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JPH02141095

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DESCRIPTION JPH02141095
[0001]
[Purpose of the invention] (Industrial field of application) In the duct-like structure through
which sound propagates, the noise is silenced by collecting the sound and outputting the sound
in the opposite phase of the sound. It relates to the device. (Prior Art) For example, a silencer as
shown in FIG. 9 can be considered as a silencer that actively muffles. That is, the sound emitted
from the noise source becomes a plane wave by propagating through the duct 101. This sound is
then collected by the measurement microphone 103, and the electrical signal from the
measurement microphone 103 is signal processed as described below, and an input for the
muffling speaker 104 at a position separated by Q from the measurement microphone 103. First,
the procedure of signal processing will be described according to FIG. The electric signal from
the measurement microphone 103 is amplified by the amplifier 105 and corrected by the delay
correction circuit 106 in consideration of the delay time τ required for the sound to advance by
Q, and the phase of the correction signal is inverted by the phase inversion circuit 107. And
amplified by the speaker amplifier 108 and input to the muffling speaker 104. The sound
generated from the muffling speaker 04 is propagated in two directions of the upstream side and
the downstream side of the duct-like structure. Of these, the sound propagated to the upstream
side is further input to the measurement microphone 103 to form a so-called feedback loop. The
sound propagating to the upstream side has a time delay due to having traveled acoustically by
the distance Q. The closed loop transfer function G of the above feedback loop is expressed as 1,
1 ′ ′ 2 sincvt − 2 C: the speed of sound of air. Equation 0 shows that the closed loop transfer
function G has a phase difference of π / 2. Therefore, when the sound from the noise source and
the sound from the muffling speaker 104 are synthesized, the phase difference 音 of the sound
that ultimately propagates to the downstream side is expressed as 2πΩΦ = π−10−−λ 2 λ:
the wavelength of the sound . And the specific frequency f. (= C / λ. In, the phase difference と
き when the sound is synthesized on the downstream side. Becomes .pi..pi. =. Pi .-. Quadrature .-.
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Quadrature. =. Pi. ("," Q =) L)-. Circle-solid. However, such a configuration has a problem that a
sufficient noise reduction effect can be obtained only with a specific frequency λ6 determined
by the distance Ω of the measurement microphone 103 and the muffling speaker 104 and
components in the vicinity thereof. Moreover, the principle of this noise reduction is applied to
what becomes a plane wave (one that propagates in one dimension with a mode only in the duct
direction) by the sound propagating in the duct, and the sound in the duct is two-dimensional.
There is also a problem that the sound propagation effect can not obtain the sound reduction
effect.
(Problems to be Solved by the Invention) As described above, in the conventional silencer, there
is a problem that the noise reduction effect can be obtained only at a specific frequency
determined by the distance between the sound receiver and the sound generator and
components in the vicinity thereof. doing. In addition, there is also a problem that noise
reduction is effective only in the one-dimensional sound propagation in the duct. The present
invention has been made in view of the above circumstances, and a first object of the present
invention is to provide a silencer capable of effectively muting a variety of frequency bands, and
a second object is to provide two-dimensional or three-dimensional. It is an object of the present
invention to provide a silencer that can effectively mute even the sound that is transmitted.
[Configuration of the Invention] (Means for Solving the Problems) In the first invention, there is
provided a receiver for receiving energy of sound propagating substantially as a plane wave from
a sound source and converting it into an electric signal, and energy of sound from the electric
signal. A sound generator for converting sound into sound, phase inverting means for generating
sound from the sound generator that propagates as a plane wave substantially in reverse phase
to the phase of the sound received by the sound receiver; The time required for the sound
received by the receiver to travel from the sound generator arranged at a predetermined distance
from the sound receiver to the sound generator arranged at a predetermined distance from the
sound generator is delayed to reverse the sound generator from the sound generator And a time
compensation means for generating phase sound. There is provided a filter for selecting from the
sound receiver only an electric signal corresponding to a desired frequency band desired to be
muted out of the sound from the sound source, and an output signal of this filter is either the
phase inverting circuit or the time compensating circuit. A plurality of input signals are provided,
the output signal of which is the other input signal, and at least one of the sound receiver or the
sound generator is provided according to the number of frequency bands to be muted. The
predetermined distance is set according to the frequency band of (1). In the noise reduction
device of the second aspect of the present invention, detection means for detecting the amplitude
and phase of the sound propagating from the sound source in two or three dimensions or the
vibration of the sound source, and the sound propagating in two or three dimensions A sound
generator generates a sound to be generated, and a sound having substantially the same
amplitude and substantially opposite phase as the amplitude of the sound of the sound source at
the control target point to mute the sound of the sound source at the control target point And
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control means for controlling as described above. (Operation) According to the first aspect of the
present invention, a plurality of sound receivers or sounders are provided according to the
number of various frequency bands to be muffled, and the distance between the sound receiver
and the sound generator is muttered according to the frequency band The frequency range to be
muted can be reliably muffled in order to set the distance to a predetermined distance and to set
the sound frequency selection means at high speed to scan and synchronize and sound in the
opposite phase.
In the second invention, even for sounds propagating in two or three dimensions, it is ensured
that the sound generator emits a sound whose phase is approximately 1806 different in
amplitude from the sound of the sound source at the control target point. It can be muffled. The
present invention will be described with reference to the drawings. FIG. 1 is a conceptual
diagram for explaining a first embodiment of the first invention. The sound emitted from the
noise source substantially propagates in the duct 10 to become a plane wave. This sound is
collected by the measurement microphone 1. Speaker 2a for muffling. 2b and 2c are respectively
distances Q1. Q2. It is separated by Q3 and its distance is determined from the above
equation 0 by the frequency f (= C / λ1), f, C = C / λ, and f3 (= C / λ3) to be muffled as follows:
Ru. f11 = Y Q2 = mutual-mutual λ4, 4. Q3-4 where λ1. λ2. The wavelength C of the sound to
be muffled is the sound velocity of the air, and the distance Q1 ° 12 of the microphone 1 to the
speakers 2a, 2b and 2c, and Q3 are not necessarily limited to the exact distance determined by
the equation 0 It is valid. The reason is as follows. That is, the closed loop transfer function H (Q)
when the transient state of the closed loop transfer function G shown in the (G) equation is
considered is expressed as follows. Therefore, the stability discriminant (a condition that does not
diverge) is 0 according to equation 0, and therefore, it is stable when sin; 4Q 1). This range is
−π> in> −> mouth> lπ 66,66. (At this time, Ura = ω / C, ω = 2πf) and when 1 sin lffil = 1, it
becomes stable most rapidly. That is, even if the distance Q between the microphone 1 and the
speaker 2 has a certain degree of margin, the sound reduction effect is produced. A sound wave
propagating as a substantially plane wave in the duct 10 is received by the miguel and converted
into a voltage by the amplifier 3. The converted sound signal is scanned and selected at high
speed only for the frequency signal to be silenced by the high speed scanning filter 4 according
to the frequency to be silenced. The filtered signal has an acoustic wave distance from the
microphone 1 to the speakers 2a, 2b, 2c Q1. The time compensation circuit 5 corrects the time
required to advance to ff 2.123. The time-corrected signal is inverted in phase by 180 degrees by
the phase inverting circuit 6. For example, in the embodiment shown in FIG.
Speakers 2a and 2b at positions Ql and Q3. 2c is arranged, and three frequency bands are
desired to be muffled. The three frequency bands are scanned at high speed with a minute time
difference, the time compensation circuit 5 sequentially compensates for the delay time, the
phase inversion circuit 6 inverts the phase, and the high speed scanning amplifier 7 each speaker
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2 a To pronounce 2c. At this time, the synchronous circuit 9 synchronously controls the highspeed scanning amplifier 7 for producing the speakers 2a to 2c arranged at a predetermined
distance from the frequency band selected by the high-speed scanning filter 4. Therefore, each of
the speakers 2a to 2c can generate a sound of the opposite phase of the sound of the frequency
band to be muffled, and can be surely muffled on the downstream side (right side in the figure) of
each of the speakers 2a to 2c. In the above embodiment, the high-speed scan filter 4 in place of
the high-speed scan amplifier 7 and the synchronization circuit 9 is a filter which can select as
many frequency bands as desired, ie, a plurality of frequency bands, as shown in FIG. 4 is
provided, and the sound in each frequency band can be muted in a similar manner if it is inverted
by one time compensation and two phases, and sounded from the corresponding speakers 2a to
2c. In the above embodiment, instead of providing the high-speed scanning filter 4, as shown in
FIG. 4, filters 4 are provided which can select the number of frequency bands to be muted, that
is, a plurality of frequency bands. The respective sounds can be muted similarly if they are
respectively time-compensated and phase-reversed by 2 and sounded simultaneously from the
speaker 2. At this time, if the microphones la, lb, lc, and ld are attached to the mic traverse device
to be movable, it is easy to set the distance and it is practical. Next, a second embodiment of the
first invention will be described with reference to FIG. la, lb, lc, ld are microphones for receiving
sound, and 2 is a speaker for muffling. 10 is a duct, and sound propagates from the left as a
plane wave. Microphones la, lb, lc and ld for sound reception are Ql and Ql, respectively. It is
separated from the muffling speaker 2 by a distance I13.424, and the distance is determined by
the above-mentioned 弐 according to the frequency to be muffled. The sound waves propagated
in the duct 10 are received by the microphones la, tb, lc and tct, and converted into voltages by
the amplifiers 3a, 3b, 3c and 3d, respectively. After that, the high-speed scan filter 4 selects only
the frequency signal to be muted according to the distance Q1, Q2 [3 and Q4. It is scanned at
high speed.
As for those signals, the sound waves have a distance Q1 ° Q2. Q3. After being time
corrected by the time compensation circuit 5 which corrects the time required to advance by Q4,
the phase inversion circuit 6 inverts the phase by 180 degrees. The inverted signal is output
from the muffling speaker by the speaker amplifier 8, and the sound propagating in the duct 10
is effectively muffled downstream thereof according to its frequency. As described above, in the
first invention, since the filter 4 is provided, the frequency band to be muffled can be selected
(the frequency band to be muffled is generally set in advance, but if the sound source is, for
example, a rotating machine) For example, the rotation frequency and its integral multiple
frequency components are selected. ) Mute the frequency band you want to muffle securely.
Next, the second invention will be described. Although the previous invention discussed the case
where a one-dimensional plane wave propagates in the duct, in practice there are various modes
in the sound wave, and not all one-dimensional plane waves. For example, in the case of a platelike sound source 21 as shown in FIG. 5, the sound wave from the sound source 21 propagates in
two dimensions in the duct 30. The duct 31 in which the plate-like silencer 22 is disposed is
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joined to the duct 30 in which the sound source 21 is disposed at a predetermined angle. このダ
クト30. The sound propagating in the duct 31 is synthesized at the junction of the ducts to
form an outlet platform. Here, when the sound source 21 has a mode in a two-dimensional
direction as shown in FIG. 6, for example, the sensors 23a, 23b, 23c, and 23d are disposed on the
sound source 21 to detect the vibration of the sound source 21. Do. Signals of the vibrations
detected by the sensors 23a, 23b, 23c, 23d are sent to the phase / amplitude converter 24. On
the other hand, the exit stand where the sound source 21 and the sound of the silencer 22 are
synthesized is detected by the monitor microphone 25 and fed back to the phase / amplitude
converter 24 by the feedback circuit 26. The phase / amplitude converter 24 converts the phase
and amplitude from the sensors 23a, 23b, 23c, 23d according to the position where the silencer
22 is disposed so that the outlet stand is minimized, and the signal output thereof As an input to
an amplifier 28 which drives a vibrator 27. The sensors 23a, 23b, 23c, and 23d are, for example,
vibration sensors that can detect the frequency of the sound source 21 and its vibration form,
and are installed at positions where the vibration mode of the sound source 21 can be acquired.
Next, FIG. 7 shows a modification of the second invention, in which the number and arrangement
of the microphones 25 for monitoring the outlet of the duct 30.31 according to the mode, for
example, in FIG. In the case of the vibration mode as shown, the monitor accuracy is improved by
installing four microphones 25a, 25b, 25c and 25d.
FIG. 8 is a block diagram according to the invention of the second invention, in which the double
arrowed line indicates the flow of sound and the single arrowed line indicates the flow of signal.
Further, although the above configuration is configured to obtain the muffling effect by detecting
the vibration of the plate-like sound source 2 serving as the vibrating body, the acoustic mode
generated in the duct 30 is detected by the acoustic microphone instead of the vibration sensor.
A similar muffling effect can be obtained by controlling the muffler (muffling plate) 24 so that
the corresponding acoustic mode is generated. In the configurations of FIGS. 5 and 7, it is
assumed that the acoustic mode and the natural vibration mode possessed by the silencer 22
coincide with each other, but a plurality of vibrators 27 are provided at positions corresponding
to the acoustic mode. The same action and effect can be obtained by attaching and forcing
vibration. According to the invention of the cylinder 2 as described above, it is possible to obtain
a noise reduction effect for the sound spreading in two dimensions. As described in detail above,
according to the first aspect of the present invention, sounds in various frequency bands to be
muffled can be muffled. Further, according to the second aspect of the invention, it is possible to
mute the sound propagating in two or three dimensions.
[0002]
Brief description of the drawings
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[0003]
FIG. 1 is a schematic view showing the first actual flow side of the noise suppressor according to
the first invention, FIG. 2 is a schematic view showing a modification of the first embodiment, and
FIG. 3 is a first invention. FIG. 4 is a schematic view showing a second embodiment of the
silencer according to the present invention, FIG. 4 is a schematic diagram showing a modification
of the second embodiment, and FIG. 5 is a schematic diagram showing an embodiment of the
silencer according to the second invention. 6 and FIG. 6 relate to the second invention, and are
conceptual diagrams showing sound mode patterns, FIG. 7 is a schematic view showing a
modification of the noise suppressor according to the second invention, and FIG. 8 is the second
invention. FIG. 9 is a schematic view of a conventional muffler according to the present invention.
1, la, lb, lc, ld-microphone (receiver) 2, 2a, 2b, 2 cm speaker (sound generator) 4 ... filter 5 (filter
5) ... time compensation circuit 6 ... phase inversion Circuit 10: Duct 21: Sound source 22:
Sounding device 23a, 23b, 23c, 23d-sensor (detection means) 24: Phase / amplitude converter
25: Microphone (reception W? /) 26 ··· Feedback circuit 27 · · · Vibrator 30, 31 · · · Duct
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