JP2000194379A - Active muffler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To muffle perfectly primary noise and to simplify a circuit by preventing the occurrence of howling caused when secondary noise occurs. SOLUTION: This device is the device muffling the primary noise caused from a fan 1, etc., provided in the vicinity of a blower hole of a ventilation duct 2. In such a case, the primary noise is collected by a microphone 3, and a signal based on the noise is supplied to one side input of an adaptive filter 7, and the signal based on an error noise collected from the microphone 8 is supplied to the other side input, and the prescribed muffling signal is generated based on these signals. Then, the generated signal is supplied to a modulator 20 to be amplitude modulated, etc., and to be supplied to a secondary noise generator 21 constituted of an ultrasonic element, and the secondary noise of a single and narrow directional characteristic based on a parametric phenomenon is generated from this generator 21, and the primary noise is muffled perfectly by the secondary noise.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a muffler for removing noise from a ventilation duct, for example.

[0002]

2. Description of the Related Art Conventionally, there has been an active silencer for removing noise by actively controlling a noise source. FIG. 2 is a block diagram showing an example of such a case. For example, there is an active silencer for removing noise generated from a noise source such as a fan through a ventilation duct. This active silencer is applied, for example, to prevent noise generated from a fan 1 which is a noise source provided near a ventilation opening of a ventilation duct 2 from being emitted through the ventilation duct. A microphone 3 for collecting the primary noise from the first and a secondary noise acting in such a manner that the primary noise is out of phase with the primary noise and are mutually muted, and the directional characteristics thereof are in the direction in which the microphone 3 is provided A secondary noise generator (speaker) 4 provided in a direction opposite to the direction shown above, and a filter provided in parallel with the ventilation duct 2 for passing a return signal of the secondary noise toward the microphone 3 5, a subtractor 6 for canceling a signal based on the secondary noise returning through the filter 5 and a signal based on the secondary noise returning from the ventilation duct 2 side;
A large number of coefficients prepared inside are convolved by a filter composed of, for example, an FIR filter,
Adaptive filter 7 for generating a signal for generating secondary noise
When error noise is also generated by the mutual cancellation of the primary noise transmitted through the ventilation duct 2 and the secondary noise generated from the secondary noise generator 4, the error noise is collected. Microphone 8. Therefore, according to this device, the primary noise generated from the fan 3 is picked up by the microphone 3, and the microphone returns when the secondary noise emitted from the secondary noise generator 4 is returned. The noise is also collected and supplied to the subtractor 6. In the subtracter 6, the return of the secondary noise from the ventilation duct 2 and the return of the secondary noise supplied through the filter 5 are subtracted from each other and canceled. As a result, only the signal based on the primary noise is output from the subtracter 6 and supplied to one input of the adaptive filter 7.

On the other hand, the microphone 7 has a ventilation duct 2
If there is an error noise that is not canceled by the mutual cancellation of the primary noise transmitted through the secondary noise generator and the secondary noise generated by the secondary noise generator 4, the signal is collected and the adaptive filter 7 is used. Is supplied to the other input.

The adaptive filter 7 refers to the signal based on the error noise and the signal based on the primary noise, and determines the generation of the error noise by performing a convolution operation based on the stored coefficients. A signal to be eliminated is generated, that is, a signal having a phase opposite to that of the primary noise is generated and supplied to the secondary noise generator 4.

The adaptive filter 7, the secondary noise generator 4 and the microphone 8 constitute a circuit of a circulation type. The error signal is reduced to zero while circulating a signal based on the error noise in these circuits. That's what you are trying to do.

[0006]

However, in such an apparatus as described above, in particular, the filter 5 and the subtractor 6 cancel the secondary noise to the microphone 3 side. There has been a problem that the primary noise cannot be completely silenced because it cannot be canceled and howling occurs, and further simplification of the circuit has been demanded. Accordingly, the present invention is to provide a device that can solve the above-described problems and respond to the demands.

[0007]

The device according to the present invention comprises the following means in order to solve the above-mentioned problems.
That is,

[0008] First sensing means for sensing primary noise emitted from a noise source, secondary noise generating means for emitting secondary noise so as to mute the primary noise, and emission from the secondary noise generating means. Second sensing means for sensing error noise caused also by the mutual silencing action of the secondary noise and the primary noise, a signal based on the error noise obtained from the second sensing means, and the first sensing. And a filter means for generating a signal for silencing the primary noise based on the primary noise signal obtained from the means and supplying the generated signal to the secondary noise generating means. A noise reduction device, wherein the secondary noise generating means is constituted by an ultrasonic element, and the signal generated by the filter means is amplitude-modulated so as to cause a parametric phenomenon in the ultrasonic element. Active silencer that characterized in that a regulating means.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described with reference to preferred embodiments. FIG. 1 is a schematic block diagram of an active silencer according to an embodiment of the present invention. In this embodiment as well, an apparatus for preventing noise generated when a fan is rotating through a ventilation duct is used as an example. explain. Note that the same components as those of the configuration of the conventional example are denoted by the same reference numerals for easy understanding.

In FIG. 1, an active silencer according to the present embodiment has a microphone 3 for collecting primary noise from a fan 1.
When a predetermined signal is input, a secondary noise is generated by a parametric phenomenon in order to mute the primary noise, and the directional characteristic of the microphone 3 is reduced. Secondary noise generator 2 provided in a direction opposite to the direction in which it is provided
1, a microphone 8 for collecting the error noise when the mutual noise by the secondary noise and the primary noise cancels each other, and a signal based on the error noise from the microphone 8. , By referring to the primary noise obtained from the microphone 3, a convolution operation is performed by an FIR filter using a plurality of internally prepared coefficients to generate a predetermined signal having a phase opposite to that of the primary noise. And a modulator 20 that amplitude-modulates a signal output from the adaptive filter 7 to cause the secondary noise generator 21 to cause a parametric phenomenon. ing.

Next, the operation will be described. Fan 1
The primary noise at the time of rotation is collected by the microphone 3 and
It is transmitted through the ventilation duct 2 in the direction of the secondary noise generator 21. The signal based on the primary noise collected by the microphone 3 is supplied to one input of the adaptive filter, and at the same time, the signal based on the error noise is supplied from the microphone 8 to the other input. The adaptive filter refers to both of these signals, and generates a signal having a phase opposite to that of the primary noise so that a signal based on the error noise is zero. Then, a convolution operation using each coefficient is performed.

The signal generated by this convolution operation is supplied to the modulator 20 at the next stage, where it is converted into a signal that causes a parametric phenomenon in the ultrashort wave element constituting the secondary noise generator 21 at the next stage. Amplitude modulated.

The secondary noise generator 21 generates secondary noise, such as a beat sound, which is a parametric phenomenon, when the modulated signal is received. The sound caused by the parametric phenomenon due to the ultrasonic wave is known as a phenomenon that provides a single and narrow directional characteristic. The secondary noise generated from the secondary noise generator 21 is different from the conventional configuration. It does not return to the direction where the microphone 3 is provided again through the ventilation duct 2.

When the secondary noise and the primary noise generated from the secondary noise generator 21 are mutually out of phase with each other in an opposite phase relationship, and error noise that cannot be completely eliminated occurs at that time. Is collected by the microphone 8.

A signal based on the error noise collected by the microphone 8 is supplied to the other input of the above-mentioned adaptive filter 7, and the above-described filter operation is repeated by these circulation paths. The error noise is reduced to zero. That is, the primary noise is completely silenced by the secondary noise.

As described above, according to the apparatus of this embodiment,
In particular, since the secondary noise generator 21 is constituted by an ultrahigh-frequency element, and this element is used to generate secondary noise applying a parametric phenomenon, as a result, a single and
Narrow directional noise can be generated, secondary noise does not need to be returned unlike conventional devices, primary noise can be completely silenced, and filters and subtractions for removing secondary noise can be removed. This eliminates the need for a device and simplifies the circuit scale.

Although the apparatus of this embodiment has been described as being applied to an air duct for simplicity of explanation, the present invention is not limited to this, but may be applied to any place where noise is generated. Of course, the same effect can be obtained.

[0018]

According to the active silencer of the present invention, in particular, the secondary noise generating means is constituted by a single ultra-short wave element capable of generating noise with narrow directional characteristics.
The primary noise can be completely removed without worrying about the return of the secondary noise, and there is an effect that an extra circuit such as a filter and a subtractor for removing the return of the secondary noise is not required. .

[Brief description of the drawings]

FIG. 1 is a schematic block diagram of an active silencer according to one embodiment of the present invention.

FIG. 2 is a schematic block diagram illustrating an example of a conventional active silencer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Fan (noise generating source) 2 Ventilation duct 3, 8 Microphone 7 Adaptive filter 20 Modulator 21 Secondary noise generator

Claims (1)

[Claims] 1. A first sensing means for sensing primary noise emitted from a noise source; a secondary noise generating means for emitting secondary noise so as to mute the primary noise; and a secondary noise generating means. A second noise detecting means for detecting an error noise caused also by a mutual silencing effect of the secondary noise emitted from the first noise and the primary noise, a signal based on the error noise obtained from the second noise detecting means, and the first noise. A signal for silencing the primary noise based on a signal based on the primary noise obtained from the sensing means, and a filter means for supplying the generated signal to the secondary noise generating means. An active silencer comprising: the secondary noise generating means comprising an ultrasonic element, and amplitude-modulating a signal generated by the filter means so as to cause a parametric phenomenon in the ultrasonic element. An active silencer comprising a modulating means.