JPH0598926A - Low noise equipment - Google Patents

Abstract

PURPOSE:To reduce the noise of a wide belt area efficiently to obtain a quiet low noise equipment by providing a sounding body so that the area of the sounding body is larger than the area of the opening surface and that the center axis of the sounding body and the center axis of the opening surface nearly coincide with each other and that the sounding body is provided with a certain distance from the opening surface. CONSTITUTION:A piezoelectric speaker 5 is fitted on the center axis of an opening part 7 of an equipment case so as to be separated from the opening part 7 by a certain distance (d). Since the noise of a fan 3 form the opening surface 7 and the sound wave from the piezoelectric speaker 5 are radiated outside of a case 4 of an equipment 1 with the same directivity pattern, the muffling effect is larger, as the frequency is lower. On the other hand, since the area of the piezoelectric speaker 5 as the sounding body is formed so as to be larger than that of the opening surface 7 the noise from the fluid machine 3 diffracts along the periphery of the piezoelectric speaker 5, and is transmitted from the opening surface 7 of the equipment 1 to the surroundings thereof. At this stage, the muffling work by the diffraction is generated, and the sound reduction effect is increased, as the frequency is higher.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to low noise equipment suitable for small computers, air conditioners 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 silencer having a porous sound absorbing material lined in a flow path or a reactive silencer device utilizing a cross section change has been widely used. It is being appreciated. However, in the case of targeting low frequency noise such as fluid machinery, there are many demands for improvement such that the equipment becomes large and the weight increases.

On the other hand, as another method, an active silencer that has been proposed for a long time, that is, an additive sound having an opposite phase is added to a propagating wave from a sound source, and the silence is forced by sound wave interference. A method of generating noise, that is, a destructive muffling method is attracting attention.

With the rapid development of electronic devices, signal processing technology, and the like, research results from various viewpoints have recently been announced one after another for the active silencer.

By the way, as shown in the silencer disclosed in Japanese Unexamined Patent Publication No. 261997/1990, the sounding body is surrounded by a ring around the opening of the duct to suppress the reduction of the silencing effect due to the unevenness of the sound field. The device is open to the public. Only active muffling is shown.

[0006]

Generally, since the evaluation position of the equipment noise is not fixed, any position in the room where the equipment is housed must be quiet. Therefore, the energy of the radiated noise from the opening surface of the equipment is reduced. Must be small. Therefore, it is inevitably necessary to provide the sounding body in the vicinity of the noise emission surface, that is, the opening surface. In this case, this silencing effect is proportional to the ratio of the distance between the central axes of the aperture and the sounding body to the wavelength of the sound wave to be silenced,
It is necessary to devise the structure of the device equipped with a silencer so that this distance will be as small as possible, but in the method of mounting the sounding body so as to surround the opening surface, try to reduce the distance between the opening surface and the center axis of the sounding body. Even so, reducing the size of the sounding body or the opening surface leads to a decrease in radiation power at low frequencies and an increase in fluid resistance due to an increase in flow velocity.
I cannot mute effectively. In addition, the noise radiated from the equipment opening surface is a low frequency component sound such as a blade noise determined by the product of the rotational speed of the fluid machine and the number of blades, and the turbulent sound generated by the separation of the blade surface. , Which is composed of relatively high-frequency component sounds, and it is necessary to reduce a wide range of sounds from low frequencies to high frequencies in order to realize quiet equipment, but it is essentially only active sound-deadening means. , High frequency sound muffling effect can not 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 device opening surface over the entire frequency band.

[0008]

In order to achieve the above object, the present invention detects a noise signal of a noise source or a signal having a high correlation with a noise signal by a sensor, and the detected signal is detected by a signal processing device. After processing, a low-noise device equipped with an active muffling device that muffles sound waves from a noise source by interfering with sound waves from the sound source by generating sound as a sound Wider than the plane,
And, the central axis of the sounding body and the central axis of the opening surface are almost equal,
The sounding body is characterized by being provided at a constant distance from the opening surface.

[0009]

In the present invention, since the central axis of the sounding body and the central axis of the opening surface are substantially equal and the sounding body is provided at a constant distance from the opening surface, the noise of the opening surface and the sound wave of the sounding body are both Also,
Since they are radiated to the outside of the equipment casing in the same directivity pattern, if they are controlled so that the amplitudes of the sounds are equal and the phases are reversed, they will be completely mixed in space,
Destructive interference is caused, and particularly, noise having a relatively low frequency is greatly reduced, and this silencing effect is decreased as the frequency is increased. On the other hand, in the device of the present invention, since the area of the sounding body is made larger than the opening surface at the same time, the noise source, that is, the noise from the fluid machine is diffracted around the sounding body and is emitted from the opening surface of the device. Propagates around the device,
At this time, a sound-reducing effect due to diffraction occurs, and the sound-reducing effect increases as the frequency becomes high, which the active sound-deadening method is not good at.

[0010]

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

FIG. 1 is an explanatory view showing the configuration of a device equipped with a silencer according to an embodiment of the present invention. The difference between this device and the conventional device is that the area of the sounding body is wider than the opening surface, 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.

The operation of this 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 the case 4
After propagating through the inside of the housing, the heating element 2 is cooled, and then passes through the sound / flow channel 6 between the piezoelectric speaker 5 as the sounding body and the housing 4, and is radiated to the surroundings from the housing opening 7. On the other hand, the microphone 8 which is a noise detection sensor mounted near the fluid machine 3
The output signal 9 of is input to the adaptive signal processing device 10.
Based on this signal, the signal processing device 10 has the same amplitude as that of the noise from the fan 3 and an opposite phase so that the output value from the sound collecting microphone 11 which is the second sensor is always minimized according to the adaptive algorithm. Piezoelectric speaker 5 that produces sound waves
The coefficients in the adaptive signal processing device 10 are adjusted so as to radiate from.

By the way, since the piezoelectric type speaker 5 is mounted on the central axis of the device housing opening 7 and at a certain distance d from the opening 7, the piezoelectric speaker 5 is attached to the fan 3 from the opening surface 7. 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, so that the amplitudes of the sounds should be equal and the phases should be reversed. For example, they completely mix in space and cause destructive interference, which is greatly reduced, especially for relatively low-frequency noise, and this silencing effect becomes greater at 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 the sounding body, is equal to the opening surface 7.
Since it is configured to be wider, the noise source, that is, the noise from the fluid machine 3 is diffracted around the piezoelectric speaker 5 and propagates from the device opening surface 7 to the device 1 at this time. The sound reduction effect due to the diffraction occurs, and the sound reduction effect increases as the frequency becomes high, which the active noise reduction method is not good at. When the sensor is a power supply frequency detection sensor, noise of this frequency and its harmonic components is silenced by destructive interference. Similarly, when the sensor is a pressure pulsation detection sensor provided in the immediate vicinity of the fluid machine, noise of this frequency and its harmonic component is silenced by destructive interference. FIG. 2 shows another embodiment of the present invention showing the configuration of the sound deadening body attached to the housing. Further, 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 wave for silencing can be radiated from the periphery of the opening surface 7 so as to wrap the radiated noise from the opening surface 7, there is no unevenness in the sound field, and the total vibrating surface area of each sounding body can be increased, so that it is low. The acoustic 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 the noise can be drastically reduced. In the embodiment shown in FIGS. 1 and 2, a piezoelectric speaker 5 which is a flat speaker is adopted as a sounding body. This is because the volume of the speaker is small,
This has the advantage that the space inside the housing 4 of the device 1 can be used efficiently. FIG. 3 shows another embodiment and shows the structure of the sound deadening body attached to the housing. The piezoelectric speaker 5 is installed in the housing 4
Is provided outside of the above, and this embodiment exhibits the same operation and effect as the present invention. FIG. 4 shows another embodiment and shows the structure of a sound deadening body attached to a housing. As in this embodiment, the speaker box 12 is not limited to a flat speaker.
The electro-dynamic loudspeaker 12 has a structure in which the vibrating surface 12a is cone-shaped and is driven by the actuator 12b.
However, if the speaker is provided in the housing 4 at least on the same axis as the central axis of the opening surface 7, the sound / flow channel 6 is not hindered, and thus the same operation and the same effect as the present invention can be obtained. can get. Further, in FIGS. 1 and 2, the piezoelectric speaker 5, which is a sounding body, is provided inside the housing 4. However, if the planar speaker is substantially on the same axis as the opening surface 7, it is provided outside the housing. However, the same operation and the same effect as the present invention can be obtained.

[0014]

The noise signal of the noise source or the signal having a high correlation with the noise signal is detected by the sensor, and the detected signal is processed by the signal processing device and then generated as a sound from the sounding body. In a low-noise device equipped with an active muffling device that muffles sound waves by interfering with sound waves from a sound source, the area of the sounding body is wider than the opening surface, and the central axis of the sounding body and the central axis of the opening surface are Almost the same, the sounding body is provided at a constant distance from the opening surface, so that noise reduction at a relatively low frequency due to active noise reduction and 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 an active silencer that is quiet can be realized.

[Brief description of 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 sound deadening body attached to a housing.

FIG. 3 is an explanatory view of a sound deadening body attached to a housing according to another embodiment.

FIG. 4 is an explanatory diagram of a sound deadening body attached to a housing according to another embodiment.

[Explanation of symbols]

1 ... Equipment, 2 ... Heating element, 3 ... Fan, 5 ... Piezoelectric speaker, 6 ... Sound / flow path, 7 ... Opening surface, 8 ... Microphone, 10 ...
Adaptive signal processor, 11 ... Sound collecting microphone.

Claims (1)

[Claims] 1. A device that detects a noise signal of a sound source or a signal having a high correlation with the noise signal by a sensor, processes the detection signal by a signal processing device, and then generates the sound from a sounding body to generate a sound from a noise source. In a low-noise device provided with an active muffling device that propagates through the inside of the device, the sound wave emitted from the device opening face and the sound wave from the sounding body interfere with each other, and the sounding body has an area of the device opening face. Wider, the central axis of the sounding body and the central axis of the device opening surface are substantially equal to each other, and the sounding member is provided at a constant distance from the device opening surface.