JP2935592B2 - Noise control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a noise control device for canceling noise by outputting a signal having the same sound pressure in opposite phase to noise from a speaker, and more particularly to an adaptive noise control device used in a noise control device. It is an object of the present invention to enable a filtering unit to easily follow a steep change in a noise cycle.

[0002]

2. Description of the Related Art Passive silencers such as mufflers have conventionally been used to reduce noise generated from an internal combustion engine or the like, but improvements have been made in terms of size and silencing characteristics. On the other hand, conventionally, an active noise control device has been proposed in which a compensating sound having the opposite phase and the same sound pressure as the noise generated from a sound source is output from a speaker to cancel the noise.

[0003] Incidentally, the frequency characteristics or stability of the active noise control device itself is not sufficient, and its practical use has been delayed. In recent years, a signal processing technique using a digital circuit has been developed and the frequency range that can be handled has been expanded, and as a result, a number of practical noise control devices have been proposed (for example, JP-A-63-311396).

[0004] This is because noise is detected by a noise source microphone installed upstream of the duct, and a signal of opposite phase and equal sound pressure to the noise is output from a speaker installed downstream of the duct by a signal processing circuit. Is a so-called 2-microphone / 1-speaker type active noise control device that combines a feedback system that detects and feeds back with a microphone for a silencing point and feeds back.

On the other hand, in order to obtain a noise-reducing effect in a space where the noise source is unclear, for example, in the interior of a car, one microphone 1 uses only a feedback system that does not require the installation of a microphone in the noise source. It is necessary to use a speaker configuration device.

[0006]

However, in an active noise control device composed of one microphone and one loudspeaker having only a feedback system, a disadvantage of the feedback system is that the noise period of the noise source changes sharply. Since the delay is at least as long as the sound wave transmission characteristic from the speaker to the microphone, there is a problem that the noise reduction effect is reduced.

Accordingly, the present invention has been made in view of the above problems,
An object of the present invention is to provide a noise cycle control device capable of following a steep change in a noise cycle.

[0008]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides an electric signal / sound wave converter for outputting a compensated sound wave to a space to be silenced in order to eliminate noise from a noise source. A first adaptive filtering and transfer characteristic simulation in a noise control device having a sound-to-electric signal converter for converting a residual sound of noise eliminated by the compensation sound wave from the electric signal-to-sonic wave converter into an electric signal. Means, difference signal calculating means,
A signal generator, a second adaptive filtering means and an adding means are provided.

The first adaptive filtering means controls a filter coefficient on the basis of the signal of the sound wave / electric signal converter to form a compensation signal for eliminating the stationary noise to the electric signal / sound wave converter. The transfer characteristic simulating means simulates the transfer characteristics of the electric signal / sound wave converter, the sound wave / electric signal converter, and the sound wave in the space to be silenced.

The difference signal calculating means calculates a difference signal between the output of the sound wave / electric signal converter and the transfer characteristic simulating means, and supplies the calculated difference signal to the adaptive filtering means. The signal generator is
A constant waveform signal is generated based on a timing signal related to a noise generation cycle of the noise generation source 1. The second adaptive filtering means receives the signal, and controls the filter coefficient based on the signal of the sound wave-to-electrical signal converter to compensate the fluctuating noise to the electric signal-to-sound wave converter. To form

The adding means adds the output of the first adaptive filtering means and the output of the second adaptive filtering means, and outputs the added signal to the electric signal / sound wave converter and the transfer characteristic simulating means. I do.

[0012]

According to the noise control device of the present invention, in a steady state in which the noise period of the noise source is substantially constant, the noise in the muffler, which is the target space for noise reduction, is opposite in phase from the electric signal / sound wave converter. The sound is eliminated by the sound wave having the same sound pressure, and the residual sound is detected by the sound wave-to-electric signal converter and input to the coefficient updating unit of the first adaptive filtering means 4, and the input signal is minimized by the least square method. The filter coefficient is set. The signal from the sound wave-to-electric signal converter is inverted from the signal from the transfer characteristic simulating means and added by the difference signal calculating means to form a reproduced signal. This reproduced signal is input to the first adaptive filtering means. It becomes a signal and forms a correction signal to the electric signal / sonic wave converter.

On the other hand, when the noise period fluctuates, the first adaptive filtering means causes a transmission delay due to feedback. However, the signal generation means uses a timing signal related to the noise generation cycle of the noise source to generate the fundamental frequency. , A signal of the harmonic is formed, inputted to the second adaptive filtering means, the filter coefficient is adjusted based on the residual sound of the sound wave / electric signal converter, and a compensation signal is outputted to the electric signal / sound wave converter. As a result, the transmission delay is reduced, and the noise reduction effect is improved even in the case of fluctuation.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram illustrating a noise control device according to an embodiment of the present invention. The configuration of this drawing will be described. FIG. 1 shows a speaker 2 attached to a muffler to which noise from a noise source 1 such as an automobile engine or a motor arrives via an exhaust pipe to eliminate noise, and an amplifier 201 connected to the speaker 2. And a digital circuit connected to the amplifier 201.
An analog converter (D / A) 202; a microphone 3 for converting the noise from the noise source 1 with a sound wave from the speaker 2 to convert a residual sound of the noise into an electric signal; and a connection to the microphone 3 Amplifier 301 to be implemented and the amplifier 30
Analog-to-digital converter (A / D) connected to 1
02 and a signal from the difference signal calculating means 6 described later,
Based on the signal from the A / D converter 302, the speaker 2
To form a compensation signal for canceling stationary noise
, The speaker 2, the microphone 3, and the sound transmission characteristics (H
Transfer characteristic simulating means 5 for simulating ( _SPMIC ), difference signal calculating means 6 for calculating a difference signal between the output of the microphone 3 and the transfer characteristic simulating means 5 and supplying the difference signal to the first adaptive filtering means 4. A signal for generating a sine wave as a fundamental wave or a harmonic signal thereof based on a rotation timing signal obtained from, for example, an engine speed detector of the noise generating source 1 or an ignition timing control device, or an ignition timing signal. A signal from the signal generator 7 is input to the speaker 2 based on a signal from the microphone 3.
A second adaptive filtering means 8 for forming a compensation signal for eliminating fluctuating noise, an output of the first adaptive filtering means 4 and an output of the second adaptive filtering means 8, and And an adder for outputting an addition signal to the speaker and the transfer characteristic simulator.

Here, the first and second adaptive filtering means (4, 8), the transfer characteristic simulating means 5, the difference signal calculating means 6, the signal generating section 7, and the adding means 9 are composed of a DSP (Digital S
Ignal Processor). FIG. 2 is a diagram showing the configuration of the adaptive filtering means of FIG. Specifically, the adaptive filtering means 4 and 8 in the figure are composed of a series of delay units 101 for delaying a sampling period, a plurality of multipliers 102 connected to each of the delay units, A plurality of adders 103 for adding the outputs; and each of the multipliers 10 so that the output of the A / D converter 302 is minimized by the least square method.
2 includes a coefficient updating unit 104 for controlling the multiplication coefficient. The transfer function of the transfer characteristic simulating means 5 is equalized at the initial stage.

Next, the operation will be described. When the engine, which is the noise generation source 1, is rotating at a constant speed in a steady state, a compensating sound wave having an equal sound pressure in a phase opposite to that of the noise is output from the speaker 2 to the muffler target space. 3 converts the residual sound that is not eliminated into an electric signal,
The signal is input to the coefficient updating unit of the first adaptive filtering means 4 via the A / D converter 302 and 301. In this coefficient updating section, the multiplier coefficient of the multiplier of the non-recursive filter (FIR) constituting the first adaptive filtering means 4 is modified so that the input signal is minimized by the least square method, and the first adaptive The input signal of the type filtering means 4 is adjusted,
The compensation signal is output to the speaker 2 via the adding means 9, the D / A converter 202, and the amplifier 201.
This compensation signal is shaped through the transfer characteristic simulating means 5, inverted in the difference signal calculating means 6, added with the residual signal from the microphone 3 to form a reproduced signal, and fed back to the input of the first adaptive filtering means 4. I do. As described above, in the steady state, the fundamental frequency of the noise generated in the noise source 1 and its harmonic noise generated in the exhaust pipe, the muffler, etc. are eliminated by the feedback system centering on the first adaptive filtering means 4. You.

In a fluctuating state where the engine speed of the noise generating source 1 suddenly rises or falls (during racing), a transfer system is simulated in a feedback system centering on the first adaptive filtering means 4. There is a delay corresponding to the transfer characteristic H _SPMIC of the means 5, and the _noise reduction effect is reduced. In this fluctuating state, a sine wave signal is generated in the sine wave generator 7 by the timing signal of the noise generation source 1 and input to the second adaptive filtering means 8 where the compensation signal is added to the adding means 9 and the D / A conversion. The signal is output to the speaker 2 via the amplifier 202 and the amplifier 201. The residual sound from the microphone 3 is input to the coefficient updating unit of the second adaptive filtering means 8 via the amplifier 301 and the A / D converter 302.
In this coefficient updating unit, similarly to the above, the multiplication coefficient is corrected so that the input signal is minimized by the least square method,
The input signal of the second adaptive filtering means 8 is adjusted to become a compensation signal.

In such a fluctuating state, a second adaptive filtering means 8 for forming a simulation signal of a noise signal from the timing signal from the noise generation source 1 and inputting it.
With the feedforward system centered on the noise, the noise suppression effect due to the fluctuation of the fundamental frequency of the noise that cannot be obtained by the first adaptive filtering means 4 can be easily obtained. If the sine wave generator 7 generates not only a sine wave but also its harmonics, it is also possible to mute harmonics generated by a muffler or the like.

By adding the second adaptive filtering means 8 in this manner, it is possible to ensure a noise reduction effect not only in a steady state but also when the noise period of the noise source 1 fluctuates. . The timing signal is not only extracted from an engine speed detector or an ignition timing control device, but also from a noise transmission path (for example, a muffler) from the noise source 1 to the sound wave-to-electric converter 3 using a vibrometer or the like. You may make it extract.

[0020]

As described above, according to the present invention, even if the noise period of the noise source suddenly changes, an adaptive type for forming a simulation signal based on the timing signal of the noise source and forming a compensation signal. The addition of filtering means makes it possible to follow steep frequency changes.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a noise control device according to an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of an adaptive filtering means of FIG. 1;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Noise generation source 2 ... Electric signal / sound wave converter 3 ... Sound wave / electric signal converter 4 ... 1st adaptive filtering means 5 ... Transfer characteristic simulation means 6 ... Difference signal calculation means 7 ... Signal generation part 8 ... 2 adaptive filtering means 9 ... adding means

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) F01N 1/00 G10K 11/16

Claims (1)

(57) [Claims] An electric signal / sound wave converter (2) for outputting a compensating sound wave to a sound cancellation target space for eliminating noise from a noise source (1), and the electric signal / sound wave converter (2). A sound wave / electric signal converter (3) for converting a residual sound of noise eliminated by the compensation sound wave into an electric signal, based on the signal of the sound wave / electric signal converter (3). First adaptive filtering means (4) for controlling a filter coefficient to form a compensation signal for eliminating stationary noise in the electric signal / sound wave converter (2); and the electric signal / sound wave converter (2). ), A transfer characteristic simulating means (5) for simulating the transfer characteristics of the sound wave / electric signal converter (3) and the sound wave in the target space, and an output of the sound wave / electric signal converter (3) and the transfer characteristic simulation. Calculating the difference signal from the means (5), and A difference signal calculating means (6) to be supplied to the ring means (4); a signal generating section (7) for generating a predetermined waveform signal based on a timing signal related to a noise generation cycle of the noise generating source (1); The signal is input, a filter coefficient is controlled based on the signal of the sound wave / electric wave signal converter (3), and a compensation signal for eliminating fluctuating noise is formed in the electric wave signal / sound wave converter (2). A second adaptive filtering means (8), an output of the first adaptive filtering means (4) and an output of the second adaptive filtering means (8) are added, and the added signal is added to the electric signal. A noise control device comprising: a sound wave converter (2) and an adding means (9) for outputting to the transfer characteristic simulating means (5).