JPH04282694A - Active noise reduction device - Google Patents

Abstract

PURPOSE:To obtain the active noise reduction device which prevents a noise larger than a propagation noise from being generated owing to the divergence of a control system when the disorder of the control system is caused by disturbance as a sound wave and becomes worse. CONSTITUTION:The above device consists of an averaging means 6 which detects and averages the output signal of a 2nd microphone, a comparing means 7 which compares the averaged output signal with a certain set value, and a stopping means 8 which stops the operation of the active noise reduction device with the comparison output signal. If the control system is disordered, a circuit stops the operation of the active noise reduction device to prevent the noise larger than the propagation noise from being generated.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention artificially generates a sound wave having the same amplitude and opposite phase to the propagating sound wave of a noise source (hereinafter referred to as the propagating noise), and the sound wave and the propagating noise are The present invention relates to an active noise reduction device that mutes noise through mutual interference.

0002

2. Description of the Related Art FIG. 3 is a diagram showing the principle of a conventional active noise reduction device disclosed, for example, in Japanese Utility Model Application No. 63-45599. In the figure, an air conditioning duct 1 that serves as a propagation path for sound waves includes a first microphone 2 and a second microphone 3 located downstream from the installation position of the first microphone 2 for evaluating the silencing effect. Each is installed. Further, a muffling speaker 4 is provided between the first and second microphones 2 and 3. Further, a control device 5 is provided between the first microphone 2 and the muffling speaker 4.

Next, the operation will be explained. In the above configuration, propagated noise is first detected by the first microphone 2, converted into an electrical signal, and input to the control device 5. Furthermore, an evaluation signal for evaluating the silencing effect from the second microphone 3 is input to the control device 5 . The control device 5 transmits a drive signal to the silencing speaker such that the output of the second microphone 3 becomes zero due to mutual interference between the silencing sound wave emitted from the silencing speaker 4 and the propagating noise at the installation position of the second microphone 3. Output to 4. With this configuration, it is possible to eliminate propagated noise at the location where the second microphone 3 is installed.

0004

[Problems to be Solved by the Invention] Since the conventional active noise reduction device is configured as described above, it is difficult to prevent sudden changes in propagated noise due to load fluctuations of an air conditioner, for example,
The influence of the return of sound waves from the duct 1 to the first microphone 2, the input of disturbances in the form of sound waves such as vortex noise from outside the duct 1, and the case of deterioration or failure of the silencer speaker 4, etc. In this case, the control system of the active noise reduction device may be disturbed and become unstable. If the control system becomes unstable, the silencing speaker 4 will no longer output a silencing sound wave signal having the opposite phase and the same amplitude as the propagating noise, and if the situation worsens further, the control system will diverge. In such a state, the sound from the muffling speaker 4 is added to the propagating noise downstream from the position of the second microphone 3, and there is a problem in that the noise becomes even louder than the propagating noise.

The present invention has been made to solve the above-mentioned problems, and detects disturbances in the control system due to disturbances in the form of sound waves using the output signal of the second microphone 3, and controls the active noise reduction device. It is an object of the present invention to obtain an active noise reduction device that stops the operation and prevents the noise from becoming louder than the propagation noise at the position of the second microphone 3.

[0006]

[Means for Solving the Problems] The active noise reduction device according to the present invention detects the output signal of a second microphone, averages the detected output signal, and compares the average output signal with a certain set value. The operation of the active noise reduction device is stopped based on the comparison output signal.

Furthermore, the active noise reduction device according to the present invention has, in addition to the above-described configuration, a time delay circuit provided at a subsequent stage of the averaging means for averaging the output signal of the second microphone.

[0008]

[Operation] The active noise reduction device of the present invention detects disturbances in the control system due to disturbances in the form of sound waves using the output signal of the second microphone, and uses that signal to generate a signal to stop the operation of the active noise reduction device. , to prevent noise greater than propagation noise from being generated at the position of the second microphone.

[0009]

[Example] Example 1. Hereinafter, FIG. 1, which is an embodiment of the present invention, will be described. In the figure, an air conditioning duct 1 that serves as a propagation path for sound waves has a first microphone 2 and a second microphone 3 located downstream from the installation position of the first microphone 2 for evaluating the silencing effect. is set up. Furthermore, the first and second
A muffling speaker 4 is provided between the microphones 2 and 3. Also, a first microphone 2 and a silence speaker 4
A control device 5 is provided between the two. A second microphone 3 is connected between the second microphone 3 and the control device 5.
an averaging means 6 for averaging the output signals of , a comparison means 7 for comparing the averaged output signal with a certain set value, and a stop means 8 for stopping the operation of the active noise reduction device in response to the comparison output signal. It is being

Next, the operation of the present invention will be explained. In the above configuration, propagated noise is detected by the first microphone 2, converted into an electrical signal, and input to the control device 5. A signal from the second microphone 3 for detecting a sound wave synthesized by mutual interference between the propagating noise and the silencing sound wave is also input to the control device 5 after being converted into an electric signal. The control device 5 first receives a signal from the first microphone 2, generates a silencing sound wave signal having the same amplitude and opposite phase, and outputs it to the silencing speaker. A muffling speaker converts an electrical signal into a mechanical signal and emits sound waves for muffling. Here, the propagating noise and the silencing sound wave mutually interfere and are synthesized.
Due to differences in acoustic conditions in the propagation path, sufficient noise reduction is not achieved. Therefore, the second
By applying feedback to the control device 5 to correct the output of the microphone 3 to zero, and again applying a drive signal to the silencing speaker, and repeating this operation, a sufficient silencing effect is obtained. The above operations are performed, but if disturbances in the form of sound waves are input to the instinctive noise reduction device, the control system will be disturbed and become unstable, and the noise reduction operation will not take place, eventually causing divergence. I end up. In this case, the propagated noise and the sound waves from the silencing speaker are added, and a noise greater than the propagated noise is generated. Here, we will enumerate the causes of disturbances in the control system of active noise reduction devices. First, there are sudden changes in propagated noise due to load fluctuations of air conditioners, effects of sound waves from the silencer speaker 4 returning to the first microphone 2, abnormal noises due to malfunctions of rotating equipment, and other vortices from outside the duct 1. There are many possibilities, such as input of disturbance in the form of sound waves due to passing sounds, malfunction of the silencer speaker due to static pressure in the duct, deterioration or failure of the silencer speaker 4, and mechanical vibration. If even one of these causes is present, the control system will be disturbed.

In order to deal with such a situation, disturbances in the control system are detected by the output signal of the second microphone, and the operation of the active noise reduction device is stopped, thereby preventing the generation of noise greater than the propagation noise. This was prevented. The second microphone output signal is detected, the detected output signal is input to the averaging means 6 to average the signal, and the average output signal is input to the comparing means 7 and compared with a certain set value. This set value is set to an equivalent value that is larger than the average value of steady propagation noise values, or a value that is higher than the average value after muffling. By operating the means 8 for stopping the operation of the active noise reduction device based on the output signal of the comparison means 7, the operation of the active noise reduction device is stopped. Although FIG. 1 shows the case where the operation of the control device 5 is stopped,
A method of stopping the operation of the silence speaker 4 may also be used. As a result, even if the control system is disturbed, the operation of the active noise reduction device can be obtained reliably, and it is possible to prevent noise greater than propagation noise from being generated.

Example 2. Further, FIG. 2, which is an embodiment of the present invention, will be explained. In the configuration shown in FIG. 1, a time delay means 9 is provided at a stage subsequent to the averaging means for averaging the output signal of the second microphone.

Next, the operation will be explained. This is to deal with the case where the average output signal of the second microphone 3 pulsates, and the active noise reduction device is made to output an operation stop signal only when the disturbance in the control system continues for a certain period of time. It is something. This makes it possible to obtain more stable operation. Also, comparison means 7
A similar effect can be obtained by giving hysteresis characteristics to the hysteresis characteristic. The operations of other parts are the same as those shown in FIG. 1, so their explanation will be omitted.

Example 3. In addition, although the above embodiment shows an active noise control device in an air conditioning duct, other applications are also possible, and the system does not need to be a system with two microphones and one speaker, but a system using a plurality of the above devices. Any active noise reduction device may be used as long as it generates a silencing sound wave of the same amplitude and opposite phase to the propagating noise, and mutes the sound by mutual interference with the propagating noise.

Example 4. In the above embodiment, the sound wave signal is detected by a microphone, but any vibration that is correlated with the sound wave may be detected by electromechanical conversion means, and any electromechanical conversion means may be used instead of the muffled speaker.

Example 5. Although FIG. 1 of the above embodiment shows the case where the operation of the control device 5 of the active noise reduction device is stopped, the operation of the control device 5 of the active noise reduction device is stopped.
It is also possible to stop the operation.

[0017]

As described above, according to the present invention, disturbances in the control system of an active noise reduction device are detected by the output signal of the second microphone, the output is averaged, and further compared with a set value, Since the operation of the active noise reduction device is stopped at that output, it is possible to obtain an active noise reduction device that can prevent the generation of noise greater than propagation noise.

[Brief explanation of the drawing]

FIG. 1 is a system diagram of an active noise reduction device showing a first embodiment of the present invention.

FIG. 2 is a system diagram of an active noise reduction device showing a second embodiment of the present invention.

FIG. 3 is a system diagram of a conventional active noise reduction device.

[Explanation of symbols]

1 Air conditioning duct 2 First microphone 3 Second microphone 4 Silencer speaker 5 Control device 6 Averaging means 7 Comparison means 8 Stopping means 9 for stopping the operation of the active noise reduction device
time delay means

Claims (2)

[Claims] Claim 1: A first microphone provided to detect a propagating sound wave from a noise source in a sound wave propagation path; , a muffling speaker for muffling the propagating sound wave by the sound wave interference, a second microphone detecting a composite sound wave of the propagating sound wave from the noise source and the radiated sound wave from the muffling speaker, and the first microphone. An active device comprising a control device that receives an output signal, generates a signal having opposite phase and same amplitude characteristics, and controls the drive signal of the silencer speaker so that the output signal of the second microphone becomes zero. In the noise reduction device, an averaging means for averaging an output signal of a second microphone that detects a synthetic sound wave with a sound wave radiated from the silencing speaker, and comparing an output signal of the averaging means with a certain setting value. An active noise reduction device comprising: a comparison device; and a stop device for stopping the operation of the active noise reduction device in response to an output of the comparison device. 2. A time delay means is provided at a stage subsequent to the averaging means for averaging the output signal of the second microphone that detects the synthesized sound wave with the sound wave radiated from the muffling speaker. The active noise reduction device according to item 1.