that generates the secondary sound, a sound sensor that is arranged near a vibrating surface of the speaker, and a sound signal detected by the sound sensor are provided. Integrating means for integrating is provided, and a secondary sound based on the sound signal integrated by the integrating means is generated from the speaker.

[0009]

In the sound sensor of the active muffler of the present invention,
Generally, the primary sound generated by the primary sound source and the secondary sound generated by the speaker are input. However, since the sound sensor is placed in the vicinity of the speaker, both the sound radiated from one surface of the vibrating surface of the speaker and the sound radiated from the other surface of the speaker are input to this sound sensor, and Sound is applied to the sound sensor in opposite phase to each other. As a result, the sound sensor outputs only the sound signal representing the primary sound, and the howling problem is solved. The integrating means integrates the sound signal obtained by the sound sensor, and the secondary sound based on the integrated sound signal is generated from the speaker and overlaps with the primary sound, whereby the primary sound and the secondary sound are mutually generated. Offset.

Here, the reason why the integral calculation is necessary will be described. Many normal sound sources can be regarded as monopole sound sources. For example, a human voice is an example of this. Even in the case of a monopole sound source, the sound property approaches a plane wave at a position sufficiently distant from the sound source. In the case of a monopole sound source, the sound pressure is given by the following formula (eg Kenichi Kido,
See "Acoustic Engineering" Corona).

P = [(jωρQ) / (4πr)] e ^−jkr (1) where P is sound pressure, ω is angular frequency, ρ is air density, Q is volume velocity, k is wave number, and r is It is the distance from the sound source to the sound receiving point. Further, j represents an imaginary unit. On the other hand, when the speaker is used without being put in the box, sounds having opposite phases to each other are generated on both sides of the diaphragm as described above, so that the speaker can be regarded as a dipole sound source. The sound field due to a dipole sound source is a sound field when two opposite-phase monopole sound sources exist at a distance (d) much smaller than the wavelength of sound, and the sound pressure at that time is given by the following equation. (See the above reference).

[0012]

[Equation 1]

Rewriting this,

[0014]

[Equation 2]

Here, c is the speed of sound, and θ is the angle between the dipole axis (a straight line connecting two monophase sound sources of opposite phases) and the observation point. Furthermore, kr >> 1 and θ =
When the condition of 0 is satisfied, the above equation is expressed as the following equation.

[0016]

(Equation 3)

The difference between equations (1) and (2) is that [(d /
c) (jω)]. jω represents a derivative, and (d / c) represents a difference in sound pressure level. In short, the difference in the sound field between the monopole and the dipole is that the latter is differentiated from the former with the magnitude. That is, in the case of a dipole sound source, in order to realize the same sound field as in the case of a monopole sound source, it is necessary to integrate the signal of the sound sensor in addition to simply amplifying it.

Since the active muffler of the present invention integrates the sound signal output from the sound sensor and generates the secondary sound based on the integrated sound signal, the sound sensor is placed close to the speaker. Even if it is placed and configured to be convenient for carrying, it has an excellent sound deadening effect.

[0019]

Embodiments of the active muffling apparatus of the present invention will be described below. FIG. 1 is a schematic configuration diagram showing an embodiment of the active silencer of the present invention. Active silencer 4
At 0, a speaker 41 that generates a secondary sound that cancels the noise generated by the noise source 30 and a vibrating surface 4 of the speaker 41.
There is provided a sound sensor 42 arranged on the extension of the spread of 1a, an integrator 45 for integrating the sound signal of the sound sensor 42, and an amplifier 46 for amplifying the sound signal integrated by the integrator 45.

The action of the active noise canceling device 40 to cancel noise will be described. Generally, the noise emitted from the noise source 30 and the secondary sound generated from the speaker 41 are input to the sound sensor 42. The sound sensor 42 is arranged at a position on the extension of the spread of the vibration surface of the speaker. Because
The secondary sound emitted from the speaker 41 is not input to the sound sensor 42. Therefore, the secondary sound is not input to the integrator 45 and is not a target of integration processing. On the other hand, the sound sensor 4
The sound signal representing the noise input to 2 is integrated by the integrator 45 and input to the amplifier 46. In the amplifier 46, the integrator 45
The sound signal integrated by is amplified to a level that cancels noise. This amplified signal is input to the speaker 41,
When the secondary sound is generated from the speaker 41, the noise and the secondary sound are overlapped with each other to cancel the noise.

Here, the amplifier 46 may be one that simply amplifies the sound signal integrated by the integration value 45 at a predetermined amplification factor, but it depends on the frequency characteristic of the speaker 41, the sound receiving position, and the like. It is preferable that not only the amplification factor of the sound signal but also the frequency transfer characteristic and the phase characteristic can be adjusted from the outside. As described above, in the active muffling device 40 of the above-described embodiment, the secondary sound generated from the speaker 41 is not input to the sound sensor 42, and only noise is input. Therefore, the speaker 41 and the sound sensor 42 are placed close to each other. Can be placed. Further, since the output of the sound sensor is integrated and input to the speaker, it has an excellent silencing effect.
As a result, it is possible to configure a portable active silencer that is convenient to carry and has excellent silencing effect.

FIG. 2 is a schematic configuration diagram showing another embodiment of the active muffler of the present invention. Corresponding components in the embodiment shown in FIG. 1 are indicated by the same numbers as those given in FIG. 1, and only the differences will be described. In the embodiment shown in FIG. 2, two sound sensors 42 and 43 arranged at positions symmetrical to each other with respect to the vibration surface 41a of the speaker 41 are shown. Both the noise emitted from the noise source 30 and the secondary sound generated from the speaker 41 are input to the sound sensors 42 and 43, and a sound signal representing the noise and the secondary sound is input to the adder 44. . Sound sensor 4
Since the reference numerals 2 and 43 are arranged in mutually symmetrical positions with respect to the vibrating surface 41 a of the speaker 41, the secondary sound input to the sound sensor 42 and the secondary sound input to the sound sensor 43 have mutually different sound pressure phases. It is the opposite. Therefore, the sound sensor 4
When the sound signals input to 2, 43 are added by the adder 44, the sound signals representing the secondary sounds cancel each other and become zero. As a result, the sound signal representing the secondary sound is not input to the integrator 45, and only the sound signal representing the noise is input and integrated. After that, the embodiment described above (see FIG. 1)
In the same manner as above, the secondary sound for canceling the noise is emitted from the speaker 41.

In the case of the embodiment shown in FIG. 2, the sound signal of the sound sensor 43 is used to amplify the sound signal to zero by the amplifier 46.
It is also possible to have a configuration in which the amplification factor is automatically adjusted.
Also works as. Further, in any of the above-mentioned embodiments, when two speakers 41 are prepared, and the vibrating surfaces of these two speakers face each other and are brought into contact with each other, and the two speakers generate sounds in opposite phases to each other, these two speakers are generated. The transfer characteristics of the left and right sound fields sandwiching the vibrating surface of the speaker are the same, so that the secondary sound whose phase of the sound pressure is more accurately reversed is input to the sound sensor. Therefore, with this configuration, it is possible to prevent a reduction in the silencing effect due to the residual secondary sound.

FIG. 3 is a graph showing a simulation result for confirming the effectiveness of the present invention. S shown in FIG.
0 = −0.5 is a position where the noise source is −0.5 m with respect to the vibration surface of the speaker (for example, a position 0.5 m to the left of the vibration surface 41a of the speaker 41 in FIG. 1). X = 0.5 indicates that this graph is at a position 0.5 m away from the vibration surface of the speaker (for example, in the right side of the vibration surface 41a of the speaker 41 in FIG.
5m position) is a graph showing the sound deadening effect, and amx = 0, amy = 0.04 means that the position (x, y) of the sound sensor is (0m, 0.04m). For example, in FIG. 1, the horizontal direction of the drawing is on the vibration surface 41a of the speaker 41, and the vertical direction of the drawing is at a position 4 cm away from the center point of the vibration surface 41a of the speaker 41. 0d of the graph shown in FIG.
B represents the reference level when the noise is not canceled at all.

The graph of FIG. 3 shows that noise is reduced to -10 dB or less in the frequency range of 300 Hz to 4 kHz, which occupies an important position among human audible sounds. FIG. 4 is a graph similar to FIG. 3, showing the silencing effect at a position 0.7 m away from the vibration surface of the speaker.

Although the sound deadening peak is lower than that of the graph shown in FIG. 3, the important frequency band of about 300 Hz to 3 kHz has a sound deadening effect of -10 dB or more.

[0027]

As described above, according to the active muffler of the present invention, the secondary sound generated from the speaker is not received, or is canceled even if it is once received. The sound sensors can be placed in close proximity. Further, since the sound signal representing the noise received by the sound sensor is integrated to generate the secondary sound based on the integrated sound signal, an excellent silencing effect can be achieved. As described above, according to the present invention, it is possible to configure an active silencer that is convenient to carry and has an excellent silence effect.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of an active silencer of the present invention.

FIG. 2 is a schematic configuration diagram showing another embodiment of the active silencer of the invention.

FIG. 3 is a graph showing a simulation result for confirming the effectiveness of the present invention.

FIG. 4 is a graph similar to FIG. 3, showing the sound deadening effect at a position 0.7 m away from the vibration surface of the speaker.

FIG. 5 is a schematic configuration diagram showing a conventional active silencer used to eliminate noise in an air conditioning duct.

[Explanation of symbols]

 30 noise source 40 active silencer 41 speaker 41a vibrating surface 42, 43 sound sensor 44 adder 45 integrator 46 amplifier

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display H04R 3/02

Claims (1)

[Claims] 1. An active muffling apparatus that detects a primary sound generated by a primary sound source to obtain a sound signal and generates a secondary sound that cancels the primary sound based on the sound signal. A speaker that generates sound, a sound sensor that is arranged in the vicinity of the vibrating surface of the speaker, and an integrating unit that integrates the sound signal detected by the sound sensor, and based on the sound signal integrated by the integrating unit. An active silencer, wherein a secondary sound is generated from the speaker.