JP2000242278A - Active type noise reducing device with automatic microphone gain adjusting function - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an active type noise reducing device which is provided with an automatic microphone gain adjusting function in which gain adjustment is easily performed. SOLUTION: A muffling duct is divided into plural spaces along its longitudinal direction and input microphones, speakers, evaluation microphones and noise reduction control means are provided in every divided space. Spurious noise is generated from speakers (a step 110) and gain adjusting coefficients of respective microphones are calculated by detecting spurious noise with an input microphone and an evaluation microphone in every divided space (steps 120, 130) and when the calculated gain adjusting coefficients are within the range of predetermined thresholds (a step 160), the gain adjusting coefficients are set (a step 170). When the calculated gain adjusting coefficients are out of the range of the predetermined thresholds (the step 160), an abnormality is reported (a step 180).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active noise reduction apparatus with an automatic microphone gain adjustment function for reducing noise in a sound deadening duct by acoustic interference between noise and inverted sound.

[0002]

2. Description of the Related Art Conventionally, in order to reduce noise in a low frequency range, an active noise is generated by generating a reversed sound having the same amplitude as that of the noise and in the opposite phase and causing the noise to interfere with the reversed sound. Japanese Patent Application Laid-Open No. 5-333877 describes a reduction device.
Japanese Patent Application Laid-Open Publication No. 8-248964 and the like are known. These devices use an input microphone to detect noise, a speaker to emit inverted sound, an evaluation microphone to detect residual sound, and an adaptive digital filter as a filter to generate inverted sound with the same amplitude and opposite phase as the noise. And a control circuit for generating an inverted sound by adaptive control.

[0003] Further, these devices have a limit value determined by the diameter of the silencing duct in the silencing frequency in the silencing duct space, and can only reduce noise in a frequency band that propagates in the space in a one-dimensional mode. This theoretical upper limit frequency fli at which sound can be silenced
mit is represented by the following equation. Where V is the speed of sound (m / s)
X represents the diameter in the case of a round duct and the long side (m) in the case of a rectangular duct.

Flimit = V / (2X) In the case of a rectangular duct having a square section of 450 mm on a side, the upper limit frequency flimit is about 380 Hz, but one side is 90
For a 0 mm duct, the upper limit frequency flimit is about 19
0 Hz, which is considerably lower. Therefore, one side is 450 mm in the longitudinal direction in the duct having a side of 900 mm.
Is divided into four spaces by a partition plate. Thereby, the upper limit frequency flimit can be set to about 380 Hz.

In Japanese Unexamined Patent Application Publication No. Hei 5-333877, noise and residual sound are detected in a specific space among the four divided ones, and inverted sound is emitted from a speaker to all spaces. Thus, the frequency limit at which sound can be muted with a simple configuration is increased.

[0006]

However, in such a conventional device, sound can be effectively silenced in a specific space, but an approximately inverted sound is radiated in other spaces, so that sufficient silencing can be achieved. There was a problem that there might not be. Therefore, when trying to sufficiently mute sound in a plurality of spaces, an input microphone, a speaker,
Although multiple systems such as an evaluation microphone and a control circuit will be provided, adjustments must be made for each system.
There was a problem that the work was troublesome.

It is an object of the present invention to provide an active noise reduction device with an automatic microphone gain adjustment function that can be easily adjusted.

[0008]

In order to achieve the above object, the present invention takes the following means to solve the problem. That is, noise is detected by an input microphone provided on the upstream side of the muffling duct, and a reversed sound having the opposite phase to the noise is emitted from the speaker, and the noise and the noise are evaluated by an evaluation microphone provided on the downstream side of the speaker. Noise reduction control for detecting a residual sound after interference with a reverse sound, controlling the reverse sound from the speaker according to the noise, and performing feedback control of the reverse sound from the speaker according to the residual sound. In an active noise reduction device comprising means,
The sound deadening duct is divided into a plurality of spaces along the longitudinal direction, and the input microphone, the speaker, the evaluation microphone, and the noise reduction control unit are provided for each of the divided spaces, and a pseudo noise is provided for each of the divided spaces. Active noise with automatic microphone gain adjustment function, characterized by comprising an adjustment control means for detecting the input microphone and the evaluation microphone, calculating a gain adjustment coefficient of each microphone, and setting the gain adjustment coefficient. The reduction device is that.

[0009] The adjustment control means may be configured to generate the pseudo noise from the speaker. Alternatively, the adjustment control means may be configured to set the gain adjustment coefficient when the calculated gain adjustment coefficient is within a range of a preset threshold value. Further, the adjustment control means may be configured to notify an abnormality when the calculated gain adjustment coefficient is out of the range of a preset threshold value.

[0010]

Embodiments of the present invention will be described below in detail with reference to the drawings. As shown in FIG. 1, reference numeral 1 denotes a sound deadening duct. The sound deadening duct 1 is provided between an upstream duct 2 connected to a blower (not shown) and a downstream duct 4 connected indoors.

In this embodiment, the outer shape of the sound deadening duct 1 is a square having a side of 900 mm as shown in FIG. 2A, and the space inside the sound deadening duct 1 is as shown in FIG. As shown, a "+"-shaped partition plate 6 provided in the longitudinal direction is provided.
Is divided into squares of 450mm on each side.
It is divided into four spaces, number four.

For each of the first to fourth divided spaces, 4
The input microphones 8 and 9 (only some of which are shown) are provided so as to face each divided space. Also, input microphone 8,
9 and four speakers 10 for each divided space.
To 12 (only some are shown), and four evaluation microphones 14 and 15 (only some are shown) are provided on the downstream side.

Each of the input microphones 8 and 9 is connected to four corresponding amplifiers 16 to 19,
Reference numerals 6 to 19 are configured to amplify noise signals from the input microphones 8 and 9 and output the amplified signals to four noise reduction control circuits 20 to 23. Each of the amplifiers 16 to 19 has a configuration in which the gain can be varied according to an external signal.

Each of the speakers 10 to 12 is connected to four amplifiers 24 to 27, respectively. The amplifiers 24 to 27 amplify inverted signals from the noise reduction control circuits 20 to 23 and output the inverted signals to the respective speakers 10 to 12. And each speaker 10-12
, The reverse sound is radiated to the first to fourth divided spaces.

Each of the evaluation microphones 14 and 15 is connected to four corresponding amplifiers 28 to 31, and the amplifiers 28 to 31 amplify the residual sound signal from each of the evaluation microphones 14 and 15 and It is configured to output to the noise reduction control circuits 20 to 23. Each noise reduction control circuit 20-2
3 is based on noise signals from the input microphones 8 and 9,
The inverted sound having the same amplitude as the noise and opposite phase is output to the speakers 10 to 12 via the amplifiers 24 to 27. Then, noise is reduced due to sound wave interference between the inverted sound from the speakers 10 to 12 and the noise.

Further, the evaluation microphones 14 and 15 detect the residual sound, and output the noise reduction control circuit 20 via the amplifiers 28 to 31.
To 23. Noise reduction control circuit 20-
23 generates a reverse sound so as to reduce the noise by sequentially updating the filter coefficient according to the residual sound.

On the other hand, the amplifiers 16 to 16 of the input microphones 8 and 9
19. An adjustment control circuit 50 for setting the gains of the amplifiers 28 to 31 of the evaluation microphones 14 and 15 is provided. The adjustment control circuit 50 includes a well-known CPU 52, ROM 54, and RAM.
An input / output circuit 58 for performing input / output with the outside is connected to each other via a common bus 60.

The CPU 52 inputs signals from the input microphones 8 and 9 and the evaluation microphones 14 and 15 via an input / output circuit 58. On the other hand, these signals and the ROM 54 and the RAM 5
6 and the control program stored in advance, the CPU 52 controls the amplifiers 16 through
The gain adjustment coefficients are output to 19, 28 to 31.

Next, control processing performed by the above-described adjustment control circuit 50 will be described with reference to a flowchart shown in FIG. This control process is executed every time the power is turned on at the start of operation or the like. First, a process of setting 1 to a counter k is executed (step 100). Next, the outputs of the amplifiers 24 to 27 are increased to a predetermined output, and white noise as pseudo noise is generated from the speaker 10 in the first division space (step 110). Note that the pseudo noise may be generated from a dedicated speaker provided separately, or
The fan may be operated to generate pseudo noise.

Subsequently, noise in the first divided space due to generation of white noise is detected by the input microphone 8, and a noise signal is input via the input / output circuit 58. From this noise signal, a gain adjustment coefficient gain1 is calculated by the following equation (1) (step 120). Here, G is a gain reference constant, which is determined in advance by experiments or the like. PS is the speaker 10
12 is an output power value, and Pm is an input power value of the input microphones 8 and 9. The subscript k indicates the first to fourth numbers.

[0021]

(Equation 1)

Next, noise in the first divided space due to the generation of white noise is detected by the evaluation microphone 14, and a residual sound signal is input via the input / output circuit 58. From this residual sound signal, a gain adjustment coefficient gain2 is calculated by the following equation (2) (step 130). Here, G is a gain reference constant, PS is the output power value of the speakers 10 to 12, and Pn is the input power value of the evaluation microphones 14 and 15.

[0023]

(Equation 2)

Subsequently, the driving of the speaker 10 in the first division space is stopped (step 140), and it is determined whether or not the counter k is 4 (step 150). If it is not 4, 1 is added to the counter k (step 155), and the processing of steps 110 to 155 is repeatedly executed until the value of the counter k becomes 4.

By executing these processes, each of the speakers 10 to 1 is divided into the first to fourth divided spaces.
2 generates white noise from each input microphone 8,
9 as well as the gain adjustment coefficient gaink2 of each of the evaluation microphones 14 and 15.

Then, each of the calculated gain adjustment coefficients gai
It is determined whether nk1 and gain2 are within a predetermined threshold range (step 160). This threshold Gmi
n and Gmax are determined in advance by experiments or the like. When the gain adjustment coefficients gain1 and gain2 are within the range of the predetermined threshold value, the calculated gain adjustment coefficients gain1 and gain2
System identification is performed based on ink2 (step 17)
0). On the other hand, when the gain adjustment coefficients gain1 and gain2 are not within the predetermined threshold range, it is determined that an abnormality has occurred in the input microphones 8 and 9 or the evaluation microphones 14 and 15 and a lamp (not shown) for notifying the abnormality. Are turned on to notify the abnormality (step 170).

As described above, in the active noise reduction apparatus with an automatic microphone gain adjustment function of the present embodiment, the gain adjustment coefficients gain1 and gain2 of the input microphones 8 and 9 and the evaluation microphones 14 and 15 are set by the pseudo noise. Easy to adjust. In addition, the pseudo noise is applied to each speaker 10-1.
2, the gain adjustment coefficients gain1 and gain2 can be automatically set each time the operation is started.

As described above, the present invention is not limited to such an embodiment, and can be implemented in various modes without departing from the gist of the present invention.

[0029]

As described above in detail, in the active noise reduction apparatus with automatic microphone gain adjustment function of the present invention, the adjustment is easy because the gain adjustment coefficient of each input microphone and the evaluation microphone is set by the pseudo noise. This has the effect.
In addition, by generating the pseudo noise from each speaker, the gain adjustment coefficient can be automatically set at each start of work. Further, it is also possible to determine whether each microphone is normal or abnormal by comparing the gain adjustment coefficient with the threshold value.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an active noise reduction device with an automatic microphone gain adjustment function as one embodiment of the present invention.

FIG. 2 is a sectional view of the sound deadening duct of the embodiment.

FIG. 3 is a flowchart illustrating an example of a control process performed in the adjustment control circuit according to the embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Silence duct 2 ... Upstream duct 4 ... Downstream duct 6 ... Partition plate 8, 9 ... Input microphone 10-12 ... Speaker 14, 15 ... Evaluation microphone 16-19, 24-31 ... Amplifier 20-23 ... Noise reduction Control circuit 50: Adjustment control circuit

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Hideki Kurita 1-1, Sanbonmatsucho, Atsuta-ku, Nagoya-shi, Aichi Prefecture Inside Japan Vehicle Manufacturing Co., Ltd. (72) Inventor Yasuyuki Furuta 1-1, Sanbonmatsucho, Atsuta-ku, Nagoya-shi, Aichi Prefecture No. Japan Vehicle Manufacturing Co., Ltd. (72) Inventor Kenji Hiraoka 4-4-20 Nihonbashi, Chuo-ku, Tokyo Mitsui 2nd Annex Shin Nippon Air Conditioning Co., Ltd. −182 New Japan Air Conditioning Co., Ltd. F-term (reference) 3G004 CA00 CA12 DA00 DA21 DA25 3L080 AE02 5D061 FF02

Claims (4)

[Claims] 1. An input microphone provided on the upstream side of a muffling duct detects noise, a reverse sound having a phase opposite to that of the noise is radiated from a speaker, and the noise is detected by an evaluation microphone provided downstream of the speaker. A residual sound after interference between noise and the inverted sound is detected, the inverted sound from the speaker is controlled according to the noise, and the inverted sound from the speaker is feedback-controlled according to the residual sound. In an active noise reduction device including noise reduction control means, the noise reduction duct is divided into a plurality of spaces along a longitudinal direction, and the input microphone, the speaker, the evaluation microphone, and the noise reduction control are provided for each of the divided spaces. Means, for each of the divided spaces, detecting pseudo noise by the input microphone and the evaluation microphone, and calculating a gain adjustment coefficient of each microphone. , The gain adjustment factor automatic microphone gain adjusting function with active noise reduction apparatus, comprising the adjustment control means for setting the. 2. The active noise reduction device with an automatic microphone gain adjustment function according to claim 1, wherein said adjustment control means generates said pseudo noise from said speaker. 3. The apparatus according to claim 1, wherein the adjustment control unit sets the gain adjustment coefficient when the calculated gain adjustment coefficient is within a range of a preset threshold value. Item 2. An active noise reduction device with an automatic microphone gain adjustment function according to item 2. 4. The apparatus according to claim 1, wherein the adjustment control unit notifies an abnormality when the calculated gain adjustment coefficient is out of a range of a preset threshold value. Active noise reduction device with automatic microphone gain adjustment function.