JPH0241954A - Device for reducing sound confined in vehicle - Google Patents

Abstract

PURPOSE:To reduce confined sounds originating from the vibration of an engine by processing in a way to generate additional sounds of opposite phases with a phase converter and putting them out from a speaker, after filtering detection signals of a vibration sensor which detects confined sounds. CONSTITUTION:A vibration sensor 1 is installed on the ceiling, etc. inside a vehicle cabin, which vibrates level-wise in correlation with the confined sound originating from engine vibration. Signals detected by the vibration sensor 1 are put into a detected signal processing circuit 10. After having been passed through a preamplifier 11, noise components are removed by a band pass filter 12 that signals of confined sound of nearly sinusoidal wave are put out. The output signals are phase-controlled with a phase converter 13 by a delayed phase angle 180 deg.+theta-alpha, then amplified with a power amplifier 14. The amplified output is furtherly delayed by the phase alpha which is due to the phase characteristics of a speaker 2, and additional sounds are put out, which are on the same level as those of confined sounds and with a delay of 180 deg. at a hearing point A. Therefore, both sound waves on a same level but with opposite phases are set off through interference to reduce the confined sounds.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention is a vehicle muffled sound reduction device that reduces muffled sound in a vehicle interior caused by engine vibration by interfering with additional sound. It is related to.

(Prior art) A device for generating an additional sound having the same amplitude and opposite phase as the muffled sound at the listening point from a speaker based on the muffled sound signal detected by this type of microphone is well known (Japanese Patent Laid-Open No. 6O-151
150), a device that detects the engine signal and determines the loudness and phase of the sound generated from the additional sound source is also well known (Utility Model Application Publication No. 127051/1983).
.

(Problems to be Solved by the Invention) However, these devices control a separately prepared oscillator based on the detection signal, and the overall circuit configuration becomes complicated.

Therefore, an object of the present invention is to provide a muffled sound reduction device that can reliably reduce muffled sound with a simple circuit configuration.

(Means for Solving the Problems) In order to achieve this object, the present invention addresses the problem of muffled f, which is particularly problematic in the resonant frequency region within the vehicle interior, and which is suitable for the muffled sound source in this state. We focused on the fact that there is a part of the vehicle that vibrates, and installed a vibration sensor at a specific part of the vehicle body that vibrates in a level correlated to the muffled sound at a specific engine rotation speed that causes the muffled sound.

A speaker that outputs additional sound into the vehicle interior to cancel out the muffled sound, a bandpass filter that passes the frequency band of muffled sweat in the detection signal of the vibration sensor, and a level corresponding to the muffled sound at a predetermined listening point. It'll amplify the additional sound so that it is output from the speaker.
and a detection signal processing circuit having a phase converter for controlling the phase of the output signal by a predetermined phase angle so that the output signal is in phase with the added sound or in reverse phase with respect to the muffled sound at a predetermined listening point. There is.

[Effect]

The vibration sensor detects vibrations of the vehicle body caused by engine operation in a specific rotational speed range as a signal correlated to muffled noise through a bandpass filter.

This detection signal is converted by the signal processing circuit into an additional sound signal having a level and an opposite phase corresponding to the muffled sound, and the additional sound is output from the speaker.

At this time, since the vibration sensor directly detects the vibration of the vehicle body, the loop gain including the positive feedback path from the speaker to the vibration sensor is reduced to suppress the occurrence of howling.

(Embodiments of the Invention) Next, the muffled sound reduction device of the present invention will be described based on embodiments with illustrations.

In FIG. 1, reference numeral 1 denotes a vibration sensor installed, for example, inside the central portion of the roof, which has a correlation between the muffled current level and the corresponding body vibration level. FIG. 2 shows test data for making such a determination. That is, at various locations on the vehicle body, the engine load was varied by turning the air conditioner on and off at a specific engine speed that produced the loudest muffled noise, for example 45 Hz, and for three vehicles of the same model. The correlation, that is, the proportional relationship, between the muffled a level and the vibration detection level at all six listening points A was measured, and the figure shows the one at the center of the roof where the best data can be obtained. In other words, this part vibrates in resonance with the engine vibration. A speaker 2 that generates additional sound toward a listening point A is attached to the rear of the roof.

IO is a detection signal processing circuit that receives the detection signal of the vibration sensor 1 as an input and supplies an additional sound signal to the speaker 2.

This circuit includes a preamplifier 11 for the detection signal of the vibration sensor l, and a vibration frequency range, for example 45±51, corresponding to the muffled sound due to normal resonance, for the preamplifier signal.
A bandpass filter 12 whose passband is 12, and a phase converter 1 that delays the phase of the filtered output signal.
3 and a power amplifier 14 for the phase-converted signal.

The delay phase angle in the phase converter 13 is set so as to generate an additional sound delayed by 180 degrees with respect to the muffler 7g (dotted line in Figure 3), that is, in the opposite phase! It is set to 80°+0-α. In other words, 0 is the phase shift of the muffled sound with respect to the detection/filter signal waveform of the vibration sensor l (solid line in Figure 3), and α is the phase shift of the additional sound, which is the output signal, with respect to the input signal of the speaker 2. . Further, the overall gain of the preamplifier II and the power amplifier 14 with respect to the detection signal of the vibration sensor I is set so that the level of the additional sound output from the speaker 2 exactly corresponds to the level of the muffled sound at the listening point A.

The operation of the muffled sound reduction device configured as described above is as follows.

When the engine is running at a speed that causes muffled noise in the passenger compartment, the center of the roof vibrates in response to the engine vibrations. As a result, a vibration signal (FIG. 3a) is detected by the vibration sensor 1, and the bandpass filter I
2, the noise component is removed and a nearly sinusoidal muffled sound signal (solid line in Figure 3) is output. This output signal is subjected to phase control by a delay phase angle of 180°+θ-α by a phase converter 13 (FIG. 3C), and power amplified by a power amplifier 14. The amplified output is further delayed by a phase α due to the phase characteristics of the speaker 2, and an additional sound at the same level as the muffled sound at the listening point A and delayed by 1806 is output.

Therefore, the sound waves of the same level and opposite phase from both sides interfere and cancel each other out, reducing the muffled sound. Since the microphone does not directly detect muffled sounds when the engine is stopped, the loop gain can be kept small and no howling occurs. FIG. 4 shows this test data, and it was confirmed that a reduction effect of 10 dB or more was obtained around the listening point A, and that almost the same reduction effect was obtained throughout the entire vehicle interior.

〔Effect of the invention〕

According to the present invention, with a simple circuit configuration that simply amplifies the vibration detection signal and adjusts the phase, it is possible to significantly reduce muffled sound in the frequency range that is actually a problem, without causing howling. becomes.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of a muffled sound reduction device according to an embodiment of the present invention, and FIG. 2 is a diagram showing the arrangement position δ of the vibration sensor of the same embodiment.
FIG. 3 is a diagram showing waveforms of various parts of the signal processing circuit of the same embodiment, and FIG. 4 is a diagram showing measurement data for confirming the effects of the present invention. l...Vibration sensor, 2...Speaker.

Claims (1)

[Scope of Claims] A vibration sensor attached to a specific location on a vehicle body that vibrates in a level-correlation with the muffled sound at a specific engine speed that produces the muffled sound; a speaker that outputs into the room; a bandpass filter that passes the frequency band of the muffled sound in the detection signal of the vibration sensor; and an output signal of the filter that outputs the additional sound at a level corresponding to the muffled sound at a predetermined listening point. an amplifier that amplifies the output signal so that it is output from a speaker; and a phase converter that controls the output signal by a predetermined phase angle so that the phase of the additional sound is in reverse phase with respect to the muffled sound at the predetermined listening point. What is claimed is: 1. A muffled sound reduction device for a vehicle, comprising: a detection signal processing circuit having a detection signal processing circuit.