JP2994809B2 - Silencer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a noise reduction device for lowering the noise level in a room such as an aircraft, a car, a vehicle, and a building.

[0002]

2. Description of the Related Art A conventional noise reduction technique will be described by taking an example of a method for reducing in-flight noise of an aircraft. FIG. 8 shows an example of passive soundproofing measures of a conventional aircraft.

[0003] An interior trim is installed along the outer panel shape inside the body outer panel structure, and the space between the outer panel and the interior trim is filled with glass wool having excellent sound absorbing properties. By taking such a double structure of the outer panel and the interior trim, sound insulation is improved. A damping material is attached to the outer panel to take measures to reduce the vibration radiation sound of the outer panel. At present, passive soundproofing measures utilizing characteristics such as sound absorption and sound insulation as described above are currently implemented as practical methods.

On the other hand, soundproofing measures in an aircraft cabin using an active method of adding a secondary sound to reduce noise have been proposed and trials have been made. It does not mention how to determine the position reasonably.

[0005]

The problem to be solved by the present invention will be described by taking as an example the reduction of in-flight noise of an aircraft or helicopter. Aircraft and helicopter cabin noise
(1) sound that is radiated into the aircraft by vibrating the outer plate due to pressure fluctuations in the boundary layer; (2) solid-borne sound that propagates through the structure due to engine vibration of an aircraft or transmission vibration of a helicopter; ) There is a sound such as a jet engine sound or a propeller sound propagating in the air and passing through the outer panel.

[0006] Among these noises, high frequency components can be relatively efficiently reduced by the prior art utilizing the characteristics of sound insulation and sound absorption, but sufficient noise reduction is achieved for low frequency components. In order to achieve the effect, the required space and weight become enormous, so that it was not practical.

[0007] It has been proposed to add a secondary sound to reduce low-frequency sound in a room to reduce the sound.
There is a problem that the noise reduction range is very limited, and the method is not an effective method. This is partly because it is not clear where the secondary sound should be added. SUMMARY OF THE INVENTION An object of the present invention is to provide an apparatus that solves the above problems of the conventional method.

[0008]

Silencer according to the present invention SUMMARY OF THE INVENTION comprises a noise source characteristics detector 1 which is provided in the vicinity of the noise source emitting noise into (A) interior space, the noise in (B) the indoor space a plurality of noise received sound signal detector 2 to be installed in the vicinity of the region aimed at reducing, with a plurality of secondary sound adder 3 for canceling noise at the position of (C) the noise received sound signal detector, ( D) a noise control device 4 ; (E) the noise control device 4 receives the signal obtained by the noise source characteristic detector 1 and convolves a signal obtained by convolving the signal with a filter coefficient with the secondary sound adder 3; And (F) detecting the plurality of noise reception signals. The adaptive noise correction means further comprises: adaptive means for modifying a filter coefficient so as to minimize a signal detected by the noise reception signal detector 2. The vessels 2 are installed so as to be distributed almost evenly in the target area, (G) The plurality of secondary sound adders 3 are installed at optimal positions obtained by an optimization method using an integral value of the square of the sound pressure in the target area without the target area as an objective function.

[0009]

The noise source signal is detected by a noise source characteristic detector (for example, an engine rotation pulse detector, an engine vibration detector, etc.) provided near a noise source that emits noise. The noise control device receives this signal and inputs a drive signal to the secondary sound adding means. This drive signal is set in the noise control device such that the secondary sound forms a sound field that cancels the noise. The secondary sound adding means forms a secondary sound field for canceling noise according to the drive signal. In addition, the most effective sound reduction effect in the sound reduction target area can be achieved by installing the secondary sound adding means at a position determined based on the optimum method.

[0010]

1 to 4 show a first embodiment of the present invention.

In the first embodiment, a noise source characteristic detector 1 provided near a noise source, a noise receiving signal detector 2 provided near a region where noise is to be reduced, and a noise receiving signal detector And a noise control device 4 which receives a signal obtained by the noise source characteristic detector and sends a signal obtained by convolving a filter coefficient to the secondary sound adder 3 to the secondary sound adder 3. This is an adaptive controller configured to modify the filter coefficient in the noise control device 4 so as to minimize the signal detected by the noise receiving signal detector 1.
The control method of the noise control device 4 and the installation method of the secondary sound adder 3 will be described below. When such a sound field control is performed, an effective sound reduction effect is obtained in a hatched portion (a region where sound reduction is aimed) in FIG.

Next, the contents of processing by the noise control device 4 of the first embodiment will be described with reference to FIG. Convolve the filter coefficients W _Si of N sets of secondary sound adders (the names of the secondary sound adders are S ₁ ... S _i ... _SN ) used for the noise source characteristic data taken from the noise source. The input signal is input to each secondary sound adder. Here, the filter coefficient W _Si is modified by an LMS (Least Mean Square) algorithm so that the sum of the squares of the received signals obtained by the M noise received signal detectors 2 is minimized. And In FIG. 2, h _Si and _Mj are impulse responses indicating transfer characteristics from each secondary sound adder 3 to each noise receiving signal detector 2.
Before starting the control, the transfer function is measured or determined by an adaptive identification method. The signal obtained by convolving the filter coefficient W _Si is a signal obtained by processing the following equation (1).

[0013]

(Equation 1) The above processing can be easily executed by a digital signal processor.

Next, a method of installing the secondary sound adder 3 of the first embodiment will be described with reference to FIG. FIG. 3 shows the secondary sound adder 3
An example in the case of the number is shown. Sound pressure value P of the angular frequency omega in a room coordinate <x> is n-order mode [psi _n <x>, with the complex amplitude a _n (omega) is expressed as follows.

[0015]

(Equation 2)

The complex amplitude due to the noise source is a _pn (ω), m =
Assuming that the intensity of each of the secondary sound adders 1 to M is q _sm (ω) and the contribution rate of each secondary sound adder to the n-mode is B _nm (ω), the noise source and each secondary sound addition The complex amplitude a _n (ω) due to the total contribution from the vessel is given by:

[0017]

(Equation 3)

Now, it is assumed that the noise source and each secondary sound source are working. The time domain integral value E _p of the sound pressure squared in sound reduction target region V shown by the shaded portion of FIG. 3 can be expressed as follows.

[0019]

(Equation 4) From equations (2) to (4)

[0020]

(Equation 5)

When this value is determined and the position of the secondary sound adder is determined and optimal active acoustic control is performed, the minimum value of the area integration of the square of the sound pressure obtained in the sound reduction target area is obtained. Here, in order to obtain the positions of the N secondary sound adders that minimize the expression (5B), the frequency ω ₀ to be determined is determined and 1 to N 2
By providing the initial value of the position of the secondary sound adder and solving the optimization problem using the equation (5B) as the objective function, the optimum secondary sound adder position can be obtained. By installing the secondary sound adder at the position obtained by the above procedure, the best sound reduction effect can be achieved in the sound reduction target area.

When the noise is a random sound, even if the control method shown in FIG.
The filter coefficient W of FIG. 2 may not be established at the position of the secondary sound adder, but such a problem does not occur when the noise is a synchronous sound. "The filter coefficient W of FIG. 2 may not be satisfied at the position of the secondary sound adder due to the relationship of causality" means the case as shown in FIG. 4B.

In the case shown in FIG. 4A, that is, when the distance l ₁ between the noise source and the evaluation point is larger than the distance l ₂ between the secondary sound adder and the evaluation point, Δt = (l ₁ −l ₂ ) By using the time difference of / (sound speed), it is possible to create a secondary sound that cancels out the sound generated by the noise source at the evaluation point, but in the case as shown in FIG.
₁ When l ₂ smaller than can not sound generated from the noise source to the future time of canceling noise unless predictable. Prediction of a sound at a future time is impossible in the case of a general random sound having no periodicity (causality). Therefore, in the case of a random sound, if a secondary sound addition position that does not satisfy the condition (l ₁ > l ₂ ) is taken, noise cannot be canceled.

When noise control is actually performed, a secondary sound adder is installed at a position determined by the above-described method, and a plurality of noise receiving signal detectors are installed so as to cover a sound reduction target area. , The control shown in FIG. FIG. 5 shows a second embodiment of the present invention.

The second embodiment shows an example in which the present invention is applied to reduction of in-flight noise of an aircraft. As shown in FIG. 5, the propeller rotation pulse and the like are detected by the noise source characteristic detector 1, and the noise receiving signal detector 2 is distributed in the space near the ear of the seat, and the optimum position shown in the first embodiment is obtained. By installing a secondary sound adder and performing the control shown in FIG. 2, effective sound reduction can be achieved at the ear position of the seat. FIG. 6 shows a third embodiment of the present invention. The third embodiment shows an example in which the present invention is applied to reduction of in-flight noise of a helicopter.

Rotational pulses of the main rotor, tail rotor, transmission and the like are detected by the noise source characteristic detector 1, and the noise receiving signal detector 2 is distributed in the space near the ear of the seat. By installing the secondary sound adder at the optimum position shown and performing the control shown in FIG. 2, effective sound reduction can be achieved at the ear position of the seat.
FIG. 7 shows a fourth embodiment of the present invention. The fourth embodiment shows an example in which the present invention is applied to sound reduction in a room where quietness is required near a large noise source.

The vibration of the noise source is detected by the noise source characteristic detector 1, and the noise reception signal detector 2 is distributed in an area where quietness is particularly required, and the noise reception signal detector 2 is located at the optimum position shown in the first embodiment.
By installing the secondary sound adder and performing the control shown in FIG. 2, it is possible to achieve effective sound reduction in a desired area.

As described above, the noise reduction device of the present invention reduces noise by adding a secondary sound to cancel room noise to room noise. Therefore, secondary sound is generated 2
By appropriately controlling the secondary sound adder 3 by the noise control device 4, a secondary sound field that cancels the noise well is formed. The noise control device 4 receives the signal obtained by the noise source characteristic detector 1 as an input, and the LMS filter (B, Wi
drow and SDSteans, Adaptive Signal Processing, E
nglewood Clitfs, NJ: Prentice-Hall 1985). Also, at this time, the optimization problem is solved by using the coordinate values of the installation positions of a specified number of secondary sound adders as variables, and using the area integrated value of the sound pressure square value in the sound reduction target area as the objective function. The secondary sound adder is installed by finding the position of the secondary sound adder. In the case of performing actual control, the noise receiving signal detector 2 is installed so as to cover the sound reducing area almost evenly within the sound reducing area, and the secondary sound added sound is installed at the optimum position as described above. The sound control device 4 is controlled by the noise control device 4 to achieve the most effective sound reduction in the sound reduction target area.

[0029]

Since the present invention is configured as described above, it has the following effects. (1) Low frequency sounds that were difficult to countermeasure with the prior art,
For example, 1) sound that is radiated into the cabin due to pressure fluctuations in the boundary layer that excites the skin, 2) solid-state propagating sound where the engine vibration of an aircraft or the transmission vibration of a helicopter propagates through the structure, 3) jet engine It is possible to effectively reduce sound, propeller sound, and the like that propagate through the air and pass through the outer panel. This is particularly effective for aircraft or the like in which reducing the weight is strictly limited for soundproofing.

(2) In order to obtain a quiet indoor space near a noise source that generates a loud noise, a large-scale soundproofing work is required in the prior art. It is possible to take. (3) When the method of installing a secondary sound adder of the present invention is used,
The best sound reduction effect can be achieved in a desired sound reduction area of the indoor space.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first embodiment of the present invention.

FIG. 2 is a diagram showing a processing method by the noise control device.

FIG. 3 is a view showing a method of installing a secondary sound adder.

FIG. 4 is a diagram showing the relationship between the position of a secondary sound adder and causality.

FIG. 5 is a diagram showing a second embodiment of the present invention.

FIG. 6 is a diagram showing a third embodiment of the present invention.

FIG. 7 is a diagram showing a fourth embodiment of the present invention.

FIG. 8 is a diagram showing a conventional noise reduction technique.

[Explanation of symbols]

1: noise source characteristic detector, 2: noise reception signal detector, 3:
Secondary sound adder, 4 ... Noise control device, 4111-4122
... Convolution means for impulse response, 4211
4222... Filter coefficient correction means, 431 to 432.
Convolution means for filter coefficients.

Continuation of front page (58) Fields investigated (Int.Cl. ⁶ , DB name) G10K 11/178 B60R 11/02 B64D 11/00 F24F 13/02 G10K 15/00 H04R 1/40

Claims (1)

(57) [Claims] (A) a noise source characteristic detector (1) provided near a noise source that emits noise to an indoor space; and (B) a plurality of noise source characteristic detectors installed near an area of the indoor space where noise is to be reduced. (C) a plurality of secondary sound adders (3) for canceling noise at the position of the noise receiving signal detector; and (D) a noise control device ( consists 4), (E) the noise control device (4) receives a signal obtained by the noise source characteristics detector (1), signal secondary sound adder which convolved filter coefficients to the signal ( (F) the plurality of noises; and (3) adaptive means for modifying a filter coefficient so as to minimize a signal detected by the noise receiving signal detector (2). received sound signal detector (2) is placed so as to be distributed substantially uniformly in the target region, (G The plurality of secondary sound adders (3) are installed at an optimum position obtained by an optimization method using an integrated value of the square of the sound pressure in the target area as an objective function. apparatus.