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BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
loudspeaker that amplifies a voice signal from a microphone and outputs the signal from a
speaker, and more particularly to a loudspeaker capable of suppressing harmful noise.
(Background) In general, a loudspeaker as shown in FIG. There is a problem that the output of
the force 4 is fed back to the input of the microphone 10 to cause yawling, and the output level is
limited. Heretofore, as a measure to prevent the yawling, usually, the speaker or the microphone
is given appropriate directivity, and the setting causes the yawling to occur. . However, this
method has a drawback that it can not be used when the positional relationship between the
speaker and the microphone can not be fixed, as in the case of the microphone / required
microphone. Also, at the experimental level, the input signal from the microphone is divided into
a plurality of bands, and the signal energy of each band divided into one is compared to detect
the occurrence of Nori 7g, and when howling occurs, Although methods for attenuating signals
passing through a band have been tried, etc., there is a problem that the sound quality of the
circuit becomes complicated and the like. In addition, there is a disadvantage that the device can
not obtain a large improvement in the ringing margin in spite of the complexity of the device.
(Purpose) The object of the present invention is to improve the point at which the volume of the
loudspeaker is not raised in the prior art due to the occurrence of noise, to suppress the
occurrence of howling and to increase the margin for noise. (Summary) A feature of the present
invention is to attenuate a specific frequency and change its frequency successively for a fixed
period of time in a closed feed van cruise made by a microphone, amplifier, speaker and
microphone). Thus, the loop gain with respect to the frequency is dropped to stop the oscillation,
and by stopping this oscillation again, the oscillation is suppressed before it becomes a large
amplitude howling. EXAMPLES The present invention will be described below by way of
examples. FIG. 2 shows a first embodiment of the present invention. In the figure, a signal input
from a microphone 1 is supplied to an attenuator 6 according to the present invention through
an amplifier 2. The output of the attenuator 6 is supplied to the speaker 4 through the amplifier
6. Here, the damping device 6 will be described in detail. The attenuation device 6 is an AD
converter 7. Dintal filter 8, Katake day, DA converter 12. The circuit comprises a coefficient
memory 13, a random address generator 14 and a timing generator 15.
(No. 1 is converted into a digital signal by the AD converter 7 and is sent to the first and second
digital filters 8-1 and 8-2). The digital filter 8-1.8-2 is a non-recursive digital filter, and can
change its filter characteristics without phase change. The first and second digital filters 8-1 to 82 are composed of a delay circuit group 9, a multiplier 2Iilo and an adder 11, and multiplication
and addition are all performed digitally. Also, the characteristics of the digital filter are
determined by the coefficients given to the multiplier 1plo. The outputs of the first and second
digital filters 8-1 and 8-2 are added by the adder 11 and converted back to an analog signal by
the DA converter +2. Then, the signal is amplified by the amplifier 6 and output from the speaker
4. The characteristic coefficients of the first and second digital filters 8-1 + 8-2 are stored in first
and second coefficient memories 16-1 and 16-2. This factor achieves the properties of the class
Nl 1l to realize a band elimination filter (BEF) which gives the center frequency f N r attenuation
tDN. This coefficient is determined by the first and second random address generating circuits +1
to 4.14-2 which sequentially switch the calling BEF at random and the timing generating circuit
15 which generates the timing of the entire attenuator 6. Coefficient note jjl! It is read from 1-1
and 16-2. FIG. 5 illustrates the characteristics of the digital filter 8-1 or 8-2. Curve +6 in the
figure is an example of the frequency characteristic of the entire system. Also, the digital filter 8
in which the coefficients are successively switched is as shown by curves 17 to +9! In this
embodiment, as shown in FIG. 4, the first digital filter 8-1 of FIG. 2 is used as the first formant of
the audio signal, as shown in FIG. The first coefficient memory 16-1 is preset so that an 18second BEF with a bandwidth attenuation of 20 dB K can be formed within the 100Hz to IKIIz
distribution. In addition, the attenuation of the 100 Hz bandwidth is 30 dB in the IKHz to 4 KHz
band, which is a frequency band in which the Uwling is likely to occur 301! The second IJ1
number memory 16 is blescent 17) so that 11 BEFs are formed. In this embodiment, the first and
second coefficient memories 13-1 and 13-2 are changed by the first and second address
generation circuits 14-1. 14. 2 whose addresses change in synchronization with the output of the
timing generation circuit 15. .
Since the coefficient bursted to I-2 is accessed, the first and second tintal filters 8-1-8-2 change
their BEF characteristics sequentially. The output of the digital filter 8-1.8-2 is added by the
meter 11. Thus, according to the embodiment, the -f! It is blocked when the frequency
component is 1 ≦. For this reason, there is an opportunity to attenuate the gain at the resonant
frequency of the system that generates howling, and howling is prevented. Attenuated 11.
Howling rises again when fN changes from a resonant frequency that is C to another attenuation
frequency, but the rate of rise is negative to the loop gain of the system. Therefore, a margin for
howling can be obtained by switching the resonance frequency of the first and second digital
filters 8-L 8-2 with a known cycle with respect to the rise time to shut off the loop. Moreover,
since the band to be blocked is a part of the liver voice formant (it is a part and in a short time, it
can be realized with almost no loss of the tone of the speaker and without losing the sense of
volume. In addition, first and second address control circuits 14-1. If the random address
generation function is added to + 4−2, noise generated by the effect of switching becomes a low
level white noise, which causes less problem in hearing. Further, the digital filter of this
embodiment can be realized by an LSI, and the coefficient memory can be easily manufactured
since it can be controlled by a CPU or the like. The following is a modification of this
embodiment. That is, the frequency is moved within the use range of the microphone 1 and the
frequency at which the howling has occurred is measured beforehand by a spectrum analyzer or
the like. Then, at the frequency at which the urling occurs in the coefficient memory 13, a
coefficient U which realizes a BEF which takes a large amount of attenuation DN is stored. In this
way, the efficiency can be further reduced (howling can be suppressed. FIG. 5 shows the housing
of a second embodiment of the present invention. In this embodiment, N number of BEFs 20
whose center frequency and attenuation amount are set in advance are provided as filters, and
are sequentially switched by the switch 21 in time series. If the switching repetition cycle of the
switch 21 is selected below the audible band and noise due to this is blocked by the bypass filter
22, the audibility effect can be ignored. If a phase linear filter is used as BEF2G, the same effect
as the first embodiment can be obtained. When a filter with phase displacement is used as
BBF2Q, the resonance condition of the system changes each time the BEF 20 is switched, so that
howling can be suppressed before the amplitude becomes large.
As described above, according to the present invention, howling is regarded as oscillation of a
system that feeds back from a microphone to a speaker, the gain inserted at a specific frequency
is lowered by a filter inserted in the system, and this frequency is successively switched. I can do
things. Since this system starts to oscillate again when the gain is restored, in the case of a hand
microphone, the frequency at which the howling occurs is generally changed because the
microphone moves, and howling starts at another frequency. However, the kneading is
successively suppressed at the switching period of the filter, and does not grow into a large
amplitude howling, etc., to save etc. A gain margin for urling occurs. If the bandwidth of the
selected BEF is narrow (and if the switching period is 11 or less to 50 ms), the input speech does
not change significantly, which is practically sufficient. Although the non-feedback type Dintal
filter is used as the gain filter in the explanation, the same effect can be obtained by using an
engineering feedback type filter as the filter. (Effects) As is apparent from the above description,
according to the present invention, in a loudspeaker apparatus for amplifying an audio signal
from a microphone and outputting it from a C speaker, suppressing occurrence of howling and
increasing a margin for howling. Let's do it
Brief description of the drawings
1 is a conceptual diagram of a conventional loudspeaker system, FIG. 2 is a block diagram of a
first embodiment of the present invention, and FIGS. 3 and 4 are characteristic diagrams showing
one example of characteristics of BEF used in the present invention, FIG. FIG. 5 is a block diagram
of an essential part of a second embodiment of the present invention.
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jps6096997, description
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