JPH0727391B2 - Noise reduction device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a bandpass filter means or an engine speed means having a plurality of mutually different pass bands, and a frequency specified by the bandpass filter or the engine speed means. A noise reduction device having a delay means for delaying the phase of a noise wave, which can reduce noise by following changes in noise frequency.

[Industrial application field]

The present invention relates to a noise reduction device in a vehicle. Generally, as a noise reduction device in a vehicle, a muffler for suppressing noise, a noise insulating material, a sound absorbing material and the like are provided.

[Conventional technology]

FIG. 10 is a diagram for explaining a conventional noise reduction device. The configuration of this figure is shown below. Throughout the drawings, the same components are denoted by the same reference numerals or symbols. The noise reduction device in this figure includes a microphone 14, a delay unit 2 connected to the microphone 14, a power amplifier 18 connected to the delay unit 2, and a speaker 15 connected to the power amplifier 18.

Next, the operation of the noise reduction device will be described. Noise source points in Fig. 10
When the noise wave a is generated in Pa, the microphone 14 converts the noise wave a into an electric signal. The electric signal is delayed by the delay means 2. The delayed signal is power-amplified by the power amplifier 18 and converted into sound by the speaker 15. Speaker like this
A sound whose phase is shifted with respect to the noise wave a can be generated from 15. On the other hand, when the noise wave a generated at the noise source point Pa reaches the listening point Pb, the delay amount of the delay means 2 is adjusted,
If the noise wave b whose phase is inverted with respect to the noise wave a reaching the listening point Pb is radiated from the speaker and overlapped, the noise wave a cancels the noise wave a and noise can be reduced.

[Problems to be Solved by the Invention]

As a means to reduce the noise coming into the car,
Methods such as increasing the rigidity of the vehicle body and increasing the muffling performance of the muffler, which is the exhaust sound source, have been taken, but the weight of the vehicle body increases, resulting in reduced performance and a significant cost increase. Therefore, an economical noise reduction means is desired. The noise reduction device in FIG. 10 is economically excellent, but there are the following problems in reducing noise in the automobile.

In a car, low frequency noise is generated with exhaust noise as a noise source. This noise is caused by exhaust noise, that is, pressure fluctuation due to exhaust that is periodically pushed out by the explosion of the engine, and the frequency changes as the engine speed changes. This generation frequency is several tens to several hundreds Hz. Therefore, in the noise reduction device of FIG. 11, there is no problem if the frequency of the noise wave a is constant, but when the frequency of the noise wave a changes with the engine speed like noise in a car, the phase of the noise wave a is changed. This is a problem that it becomes difficult to form the inverted sound wave b.

Therefore, in view of the above problems, it is an object of the present invention to provide a noise reduction device that reduces noise in a vehicle whose frequency changes.

[Means for Solving the Problems]

FIG. 1 is a diagram showing a first principle configuration of the present invention. In the present invention, the first and second bandpass filter means 1, 1'have a plurality of mutually different pass bands, and separate the electric signal Sin obtained by converting the noise wave into a plurality of frequency bands. The delay means 2 is connected to each of the plurality of bandpass filter means 1 and delays the signals separated by the bandpass filter means. The amplifying means 4 adjusts the gain of each delayed signal. The adding means 3 adds the gain-adjusted signals and outputs a mute signal Sout. The averaging means 6 averages the outputs of the respective second band pass filter means 1 '. The gain control means 7 controls the gain of the amplification means 4 according to the output level of the averaging means 6. The first and second bandpass filter means 1, 1'may be the same. That is, the first bandpass filter means 1 (BPF
1, BPF2, ... BPFn) outputs are output by averaging means 6 (averaging means 1,
You may make it respectively input into each averaging means 2, ... Averaging means n).

FIG. 2 is a diagram showing a second principle configuration of the present invention. In the present invention, the delay means 2 variably delays the electric signal Sin obtained by converting the noise wave. The amplifying means 4 variably amplifies the delayed signal and outputs a muffling signal Sout. The bandpass filter means 1'has a plurality of different pass bands and separates the electric signal Sin into a plurality of frequency bands. The averaging means 6 averages the outputs of the respective bandpass filters 1 '. The maximum level band detecting means 8 detects and outputs the frequency band in which the output level of the averaging means 6 is maximum. The parameter memory means 9 is the maximum level band detection means 8
The delay constant and the gain constant, which are read out in accordance with the output from and are set in the delay means 2 and the amplification means 4, are stored.

FIG. 3 is a diagram showing a third principle configuration of the present invention. In the present invention, the delay means 2 variably delays the electric signal Sin obtained by converting the noise wave. The amplifying means 4 variably amplifies the delayed signal and outputs a muffling signal Sout. The engine speed detecting means 10 detects the engine speed by a crank angle sensor used for detecting ignition timing, for example,
Output. The parameter memory means 9 stores the delay constant and the gain constant which are read out corresponding to the output of the engine speed detecting means 10 corresponding to the engine speed and are set in the delay means 2 and the amplifying means 4, respectively. .

FIG. 4 is a diagram showing a fourth principle configuration of the present invention. In the figure, the engine speed detecting means 10 detects and outputs the engine speed by a crank angle sensor used for detecting ignition timing, for example. The signal generating means 11 generates a sine wave signal having a frequency corresponding to the detected engine speed output from the engine speed detecting means 10. The phase control means 12 controls the phase of the output signal from the signal generator 11 in accordance with the detected rotation speed. The amplitude control means 13 controls the amplitude of the output signal from the phase control means 12 in accordance with the rotation speed. The parameter means 9 stores the phase constant and the amplitude constant set in the phase control means 12 and the amplitude control means 13 which are read out corresponding to the detected rotation speed which is the output of the engine speed detection means 10.

In the invention shown in FIGS. 1 to 4, the microphone 14 is for converting a noise wave into an electric signal and is arranged in the trunk of an automobile. The speaker 15 converts the processed electric signal into sound and generates a sound wave, and is arranged in the passenger compartment.

[Action]

In FIG. 1, the input electric signal Sin passes through one of the second band pass filter means 1 ′ and is further averaged by the averaging means 6. The gain control means 7 controls the gain of the amplification means 4 in a stepwise increase or decrease according to the output of each averaging means 6, and, for example, the maximum one of the average values corresponds to the amplification means 4. The gain is controlled to a predetermined value and the others are controlled to 0. As a result, only the signal in the frequency band having the maximum amplitude of the input electric signal Sin passes through the first band-pass filter means 1, is delayed and amplified, and becomes a sound wave through the adding means 3. In this way, the gain of the amplifying means 4 is adjusted to remove the influence of the cutoff region of the first bandpass filter means 1 in the adjacent frequency band.

In FIG. 2, the input electric signal Sin is a variable delay means 2
Is delayed by the variable gain amplifying means 4 and is amplified by the variable gain amplifying means 4 to form a silenced signal Sout. On the other hand, the input electric signal Sin passes through the band-pass filter means 1 ', is averaged by the averaging means 6, and the maximum level band detecting means 8 selects the maximum level of the average values to determine the frequency of the input electric signal. The belt is specified. The specific frequency from the maximum level band detecting means 8 is output to the parameter memory means 9, and the delay amount and the gain amount corresponding to the specific frequency band are read from the parameter memory means 9 to the delay means 9 and the amplifying means 4. Is set.

In FIG. 3, the rotation speed detected by the engine rotation speed detecting means 10 is output to the parameter memory means 9, and the delay amount and gain amount corresponding to the engine rotation speed are read out from the parameter memory means 9 to obtain the delay means 9 and Amplifying means 4
Is set to. The fact that the engine speed is closely related to the frequency of the noise wave is used. The input electric signal Sin is delayed by the delay amount and the gain amount corresponding to the frequency,
It is amplified and becomes a sound wave elimination signal Sout.

In FIG. 4, a signal having a frequency corresponding to the engine speed detected by the engine speed detecting means 10 is generated by the signal generating means 11, and the phase constant and the amplification constant of the frequency corresponding to the engine speed are obtained from the parameter memory means 9. The generated signal is phase-controlled and amplitude-controlled by the phase control means 12 and the amplitude control means 13 that are read out and set, and then the signal of the sound wave disappears.
Become Sout.

In the inventions of FIGS. 1 to 4, howling can be prevented by separating the microphone 14 and the speaker 15.

EXAMPLES Examples of the present invention will be described in detail below with reference to the drawings. FIG. 5 is a diagram for explaining the noise reduction device according to the first embodiment of the present invention. In this figure, components different from those in FIG. 11 are an A / D converter 16 connected to the microphone 14, and a plurality of bandpass filter means 1 (BPF1, BPF2, BPF3, ..., Connected to the A / D converter 16). BPFn), a plurality of delaying means 2 connected to each of the bandpass filter means 1, a plurality of amplifying means 4'connected to each of the delaying means 2,
An adding means 3 connected to each of the amplifying means 4 ′, and a D / A converter 17 connected to the adding means 3 and a power amplifier 18. The components within the square frame in the figure, the bandpass filter means 1 in the other embodiments as well,
The delay means 2, the amplification means 4'and the addition means 3 are DSP (Dig
Ital signal processor) is used to speed up and reduce the size of the noise reduction device.

Next, the operation of the noise reduction device according to the first embodiment will be described. The electric analog signal of the microphone 14 which has received the noise wave a is converted into a digital signal Sin by the A / D converter 16 and supplied to the processing of the DSP. The digital signal Sin is separated into a plurality of frequency band signals by the plurality of band pass filter means 1. Each of the separated signals is individually delayed by each of the delaying means 2, each of the delayed signals is separately amplified by each of the amplifying means 4 ′, and each of the amplified signals is added by the adder 3. Next, the added signal Sout is converted to an analog signal by the D / A converter 17, power-amplified by the power amplifier 18, and becomes a sound wave b emitted from the speaker 15. The sound wave b is erased by overlapping with the noise wave a at the listening point Pb. The delay amount t ₁ , t ₂ ,
t _3, ..., t _n, the gain G _1, G _2, G ₃ for each amplifying means, ..., G _n is
It is determined that the simulated noise wave is used at the noise source point Pa, and the simulated noise wave is eliminated by the sound deadening at the listening point. Therefore, even if the frequency of the noise wave a changes, the delay amount that is sufficiently appropriate to eliminate the noise wave a in any of a plurality of frequency bands.
A sound wave b having ti and a gain amount Ai can be formed.

FIG. 6 is a diagram for explaining the noise reduction device according to the second embodiment. In this figure, the components different from those in FIG. 5 are the amplifying means 4 ″ for mixing provided between the amplifying means 4 ′ and the adding means 3 and separating the digital signal Sin into a plurality of frequency bands. A plurality of bandpass filter means 1 '
(KBPF1, KBPF2, KBPF3, ..., KBPFn), a plurality of averaging means 6 connected to each of the bandpass filter means 1 ′, for example, an absolute value converting means ABS and LPF and each of the averaging means 6. And a mixing control means 7 connected to the amplifying means so as to adjust the gain.

A plurality of band pass filter means 1 '(KBPF1, KBPF2,
KBPF3, ..., KBPFn) are multiple bandpass filter means 1
(BPF1, BPF2, BPF3, ..., BPFn) have the same center frequency but different Q (sharpness), the bandpass filter means 1 has a low Q, and the bandpass filter means 1 ′ has a Q value.
Is set high.

Next, the operation of the noise reduction device of the second embodiment will be described. The digital signal Sin is clearly separated into a plurality of frequency band signals by a plurality of bandpass filter means 1'having a high Q. Each of the separated signals is converted into an averaged voice level by converting the positive and negative voice signals into absolute values by the averaging means 6 and output to the mix control means 7. The mix control means 7 selects, for example, a frequency band having the maximum sound level from the voice level of each frequency band, sets the gain of one amplification means 4'corresponding to this frequency band to G'imax = 1, and the other amplification. The gain G'i (i ≠ imax) of the means 4'is set to 0 to control the mix of the audio signal in each frequency band. In order to simplify the control, in the present embodiment, the variable amplifying means 4 is constituted by the fixed amplifying means 4'and the amplifying means 4 "whose coefficient is switched stepwise between 1 and 0. The variable amplifying means 4 whose coefficient can be switched stepwise between 0 and 0. In the present embodiment, the technique for controlling the mixing of audio signals in each frequency band is adopted in the adjacent frequency band. The signal passing through the cutoff region of the bandpass filter means 1 of
This is to prevent the original signal from being deformed by being superposed on each other. Therefore, the signal of the bandpass filter means 1 in the frequency band of the maximum level is passed, the signals in the other frequency bands are blocked, and the influence due to the passage of the cutoff region is removed. The output of the bandpass filter 1 may be connected to the averaging means 6 instead of the bandpass filter 1 ', that is, the bandpass filter 1 and the bandpass filter 1'may be the same, but preferably the present embodiment is used. It is better to separate and make Q different as in the example.

FIG. 7 is a diagram for explaining a noise reduction device which is a third embodiment of the present invention. In this figure, constituent elements different from those in FIG. 6 are a plurality of band pass filter means 1, a plurality of delay means 2, a plurality of amplification means 4 and 4'and an addition means 3.
Of the maximum level band detecting means 8 connected to the amplifying means 4 connected to the delay means 2 and further connected to the D / A converter 17, the averaging means 6, and the maximum level. Parameter memory means 9 for storing constants read by the output from the band detection means 8 and set in the delay means 2 and the amplification means 4.

Next, the operation of the noise reduction device of the third embodiment will be described. The digital signal Sin is separated into each frequency band by the bandpass filter means 1 ′ and further averaged by the averaging means 6. The maximum level band detection means 8 detects the averaged signal having the maximum level from the plurality of averaged signals, and outputs the frequency band for this signal.
Since the parameter memory means 9 stores a set of delay constants and gain constants (ti, Gi; i = 1, ..., N) corresponding to the frequency band of each bandpass filter means 1 ',
The constant level set corresponding to this output is read out by the output from the band detecting means 8 at the maximum level and set in the delay means 2 and the amplifying means 4, respectively. Even if the frequency of the digital signal Sin changes, the delay unit 2 and the amplifying unit 4 having the constants set in this way can delay and amplify the digital signal corresponding to the frequency. Therefore, compared to the second embodiment, the present embodiment reduces the number of parts such as the bandpass filter means by providing the parameter memory means 9 and similar effects can be obtained.

FIG. 8 is a diagram for explaining a noise reduction device which is the fourth embodiment of the present invention. In this figure, the components different from those in FIG. 7 are an engine speed detecting means 10 in place of the bandpass filter means 1 ', the averaging means 6 and the maximum level band detecting means 8. A constant corresponding to the engine speed is read from the parameter means 9 by the detected speed output from the engine speed detecting means 10 and set in the delay means 2 and the amplifying means 4. As the engine speed detecting means 10, for example, a crank angle sensor for detecting ignition timing is used. The description of the operation of the noise reduction device of the fourth embodiment, that is, the operation of generating the sound wave canceling b, is omitted because it is redundant with the above description. Compared to the third embodiment, the present embodiment is provided with the engine speed detecting means that utilizes the close relationship between the engine speed and the frequency of the noise wave a as described above. Similar effects can be obtained by reducing the number of parts such as'.

FIG. 9 is a diagram for explaining a noise reduction device which is a fifth embodiment of the present invention. In this figure, the components different from those in FIG. 8 are those in which the microphone 14 and the A / D converter 16 are removed, and the signal generator 11; the phase controller 12 connected to the signal generator 11 and the phase controller 12 Is an amplitude control unit 13 connected to the D / A converter 17 and to the D / A converter 17. The parameter memory means 9 stores constants of the phase controller 12 and the amplitude controller 13 corresponding to the engine speed.

Next, the operation of the noise reduction apparatus of the fifth embodiment will be described. This embodiment utilizes the fact that the engine speed and the frequency of the noise wave a are more closely related to each other than in the fourth embodiment. In the signal generator 11, the engine speed detection means 10
For example, a sine wave having a frequency corresponding to the detected rotation speed, which is the output of, is generated. The time reference of this sine wave is obtained, for example, by detecting the ignition timing of the crank angle sensor. From the parameter memory means 9 to the phase control section 12 and the amplitude control section 13 corresponding to the detected rotation speed which is the output of the engine rotation speed detection means 10.
The phase constant and amplitude constant are output to. Therefore, the phase control unit 12 delays the sine wave generated by the signal generation unit in accordance with the engine speed, and then the amplitude control unit 13 changes the amplitude in accordance with the engine speed to output the output signal Sout.
Is generated. The operation of generating the quenching wave b is the same as described above. Compared to the fourth embodiment, the noise wave a according to the detected rotation speed of the engine rotation speed detection means 10 is different in this embodiment.
Since the signal to be silenced is generated, it is possible to reduce the parts such as the microphone and the like, and it is not necessary to consider the influence of howling by the microphone.

Next, a noise reduction device which is a sixth embodiment will be described. The microphone 14 according to the first to fourth embodiments is arranged in the trunk room of the automobile, and the microphone 14
The speaker 15 that processes the noise wave a added to the and emits the sound wave b is placed in the passenger compartment. If the microphone 14 and the speaker 15 are installed in the same room, sound is apt to circulate and howling is likely to occur. For this reason, the microphone 14 is arranged in the trunk room and is provided at a position farther from the speaker 15. Such an arrangement of the microphone 14 is preferable because it is located near the muffler that generates the exhaust noise, which is the noise source a.

〔The invention's effect〕

As described above in detail, according to the present invention, the frequency at which the noise wave changes is specified by the bandpass means or the engine speed detection means having a plurality of mutually different pass bands, and further the specified frequency is specified by the delay means. Since it becomes possible to form a sound wave that inverts the phase of the noise wave, the noise can be reduced by following the change in the noise frequency.

[Brief description of drawings]

FIG. 1 is a first principle configuration diagram of the present invention, FIG. 2 is a second principle configuration diagram of the present invention, FIG. 3 is a third principle configuration diagram of the present invention, and FIG. 4 is a block diagram showing the principle of No. 4, FIG. 5 is a diagram for explaining a noise reduction device according to the first embodiment of the present invention, and FIG. 6 is a diagram for explaining a noise reduction device according to the second embodiment of the present invention. FIG. 7 is a diagram for explaining a noise reduction device which is the third embodiment of the present invention, FIG. 8 is a diagram for explaining a noise reduction device which is the fourth embodiment of the present invention, and FIG. 9 is the present invention. FIG. 10 is a diagram for explaining a noise reducing device as a fifth embodiment of the present invention, and FIG. 10 is a diagram for explaining a conventional noise reducing device. In the figure, 1,1 '... bandpass filter means, 2 ... delay means,
3 ... Addition means, 4, 4 '... Amplification means, 6 ... Average means, 7 ... Gain control means, 8 ... Maximum level band detection means, 9 ... Parameter memory means, 10 ... Engine rotation Number detecting means, 11 ... Signal generating section, 12 ... Phase controlling means, 13 ... Amplitude controlling means.

Claims (5)

[Claims] 1. A noise reduction device for silencing a noise wave by superimposing a sound wave of which the phase of the noise wave is shifted, into a plurality of frequency bands so as to separate the electrical signal (Sin) of the noise wave into a plurality of frequency bands. First band pass filter means (1) having mutually different pass bands, a plurality of delay means (2) for delaying each of the separated signals, and a plurality of gain adjusting means for each of the delayed signals. Amplifying means (4) and the gain-adjusted signals are added to each other, and a mute signal (Sout) is added.
And a second bandpass filter means (1 ') having a plurality of mutually different pass bands so as to separate the electric signal (Sin) into a plurality of frequency bands, and Of the plurality of averaging means (6) for averaging the outputs of the second band pass filter means (1 ') and of the plurality of amplifying means (4) according to the output level of each of the plurality of averaging means (6). A noise reduction device comprising: a gain control means (7) for controlling a gain. 2. A noise reduction device for silencing a noise wave by superimposing the noise wave with the phase of the noise wave shifted, with a delay means (2) for variably delaying the electrical signal (Sin) of the noise wave. , The delayed signal is variably amplified to generate a mute signal (Sou
amplification means (4) for outputting t), bandpass filter means (1 ') having a plurality of mutually different pass bands so as to separate the electric signal (Sin) into a plurality of frequency bands, and each of the bands A plurality of averaging means (6) for averaging the output of the pass filter (1 '), and a maximum level band detecting means for detecting and outputting a frequency band where the output level of the plurality of averaging means (6) is maximum ( 8) and parameters for respectively storing the delay constant and the gain constant which are read out in correspondence with the output from the band detecting means (8) of the maximum level and are set in the delay means (2) and the amplifying means (4). A noise reduction device comprising a memory means (9). 3. A noise reduction device for muting a noise wave by superimposing the noise wave with the phase of the noise wave shifted, with a delay means (2) for variably delaying the electrical signal (Sin) of the noise wave. , The delayed signal is variably amplified to generate a mute signal (Sou
amplification means (4) for outputting t), engine speed detection means (10), and the output means of the engine speed detection means (10), which are successively output corresponding to the detected rotation speed of the engine, and the delay means. (2) and parameter memory means (9) for storing the delay constant and gain constant set in the amplifying means (4), respectively, are provided. 4. A noise reduction device for silencing a noise wave by superimposing a sound wave having a phase of the noise wave shifted, and an engine speed detecting means (10) and an output of the engine speed detecting means (10). And a signal generation means (11) for generating a signal of a frequency corresponding to the detected rotation speed of the engine, and a phase control for controlling the phase of the output signal from the signal generation means (11) in accordance with the detected rotation speed. Means (12), amplitude control means (13) for controlling the amplitude of the output signal from the phase control means (12) in accordance with the rotation speed, and output of the engine rotation speed detection means (10). The phase control means (12) is read out corresponding to the detected rotation speed.
And a parameter memory means (9) for storing the phase constant and amplitude constant set in the amplitude control means (13). 5. A noise comprising at least a microphone (14) for converting a noise wave of an automobile into an electric signal and a speaker (15) for delaying the electric signal to generate a sound wave extinguishing the phase of the noise wave. The noise reduction device according to any one of claims 1, 2, 3 or 4, wherein the microphone (14) is arranged in a trunk of an automobile and the speaker (15) is arranged in the passenger compartment.