JP2961996B2 - Low noise equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low noise device suitable for a small computer, an air conditioner and the like.

[0002]

2. Description of the Related Art Conventionally, in order to reduce noise generated from a fluid machine, a method of mounting it on an absorption type silencer in which a flow passage is lined with a porous sound absorbing material or a reactive type silencer device utilizing a change in cross section has been widely used. Have been done. However, in the case of low-frequency noise such as a fluid machine, there are many demands for improvements such as an increase in the size of a device and an increase in weight.

[0003] On the other hand, as another method, an active type silencer that has been proposed for a long time, that is, an additional sound having an opposite phase is added to a propagated wave from a sound source, and the silence is forced by sound wave interference. Attention has been focused on a method of causing noise, that is, a destructive noise reduction method.

[0004] With the rapid development of electronic devices, signal processing technology, and the like, active silencers have recently been successively announcing research results from various viewpoints.

By the way, as shown in the sound deadening device described in Japanese Patent Application Laid-Open No. 2-261997, a sound deadening body is formed so as to surround a sound opening body in an annular shape around a duct opening so as to be able to suppress a reduction in the sound deadening effect due to uneven sound field. The device is open to the public. Here, only active silence means are shown.

[0006]

Generally, since the evaluation position of the equipment noise is not fixed, any position in the room in which the equipment is stored must be quiet, so that the energy of the noise radiated from the opening surface of the equipment is reduced. Must be smaller. Therefore, it is necessary to provide a sounding body in the vicinity of the noise radiation surface, that is, the opening surface. In this case, the noise reduction effect is proportional to the ratio of the distance between the central axis of each of the aperture and the sounding body to the wavelength of the sound wave to be reduced,
The structure of the silencer-equipped device must be devised so that this distance is reduced as much as possible.However, if the sounding body is mounted so as to surround the opening, the distance between the opening surface and the central axis of the sounding body should be reduced. Even so, reducing the sounding body or the aperture surface would cause a reduction in radiation power at low frequencies and an increase in fluid resistance with an increase in flow velocity, respectively.
No effective silencing. In addition, the noise radiated from the device opening surface is a low frequency component sound such as a blade sound determined by the product of the rotation speed of the fluid machine and the number of blades, and a turbulent sound generated due to the separation of the blade surface. It is composed of sounds with relatively high frequency components like this.To realize quiet equipment, it is necessary to reduce a wide range of sounds from low frequencies to high frequencies. The silencing effect of high frequency sounds cannot be expected.

An object of the present invention is to provide a low-noise device equipped with a silencer for effectively reducing the noise radiated from the opening of the device over the entire frequency band.

[0008]

According to the present invention, in order to achieve the above object, a noise signal of a noise source or a signal having a high correlation with the noise signal is detected by a sensor, and the detected signal is detected by a signal processing device. After processing, in a low noise device equipped with an active silencer that generates sound as sound from the sounding body and interferes with the sound wave from the noise source and the sound wave from the sounding source, the area of the sounding body is open. Wider than the face,
And the central axis of the sounding body and the central axis of the opening surface are almost equal,
The sounding body is provided at a certain distance from the opening surface.

[0009]

According to the present invention, the central axis of the sounding body is substantially equal to the central axis of the opening surface, and the sounding body is provided at a fixed distance from the opening surface. Also,
Since they are radiated to the outside of the equipment casing with the same directional pattern, if they are controlled so that the amplitude of each sound is equal and the phases are reversed, they are completely mixed in space,
It causes destructive interference, especially for relatively low-frequency noise, and is greatly reduced, and the noise reduction effect becomes smaller at higher frequencies. On the other hand, in the device of the present invention, since the area of the sounding body is configured to be larger than the opening surface at the same time, noise from the noise source, that is, noise from the fluid machine is diffracted around the sounding body and from the device opening surface. Propagate around the device,
At this time, a sound reduction effect due to diffraction occurs, and the sound reduction effect increases at a higher frequency at which the active noise reduction method is not good.

[0010]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is an explanatory diagram showing the configuration of a device equipped with a muffler according to an embodiment of the present invention. The point that this device differs from the conventional device is that the area of the sounding body is larger than the opening surface, and the center axis of the sounding body and the center axis of the opening surface are almost equal,
The sounding body is provided at a certain distance from the opening surface.

The operation of the silencer will be described below. A fan 3, which is a fluid machine, is provided to cool the heat generating portion 2 of the device 1. The noise generated from this is
After cooling the heating element 2, it is radiated from the housing opening 7 to the surroundings through a sound / flow channel 6 between the piezoelectric speaker 5, which is a sound generator, and the housing 4. On the other hand, a microphone 8 which is a noise detection sensor attached near the fluid machine 3
Is output to the adaptive signal processing device 10.
Based on this signal, the signal processing device 10 generates a signal having the same amplitude and opposite phase as the noise from the fan 3 so that the output value from the sound collecting microphone 11 as the second sensor is always minimized according to the adaptive algorithm. Piezoelectric speaker 5 that emits sound waves
The coefficients in the adaptive signal processing device 10 are adjusted to radiate from.

Since the piezoelectric speaker 5 is mounted on the central axis of the device housing opening 7 and separated from the opening 7 by a certain fixed distance d, the fan 3 Since both the noise and the sound wave from the piezoelectric speaker 5 are radiated to the outside of the housing 5 of the device 1 in the same directivity pattern, control is performed so that the amplitudes of the sounds are equal and the phases are opposite. They can, for example, mix completely in space and cause destructive interference, especially for relatively low-frequency noise, which is greatly reduced, and this silencing effect increases with lower frequencies. On the other hand, in the device of the present invention,
At the same time, the area of the piezoelectric speaker 5, which is a sounding body, is increased by the opening surface 7.
Since it is configured to be wider, noise from the noise source, that is, noise from the fluid machine 3 is diffracted around the piezoelectric speaker 5 and propagates from the device opening surface 7 to the periphery of the device 1. The sound reduction effect is caused by diffraction, and the sound reduction effect increases as the frequency becomes weaker for the active noise reduction method. If the sensor is a detection sensor for the power supply frequency, the noise of this frequency and its harmonic components are muted by destructive interference. Similarly, if the sensor is a pressure pulsation detection sensor provided very close to the fluid machine, the noise of this frequency and its higher harmonic components are silenced by destructive interference. FIG. 2 shows another embodiment of the present invention showing the configuration of a sound-generating body for noise reduction attached to a housing. When the piezoelectric speakers 5b and 5c are provided around the opening surface of the low-noise device so as to surround the opening surface, in addition to the opening surface 7,
Since the sound for silencing can be radiated from the periphery of the opening surface 7 so as to envelop the noise radiated from the opening surface 7, the sound field does not become uneven, and the area of the vibration surface of each sounding body can be increased. The sound radiation power in the frequency band also increases. Due to these combined actions, outside the housing 4 of the device 1, these waves cause completely destructive interference and can greatly reduce the noise. In the embodiment shown in FIGS. 1 and 2, a piezoelectric speaker 5 which is a planar speaker is used as a sounding body. This is because the volume of the speaker is small.
There is an advantage that the space in the housing 4 of the device 1 can be used efficiently. FIG. 3 shows another embodiment, and shows a configuration of a muffling sounding body attached to a housing. The piezoelectric speaker 5 is attached to the housing 4
This embodiment has the same operation and effect as the present invention. FIG. 4 shows another embodiment, and shows the configuration of a muffling sounding body attached to a housing. As in this embodiment, the sounding body is not limited to the flat type, and the speaker box 12
c, the vibrating surface 12a has a cone shape and is driven by an actuator 12b.
If the speaker is provided in the housing 4 at least on the same axis as the center axis of the opening surface 7, the sound / flow channel 6 is not obstructed. can get. Further, in FIGS. 1 and 2, the piezoelectric speaker 5 as a sounding body is provided inside the housing 4. However, if the flat speaker is substantially coaxial with the opening surface 7, the speaker is provided outside the housing. Also, the same operation and the same effect as the present invention can be obtained.

[0014]

The noise signal of the noise source or a signal having a high correlation with the noise signal is detected by a sensor, and the detected signal is processed by a signal processing device and then generated as a sound from a sounding body. In a low-noise device provided with an active silencer that silences sound waves by interfering sound waves and sound waves from sound sources, the area of the sounding body is larger than the opening surface, and the center axis of the sounding body and the center axis of the opening surface are Since the sound generators are provided at a certain distance from the opening surface, the noise reduction at a relatively low frequency by active silencing and the reduction of high frequency noise due to diffraction can both be realized. As a result, broadband noise can be efficiently reduced from a low frequency to a high frequency, and a low-noise device equipped with a quiet active silencer can be realized.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a device to which a silencer according to an embodiment of the present invention is applied.

FIG. 2 is an explanatory view of another embodiment of the present invention, showing a configuration of a muffling sounding body attached to a housing.

FIG. 3 shows another embodiment, and is an explanatory view of a muffling sounding body attached to a housing.

FIG. 4 shows another embodiment, and is an explanatory view of a muffling sounding body attached to a housing.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Device, 2 ... Heating element, 3 ... Fan, 5 ... Piezoelectric speaker, 6 ... Sound / flow path, 7 ... Opening surface, 8 ... Microphone, 10 ...
Adaptive signal processing device, 11 ... sound collecting microphone.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-58-214614 (JP, A) JP-A-1-251214 (JP, A) JP-A-2-261997 (JP, A) JP-A-2- 285799 (JP, A) Japanese Utility Model Application Hei 4-15387 (JP, U) (58) Fields investigated (Int. Cl. ⁶ , DB name) F01N 1/00 G10K 11/178

Claims (1)

(57) [Claims] A noise source of a sound source or a signal having a high correlation with the noise signal is detected by a sensor, and the detected signal is processed by a signal processing device and then generated as a sound from a sounding body. In a low-noise apparatus provided with an active noise reduction device that propagates through and interferes with sound waves emitted from a device opening surface and sound waves from the sounding body, the area of the sounding body is reduced by the device opening surface. A low-noise device, wherein the center axis of the sounding body is substantially equal to the center axis of the device opening surface, and the sounding body is provided at a fixed distance from the device opening surface.