JPH02230897A - Sound pressure controller - Google Patents

Abstract

PURPOSE:To attain stable operation of the controller by utilizing the principle that the sound of opposite phase to each other is generated from the front side and the rear side of a speaker thereby avoiding the sound from the speaker does not form a feedback loop. CONSTITUTION:Microphones 5, 6 are placed very close to a diaphragm on the front and rear sides of a speaker 4. Filters 7, 8 correct the characteristic of the microphones 5, 6 and correct the characteristic of sound radiating from a front and rear side of a diaphragm of the speaker 4 to adjust the synthesized output of the microphones 5, 6 to be zero. A filter 9 corrects the characteristic of the speakers and the sound in opposite phase to the sound from the microphone 6 radiates from the speaker 4 and is cancelled out with the sound from the microphone 6 to be zero through the adjustment. Thus, the oscillation caused by the signal through the feedback loop is prevented and stable operation is attained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a sound pressure control device that controls sound pressure near a speaker using feedback control.

[Conventional technology] Among sound pressure control devices, the H. F. 0
1son (Reference 1: “Electro-
nic Control of Noise,V
ibration, and reverberation
ion. ” J. Acoust. Soc. Am., 2
8(5), 966-9b 2 (1956)) is known.

FIG. 3 is a diagram schematically showing this device, in which 1 is a filter, 2 is a speaker, and 3 is a microphone. The microphone 3 receives the sound output from the speaker 2 and the external sound, and the microphone 3 receives negative feedback through a filter.
The sound pressure at the position is ;. In this case, filter 1
If the gain of is A and the sound pressure due to external sound is p, then the residual sound pressure E in the microphone 3 is expressed by equation (1).

E=p (1)1+A From equation (1), it can be seen that if A is made infinite, the residual sound pressure E becomes zero.

[Invention/) <Problem to be Solved] However, in this type of sound pressure control device, when the gain A is made infinite in order to make the residual sound pressure E zero, it actually causes the influence of noise and speaker characteristics. This had the disadvantage that it oscillated due to the noise, making the operation unstable.

Therefore, an object of the present invention is to provide a device for controlling the sound pressure near a speaker so as to solve the problem of unstable operation when flattening the residual sound pressure E using the conventional method. .

A sound pressure control device according to the present invention includes a speaker, a pair of microphones placed near the front and back sides of a diaphragm of the speaker, and a sound pressure control device according to the present invention. The summation and synthesis output of mutually opposite-phase sounds obtained from the front and back of the speaker's diaphragm;
This device includes a pair of filters adjusted so that the following is true, and a filter adjusted so that the sound from the microphone placed near the front of the speaker is canceled out.

[Function] The wooden invention places microphones near the front and back sides of the speaker diaphragm, and in response to the sound coming from the speaker, it emits sound with opposite phase from the front and back sides of the diaphragm. By receiving sounds and adding them, the human power applied to the speaker due to the sound from the speaker is set as τ, and the signal creates a feedback loop to prevent oscillation. On the other hand, the conventional technology differs in that a signal feedback loop is created and control is performed by applying negative feedback with infinite loop gain.

[Embodiments] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

Embodiment 1 FIG. 1 is a diagram illustrating an embodiment of the present invention, in which 4 is a speaker, 5 and 6 are microphones, and 7 to 9 are filters.

The microphones 5 and 6 are placed on the front and back of the diaphragm of the speaker 4 very close to the diaphragm. The filters 7 and 8 correct the characteristics of the microphones 5 and 6 and the characteristics of the sound coming from the front and back sides of the diaphragm of the speaker 4, and adjust the combined output of the microphones 5 and 6 to be τ. has been done.

The filter 9 corrects the characteristics of the speaker and is adjusted so that a sound having a phase opposite to the sound from the microphone 6 comes out from the speaker 4 and cancels out the sound from the microphone 6, resulting in τ.

Sounds coming from the outside to the device according to the first embodiment are first received simultaneously by the microphones 5 and 6 and added, but are not canceled because they are received in the same phase. Then, it passes through the filter 9 and is output from the speaker 4.

Since the sound at the microphone 6 is canceled by the filter 9 with the sound coming from the speaker 4, the sound is always zero.

The residual sound pressure E at the position of the microphone 6 is expressed by equation (2), where ρ is the sound pressure due to external sound, and A is the gain from the microphone 6 to the speaker 4.

E = p − A p (2
) As can be seen from equation (2), when the gain A is 1, the residual sound pressure E becomes τ.

On the other hand, in equation (1) in the case of the prior art, the gain A had to be infinite in order to set the residual sound pressure E to τ, which caused oscillation and instability due to a slight change in the characteristics. .

However, in this example, the gain A is 1, and the sound from the speaker is prevented from looping by taking advantage of the fact that sound with opposite phase is produced between the front and back sides of the speaker's diaphragm, so the operation is stable. .

That is, since the present embodiment prevents the sound generated from the speaker from forming a loop within the device, the stability of operation is improved compared to the prior art.

In the first embodiment described above, the sound pressure at the microphone 6 can only be controlled so as to be reduced to a drop. However, there are cases where it is desired to control the sound pressure to an arbitrary level.

Therefore, FIG. 2 shows an embodiment in which the above control is made possible by adding improvements to the first embodiment. In FIG. 2, IO is a speaker, 1l and 12 are microphones, 13 to 16 are filters, and 17 is a human input terminal. Filter 16 is adjusted to correct speaker characteristics.

The operation excluding the filter l6 and the manual terminal l7 is the same as that of the first embodiment.
is the same as

Therefore, when there is no human power at the human power terminal l7, the sound pressure is zero at the position of the microphone l2. When there is human power at the human power terminal, the filter 16 corrects the characteristics of the speaker power and the sound is generated from the speaker, so the sound pressure of the microphone l2 becomes the same as the human power.

As is clear from this, in Example 1, the filter l6
By adding the human power terminal l7, the sound pressure can be controlled arbitrarily compared to the first embodiment.

[Effect of the invention] As explained above, the wooden invention utilizes the fact that sounds with opposite phases are generated from the front and back sides of the speaker, and prevents the sound from the speakers from forming a loop within the device. Therefore, there is an advantage that the device operates stably in a device that uses feedback control to control the sound pressure near the speaker. Furthermore, the second embodiment has the advantage that the sound pressure can be controlled not only; but also arbitrarily.

FIG. 2 is a diagram illustrating a second embodiment of the tree invention, and FIG. 3 is a diagram illustrating the prior art.

1.--filter, 2...Speaker, 3...Microphone, 4...Speaker, 5, 6...Microphone, 7-9...filter, IO...Speaker, 11.12...Microphone, 13-l6...filter, l7...Manpower terminal.

Patent applicant: Nippon Telegraph and Telephone Corporation

Claims (1)

[Scope of Claims] 1) A speaker, a pair of microphones placed near the front and back sides of the diaphragm of the speaker, and mutual sound received by the microphones obtained from the front and back sides of the diaphragm of the speaker. A pair of filters adjusted so that the additive synthesis output of sounds with opposite phases is zero, and a filter adjusted so that the sound from the microphone placed near the front of the speaker is canceled out. A sound pressure control device featuring: 2) A speaker, a pair of microphones placed near the front and back of the diaphragm of the speaker, and addition of mutually opposite-phase sounds obtained from the front and back of the diaphragm of the speaker received by the microphones. a pair of filters adjusted so that the combined output is zero; a filter adjusted so that the sound from the microphone placed near the front of the speaker is canceled; and a signal input terminal to the speaker. A sound pressure control device comprising: a filter for correcting characteristics of the speaker.