JP5089447B2 - Noise canceling apparatus and method - Google Patents

Description

  The present invention relates to a noise canceling apparatus and method, and in particular, a signal corresponding to noise generated from a vehicle engine is input as a reference signal, and a combined signal of noise and canceling sound is input as an error signal. The present invention relates to a noise canceling apparatus and a method for generating a noise canceling signal so as to minimize the noise, inputting the signal to a speaker, and outputting a canceling sound from the speaker.

As a noise countermeasure, a method of reducing noise by radiating noise cancellation sound that is out of phase with the noise from the speaker (active control) has attracted attention and has been put into practical use in some indoor spaces such as factories, offices, and automobiles. Has been. This noise canceling method is called an ANC (Active Noise Control) method.
FIG. 5 is a block diagram of a conventional apparatus for realizing noise cancellation (see Patent Document 1), 11 is an engine that is a noise source, 12 is a rotation speed sensor that detects an engine speed R, and 13 is an engine speed R. The reference signal generator generates a sine wave signal having a constant amplitude and a constant amplitude as a reference signal x. When the noise source is an engine, noise generated by the engine speed has periodicity (periodic noise), and its frequency depends on the engine speed. For example, in the case of a four-cylinder engine, the periodic noise generated in the passenger compartment is dominated by the second harmonic of the engine speed, and the frequency of the noise generated in the passenger compartment during idling is 30 Hz and the rotational speed is 3600 rpm. The frequency of noise generated at the time of 120 is 120 Hz. The reference signal generation unit 13 stores sine wave data of the second harmonic in a ROM (not shown), reads out the data as necessary, and generates the reference signal x.

  Reference numeral 14 denotes a noise cancellation controller which receives a reference signal x generated from the reference signal generator 13 and also has a noise Sn and a cancellation sound Sc at a noise cancellation position (observation point, for example, near the driver's ear) in the passenger compartment. Is input as an error signal e, and adaptive signal processing is performed so that the power of the error signal is minimized to output a noise cancellation signal y. The noise cancellation controller 14 performs signal processing by convolving the propagation characteristic (transfer function) of the cancellation sound propagation system from the speaker to the noise cancellation point into the reference signal x, the adaptive signal processing unit 14a, the adaptive filter 14b having a digital filter configuration, and the reference signal x. A filter (filtered X signal creation filter) 14c for creating a reference signal r for use. 15 is a DA converter that converts the output signal (noise cancel signal y) of the adaptive filter 14b into an analog noise cancel signal, 16 is a low-pass filter LPF that removes high-frequency signals outside the cancel sound frequency band, and 17 is an amplifier for noise cancel signal. A power amplifier, 18 is a cancellation speaker that radiates a noise cancellation sound Sc, 19 is an error microphone that is arranged at a noise cancellation point, detects a synthesized sound of the noise Sn and the cancellation sound Sc, and outputs the synthesized sound signal as an error signal e , 20 is an amplifier that amplifies the error signal e, 21 is a low-pass filter that removes a noise signal outside the periodic noise band, and 22 is an AD converter that converts the low-pass filter output into digital.

  The adaptive signal processing unit 14a receives the error signal e at the noise cancellation point and the signal processing reference signal r input through the filter 14c, and uses these signals to cancel the noise at the noise cancellation point. To determine the coefficient of the adaptive filter 14b. For example, the adaptive signal processing unit 14a performs digital filter processing on the reference signal x according to a known LMS (Least Mean Square) adaptive algorithm, and outputs a noise cancellation signal y. The reference signal x must be a signal having a high correlation with the noise Sn to be deleted, and a sound having no correlation with the reference signal is not deleted.

  When the engine 11 rotates, its rotational speed R is detected by the rotational speed sensor 12, and the reference signal generator 13 generates a reference signal x having a frequency corresponding to the engine rotational speed R and inputs it to the noise cancellation controller 14. At this time, engine sound having periodicity (periodic noise) generated from the engine 11 propagates through the air having a noise propagation system having a predetermined transfer function, reaches a noise cancellation point, and becomes noise Sn. The error microphone 19 outputs an error signal e which is the difference between the noise Sn and the cancellation sound Sc, and the noise cancellation controller 14 outputs the noise cancellation signal y so that the power of the error signal e is minimized according to the LMS adaptive algorithm. .

The above is the case where the speaker is used only for noise cancellation, but it can also be shared with the audio speaker. FIG. 6 shows a conventional example in such a case, and the same parts as those in FIG. The difference is that an audio unit 51 that generates an audio signal and a synthesis unit 52 that synthesizes the audio signal and the noise cancellation signal are added.
Japanese Patent No. 3432845

  In the noise cancellation method of the above prior art, as indicated by the broken line 1 in FIG. 7, the gain characteristics may be less than or equal to a desired noise cancellation gain 3 at f0 to f1 and f2 to f3 within the ANC operating frequency range. The effect of a sufficient noise cancellation system cannot be obtained. Therefore, in order to obtain a sufficient noise canceling effect, it is considered to use speakers for two channels. However, the gain characteristics of a noise cancellation system using two channels of speakers may be as indicated by the one-dot chain line 2 in FIG. 7, and one channel is used in the frequency range indicated by the shaded portion 4 (f0 to f2 ′ in the figure). The gain characteristics are degraded when two channels are used. This is because the sound transfer characteristics are different from each speaker to the microphone, and cancel signals output from the speakers interfere with each other and cancel each other. In such a state, there is a problem that a sufficient noise canceling effect cannot be obtained even if a two-channel speaker is used.

An object of the present invention is to prevent a decrease in gain characteristics when using a two-channel speaker and to obtain a sufficient noise canceling effect.

  In the present invention, a signal corresponding to noise generated from a vehicle engine is input as a reference signal, and a combined signal of noise and cancellation sound is input as an error signal, so that the noise cancellation signal is minimized. Is a noise canceling apparatus and method for outputting a canceling sound from the speaker.

  The noise canceling method of the present invention includes a step of providing a two-channel speaker to which a noise canceling signal is input and measuring an acoustic transfer characteristic from the input side of the speaker to a noise cancellation point, and the acoustic transfer characteristic is equal to or less than a set gain. Determining a noise canceling frequency range or a vehicle engine speed range corresponding to the frequency range and storing the range in a memory; and determining whether the vehicle engine speed is within the speed range. If the step or the step of determining whether the noise frequency corresponding to the actual engine speed is in the frequency range is within the range, the polarity of the cancel signal input to one speaker is reversed. Inputting the inverted signal to the one speaker.

  The noise cancellation device of the present invention corresponds to a noise cancellation frequency range in which a gain characteristic is equal to or less than a set gain in a two-channel speaker and a sound transmission characteristic from the input side of the speaker to a noise cancellation point, or the frequency range. A storage unit for storing the engine speed range of the vehicle, a polarity inversion unit for inverting the polarity of the cancel signal input to at least one speaker, and whether the actual engine speed of the vehicle is within the speed range. Judgment is made, or it is judged whether the noise frequency corresponding to the actual engine speed is within the frequency range, and if it is within the range, the signal inverted by the polarity inversion unit is input to the one speaker. And a control unit for controlling to do so.

  According to the present invention, using a two-channel speaker, a noise cancellation frequency range or an engine speed range in which the gain characteristic of the acoustic transfer characteristic from the speaker to the noise cancellation point is equal to or less than the set gain is stored, Since the polarity of the noise cancellation signal of one channel is reversed and input to one speaker, the effect of the noise cancellation system by the two-channel speaker can be sufficiently obtained, and a predetermined level for canceling noise The noise cancellation signal can be obtained effectively.

(A) Outline of the Present Invention FIG. 1 is a schematic explanatory view of the present invention. GCP is a gain characteristic when the present invention is not applied, GCI is a gain characteristic according to the present invention, and Gs is a sufficient noise canceling effect. It is a necessary gain.

  Measure the gain characteristics (GCP) of the noise cancellation signal from the speaker input side to the noise cancellation point (for example, in the vicinity of the driver's ear) when the noise cancellation signal is input to the 2-channel speaker during quiet periods without noise. A frequency range (f0 to f2 ′ in the figure) in which the characteristic is equal to or less than a predetermined set gain Gs is obtained, and the engine speed range of the vehicle corresponding to the frequency range is stored. Then, it is determined whether the actual engine speed of the vehicle is within the engine speed range. If the engine speed is within the engine speed range, the polarity of the noise cancellation signal input to the speaker of one channel is determined. Invert. As a result, the acoustic transfer characteristics between the speaker input side and the noise cancellation point are as indicated by GCI in FIG. 1, and the gain is equal to or greater than the set gain Gs in the entire ANC operating frequency range. On the other hand, when the actual engine speed is not in the engine speed range (in the engine speed range corresponding to f2 ′ to f3 in the figure), the noise cancel signal is input to each speaker as it is. A noise cancellation signal is emitted from

(B) Embodiment FIG. 2 is a configuration diagram of an embodiment of the present invention.
The engine 23 is a noise source, the rotational speed sensor 24 detects the engine rotational speed R of the engine 23, and the reference signal generator 25 generates a constant amplitude sine wave signal having a frequency corresponding to the engine rotational speed R as a reference signal x. Occurs as. When the noise source is an engine, noise generated by the engine speed has periodicity (periodic noise), and its frequency depends on the engine speed. For example, in the case of a 4-cylinder engine, the periodic noise generated in the passenger compartment is dominated by the second harmonic of the engine speed, and the frequency of the noise generated in the passenger compartment during idling is 30 Hz and the rotational speed is 3600 rpm. The frequency of noise generated at the time of 120 is 120 Hz. The reference signal generator 25 stores second harmonic sine wave data in a ROM (not shown), reads out the data as necessary, and generates the reference signal x.

  The ANC unit 26 receives the reference signal x generated from the reference signal generation unit 25, and outputs a synthesized sound signal of noise and cancellation sound at the noise cancellation position (observation point, for example, near the driver's ear) in the passenger compartment. An error signal e is input, adaptive signal processing is performed so that the power of the error signal is minimized, and a noise cancellation signal y is output. The ANC unit 26 has the same configuration as that of the conventional example (the noise cancellation controller 14 in FIG. 5). That is, an adaptive signal processing unit, an adaptive filter having a digital filter configuration, and the reference signal x are generated by convolution of the propagation characteristic (transfer function) of the cancellation sound propagation system from the speaker to the noise cancellation point with the reference signal x. It has a filter to do. The ANC unit 26 also includes a DA converter that converts the output signal (noise cancellation signal) of the adaptive filter into an analog noise cancellation signal y.

The low pass filter (LPF) 27 removes a high frequency signal outside the ANC operating frequency band from the noise canceling sound signal.
The rotational speed range memory 28 measures the gain characteristic GCP from the speaker input side to the noise cancellation point (for example, near the driver's ear) when the noise cancellation signal is input to the two-channel speaker at a quiet time without noise. A frequency range (f0 to f2 ′ in the figure) that is equal to or less than the set gain Gs is obtained, and the engine speed range of the vehicle corresponding to the frequency range is stored. The inversion control unit 29 acquires the actual engine speed R from the speed sensor 24, determines whether the engine speed R is within the engine speed range stored in the frequency range memory 28, and the engine speed R is calculated as follows. When the engine speed is within the engine speed range, control is performed so that the noise cancel signal y ′ obtained by inverting the polarity of the noise cancel signal y output from the LPF 27 is output to one channel ch1, and the engine speed R is the engine speed. If it is not within the range, the noise cancellation signal y output from the LPF 27 is controlled to be output to the two channels ch1 and ch2. The inverting unit 30 inverts the polarity of the noise cancellation signal y output from the LPF 27 and inputs the inverted noise cancellation signal y ′ to the analog switch at the subsequent stage. The analog switch 31 outputs the noise cancellation signal y output from the LPF 27 to both channels ch1 and ch2 based on an instruction from the inversion control unit 29, or outputs the noise cancellation signal y output from the LPF 27 to one channel ch2. The output is switched to whether to output the noise cancellation signal y ′ whose polarity is inverted by the inverting unit 30 to another channel ch1. The power amplifiers 32a and 32b amplify the noise cancellation signal, and the speakers 33a and 33b receive the noise cancellation signal and emit noise cancellation sound.

  Next, the overall operation will be described. When the engine 23 rotates, the rotation sensor 24 detects the rotation number R, and inputs the rotation number R to the reference signal generation unit 25 and the inversion control unit 29. The reference signal generator 25 generates a reference signal x having a frequency corresponding to the input rotation speed R, and inputs the reference signal x to the ANC unit 26. The ANC unit 26 uses the reference signal x and the error signal e, which is the difference between the noise and the cancellation sound, to output the noise cancellation signal y so that the power of the error signal is minimized according to the LMS adaptive algorithm. The LPF 27 removes a high frequency signal outside the ANC operating frequency band of the noise cancellation signal y output from the ANC unit 26, and inputs the noise cancellation signal y to the inverting unit 30 and the analog switch 31. The inverting unit 30 inputs the noise cancellation signal y ′ obtained by inverting the polarity of the input noise cancellation signal y to the analog switch 31.

  The inversion control unit 29 determines whether or not the input actual engine speed R is within the speed range stored in the speed range memory 28. If the speed R is within the speed range, The analog switch 31 is controlled so that the noise cancel signal y is output to one channel ch2 and the noise cancel signal y ′ in which the polarity of the noise cancel signal is inverted is output to the other channel ch1 by the inverting unit 30. On the other hand, when the actual engine rotational speed R is not within the rotational speed range, the inversion control unit 29 controls the analog switch 31 so that the noise cancellation signal y is output to both channels ch1 and ch2. The analog switch 31 switches so as to output a signal based on the control of the inversion control unit 29, and outputs the signal to the power amplifiers 32a and 32b, respectively. The power amplifiers 32a and 32b amplify the input noise cancellation signals, respectively, and input the amplified noise cancellation signals to the two-channel speakers 33a and 33b. The speakers 33a and 33b receive the noise cancellation signals input from the power amplifiers 32a and 32b. A noise canceling sound is emitted based on the signal.

  As described above, the gain characteristic from the speaker input side to the noise cancellation point can be made the characteristic GCI shown in FIG. 1, and the noise (sound pressure level) of the speaker is canceled in the entire ANC operating frequency range. The sound pressure level can be exceeded.

(C) First Modification FIG. 3 is a block diagram of the first modification, and the same reference numerals are given to the same parts as those in the embodiment of FIG. The first modification is different from the embodiment in that the inversion signal is output using the inversion unit 30 in the embodiment, but the inversion unit is not used in the first modification. That is, in the first modification, the ANC unit 26 outputs the noise cancellation signal y ′ inverted from the noise cancellation signal y as a balance output and inputs it to the analog switch 31, and the inversion control unit 29 switches the analog switch 31 for control. To do.

  From the above, it is possible to obtain the same effect as in the first embodiment, and it is possible to set the sound pressure level of the speaker to be equal to or higher than the sound pressure level for canceling noise in the entire ANC operating frequency range. .

(D) Second Modification FIG. 4 is a configuration diagram of the second modification, and the same reference numerals are given to the same parts as those in the embodiment of FIG. The second modification differs from the embodiment in that an R-f converter 34 is provided and the rotation speed range memory 28 is changed to a frequency range memory 35. The Rf conversion unit 34 includes, for example, an Rf conversion table, calculates the frequency f of the noise cancellation signal corresponding to the noise at the rotation speed R using the table, and inputs the frequency f to the inversion control unit 29. . The frequency range memory 35 stores a frequency range (f0 to f2 ′) in which the gain characteristic is equal to or less than the set gain Gs as shown in FIG. The inversion control unit 29 determines whether the input frequency f is within a frequency range where the sound pressure level stored in the frequency range memory 35 is equal to or lower than a predetermined level 3, and the embodiment is based on the determination result. The analog switch 31 is controlled in the same manner as described above.

  As described above, the second modification can achieve the same effect as that of the embodiment, and the gain (sound pressure level) can be set to be equal to or higher than the sound pressure level for canceling noise in the entire ANC operating frequency range. It was.

  In the above, in the embodiment and the modification, only the case where the present invention is applied to the noise cancellation system using the speaker dedicated to noise cancellation has been described. However, the audio device and the noise cancellation device share the speaker as shown in FIG. Needless to say, the present invention can also be applied to a noise canceling system.

  As described above, according to the present invention, the gain characteristic from the speaker input side to the noise cancellation point when using a two-channel speaker is measured, and the frequency range or engine speed range where the gain characteristic is equal to or less than the set gain is stored. In this range, since the polarity of the noise cancellation signal is inverted and input to one speaker, the cancellation sound level of the noise cancellation system using the two-channel speaker can be increased to obtain a sufficient cancellation effect. It was.

It is a schematic explanatory drawing of this invention. It is a block diagram of an Example. It is a block diagram of a 1st modification. It is a block diagram of the 2nd modification. It is a block diagram of the conventional noise cancellation system. This is a noise cancellation system in which a conventional audio device and a noise cancellation device share a speaker. It is an acoustic transmission characteristic from a speaker to a noise cancellation point when a conventional noise cancellation system is used.

Explanation of symbols

GCP Conventional gain characteristics when using 2-channel speakers GCI Gain characteristics of the present invention 26 ANC section 28 Rotational speed range memory 29 Inversion control section 30 Inversion section 31 Analog switch 33a, 33b Speaker 34 Rf conversion section 35 Frequency Range memory

Claims (2)

A signal corresponding to the noise generated from the engine of the vehicle is input as a reference signal, and a combined signal of noise and cancellation sound is input as an error signal, and a noise cancellation signal is generated so that the error signal is minimized. In a noise canceling method of a noise canceling apparatus that inputs to a speaker and outputs a canceling sound from the speaker,
Provide a 2-channel speaker to which a noise cancellation signal is input,
Measure the acoustic transfer characteristics from the input side of the speaker to the noise cancellation point,
A noise canceling frequency range in which the acoustic transfer characteristic is equal to or less than a set gain, or a rotation speed range of a vehicle engine corresponding to the frequency range is obtained and the range is stored in a memory
Determining whether the rotational speed of the engine of the vehicle is within the rotational speed range, or determining whether a noise frequency corresponding to the actual engine rotational speed is within the frequency range;
If it is within this range, the polarity of the cancel signal input to one speaker is inverted and the inverted signal is input to the one speaker.
The noise cancellation method characterized by the above-mentioned. A signal corresponding to the noise generated from the engine of the vehicle is input as a reference signal, and a combined signal of noise and cancellation sound is input as an error signal, and a noise cancellation signal is generated so that the error signal is minimized. In a noise canceling device that inputs to a speaker and outputs a canceling sound from the speaker,
A two-channel speaker;
In a sound transfer characteristic from the input side of the speaker to a noise cancellation point, a storage unit that stores a noise cancellation frequency range in which a gain characteristic is equal to or less than a set gain, or a vehicle engine speed range corresponding to the frequency range;
A polarity inverting unit for inverting the polarity of the cancel signal input to at least one speaker;
When it is determined whether the actual engine speed of the vehicle is within the speed range, or whether the noise frequency corresponding to the actual engine speed is within the frequency range is within the range A control unit for controlling the signal inverted by the polarity inversion unit to be input to the one speaker;
A noise canceling device comprising:

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