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JPH0225199

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DESCRIPTION JPH0225199
[0001]
The present invention relates to an active control scheme for narrow band sound waves. Stupid!
It is generally considered that it is difficult to suppress the sound of low frequency band
compared to the ul side high frequency band, even if it is a soundproof wall or a silencer. On the
other hand, the active control method is to cancel the anti-Toshi sound by taking out the reverse
phase sound from the speaker, and in principle it will not be particularly difficult at low
frequencies, but rather in the active control method. The problem is that the control system
oscillates or becomes unstable due to the acoustic coupling between the speaker and the
microphone, the amplitude frequency characteristic and phase frequency characteristic of the
system are flattened using a computer, and the antiphase signal over the entire frequency band It
has been attempted to obtain the above and suppress the oscillation (e.g., "electronic muffling
system", Patent Publication No. 61-296392). Problems to be Solved However, the conventional
active control methods have problems in practical use because the devices are generally
complicated and therefore expensive. The present invention is an apparatus for actively
controlling sound in a relatively low frequency band, which is difficult to control with a passive
method, and it is an object of the present invention to provide a simple apparatus. Means for
Solving the Problems In order to achieve the above object, the present invention comprises a
band pass filter for extracting a specific frequency component to be controlled from an output
signal of a microphone, and amplifies the output signal of the band pass filter. In an
electroacoustic apparatus having a basic configuration including an amplifier and a speaker
driven by an output signal of the amplifier, the band pass filter has a phase characteristic of 0
degrees with respect to the specific frequency component. Also, by setting the phase
characteristic to be in the range of 90 degrees to 90 degrees with respect to the arbitrary
frequency component, the sound incident to the microphone and the sound emitted from the
speaker can be obtained with respect to the sound of the specific frequency component to be
08-05-2019
1
controlled. Have an opposite phase, and at the same time, prevent oscillation due to the in-phase
signal component, and It is intended to suppress. Below, the principle of the present invention
will be described with reference to the drawings. FIG. 151 shows a microphone 1 and a
microphone placed in a sound field, an amplifier 2, a band pass filter 3, an amplifier 4 and a
speaker 5. Here, the sound pressure of the incoming sound to be controlled at the microphone
position is Po, the sound pressure of the speaker reproduction sound is Pl, and the amplitude
characteristics and phase characteristics of the band-pass filter are shown in FIGS. 2 (a) and 2 (b).
It shall be as shown.
This frequency 'P at one. If the gain of these electroacoustic systems is increased sufficiently in
the range where oscillation does not occur, Pz ≦ −P, and hence the microphones, from the
relationship between the input and output sound pressure in the vicinity of the microphones. The
nearby synthetic sound pressure (Po + P +) is sufficiently smaller than P. Incidentally, the
constants of the electric circuit are adjusted to be matched such that the frequency f1 coincides
with the target unnoticeable dominant frequency. Embodiment FIG. 3 shows an example of a
block diagram of a sound pressure control device according to the present invention, and the
microphone 1, the microphone amplifier 2, the band filter 3 and the amplifier numbered the
same as FIG. 4 and the speaker 5 are similar. However, in this case, the band pass filter 3 is
designed so that the frequency characteristic f as shown in FIG. 2 can be adjusted independently.
F2. Three F3s are provided, and by adjusting their respective characteristics, it is possible to
suppress the sound pressure in a wider band than with a single band-pass filter. The number of
band filters connected in parallel in this manner may be appropriately increased or decreased
depending on the purpose. FIG. 4 shows a method of suppressing the noise of the air
conditioning duct 6 using the sound pressure control device according to the present invention.
The band pass filter 3 has a phase characteristic of 0 degree with respect to the dominant
frequency component of the noise propagating in the duct, and has a phase characteristic of 1
degree to 90 degrees with respect to an arbitrary frequency component. Particularly, it is
possible to suppress the dominant frequency component, and the sound pressure is canceled by
the speaker (left direction in the figure) from the speaker. FIG. 5 shows a method of suppressing
the low frequency noise of the transformer 7 using the sound pressure control devices 2 to 4
according to the present invention. By placing the speaker (s) in the vicinity of the noise source,
the vibration of the transformer does not become an acoustic wave at low frequencies, and it
causes the air between the speakers to move as if it were an incompressible fluid , Ambient
sound pressure is reduced. As described above, according to the present invention, by using a
band-pass filter having predetermined characteristics, it is possible to suppress the sound
pressure in the vicinity of the microphone without causing oscillation while having a simple
configuration. In addition, it is effective in attenuating particularly low frequency pure tone noise,
and can easily suppress low frequency noise such as generated from a motor or a transformer.
08-05-2019
2
[0002]
Brief description of the drawings
[0003]
FIG. 1 is a block diagram for explaining the present invention in detail, FIG. 2 is a diagram
showing the characteristics of the band-pass filter used in the present invention, (,) shows the
amplitude frequency characteristic, (b) shows the phase Indicates frequency characteristics.
3 is a block diagram showing an embodiment of a sound pressure control apparatus according to
the present invention, FIG. 4 is a block diagram showing an embodiment for noise suppression of
an air conditioning duct, and FIG. 5 is an embodiment for noise suppression of a transformer. It is
a block diagram which shows an example. Microphone microphone amplifier band-pass filter
amplifier speaker
08-05-2019
3
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