JPH04358775A - Muffling device for cooling system - Google Patents

Abstract

PURPOSE:To display a noise control effect in a constantly best condition with the active control of noise made in a stable condition even under a situation where ambient temperature is lowered. CONSTITUTION:An artificial sound, having a reverse phase to and a frequency and amplitude same as that of noise from a compressor 3 in a ventilating hole 2a, is generated by processing a signal from a pickup 4 to actuate a speaker 5 in a computing element 9, and the noise is eliminated by the artificial sound. This muffling effect is monitored with a microphone 6 to be converted into a frequency signal Sp, and when a monitored sound is not within an allowable range, the operation coefficient of the computing element 9 is corrected based on the frequency signal Sp to make adaptive control with an adaptive control circuit 10. When the temperature near to the speaker 5 is lowered to deteriorate its low frequency characteristic, the low-frequency component of the frequency signal Sp is not attenuated with a frequency discrimination circuit 11, performing no adaptive control in a frequency band where the low frequency characteristic of the speaker 5 is deteriorated. Consequently the diffusion of an adaptive control system is eliminated, allowing the active control of noise in a constantly stable condition.

Description

[Detailed description of the invention]

[Object of the invention]

0002

[Industrial Application Field] The present invention is a silencing device used in a cooling device such as a refrigerator, in particular, by superimposing a sound of the opposite phase on the noise generated from a compressor, the noise is actively suppressed. The present invention relates to a silencer for a cooling device that cancels out noise.

0003

2. Description of the Related Art In recent years, refrigerators that utilize active noise control to reduce noise have been put into practical use. That is, this refrigerator has a cover that has a ventilation hole for heat radiation at the opening of the machine room that houses the compressor and the piping system connected to it.
The noise from the compressor is detected by a vibration pickup attached to the compressor and converted into an electrical signal, and the electrical signal is digitally processed by a computing unit. Based on the signal, a silencing speaker is activated. By operating the speaker, the artificial sound is generated from the original sound (noise from the compressor) at the ventilation hole, which is the point to be controlled, with an opposite phase, the same wavelength, and the same amplitude, and this artificial sound and the original sound are The structure is such that a silencing effect is obtained by interfering with the

[0004] Furthermore, in realizing such active control, so-called adaptive control is performed to correct characteristic fluctuations caused by aging of components constituting the silencing signal system from the pickup to the speaker. Specifically, when such adaptive control is performed, a microphone is provided that monitors the silencing effect of the speaker at the ventilation hole portion and converts it into an electrical signal, and the above-mentioned control is performed so that the sound monitored by this microphone falls within an allowable range. The configuration includes an adaptive filter that corrects the calculation coefficient of the calculation unit based on the electrical signal.

[0005]

[Problems to be Solved by the Invention] By the way, the frequency range of noise that can be muffled by the above-mentioned active control is from 50 to
It is approximately 700 Hz, and the lowest frequency is determined by the output sound pressure frequency characteristics (particularly the low resonance frequency) of the silencing speaker. Figure 2 shows an example of the output sound pressure frequency characteristics and impedance characteristics of a general cone-shaped speaker. has. In other words, the output sound pressure level of the speaker has the property of rapidly attenuating below the low resonance frequency fo;
Since o increases as the temperature decreases and shows a rapid increase below 0° C., the ambient temperature has a negative effect on active noise control.

That is, as shown in FIG. 3, when the ambient temperature drops below freezing, the low resonant frequency fo may become higher than the power supply frequency (50 Hz or 60 Hz), and under such conditions, the speaker's The output sound pressure level is greatly attenuated in the power frequency band (that is, the frequency band corresponding to the primary rotational sound component of the compressor), and the low frequency characteristics of the speaker are extremely deteriorated. When the low frequency characteristics of the speaker deteriorate in this way, the adaptive filter cannot cope with the above-mentioned adaptive control, so the adaptive control system dissipates and the active control of noise becomes unstable. In such cases, the noise-canceling sound from the speaker may actually increase the noise.

The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to enable active noise control to be carried out in a stable state even under conditions where the ambient temperature has decreased; To provide a silencing device for a cooling device that can always exhibit a noise suppressing effect in the best condition.

[Configuration of the invention]

[0009]

[Means for Solving the Problems] In order to achieve the above object, the present invention converts the sound generated by the driving of a compressor in a machine room into an electric signal using a detection means, and converts this electric signal into an electric signal using a computing unit. In a silencing device for a cooling device that actively cancels out sound emitted from a machine room by operating a speaker based on a processed signal, the silencing effect of the speaker is monitored and converted into an electrical signal. a sound receiver, a correction means for correcting a calculation coefficient of the arithmetic unit based on the electric signal so that the sound monitored by the sound receiver falls within an allowable range, a temperature sensor for detecting a temperature near the speaker; A filter means is provided for attenuating the low frequency component of the electrical signal from the sound receiver when the temperature detected by the sensor is below the set temperature.

0010

[Operation] When the compressor is driven, the sound from the compressor is converted into an electric signal by the detection means, and the arithmetic unit operates the speaker based on a signal obtained by processing the electric signal. As a result, the sound from the compressor is canceled out by interference between this and the artificial sound output from the speaker. The silencing effect of such active control is now monitored by the sound receiver and converted into an electrical signal, and if the monitored sound is outside the permissible range, the correction means The arithmetic coefficient (acoustic transfer function) of the arithmetic unit is corrected based on the electrical signal, so that the silencing effect due to active control falls within the above-mentioned allowable range. In this way, adaptive control is performed in which the silencing ability is always kept optimal during active control.

[0011] On the other hand, when the temperature near the speaker decreases, the low frequency characteristics of the speaker deteriorate, so the adaptive control system by the correction means dissipates, and the active control of noise becomes unstable. There is a possibility that However, when the temperature near the speaker falls below the set temperature, the filter means attenuates the low frequency component of the electrical signal from the sound receiver in response to the temperature detected by the temperature sensor falling below the set temperature. Therefore, adaptive control by the correction means is no longer performed in the frequency band where the low frequency characteristics of the speaker deteriorate. As a result, the adaptive control system using the correction means does not dissipate as described above, and active control of noise can always be performed in a stable state.

0012

Embodiment An embodiment of the present invention will be described below with reference to FIG.

In FIG. 1, a machine room 1 is provided, for example, in the lower part of a refrigerator with the rear side open, and the open part has a machine room cover having a heat radiation vent 2a.
2 is installed.

A vibration pickup 4, which is a detection means, is attached to the compressor 3 housed in the machine room 1. This pickup 4 converts the vibration sound of the compressor 3, which is a noise source, into an electrical frequency signal Sf. Convert and output. The speaker 5 disposed within the machine room 1 is embedded, for example, in a portion of the wall of the machine room 1 near the ventilation opening 2a.

A microphone 6, which is a sound receiver for monitoring the silencing effect, is provided at the ventilation opening 2a, which is an active control target point, and this microphone 6 outputs an electrical frequency signal Sp corresponding to the monitored sound. do. The thermistor 7, which is a temperature sensor, is installed in the machine room 1 to detect the temperature near the speaker 5, and has a configuration in which it outputs a temperature signal Sd corresponding to the detected temperature and supplies it to the temperature detection circuit 8. It has become.

Now, the computing unit 9 operates the speaker 5 based on a signal obtained by high-speed digital calculation of the frequency signal Sf from the pickup 4, so that the noise from the compressor 3 can be heard from the speaker 5 at the ventilation port 2a. It is configured to generate artificial sounds with opposite phases, the same wavelength, and the same amplitude.

The adaptive control circuit 10 corrects the calculation coefficient (acoustic transfer function) of the arithmetic unit 9 based on the frequency signal Sp given from the microphone 6 via the frequency discrimination circuit 11 serving as a filter means. It is configured to control the monitor sound so that it falls within an acceptable range.

The frequency discrimination circuit 11 includes a switch element 12 whose operation is controlled by the output of the temperature detection circuit 8, a high-pass filter 13 whose passband frequency is, for example, 95 Hz or more, and a low-pass filter 14 whose passband frequency is, for example, 600 Hz or less. It is composed of a combination of. The temperature detection circuit 8 switches the switch element 12 to the ON state between the contacts (c and a) when the temperature near the speaker 5 indicated by the temperature signal Sd from the thermistor 7 is below the set temperature of 0°C, and also switches the switch element 12 to the ON state between the contacts (c and a), and also outputs the temperature signal. When the temperature indicated by Sd is higher than 0°C, the switch element 12 is turned into contact (c-b)
It is configured to switch to the on state for a certain period of time.

In the frequency discrimination circuit 11,
When the switch element 12 is turned on between contacts (ca), the frequency signal Sp from the microphone 6
is applied to the adaptive control circuit 10 via both the high-pass filter 13 and the low-pass filter 14, and the switch element 12
is switched to the on state between contacts (c and b),
The frequency signal Sp is provided to the adaptive control circuit 10 only through the low-pass filter 14.

According to the above configuration, the following effects can be obtained. That is, when the compressor 3 is in the driving state, the sound from the compressor 3 is converted into a frequency signal Sf by the vibration pickup 4, and the arithmetic unit 9 converts the frequency signal Sf based on the signal processed by high-speed digital calculation. to operate the speaker 5. As a result, the speaker 5 generates an artificial sound that is in opposite phase to the noise from the compressor 3 and has the same wavelength and amplitude at the ventilation port 2a, so that this artificial sound and the noise from the compressor 3 are This causes interference at the opening 2a, and as a result, the ventilation opening 2a from inside the machine room 1
The sound radiated to the outside through the device is actively canceled out.

Furthermore, the microphone 6 provided to monitor the silencing effect of the active control as described above converts the sound at the ventilation opening 2a into a frequency signal Sp and outputs the same. In this case, in a steady state where the temperature near the speaker 5 is higher than 0°C, the switch element 1 in the frequency discrimination circuit 11
2 is switched on between the contacts (c and b) by the temperature detection circuit 8, so the frequency signal Sp is given to the adaptive control circuit 10 via the low-pass filter 14.

[0022] As a result, the adaptive control circuit 10 receives the components of the frequency signal Sp of 600 Hz or less,
If the sound monitored by the microphone 6 indicated by the frequency signal Sp is outside the permissible range, the calculation coefficient of the calculator 9 is corrected based on the frequency signal Sp, so that the silencing effect due to active control is within the above permissible range. control so that it fits. In this way, adaptive control is performed in which the silencing ability is always kept optimal during active control.

On the other hand, when the temperature near the speaker 5 falls below 0° C., the low frequency characteristics of the speaker 5 deteriorate, so that the adaptive control system including the adaptive control circuit 10 dissipates. There is a risk that active noise control may become unstable. However, such a situation in which active noise control becomes unstable can be prevented in the following manner.

That is, when the temperature near the speaker 5 drops below 0° C., the switch element 12 in the frequency discrimination circuit 11 is switched to the ON state between the contacts (ca) by the temperature detection circuit 8. The frequency signal Sp from the microphone 6 is given to the adaptive control circuit 10 via a high-pass filter 13 and a low-pass filter 14. As a result, the adaptive control circuit 10 controls the frequency signal Sp
Therefore, the above-described adaptive control is no longer performed in the frequency band (95 Hz or less in this case) where the low frequency characteristics of the speaker 5 deteriorate. Therefore, the adaptive control system including the adaptive control circuit 10 does not dissipate as described above, and active control of noise can always be performed in a stable state.

In this case, active noise control is no longer performed in the frequency band corresponding to the primary rotational sound component of the compressor 3 (50 Hz or 60 Hz corresponding to the commercial power frequency), but even in this state - Since a silencing effect of about 10 dB can be obtained, there is no problem in practical use.

[0026]

According to the present invention, as is clear from the above explanation, by superimposing an artificial sound having an opposite phase to the noise caused by the compressor drive, the noise can be actively canceled and In a silencing device for a cooling device that performs adaptive control in which the active control conditions are corrected based on the results of monitoring the silencing effect, the low frequency characteristics of the artificial sound generating speaker are caused by a decrease in ambient temperature. Since the system is configured so that adaptive control is not performed in the frequency band where the characteristics deteriorate when the characteristics deteriorate, active noise control can be performed in a stable state even when the ambient temperature drops. Therefore, the noise suppression effect can always be exhibited in the best condition, which is an excellent effect.

[Brief explanation of drawings]

FIG. 1 is a diagram practically showing the electrical configuration of an embodiment of the present invention.

[Figure 2] Diagram showing the output sound pressure frequency characteristics and impedance characteristics of a general speaker

[Figure 3] Temperature characteristic diagram of low resonant frequency of general speakers

[Explanation of symbols]

In the figure, 1 is a machine room, 2 is a machine room cover, 2a is a ventilation hole,
3 is a compressor, 4 is a vibration pickup (detection means)
, 5 is a speaker, 6 is a microphone (sound receiver), 7 is a thermistor (temperature sensor), 9 is an arithmetic unit, 10 is an adaptive control circuit (correction means), 11 is a frequency discrimination circuit (filter means), 12 is a switch element, 13 is a high pass filter,
14 indicates a low pass filter.

Claims (1)

[Claims] [Claim 1] By converting the sound generated by the driving of a compressor housed in a machine room into an electrical signal using a detection means, and operating a speaker based on a signal processed from this electrical signal by a computing unit. , a sound damping device for a cooling device that actively cancels sound radiated from the machine room to the outside, comprising: a sound receiver that monitors the sound damping effect of the speaker and converts it into an electrical signal; a correction means for correcting the calculation coefficient of the arithmetic unit based on the electric signal so that the monitor sound falls within an allowable range; a temperature sensor provided to detect a temperature near the speaker; and a temperature detected by the temperature sensor. a filter means for attenuating a low frequency component of an electrical signal from the sound receiver when the sound receiver is below a set temperature.