JPH11249665A - Compartment noise reducing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the generation of the band where noise is increased inadvertently, in a passive device which generates sound waves having inverse phases of the noise from speakers so as to reduce the low frequency portion of the load noise called compartment staying sound. SOLUTION: This device is provided with a first microphone 102 which detects the noise in the vicinity of the objective place where noise is to be reduced, a first phase amplitude adjuster 104 which adjusts the phases and amplitudes of the signals from the microphones 102, second microphones which are provided in the vicinity of secondary sound sources 101 arrange on the front side section doors, second phase amplitude adjuster 105 which adjust the phases and the amplitudes of the signals from the second microphones, and power amplifiers 106 which conduct power amplification of the signals made by adding the signals from the adjuster 104 and 105. The outputs from the amplifiers 106 are radiated from the sources 101 as secondary sounds to be interfered with the noise in the compartment.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicle interior noise reduction device, and more particularly to a vehicle interior noise reduction device for actively reducing a periodic sound of 100 Hz or less which causes a feeling of muffled sound.

[0002]

2. Description of the Related Art It is considered that noise in a vehicle cabin is generated when the wall surface of the vehicle cabin which forms a closed space is vibrated by vibrating force due to rotation of an engine or force transmitted from a road during traveling.

Conventionally, to reduce such noise in the vehicle interior, passive (passive) means such as increasing the rigidity of various parts of the vehicle body and performing tuning on a transmission system have been mainly used. There were many problems such as increase and cost increase.

On the other hand, a speaker is installed in the vehicle interior and a microphone is installed near a target position where noise is to be reduced, and a noise signal in the vehicle interior detected by the microphone is fed back to an amplifier for driving the speaker. There has been proposed an active noise reduction device that generates a sound wave of the opposite phase to reduce the low-frequency portion of road noise called muffled sound in a vehicle cabin.

However, in this device, the phase in the open loop characteristic between the microphone arranged at the target position for reducing the noise in the passenger compartment and the speaker emitting the control sound is in the range of 45 ° to -45 °. On the other hand, in a certain band, the phenomenon that the noise increases conversely occurred, which was an obstacle to practical use.

[0006]

SUMMARY OF THE INVENTION According to the present invention, a speaker is installed in a vehicle cabin and a microphone is installed near a target position where noise is to be reduced, and the speaker detects a noise signal in the vehicle cabin detected by the microphone. A noise reduction device that feeds back to the amplifier and generates a sound wave of the opposite phase to the noise from the speaker to reduce the low-frequency part of the road noise called the muffled noise in the cabin. An object of the present invention is to realize a highly practical vehicle interior noise reduction device by reducing the amount of increase.

[0007]

In order to achieve the above object, a vehicle interior noise reduction apparatus according to the present invention comprises a first microphone for detecting noise near a target position where noise is to be reduced, and a first microphone for detecting noise near the target position. A first phase and amplitude adjuster for adjusting the phase and amplitude of a signal from the first microphone, a second microphone provided near a secondary sound source disposed on the front side door, and the second microphone A second phase and amplitude adjuster for adjusting the phase and amplitude of the signal from the first and second amplifiers, and a power amplifier for amplifying the power of the signal obtained by adding the signals of the first and second phase amplitude adjusters. The output from this power amplifier is radiated from the secondary sound source as secondary sound that interferes with the noise in the cabin, increasing the amount of reduction in the target silencing band and increasing noise Noise can be reduced in the frequency band

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS According to the first aspect of the present invention, there is provided a first microphone for detecting noise near a target position whose noise is to be reduced, and a signal from the first microphone. A first phase / amplitude adjuster for adjusting the phase and amplitude of the signal, a second microphone provided near a secondary sound source disposed on the front door, and a phase of a signal from the second microphone. A second phase amplitude adjuster for adjusting the amplitude; and a power amplifier for performing power amplification of a signal obtained by adding signals of the first phase amplitude adjuster and the second phase amplitude adjuster. Output from the secondary sound source as secondary sound that interferes with vehicle interior noise, thereby reducing noise in the target silencing band and generating noise at frequencies above and below the silencing band. And reduce the adverse effects of increased noise It is having an effect.

According to a second aspect of the present invention, in the first aspect, a first feedback from the first microphone to the power amplifier and the secondary sound source through the first phase and amplitude adjuster is provided. The phase and amplitude are adjusted by the first phase and amplitude adjuster using the vicinity of the frequency at which the phase characteristic in the open loop characteristic of the loop is in the opposite phase as the noise reduction band, and
The frequency at which the phase characteristic of the open loop characteristic of the second feedback loop from the microphone through the second phase amplitude adjuster to the power amplifier and the secondary sound source is opposite to that of the first open loop characteristic is 45. The phase and the amplitude are adjusted by the second phase amplitude adjuster so that the frequency becomes higher than the noise reduction band in the range of ° to -45 °. Among the bands in which the noise generated above and below the silencing band increases, there is an effect of reducing the noise increase in the frequency band above the silencing band, which is a problem in hearing.

Hereinafter, embodiments of the present invention will be described. (Embodiment 1) FIG. 1 is a block diagram of a vehicle interior noise reduction apparatus according to Embodiment 1 of the present invention.

In FIG. 1, reference numeral 101 denotes a speaker as a secondary sound source arranged at a front door of a vehicle.
Reference numeral 2 denotes a first microphone disposed near a target position for reducing noise and detects noise in the vehicle cabin, and reference numeral 103 denotes a second microphone disposed near the secondary sound source 101. 1
04 is a first microphone for adjusting the phase and amplitude of the signal of the first microphone.
105 is a second phase and amplitude adjuster for adjusting the phase and amplitude of the signal of the second microphone,
106 power-amplifies the signal to which the outputs of the first phase amplitude adjuster 104 and the second phase amplitude adjuster 105 are added,
The power amplifier drives the secondary sound source 101.

FIG. 2 is a schematic diagram for explaining the principle of silencing.
201 is a speaker, 202 is a power amplifier, 203 is a microphone, 204 is original noise, 205 is noise after noise reduction, 2
06 indicates an open loop transfer function.

FIG. 3 shows a first microphone 102 and a secondary sound source 10 in the first embodiment of the vehicle interior noise reduction device of the present invention.
1A shows an open-loop characteristic between the first and second phase control circuits, wherein FIG.
Is the open loop characteristic when there is no
Is the open loop characteristic when the microphone 103 is not connected and the first phase and amplitude adjuster 104 is provided, and (c)
Indicates an open loop characteristic when the second microphone 103 is connected and the first phase and amplitude adjuster 104 is provided.

FIG. 4 shows a second embodiment in which the first microphone 102 is not provided in the first embodiment of the vehicle interior noise reduction apparatus of the present invention.
(A) is an open loop characteristic when there is no second phase amplitude adjuster 105, and (b) is an open loop characteristic between the microphone 103 and the secondary sound source 101. This shows the open loop characteristics when is connected.

FIG. 5 is a characteristic diagram showing a reduction in vehicle interior noise in the first embodiment of the vehicle interior noise reduction device according to the present invention. Reference numeral 501 denotes a characteristic of noise before noise reduction is performed.
02 indicates the characteristic of the vehicle interior noise when the second microphone 103 is not connected, and 503 indicates the characteristic of the vehicle interior noise when the second microphone 103 is connected.

Next, the operation of the first embodiment of the present invention will be described below. First, the principle of silencing will be described with reference to FIG.

Speaker 201, amplifier 202, microphone 2
03 forms a feedback loop. In this configuration, when an external noise Vn occurs at the microphone position, this signal is amplified by the amplifier 202 and
1 radiates as sound waves. And this speaker 2
The sound radiated from 01 interferes with the original noise Vn and becomes Vm. If the open loop transfer characteristic of this system is F (s),

[0018]

(Equation 1)

## EQU1 ## That is, when the absolute value of 1-F (s) is larger than 1, the noise at the microphone position decreases. More specifically, when F (s) is represented by amplitude and phase,
Assuming that the amplitude is constant around 1, the phase is 90
The noise is reduced in the range of ° to 180 ° to -90 °, and conversely increases in the range of 45 ° to 0 ° to -45 °.

A system from the first microphone 102 to the power amplifier 106 and the secondary sound source 101 through the first phase and amplitude adjuster 104 forms a first feedback loop,
FIG. 3A shows an open-loop characteristic when the first phase and amplitude adjuster 104 is not provided. In this case, as described above, the noise decreases when the phase is in the range of 90 ° to 180 ° to −90 °, and the noise increases in the range of 45 ° to 0 ° to −45 °. The range in which the noise is reduced is indicated by 301 in FIG.
The range in which the noise increases is shown at 302. In this state, noise reduction and increase bands appear reciprocally, and increase in noise occurs even in a band with high auditory sensitivity, which is not practical.

For this reason, the high frequency is cut off by the first phase amplitude adjuster 104, and the phase of the open loop is adjusted to 108 ° at the frequency of the noise to be reduced.

FIG. 3B shows an open loop characteristic when the phase and amplitude adjuster 104 thus adjusted is connected. In FIG. 3B, the band in which the noise is reduced is 3
03, areas where noise increases are indicated by 304 and 305. In this case, only a region where the noise increases above and below the frequency of the target noise to be reduced occurs, and a band 304 where the noise increases below the band where the noise is reduced is a region where the sensitivity is low in the sense of hearing. So, it doesn't matter much,
Since the upper band 305 in which noise increases has high sensitivity in terms of hearing, it is necessary to minimize the amount of noise increase as much as possible.

FIG. 5 shows actual measured data of vehicle interior noise during actual running, which indicates reduction of vehicle interior noise in this case. Reference numeral 501 denotes the characteristic of the vehicle interior noise when the muffler is not operated, and reference numeral 502 denotes the characteristic of the vehicle interior noise when the muffler having the above configuration having the open-loop characteristic shown in FIG. It is. From this, it can be seen that the noise around 40 Hz decreases and the noise around 60 Hz increases.

On the other hand, from the second microphone 103 through the second phase and amplitude adjuster 105, the power amplifier 106 and the secondary sound source 1
01 also forms a second feedback loop, and the open-loop characteristics when the second phase and amplitude adjuster 105 is not provided are as shown in FIG. This is because the second microphone 103 is arranged near the secondary sound source 101, and thus has a characteristic substantially reflecting the acceleration characteristic of the secondary sound source 101. FIG. 4B shows a state in which the second phase amplitude adjuster 105 is connected to cut off high frequencies,
5 shows an open loop characteristic after adjusting the amplitude.

FIG. 4C shows the open-loop characteristics of the first feedback loop including the second feedback loop having the open-loop characteristics shown in FIG. 4B.
Shown in In this case, it can be seen that the gain at 60 Hz is lower than that in FIG. Decreasing the gain at 60 Hz in this manner means that the noise at 60 Hz is increased in the vehicle interior noise characteristic indicated by 502 in FIG. 5, but the increase is reduced. Also 40H
It is considered that the gain is slightly reduced even in the band where noise is reduced in the vicinity of z, and the amount of noise reduction is considered to be reduced. However, as indicated by 503 in the measured data in FIG. Noise increase is reduced to 40Hz
The amount of noise reduction is increasing.

The reason for this is that the position of the second microphone 103 is near the secondary sound source disposed on the front side door, where the vibration from the front wheels of the car is transmitted to the vehicle body. In other words, it can be considered as a place close to the noise source of vehicle interior noise.

The noise is input not only to the first microphone 102 but also to the second microphone 103, and the second feedback loop causes the second feedback loop to output a second noise close to the noise source of the vehicle interior noise. It is considered that the noise near the microphone 103 has also been reduced, and the reduction in noise near 40 Hz has increased due to the synergistic effect of the reduction in noise near the noise source and the reduction in noise due to the first feedback loop. Conceivable.

(Embodiment 2) Next, Embodiment 2 will be described.

The structure of the second embodiment is the same as that of the first embodiment, but the second structure shown in FIG.
Is used. In FIG. 6A, reference numeral 601 denotes an operational amplifier, 602 denotes a resistor, and 603 denotes a capacitor. The resistor 602 and the capacitor 603 constitute a low-pass filter. FIG. 6B shows the frequency characteristics. FIG. 7 shows the second phase and amplitude adjuster 105.
6 shows an open-loop characteristic from the second microphone 103 to the secondary sound source 101 when the configuration shown in FIG. 6 is used.

Next, the operation will be described. In FIG.
A system from the first microphone 102 to the power amplifier 106 and the secondary sound source 101 through the first phase amplitude adjuster 104 forms a feedback loop, and the open loop characteristic is as shown in FIG. .

In this case, the phase is 90 ° to 180 ° to -9.
The noise is reduced in the range of 0 ° and is set as a noise reduction band. However, the noise increases in the range of 45 ° to 0 ° to -45 °.

The region where the noise increases is shown in FIG.
305. In particular, in the region 305 above the noise reduction band in which noise increases, the sensitivity to hearing is high, so that the effect of the increase in noise is large.

In order to reduce the increase in noise in the area 305 in FIG. 3B, the secondary sound source 101 installed on the front side in FIG. 1 and the second sound source 101 arranged near the secondary sound source 101 are shown. The signals from the microphone 103 and the second microphone 103 are phase-
The open-loop characteristic in the configuration of the second phase amplitude adjuster 105 for adjusting the amplitude and the power amplifier 106 is to reduce the noise near the secondary sound source 101 installed in the front side of FIG. A first microphone 102 placed at a target position, a first phase and amplitude adjuster 104 for adjusting the phase and amplitude of a signal from the first microphone 102, and a power amplifier 10
In the configuration of No. 6, the frequency is set in the range of 45 ° to 0 ° to −45 ° of the phase characteristic in the open loop characteristic and higher than the frequency of the noise to be reduced.

By doing so, the secondary sound source 101 installed on the front side of FIG. 1, the second microphone 103 arranged near the secondary sound source 101, and the signal from the second microphone 103 are adjusted for phase and amplitude. A second phase and amplitude adjuster 105,
A secondary sound source 101 installed on the front side of FIG. 1 including a loop due to the configuration of the power amplifier 106, a first microphone 102 located at a target position for reducing noise near the driver's seat, and a first microphone 102 The first to adjust the phase and amplitude of the signal
In the open loop characteristics in the configuration of the phase amplitude adjuster 104 and the power amplifier 106, the gain in the region where the noise increases in the region higher than the frequency of the noise to be reduced is reduced as shown in FIG. In the noise increase area, the noise reduction amount in the frequency area remains unchanged.
In particular, it is possible to reduce the amount of increase in noise in a high frequency region that has a significant effect.

[0035]

As described above, according to the present invention, the noise reduction band is set by the feedback loop between the first microphone arranged at the target position for reducing noise and the secondary sound source arranged at the front side of the car. The second feedback loop between the second microphone located near the secondary sound source located on the front side of the car and the secondary sound source keeps the noise reduction in the frequency band above and below the sound deadening band. The amount of noise increase in the band where the noise generated at the frequency increases is reduced, and the noise reduction with high performance can be realized comprehensively.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a vehicle interior noise reduction device according to a first embodiment of the present invention.

FIG. 2 is a schematic diagram showing the principle of silencing by the device.

FIG. 3A is an open-loop characteristic diagram when there is no phase amplitude adjuster 104 according to the device; FIG. 3B is an open-loop characteristic diagram when there is a phase amplitude adjuster 104 according to the device; FIG. Open loop characteristic diagram when there is an adjuster 104 and a microphone 103

FIG. 4A is an open loop characteristic diagram when the phase and amplitude adjuster 105 is not used by the device; FIG. 4B is an open loop characteristic diagram when the phase and amplitude adjuster 105 is used by the device; FIG. Characteristic diagram

FIG. 5 is a characteristic diagram showing the effect of reducing noise in the vehicle interior in the same device.

6A is a circuit configuration diagram of a phase amplitude adjuster 105 according to a second embodiment of the present invention. FIG. 6B is a characteristic diagram of the phase amplitude adjuster.

FIG. 7 shows a microphone 103 and a secondary sound source 101 in the device.
Open loop characteristic diagram between

[Explanation of symbols]

 Reference Signs List 101 Secondary sound source (speaker) 102 First microphone 103 Second microphone 104 First phase amplitude adjuster 105 Second phase amplitude adjuster 106 Power amplifier

Claims (2)

[Claims] 1. A first microphone for detecting noise near a target position where noise is to be reduced, and a first phase and amplitude adjuster for adjusting the phase and amplitude of a signal from the first microphone. A second microphone provided in the vicinity of a secondary sound source disposed on a front side door, a second phase and amplitude adjuster for adjusting the phase and amplitude of a signal from the second microphone, A power amplifier for amplifying the power of the signal obtained by adding the signals of the first phase amplitude adjuster and the second phase amplitude adjuster, and causing the output from the power amplifier to interfere with the noise in the passenger compartment from the secondary sound source A vehicle interior noise reduction device configured to radiate as a secondary sound and reduce noise in the vehicle interior. 2. The method according to claim 1, wherein the first feedback loop extending from the first microphone to the power amplifier and the secondary sound source through the first phase amplitude adjuster has a frequency near the frequency at which the phase characteristic of the open loop characteristic is reversed. Open-loop characteristics of a second feedback loop from the second microphone, through the second phase and amplitude adjuster, to the power amplifier and the secondary sound source, by adjusting the phase and amplitude by the first phase and amplitude adjuster as a reduction band. The phase of the first open-loop characteristic in the phase where the phase characteristic of the opposite phase is in the range of 45 ° to -45 ° and a frequency higher than the noise reduction band by the second phase amplitude adjuster, The vehicle interior noise reduction device according to claim 1, wherein the amplitude is adjusted.