JP2660110B2 - Silencer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[Object of the Invention]

[0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silencer which is arranged in a duct-shaped space region and actively cancels a sound from a noise source having a rotary drive.

[0003]

2. Description of the Related Art In a device provided with a compressor having a rotary drive unit such as a motor, for example, a refrigerator,
Because they are often installed in the living room space of ordinary households and are used continuously regardless of the season,
One of the issues is noise reduction. In this case, the most problematic noise source of the refrigerator is noise from the machine room in which the compressor and the piping connected to the compressor are housed.

[0004] That is, in the above-mentioned machine room, the compressor itself generates relatively large noises (operation noise of the compressor motor,
Fluid noise due to the compressed gas, mechanical noise in the movable mechanical element of the compression mechanism, etc.), and the piping connected to the compressor also generates noise due to the vibration. Refrigerators make up the majority of noise. Therefore, controlling noise from the machine room greatly contributes to noise reduction of the entire refrigerator.

Therefore, conventionally, as measures for reducing noise from the machine room, in addition to reducing the noise of the compressor itself (for example, employing a rotary type compressor), the vibration-proof support structure of the compressor has been improved, and the piping system has been improved. By reducing the vibration in the vibration transmission path by improving the shape, or by installing a sound absorbing member and a sound insulating member around the compressor and the piping system, the increase in sound absorption and noise in the machine room Has been attempted to increase the transmission loss.

[0006] However, in general, a machine room of a refrigerator includes:
Since it is necessary to release heat generated by driving the compressor to the outside, a plurality of openings for heat dissipation are provided, and noise leaks out from these openings to the outside. For this reason, the conventional noise countermeasures as described above are naturally limited, and the effect of reducing the noise level can be expected to be only about 2 dB (A) at most.

On the other hand, in recent years, with the development of electronic application technologies, particularly, audio data processing circuits and acoustic control technologies, active control of noise has been attempted to reduce noise by utilizing interference of sound waves. The application of technology is attracting attention. This active control basically detects sound from a noise source by a detecting means such as a microphone provided at a specific position, converts the sound into an electric signal, and based on a signal obtained by processing the electric signal by a computing unit. By operating a control sounding device such as a speaker, the sounding device generates an artificial sound having the same wavelength and the same amplitude as the original sound (sound from the noise source) in a phase opposite to the original sound at the control target point. This is to attenuate the original sound by causing the sound to interfere with the original sound.

That is, in the active control, a microphone is installed near a compressor as a noise source, a sound generated by driving the compressor is detected, and an electric signal is processed by an arithmetic unit so as to cancel the sound, and the speaker is processed. By the operation, the sound coming out of the apparatus is attenuated due to interference between the two sounds.

[0009]

However, when the above-described active control is put into practical use, when the sound from the noise source is directly detected by a microphone or the like, the sound of only the compressor of the noise source to be controlled is generated. However, if a control sound emitted from a speaker enters the microphone, so-called howling may occur, and conversely, the sound may not be muted.

In order to solve such a problem, in order to faithfully detect the sound of only a noise source such as a compressor or the like to be controlled, it is conceivable to detect the vibration of a rotary drive unit serving as a noise source by a vibration sensor. Have been.

That is, a vibration pickup sensor composed of a piezoelectric element or the like is directly attached to a compressor, and the vibration is detected to detect only noise generated due to the vibration of the compressor. By generating a muffling signal, a muffling control sound generated from a speaker is detected to muffle the compressor sound without causing howling.

However, when the vibration pickup sensor is directly mounted on the compressor as described above, there are the following problems. That is, first, since the temperature of the compressor increases as it is used, it is necessary to use a pickup sensor capable of withstanding the high temperature, and the cost increases when heat resistance is taken into consideration. When using a pickup sensor,
Normally, a charge amplifier is used to amplify the detection signal.However, since it is difficult to arrange the charge amplifier near the compressor, a weak signal is routed through a cable, so that noise is easily superimposed. There is a problem that the electric noise resistance decreases.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a muffler capable of performing stable muffling control with a simple configuration without causing howling or the like.

[Configuration of the Invention]

[0015]

SUMMARY OF THE INVENTION The present invention detects sound from a noise source having a rotary drive unit disposed in an acoustically enclosed space formed in a duct shape, converts the sound into an electric signal, and converts the sound into an electric signal. By operating a control sounding device based on a signal obtained by processing an electric signal, the silencer is intended to actively cancel sound radiated from the space area to the outside, and is generated from the noise source. A microphone that detects a sound to be reproduced, a rotation frequency detection unit that extracts a frequency corresponding to the number of rotations of a rotation drive unit of the same noise source among the detection sounds of the microphone, and a frequency of a power supply supplied to the rotation drive unit. Power frequency detecting means for detecting, and a rotational frequency component of mechanical noise generated due to a rotational frequency of the noise source based on a rotational frequency signal from the rotational frequency detecting means. And generating a cancellation sound signal for canceling electromagnetic noise generated due to the power supply frequency of the noise source based on the power supply frequency signal from the power supply frequency detection means. And a control means for operating the control sounding device by a synthetic output of these erased sound signals.

[0016]

In general, the frequency band of sound that can be heard by human ears is set at about tens of Hz to about 20,000 Hz. However, all sounds within the frequency range do not sound uniform at the same sound pressure. For example, in a low-frequency range of about 100 Hz or less, the sensitivity decreases as the frequency decreases, and the sound is hardly heard.

Now, if the power supply frequency is 50 Hz or 60 Hz
When the rotational drive unit of the noise source rotates at a rotational frequency of a frequency in the vicinity of the noise source, mechanical noise is generated based on vibration of an integral multiple of the frequency including the frequency corresponding to the rotational speed, and the power supply frequency is also reduced. , An electromagnetic noise having an even multiple of the frequency is generated. Therefore, in this case, the noise component corresponding to the frequency of the rotation speed becomes the lowest frequency, and the sound corresponding to the rotation frequency among the noise components is hardly recognizable.

Therefore, if a noise reduction signal for silencing other frequency components other than the rotation frequency component among the noises generated from the rotary drive unit of the noise source is generated and generated from the control sound generator, The sound that remains without being silenced is a sound of a rotation frequency component that is not so noticeable to humans as noise, and substantially silences the sound of the noise source.

According to the noise suppressor of the present invention, the sound from the noise source is detected separately from the mechanical noise component and the electromagnetic noise component, and is synthesized by the control means as an erasing sound signal, and the sound is generated for control. Is operated to interfere with noise from a noise source radiated from the space area to the outside to mute the sound.

That is, when noise emitted from the rotary drive unit of the noise source is detected by the microphone, a frequency component corresponding to the number of rotations of the rotary drive unit in the detected sound is detected by the rotation frequency detection unit. On the other hand, the power supply frequency is detected by the power supply frequency detection means.

Next, the control means calculates the mechanical noise component generated by removing the rotational frequency component based on the rotational frequency of the rotational drive unit given from the rotational frequency detecting means by calculation. An elimination sound signal for noise is generated, and an elimination sound signal for electromagnetic noise generated due to the power supply frequency is generated based on the power supply frequency provided from the power supply frequency detection means. Then, the control means operates the control sounding device by a signal obtained by synthesizing the generated erased sound signal.

Thus, the noise emitted from the noise source interferes with the sound from the control sounding device before being emitted from the space area to the outside, and is thereby silenced. In this case, as described above, since the rotation frequency component is removed from the cancellation sound signal, the sound of the rotation frequency of the noise source is radiated to the outside without interference, but is audible to human ears. Because it is difficult, it does not become harsh. Further, by removing the component of the rotation frequency from the erasing sound signal, howling does not occur when the sound of the rotation drive unit is detected by the microphone.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to mitigate noise from a compressor of a refrigerator will be described below with reference to FIGS. First, in FIG. 2 showing the entire configuration of the refrigerator, a freezer compartment 2, a refrigerator compartment 3, and a vegetable compartment 4 are provided inside the refrigerator main body 1 in order from the top. A cooling system is provided inside the refrigerator, and these components will be described below.

That is, a cooler 5 is provided at the rear of the freezer 2, and cool air generated by the cooler 5 is supplied to the freezer 2 and the refrigerator 3 by the fan 6. Refrigerator body 1
A machine room 7 is disposed in the lower part on the back side of the housing, in which a rotary type compressor 8, a condenser pipe 9 and a defrost water evaporator 10 using so-called ceramic fins are accommodated. In the driving state of the compressor 8, the refrigerant from the compressor 8 is supplied to the cooler 5 through a refrigerant passage (not shown) to be cooled, and the fan 6 is driven to cause heat between the cooler 5 and the inside of the refrigerator. Exchange is to take place.

The machine room 7 has a rectangular opening only on the back surface, and this opening is closed by the machine room cover 11 to form a duct-shaped space region. At this time, the machine chamber cover 11 has its peripheral edge hermetically attached to the opening edge of the machine chamber 7, and has an elongate rectangular heat dissipation opening 11 a ( 1 (see FIG. 1). That is, in the mounted state of the machine room 11, the machine room 7 is in a closed state with the heat radiation opening 11a left. The machine room cover 11 is made of a material (for example, a metal such as iron) having excellent heat conductivity and a large sound transmission loss.
As a result, the machine room 7 converts the noise generated from the compressor 8 into a one-dimensional plane traveling wave as the radiation opening 11a.
And the heat radiation opening 11a is opened in a direction perpendicular to the traveling direction of the plane traveling wave, as described above, so that the machine room 7 is acoustically sealed.

Next, the structure of the silencer will be described with reference to FIG. 1, which schematically shows the mechanical room 7 and the electrical structure. In the machine room 7, the heat dissipation opening 11a
Is provided with an auxiliary microphone 12 for monitoring the sound volume, and monitors noise radiated to the outside. A microphone 13 for noise detection is located near the compressor 8.
And detects noise accompanying the rotation of the compressor 8. The detection output of the microphone 13 is input to a control circuit 15 serving as control means via a band-pass filter 14 serving as rotation frequency detection means. Only the input signal of a sound having a frequency in the vicinity thereof is passed and output.

The frequency of the power supply applied to the compressor 8 is detected by a frequency detection circuit 15a as frequency detection means. The detection output of the frequency detection circuit 15a is input to the control circuit 15. The control circuit 15 generates an erasing sound signal based on the power supply frequency and the rotation frequency given from the bandpass filter 14, as described later. The loudspeaker 16 serving as a control sounding device is arranged and fixed at a position facing the heat radiation opening 11a of the machine room 7, and generates an erasing sound in the machine room 7 when an erasing sound signal is given.

Next, the operation of this embodiment will be described. First, the principle of silencing by active control will be schematically described with reference to FIG.

Now, the sound generated by the compressor 8 which is a noise source is S1, the sound generated by the speaker 16 is S2, the sound detected by the microphone 13 is R1, and the auxiliary provided in the radiation opening 11a which is the control target point. The sound received by the microphone 12 is R2, and the sound transfer functions between the sound output and the input point as described above are T11, T21, T12,
When T22 is set, the following equation is satisfied as a two-input two-output system.

[0030]

(Equation 1)

Therefore, the sound to be generated by the speaker 16 is
From the above equation, S2 = (− T12 · R1 + T11 · R2) / (T11 · T22−T12 · T21) (2) is obtained. In this case, the heat radiation opening 1
Since the target is to reduce the sound level at 1a to zero, R2 = 0 can be set, and when this is substituted, the above equation (2) becomes: S2 = R1 · T12 / (T12 · T21−T11 · T22) ) (3) As can be understood from this equation, the heat dissipation opening 1
In order to make the sound R2 received by 1a zero, the sound R2 received by the microphone 13 is processed by applying a filter of F = T12 / (T12 · T21−T11 · T22) (4) to the speaker S2. It can be seen that the sound level at the heat-dissipating opening 11a can be theoretically reduced to zero by generating the noise from the heat-dissipating opening 11a. The control unit 14 is configured to provide the erasing sound signal to the speaker 16 while performing such sound processing (operation) at a high speed.

On the other hand, in the case of the refrigerator configured as described above, the noise level generated in the machine room 7 in response to the driving of the compressor 8 has a band of about 700 Hz or less and 1.
It becomes a state having the property of increasing each in the band of 5 to 5 kHz. Among the noises corresponding to these bands, the noise on the high frequency side can be attenuated by transmission loss in the machine room cover 11 and the like, and can be easily provided by installing an appropriate sound absorbing member in the machine room 7. Since the sound can be muted, the active control of noise by the microphone 13, the speaker 16, and the control unit 14 as described above may be performed with a target frequency of 700 Hz or less.

In the case of performing the above-described active noise control, the noise in the machine room 7 may be formed as a one-dimensional plane traveling wave. It is important to perform the above easily and accurately. Therefore, in the present embodiment, for example, of the dimensions D, W, and H in the depth, width, and height directions, which are three-dimensional directions in the machine room 7, for example, the dimension W in the width direction is made larger than the other dimensions D, H. Set large (specifically, W = 600m
m, D = H = 200 mm) so that a standing wave of sound in the machine room 7 is established only in the primary mode. That is, for example, assuming that the machine room 7 is a rectangular cavity, the following equation is established.

[0034]

(Equation 2)

Where f is the resonance frequency (Hz), Nx, N
y and Nz are the modes in the X, Y and Z directions, Lx and Ly
, Lz are dimensions (ie, D, W, H) in the X, Y, and Z directions in the machine room 7, and C is the speed of sound. Therefore, from the above equation,
Frequency fx of the first standing wave in each of X, Y and Z directions
, Fy and fz can be obtained.

That is, as described above, the depth dimension D = 2
00 mm, width W = 600 mm, height H = 200
mm, the frequency fx of the first standing wave in the X direction is Ny = Nz = 0, and the sound speed is 340.
If it is calculated as m / sec, the following equation is obtained.

[0037]

(Equation 3)

Similarly, the frequencies fy and fz of the first standing wave in the Y and Z directions are calculated as follows.

[0039]

(Equation 4)

As a result, the target frequency (= 70)
0 Hz) or less, the standing wave of the noise in the machine room 7 is established only in the mode in the Y direction (width direction), and the noise in the machine room 7 can be regarded as a one-dimensional plane traveling wave. . For this reason, at the time of silencing by active control of noise using the speaker 16 or the like, the theoretical handling of the wavefront is easy, and the silencing control can be performed easily and accurately.

When performing the control based on the above-described silencing principle, the intensity (power spectrum) of the noise generated from the compressor 8 is subjected to frequency analysis in a range up to, for example, 500 Hz. Has been obtained. In this case, considering that the frequency of the AC power supply is 50 Hz, the electromagnetic noise generated due to the power supply frequency has a peak at an even multiple of the power supply frequency (indicated by a circle in the figure). On the other hand, the mechanical noise generated due to the rotation frequency that is lower than the power supply frequency by the slip of the rotating portion has a peak at a frequency that is an integral multiple of the frequency (indicated by a triangle in the figure). ). Another noise component is a modulated sound appearing between the above-mentioned peaks. From this, it is understood that by suppressing the two noise components, the noise level can be sufficiently reduced to such a level that there is no practical problem.

Therefore, in this embodiment, as shown in FIGS. 3 and 4, in order to reliably detect these noise components, the noise accompanying the rotation of the compressor 8 is transmitted to the microphone 1.
3 (see FIG. 3 (a)), the detected sound is passed through a band-pass filter 14 (see FIG. 3 (b)) to extract the rotation frequency f1 of the compressor 8, and the power supply frequency f0 is detected by the frequency detection circuit 15a (see FIG. 3D). That is, only two fundamental frequencies of the rotation frequency f1 and the power supply frequency f0 (for example, 50 Hz) are individually detected with respect to the components to be silenced in the above-described noise.
The control circuit 15 performs the following arithmetic processing based on these detection results.

That is, the control circuit 15 first obtains a frequency that is an integral multiple of the rotation frequency f1 and synthesizes it with the rotation frequency f1 (see FIG. 3C). Further, with respect to the power supply frequency f0, an even multiple of the power supply frequency f0 is obtained and synthesized (see FIG. 3E). Then, the outputs shown in (c) and (e) are further synthesized into a simulated sound (FIG. 3).
(F)). Next, a muffling signal is generated by multiplying this simulated sound by a muffling transfer function (see FIG. 3G) generated based on the above-described muffling principle (see FIG. 3H). Finally, the muffling signal is processed by a filter (transfer function, see FIG. 3 (i)) which cuts the components of the fundamental frequencies f0 and f1 to generate a final muffling signal (FIG. 3 (j) )reference). Then, the erase sound signal is output to the speaker 16 and emitted into the machine room 7 as an erase sound.

Thus, the noise generated from the compressor 8 is largely attenuated by interference with the sound from the speaker 16 in the heat radiation opening 11a except for the mechanical noise component of the rotation frequency, and only the opportunity noise component of the rotation frequency is generated. Will be radiated outside without being silenced. Since the rotation frequency component is a sound having a frequency slightly lower than 50 Hz in this case, even when radiated to the outside, it does not substantially cause harsh noise.

On the other hand, at this time, the sound reaching the heat-dissipating opening 11a is detected by the auxiliary microphone 12 as a sound-extinguishing monitor, and when the noise monitor amount excluding the rotational frequency component at that time is larger than a predetermined level, That is, when the muffling effect is small, the feedback control is performed by the control circuit 15 so that the output level from the speaker 16 is adjusted to correct the transfer function. As a result,
The noise generated from the compressor 8 is transmitted to the heat dissipation opening 11.
In a, the sound is muted to the extent that there is no practical problem.

As described above, in the present embodiment, the compressor 8
Of the noise generated from the noise, the rotation frequency is detected by the microphone 13 and the band-pass filter 14 for the mechanical noise, and the power supply frequency is detected by the frequency detection circuit 15a for the electromagnetic noise. Are separately processed by the control circuit 15 to generate an erasing sound signal.

In this case, since the component of the rotational frequency of the compressor 8 is not output as an erasing sound signal, the erasing sound from the speaker 16 is output from the microphone 1.
3, the elimination sound from the speaker 16 is cut off when passing through the band-pass filter 14, so that only the rotational frequency component of the compressor 8 is detected, and the howling by the microphone 13 and the speaker 16. Will not occur.

That is, with this configuration, compared with the case where the vibration sensor is attached to the compressor 8, the noise generated from the compressor 8 is transmitted to the outside of the machine room 7 with a simple and inexpensive configuration using the microphone 13. Radiation can be reliably prevented.

[0049]

As described above, according to the sound deadening device of the present invention, the noise generated by the rotation drive unit of the noise source is converted into the mechanical noise generated due to the rotation frequency by the microphone and the rotation. The electromagnetic noise generated due to the power supply frequency is detected by the frequency detection means, the power supply frequency detection means detects the electromagnetic noise, and the control means cancels the noise component excluding the rotation frequency from the noise source. Since the mute signal is generated to operate the control sounding device, even if the noise of the noise source is detected by using a microphone, a simple and inexpensive configuration can be used. This provides an excellent effect that the sound can be reliably muted without causing howling.

[Brief description of the drawings]

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

FIG. 2 is a longitudinal sectional side view of the refrigerator body.

FIG. 3 is a frequency distribution diagram of a signal in each unit.

FIG. 4 is a frequency distribution diagram and a transfer function of a signal in each unit.

FIG. 5 is a frequency distribution diagram of noise generated by a compressor.

FIG. 6 is a frequency correction curve diagram for making the noise level correspond to human hearing.

FIG. 7 is a conceptual diagram illustrating a silencing principle.

[Explanation of symbols]

In the drawing, 1 is a refrigerator main body, 5 is a cooler, 7 is a machine room (space area), 8 is a compressor (noise source), 11 is a machine room cover, 11a is a radiation opening, 12 is an auxiliary microphone, and 13 is an auxiliary microphone. Microphone, 14 is a band pass filter (rotation frequency detecting means), 15 is a control circuit (control means,
Power frequency detecting means) and 16 are speakers (control sounding devices).

Claims (1)

(57) [Claims] 1. A method for detecting a sound from a noise source having a rotary drive unit disposed in an acoustically closed space formed in a duct shape, converting the sound into an electric signal, and processing the electric signal based on the processed signal. A microphone for detecting a sound generated from the noise source; and a microphone for detecting the sound generated from the noise source. Rotation frequency detection means for extracting a frequency corresponding to the number of rotations of the rotation drive unit of the noise source from the detected sound, power supply frequency detection means for detecting the frequency of the power supplied to the rotation drive unit, and the rotation frequency An erasing signal for canceling the mechanical noise excluding the rotational frequency component of the mechanical noise generated due to the rotational frequency of the noise source based on the rotational frequency signal from the detection means. And an elimination sound signal for canceling electromagnetic noise generated due to the power supply frequency of the noise source based on the power supply frequency signal from the power supply frequency detection means, and a composite output of these elimination sound signals is generated. And a control means for operating the control sounding device according to (1).