JPS60151150A - Confined-sound reducing apparatus for car - Google Patents

Abstract

PURPOSE:To reduce the confined sound by generating the sound which offsets the confined sound. CONSTITUTION:A phase device 20 receives a confined-sound signal detected by a microphone 10 set at a specific position on a car and advances and delays the phase. In a control circuit 30, the amount of advance and delay in the phase device is controlled so that the phase reverse to the phase of the confined sound at a hearing point is generated independently of the variation of the cycle of the confined-sound signal, and an oscillator 40 generates a rectangular-wave signal in synchronization with the signal output from the phase device 20. In a converter 50, the rectangular wave is converted to a sine wave. In a voltage-level detecting circuit 60, the voltage level of the confined-sound signal is detected, and in a voltage controlling amplifier 70, the voltage level of the sine wave is varied according to the voltage level. Then a speaker 80 is operated to generate the sound which reduces the confined sound at the hearing point.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a muffled noise reduction device that reduces muffled noise in a vehicle that is mainly caused by engine vibration.

[Prior art]

Since the muffled noise in the vehicle interior is mainly caused by engine vibration, the following three measures have been conventionally taken to reduce muffled noise.

■, Cuts off transmission of engine vibration to the vehicle body.

■ Suppresses the vibration of the main panel that radiates sound into the vehicle interior.

■, Cutting off vibration transmission to the panel.

However, measures ■ and ■ require sound insulation materials, and measure ■ requires increasing the rigidity of the panel, so in order to increase the effect of muffled sound reduction, the size of the sound insulation material and the weight of the panel must be increased. However, sufficient measures could not be taken due to constraints in terms of vehicle weight and cost.

[Purpose of the invention]

In view of such conventional problems, an object of the present invention is to reduce muffled sound by generating sound that cancels out muffled sound.

[Structure of the invention]

To achieve this objective, the present invention first detects muffled sounds by installing a microphone at a specific position in a vehicle. Next, the phase shifter receives the muffled sound signal detected by the microphone and retards its phase.

Furthermore, the control circuit controls the amount of retardation of the phase shifter so that the phase is opposite to the phase of the muffled sound at the listening point, regardless of changes in the frequency of the muffled sound signal, and the oscillator controls the delay amount of the phase shifter so that the phase shift is opposite to the phase of the muffled sound at the listening point. A square wave signal is generated in synchronization with the signal.

The converter then converts the rectangular wave signal output from the oscillator into a sine wave.

On the other hand, the voltage level detection circuit detects the voltage level of the muffled sound signal detected by the microbon, and the voltage control amplifier outputs a sine wave from the converter according to the voltage level detected by the voltage level detection circuit. change the voltage level.

The additional sound source is installed near the listening point of the vehicle, and is activated by a signal output from the voltage-controlled amplifier to generate a sound that reduces muffled sounds at the listening point.

Therefore, the sound generated by the additional sound source interferes with the muffled sound near the listening point, and the muffled sound is canceled out.

C Effects of the Invention] According to the present invention, the muffled sound is canceled by the sound generated from the additional sound source, so the muffled sound at the listening point can be reduced. Since only an electric circuit is provided, it is possible to suppress an increase in vehicle weight and cost due to muffled noise countermeasures.

Furthermore, among muffled sounds, the device of the present invention is particularly effective against low-frequency sounds for which conventional countermeasures would result in enormous weight and cost. In other words, since low-frequency sounds have long wavelengths, even muffled sounds that are slightly out of phase with the sound from the additional sound source can be canceled out, and as a result, muffled sounds with a wide range of frequencies can be countered.

〔Example〕

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

The drawing is an electrical circuit diagram of an embodiment, in which reference numeral 10 denotes a microphone, which is installed at a specific position in the vehicle interior and detects muffled sounds. The muffled sound detected by the microphone 10 is amplified by a preamplifier 11, and further, a band pass filter (BPF) 12 extracts only signals of frequencies to be reduced as muffled sound, for example, 40 to 200 Hz.

The output of the bandpass filter 12 is input to a saturation amplifier 90, where it is converted into a rectangular wave signal. The output signal of the saturation amplifier 90 is input to the phase shifter 2o, where the phase of the rectangular wave signal is delayed.

40 is a phase-locked loop (PLL) circuit which is an oscillator, and includes a phase difference detection circuit, a low-pass filter, and a voltage-controlled oscillator. The PLL 1 path 40 receives the signal from the phase shifter 20, removes harmonics superimposed on the signal, and generates a rectangular wave signal that is synchronized with the signal and ensures the symmetry of the rectangular wave (duty ratio of 50%). occurs.

Arbitrarily, 30 is a control circuit consisting of a frequency-voltage (F-■, ) converter 31 and a weighting circuit 32, and the F-V converter 31 receives the rectangular wave signal output from the PLL circuit 40 , generates a DC voltage proportional to its frequency, and the weighting circuit 32 receives the DC voltage signal from the F-V converter 31 and adjusts the phase of the rectangular wave signal input to the phase shifter 20 and the phase shifter 20. The phase shifter 20 is controlled by weighting the DC voltage signal so that the phase of the rectangular wave signal outputted by the DC voltage signal has a specific phase difference. In other words, the amount of phase delay in the phase shifter 20 is determined and controlled based on the frequency of the muffled sound.

The rectangular wave signal output from the PLL circuit 40 is sent to the converter 5.
0 is also input, where the square wave is converted to a sine wave.

On the other hand, 60 is a voltage level detection circuit, which consists of a detection circuit 61 and a smoothing circuit 62. do. Therefore, a DC voltage proportional to the sound pressure level of the muffled sound detected by the microphone 10 is obtained from the smoothing circuit 62. The output signal of the smoothing circuit 62 is supplied to the voltage control amplifier 70, and the signal from the converter 80 is input to the voltage control amplifier 70. Here, the output signal of the converter 50 is input to the voltage control amplifier 70. The signal is amplified to a signal with an amplitude proportional to the DC voltage. Then, the output of the voltage control amplifier 70 is amplified by a power amplifier 81 to a voltage necessary to drive a speaker 80, which is an additional sound source, and is supplied to the speaker 80.

As a result, the muffled sound detected by microphone 0 is
Sound having the same sound pressure level as the muffled sound at the passenger seating position in the vehicle interior, which is the listening point, and having an opposite phase is generated from the speaker 8o. However, for each frequency, m
It is necessary to investigate the position of the passenger, the microphone position, and the speaker position so that the muffled sound is canceled out by the sound emitted from the speaker 8o.

[Brief explanation of drawings]

The drawing is an electrical circuit diagram of an embodiment of the present invention. 10-111・-Microphone 20-・-1--Phase shifter 30・-----1 Control circuit 40----- PLL circuit (oscillator) 50-・Niecon bark 6 (1-----1 Voltage level detection circuit 70---1/Voltage control amplifier

Claims (1)

[Scope of Claims] A microphone installed at a specific position on a vehicle or vehicle to detect muffled sound; a phase shifter that retards the phase of a muffled sound signal detected by the microphone according to a receiving number; A control circuit that controls the retardation amount of the muffler so that the phase is opposite to the phase of the muffled sound at the listening point regardless of changes in the frequency of the muffled sound signal, and a control circuit that is synchronized with the signal output from the phase shifter. An oscillator that generates a square wave signal, a converter that converts the square wave signal output from the oscillator into a sine wave, a voltage level detection circuit that detects the voltage level of the muffled sound signal detected by the microphone, and a voltage level detection circuit. A voltage-controlled amplifier that changes the voltage level of the sine wave output from the converter according to the voltage level detected by the converter, and a voltage-controlled amplifier that is installed near the listening point of the vehicle and is activated by the signal output from the voltage-controlled amplifier. A muffled sound reduction device for a vehicle, comprising: a] sound source that generates a sound that reduces muffled sound at a listening point;