JPH06308972A - Active muffler - Google Patents

Abstract

PURPOSE:To reduce the occurrence of a standing wave in a duct by providing a speaker generating a sound wave with an opposite phase on the inside wall surface of the duct and changing a sectional area in an optional section. CONSTITUTION:This device is constituted of a duct 102 equipped with a first microphone 103 and a second microphone 104 where the sectional areas of the duct in the position 1 and in the position 2 are made the same, and further, and has an enlargement part 4 enlarging the sectional area of the duct in the position of an optional section 3 between the first microphone 103 and the speaker 105 to 1.5 times the maximum. In such a case, since no sectional areas of the duct in the section from the first microphone 103 to the second microphone 104 become the same, no standing wave depending on a distance, etc., and with a peak at a single frequency occurs.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active muffling device which superimposes a sound having an opposite phase on a noise propagating in a duct to actively muffle the noise.

[0002]

2. Description of the Related Art In recent years, it has been required to reduce noise of blowers and air conditioners used in houses and offices.

Conventionally, this type of active silencer is a silencer for reducing noise, which emits a sound having a phase opposite to that of noise propagating in the duct into the duct, thereby actively canceling the noise. Has been proposed, and is disclosed in JP-A-62-16.
The configuration shown in Japanese Patent No. 4400 has been common. The configuration will be described below with reference to FIG.

As shown in the figure, a duct 102 is connected to the outlet of the blower 101, and the noise generated by the blower 101 propagates in the duct 102 together with the air to be blown. A first microphone 103 and a second microphone 104 for detecting a propagating sound wave are installed on the downstream side in the duct 102 at positions upstream and downstream with respect to the speaker 105, respectively. A turbulent flow screen 106 is attached to the microphone 103 and the second microphone 104 to prevent the noise signal from being altered due to direct wind. The control circuit 107 creates an additional sound wave based on the propagating sound wave of the noise detected by the first microphone 103 so as to minimize the noise at the position of the second microphone 104, and radiates it from the speaker 105. Further, the characteristic of the additional sound wave is adjusted from the detection signal of the second microphone 104 so that the noise is minimized. As a result, at the position of the second microphone 104, the blower 101 due to the interference of sound waves.
The sound waves propagated from are canceled out, and the noise propagating from the blower 101 is reduced on the downstream side of the position of the microphone 104 in the blower duct 102.

[0005]

In such a conventional active silencer, there is a standing wave whose frequency is determined by the distance from the first microphone to the second microphone in the duct. There is a problem in that the characteristics of the additional sound wave are disturbed by the influence of and the volume of the sound is reduced.

The present invention is intended to solve the above problems, and it is a first object of the present invention to reduce the generation of standing waves in a duct.

A second object is to reduce the generation of turbulent noise in the duct.

[0008]

In order to achieve the above object, the active muffler of the present invention has a first means for detecting a sound wave propagating from a noise source propagating in a duct.
A second microphone is placed in the duct to create a sound wave of opposite phase from the propagating sound wave detected by the control circuit,
A speaker that generates the sound wave of the opposite phase is provided on the inner wall surface of the duct between the first and second microphones, and the duct cross-sectional areas at the first microphone position and the second microphone position are the same. The duct cross-sectional area of only an arbitrary section between the microphone and the speaker is expanded 1.2 times to 1.5 times.

The second means makes the duct cross-sectional areas of the first microphone position and the second microphone position the same and further divides the area of the same area between the first microphone position and the speaker as the first microphone position. The configuration has a branch pipe in which a mouth and a return port are arranged.

Further, the third means is to provide 6 at an arbitrary position between the first microphone and the second microphone.
A curved pipe portion having a bending angle of 0 ° to 120 ° is provided, and the duct cross-sectional area of the curved pipe portion is expanded to a maximum of 1.2 times to 1.5 times.

[0011] The fourth means is to provide 6 at an arbitrary position between the first microphone and the second microphone.
A curved pipe portion having a bending angle of 0 ° to 120 ° is provided, and a space portion having an opening having an area equal to the duct cross-sectional area is provided upstream from the bending apex of the curved pipe portion.

Further, the fifth means is a cross-sectional area enlarging portion, a branch opening, so that the inner surface of the duct in the section from the first microphone to the second microphone of the first to fourth means is a smooth surface. The return port and the opening surface are all covered with a thin film material that has minimal sound transmission loss and does not allow air to pass through.

[0013]

According to the present invention, the cross-sectional area of an arbitrary section between the first microphone and the second microphone can be obtained by the constitution of the above-mentioned first means, second means, third means and fourth means. By changing it, the generation of standing waves in the duct can be reduced.

Further, according to the constitution of the fifth means, by covering the enlarged cross-sectional area and the opening of the first means to the fourth means with a thin film material having a minimal sound transmission loss and not passing air,
The generation of turbulent noise can be reduced.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to FIG. The same parts as those in the conventional example are designated by the same reference numerals, and detailed description thereof will be omitted.

As shown in the figure, the first microphone 1
The position 1 of 03 and the position 2 of the second microphone 104 have the same duct cross-sectional area, and the duct cross-sectional area at the position of any section 3 between the first microphone 103 and the speaker 105 is 1.5 times at maximum. It is composed of a duct 102 having an enlarged enlarged portion 4.

With the above configuration, the first microphone 1
Since the duct cross-sectional areas in the section from 03 to the second microphone 104 are not the same, a standing wave having a peak at a single frequency does not occur depending on the distance and the like.

As described above, according to the active noise suppressor of the first embodiment of the present invention, the generation of standing waves in the duct can be reduced.

Next, a second embodiment of the present invention will be described with reference to FIG.
Will be described with reference to. The same parts as those in the first embodiment are designated by the same reference numerals and detailed description thereof will be omitted.

As shown in the figure, the first microphone 1
It is composed of a branch pipe 7 having a branch port 5 and a return port 6 having the same area as the position 1 between 03 and the speaker 105.

With the above configuration, the first microphone 1
Since the conduits having different lengths exist in the section from 03 to the second microphone 104, the low standing wave having a peak at a single frequency does not occur depending on the distance or the like.

As described above, according to the active muffler of the second embodiment of the present invention, the generation of standing waves in the duct can be reduced.

Next, the third embodiment of the present invention will be described with reference to FIG.
Will be described with reference to. The same parts as those in the first embodiment are designated by the same reference numerals and detailed description thereof will be omitted.

As shown in the figure, the first microphone 1
03 and the second microphone 104, a curved pipe portion 8 having a bending angle of 90 ° is provided, and the duct 102 has an enlarged portion 4 in which the duct cross-sectional area of the curved pipe portion 8 is enlarged 1.5 times. ing.

With the above configuration, the first microphone 1
Since the duct cross-sectional areas in the section from 03 to the second microphone 104 are not the same, a standing wave having a peak at a single frequency does not occur depending on the distance and the like.

As described above, according to the active noise suppressor of the third embodiment of the present invention, the generation of standing waves in the duct can be reduced.

Next, a fourth embodiment of the present invention will be described with reference to FIG.
Will be described with reference to. The same parts as those in the third embodiment are designated by the same reference numerals and detailed description thereof will be omitted.

As shown in the figure, the first microphone 1
03 and the second microphone 104 are provided with a curved pipe portion 8 having a bending angle of 90 °, and a space portion 11 having an opening 10 having the same area as the duct cross-sectional area upstream from the bending vertex 9 of the curved pipe portion 8. It consists of

With the above configuration, the first microphone 1
Since the duct cross-sectional areas in the section from 03 to the second microphone 104 are not the same, a standing wave having a peak at a single frequency does not occur depending on the distance and the like.

As described above, according to the active noise suppressor of the fourth embodiment of the present invention, the generation of standing waves in the duct can be reduced.

Next, a fifth embodiment of the present invention will be described with reference to FIG.
Will be described with reference to. The same parts as those in the second embodiment are designated by the same reference numerals and detailed description thereof will be omitted.

As shown in the figure, the branch port 5 and the return port 6
It is made of a thin film material 12 that covers the above and has a minimal sound transmission loss and does not pass air.

With the above configuration, the first microphone 1
The inner surface of the duct in the section from 03 to the second microphone 104 becomes a smooth surface, the generation of air turbulence and vortices in the duct is reduced, and the generation of turbulent noise is reduced.

As described above, according to the active silencer of the fifth embodiment of the present invention, it is possible to reduce the generation of turbulent noise in the duct.

[0035]

As is apparent from the above embodiments, according to the present invention, the generation of standing waves is reduced by changing the duct cross-sectional area in the section from the first microphone to the second microphone. An active silencer can be provided.

Further, by making the inner surface of the duct smooth, it is possible to provide an active silencer that reduces the generation of turbulent noise.

[Brief description of drawings]

FIG. 1 is a sectional view of an active silencer according to a first embodiment of the present invention.

FIG. 2 is a sectional view of an active silencer of the second embodiment.

FIG. 3 is a sectional view of an active silencer of the third embodiment.

FIG. 4 is a sectional view of an active silencer of the fourth embodiment.

FIG. 5 is a sectional view of an active silencer of the fifth embodiment.

FIG. 6 is a sectional view of a conventional active silencer.

[Explanation of symbols]

 1 1st microphone position 2 2nd microphone position 3 Arbitrary section 4 Expansion part 5 Branching port 6 Return port 7 Branching pipe 8 Bending pipe part 9 Bending apex 10 Opening 11 Space part 12 Thin film material 102 Duct 103 First microphone 104 second microphone 105 speaker 107 control circuit

Claims (5)

[Claims] 1. A first microphone and a second microphone for detecting a sound wave propagating from a noise source propagating in the duct are arranged in the duct, and a sound wave having an opposite phase is generated from the propagating sound wave detected by a control circuit, and vice versa. A speaker for generating a sound wave of a phase is provided on the inner wall surface of the duct between the first and second microphones so that the duct cross-sectional areas of the first microphone position and the second microphone position are the same, and the first microphone is further provided. The active silencer that expands the duct cross-sectional area of any section between the speaker and the speaker by 1.2 times to 1.5 times. 2. A duct cross-sectional area of the first microphone position is the same as that of the second microphone position, and a branch port and a return port having the same area as that of the first microphone position are arranged between the first microphone and the speaker. Active silencer with a branched branch. 3. A curved pipe section having a bending angle of 60 ° to 120 ° is provided at an arbitrary position between the first microphone and the second microphone, and a maximum duct cross-sectional area of the curved pipe section is 1.2. An active silencer that has been expanded by a factor of 2 to 1.5. 4. A curved pipe section having a bending angle of 60 ° to 120 ° is provided at an arbitrary position between the first microphone and the second microphone, and a duct disconnection is made upstream from a bending apex of the curved pipe section. An active silencer that has a space with an opening of the same area. 5. The inner surface of the duct in the section from the first microphone to the second microphone is a smooth surface,
5. The active sound deadening system according to claim 1, claim 2, claim 3 or claim 4, wherein all of the expanded cross-sectional area, the branch port, the return port and the opening surface are covered with a thin film material having a minimal sound transmission loss and impermeable to air. apparatus.