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JPH02230897

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DESCRIPTION JPH02230897
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
device for controlling the sound pressure in the vicinity of a speaker using feedback control
among sound pressure control devices. [As a device for controlling the sound pressure in the
vicinity of the speaker by the conventional feedback control among the conventional sound
pressure control devices, H. F. The document by O. 01son (Document 1: "Electronic Control of
Noise, Vibration, and Reverbe. ?????????? ???? Am. 28 (5), 966-9 (1956)) are
known. FIG. 3 is a schematic view of this apparatus, in which 1 is a filter, 2 is a speaker, and 3 is
a microphone. The sound from the speaker 2 and the sound from the outside are received by the
microphone 3 and the negative feedback is applied by the filter so that the sound pressure at the
position of the microphone 3 is; In this case, assuming that the gain of the filter 1 is A, and the
sound pressure of the sound from the outside is p, the residual sound pressure E in the
microphone 3 is expressed by equation (1). E = p (1) 1 + A (1) It can be understood that the
residual sound pressure E becomes zero if A is made infinite. [Invention /) <Problems 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, the noise and the shadow of the
characteristics of the speaker are actually generated. It oscillates for learning, and there is a fault
that operation becomes unstable. Therefore, an object of the present invention is to provide a
device for controlling the sound pressure in the vicinity of the speaker so as to solve the problem
that the operation becomes unstable when the residual sound pressure E is flattened by 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 of a diaphragm of the
speaker, and the sound received by the microphone. A pair of filters adjusted so that an
additively synthesized output of mutually opposite phase sounds obtained from the front and
back of the diaphragm of the speaker; and the sound at the microphone placed near the front of
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the speaker are cancelled. And a filter adjusted to be [Operation] The wood invention arranges
the microphones in the vicinity of the front and back of the speaker diaphragm, respectively, and
the sound from the speaker is the sound of the reverse phase from the front and back of the
pregnancy board respectively. By receiving the sound and adding them, it is possible to prevent
the signal from forming a feedback loop and oscillating, with ? being the human power to the
speaker by the sound from the speaker.
On the other hand, the prior art is different in that a signal feedback loop is formed and control is
performed by applying negative feedback with an infinite loop gain. Hereinafter, embodiments of
the present invention will be described in detail with reference to the drawings. Embodiment 1
FIG. 1 is a diagram for explaining 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
very close to the diaphragm on the front and back of the diaphragm of the speaker 4. The filters
7 and 8 perform characteristic correction of the microphones 5 and 6 and characteristic
correction of sounds coming from the front and back of the diaphragm of the speaker 4 so that
the combined output of the microphones 5 and 6 becomes ?. It is done. The filter 9 corrects the
characteristics of the speaker, and the sound in the reverse phase to the sound at the microphone
6 is adjusted so that it is output from the speaker 4 and cancels out the sound at the microphone
6 to become ?. The sound coming from the outside to the apparatus according to the first
embodiment is received and added simultaneously by the microphone 5 and the microphone 6
simultaneously, but is not canceled because it is received in the same phase. Then, it is output
from the speaker 4 through the filter 9. Since the sound at the position of the microphone 6 is
designed to cancel out the sound coming out of the speaker 4 by the filter 9, it is always zero.
The residual sound pressure E at the position of the microphone 6 is expressed by equation (2),
where ? is the sound pressure of the sound from the outside, and A is the gain from the
microphone 6 to the speaker 4. E = p-A p (2) (2) As understood from the equation, when the gain
A is 1, the residual sound pressure E is ?. On the other hand, in equation (1) in the case of the
prior art, in order to set the residual sound pressure E to ?, the gain A must be infinite, and
oscillation is caused by a small number of characteristic loops, resulting in instability. . However,
in this embodiment, since the sound from the speaker is prevented from looping by utilizing the
fact that the sound of the opposite phase is produced on the front and back of the diaphragm of
the speaker above 1 and the operation is stable. . That is, in the present embodiment, since the
sound generated from the speaker does not form a loop in the device, there is an improvement in
the stability of operation as compared with the prior art. Actual J0 discharge The first
embodiment described above can only control so that the sound pressure at the microphone 6 is
reduced. However, there are cases where it is desired to control to any sound pressure.
Therefore, an embodiment which enables the above control by improving the first embodiment is
shown in FIG.
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2
In FIG. 2, 10 is a speaker, 1 1 and 12 are microphones, 13 to 16 are filters, and 17 is a human
power terminal. The filter 16 is adjusted to correct the speaker characteristics. The operation
excluding the filter 16 and the manual input terminal 17 is the same as that of the first
embodiment. Therefore, when there is no human power at the human power terminal 17, the
sound pressure is zero at the position of the microphone 12. When there is human power at the
human power terminal, the characteristic of spy force is corrected by the filter 16 and the sound
pressure of the position of the microphone 12 is the same as human power because it is
generated from the speaker. As apparent from this, by adding the filter 16 and the manual power
terminal 17 to the first embodiment, the sound pressure can be arbitrarily controlled by
comparison with the first embodiment. [Effects of the Invention] As described above, the tree
invention makes use of the fact that sounds of opposite phase are generated from the front and
back of the speaker so that the sound from the speaker does not form a loop in the device.
Therefore, there is an advantage of stable operation in a device that controls the sound pressure
in the vicinity of the speaker using feedback control. In addition, in the second embodiment,
there is an advantage that the sound pressure can be controlled not only optionally; FIG. 2 is a
view for explaining a second embodiment of the present invention, and FIG. 3 is a view for
explaining the prior art. 1 иииииииииииииииииииииииииииииииииииииииииииииииииии 2 Speakers 3 и и и Microphones 4 и и и Speakers
5, 6 и и и Microphones 7-9 и и и и и и и и и и 10 Speakers 12: Microphone, 13 to 16: Filter, 17: Human
power terminal. Patent applicant Nippon Telegraph and Telephone Corporation
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