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JPH0876773

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Notice
This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate,
complete, reliable or fit for specific purposes. Critical decisions, such as commercially relevant or
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DESCRIPTION JPH0876773
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
noise reduction structure, and more particularly to a noise reduction structure suitable for
reducing the sound of a car or a building, in particular a reverberant space.
[0002]
2. Description of the Related Art In general, when reducing noise in a reverberant space, a sound
absorbing material is used, but since the sound absorbing characteristics are determined by the
sound absorbing material used, one kind of sound absorbing material is used. When used, there
is a problem that only the sound of a specific frequency can be reduced.
[0003]
For example, JP-A-5-197388 discloses a sound absorbing body provided with three sound
absorbing materials and one reflecting plate, and by combining sound absorbing materials
having different sound absorbing characteristics, a wide frequency band can be obtained. A
sound absorbing body having sound absorbing characteristics across the
However, with the above structure, it is possible to obtain an averaged sound absorption
characteristic, but it is an unspecified noise and a high frequency part of sound pressure, for
example, 500 Hz or less such as automobile engine noise and road noise. If the part of the low
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frequency band changes from moment to moment, the frequency at which the sound pressure is
maximum may deviate from the optimal value of the sound absorption characteristics of each
sound absorber, and particularly the sound absorber in the low frequency band has peaky
characteristics and In such a case, there is a problem that sound can not be suitably absorbed.
[0004]
SUMMARY OF THE INVENTION In view of the problems of the prior art as described above, the
main object of the present invention is to reduce noise even for noise whose frequency at which
the sound pressure is maximum changes. Noise reduction structure.
[0005]
SUMMARY OF THE INVENTION According to the present invention, according to the present
invention, a sound absorbing material and a resonator are disposed to change the thickness of
the air layer behind the film material of the resonator. To analyze the sound pressure distribution
with respect to the frequency of the sound detected by the film material moving means for
moving the film material, the sound sensor, and the sound sensor. Means for displacing the film
material by the film material moving means so as to match the resonance frequency to the above
frequency to control the position of the film material, which is achieved by providing a noise
reduction structure .
[0006]
In this manner, the sound pressure distribution with respect to the frequency of the sound
detected by the sound sensor is analyzed, and the film material is displaced by the film material
moving means so that the resonance frequency matches the frequency of the maximum sound
pressure portion. Thus, even if the maximum sound pressure frequency changes, the resonance
frequency of the resonator can be changed according to the change, and the sound absorption
characteristics can be changed according to the noise.
[0007]
Preferred embodiments of the present invention will now be described in detail with reference to
the accompanying drawings.
[0008]
FIG. 1 is a schematic view showing a noise reduction structure according to the present
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invention.
In FIG. 1, for example, a sound absorber 2 provided on the indoor side (left side in the drawing)
of a wall 1 of a room and its control block diagram are shown.
The present sound absorbing body 2 is opened to the indoor side and is composed of a plurality
of parts divided by the partition plate 3.
[0009]
In FIG. 1, three upper and lower parts are shown, and a resonator 4 utilizing Helmholtz
resonance is provided at the central part thereof, and a porous sound absorbing material 5 is
provided at each of the upper and lower parts. It is attached.
A movable frame 6 is provided in the resonator 4 so as to be displaceable in the direction in
which the movable frame 6 contacts and is separated from the surface of the wall 1, and the film
material 7 is stretched in the movable frame 6.
The movable frame 6 is appropriately driven by a motor 8 as a drive source of the film material
moving means. Further, in order to calculate the thickness of the air layer behind the film
material 7 of the resonator 4, a film position detection sensor 9 is provided, which comprises, for
example, an optical sensor for detecting the position of the film material 7 from the surface of
the wall 1. A sound sensor 10 is provided on the indoor side of the resonator 4 for detecting the
noise on the indoor side in order to analyze the frequency distribution of the noise.
[0010]
The control block diagram shown in conjunction with FIG. 1 is as follows. A sound signal detected
by the sound sensor 10 is input to the CPU 12 that performs main control via the first filter 11.
The position signal detected by the film position detection sensor 9 is input to the CPU 12
through the second filter 13. Further, the CPU 12 appropriately controls driving of the motor 8
via the driver 14.
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[0011]
FIG. 2 shows an example of the characteristics of the sound absorption coefficient with respect to
the frequency of the sound absorbing body 2. As shown in FIG. In FIG. 2, the horizontal axis is a
frequency and the vertical axis is a sound absorption coefficient. In the present sound absorbing
body 2, the sound absorbing material 5 is made of a material having a large sound absorption
coefficient in the middle and high frequency bands shown by the range H in FIG. 2, and the
resonator 4 is shown in FIG. The structure having the largest portion A of the sound absorption
coefficient in the low frequency band indicated by the range L is used. The maximum portion A
of the sound absorption coefficient is changed as shown by the imaginary line in the abovementioned range L by displacing the movable frame 6 to change the thickness W of the air layer
15 behind the film material 7. It is possible.
[0012]
Next, control of the present system will be shown below based on the flow chart of FIG. In step
ST1, the sound sensor 10 takes in sound, and in step ST2, since the input sound signal has the
relation of sound pressure-time by the first filter 11, the relation of the sound pressure-frequency
relation Convert to
[0013]
At step ST3, the CPU 12 analyzes the sound pressure value and the frequency by checking the
frequency of the sound pressure in the target frequency band which is above the threshold or
above the threshold of the sound pressure. Also in the next step ST4, the CPU 12 determines the
optimum film position so as to match the resonance frequency to the frequency to be reduced,
and outputs the film position determination signal to the driver 14. In step ST5, the driver 14
outputs a drive signal to the motor 8 to displace the movable frame 6 to move the film material
7.
[0014]
At step ST6, the position signal of the film material 7 detected by the second filter 13 is
converted into the distance from the surface of the wall 1 to the film material 7, and the CPU 13
determines it at step ST4 based on the distance signal. The position of the film material 7 with
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respect to the above position is determined, and if it has not reached the determined position, the
process returns to step ST5, and if it has reached the determined position, the control routine is
ended.
[0015]
By using the present noise reduction structure controlled in this manner, a relatively wide range
and high sound absorption coefficient can be obtained, and the medium and high frequency
bands are dealt with using the fixed sound absorbing material 5, and low frequency The band
noise is dealt with by the resonator 4.
That is, when the frequency at which the sound pressure is maximum is determined by sound
pressure-frequency analysis in the low frequency band, the film material 7 is used to make the
thickness of the back air layer 15 capable of absorbing sound around the frequency at which the
sound pressure is maximum. By changing the position of, it is possible to suitably cope with the
case where the maximum sound pressure frequency of noise changes, and it is possible to
actively control sound absorption of the maximum sound pressure frequency.
[0016]
Various structures can be considered as the movable frame displacement structure of the
resonator 4. For example, FIG. 4 shows a first embodiment. In FIG. 4, the structure is applicable
when the resonator 4 is provided on the ceiling, and the movable frame 23 is suspended via the
two wires 22 to the fixed portion 21 attached to a part of the ceiling or the ceiling. ing. The wires
22 are provided symmetrically in the left-right direction, one end of which is coupled to the fixed
portion 21, and the fixed portion 21 is connected to the fixed portion 21 via a pair of pulleys 24
a and 24 b disposed apart from each other in the frame portion After being wound around a
pulley 24 c provided apart from the wire bonding portion, the other end side is wound around a
winding roller 26 driven by a motor 25.
[0017]
Therefore, when the motor 25 is driven according to the film material determination position
signal, the movable frame 23, ie, the film material 7 is displaced as shown by the arrow in the
figure, and the space between the film material 7 and the fixed portion 21 is displaced. The
thickness of the back air layer 15 can be changed.
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[0018]
FIG. 5 shows a second embodiment of the movable frame displacement structure.
In the second embodiment, the same parts as those of the first embodiment are designated by the
same reference numerals and their detailed description will be omitted. In FIG. 5, four screw rods
28 parallel to one another are screwed together at four corners of the movable frame 27 in order
to move the film material 7 in a direction approaching and separating from the ceiling or wall
(not shown). The screw rods 28 can be rotated in synchronization with each other, for example,
with a timing belt 29, and one of the screw rods 28 is belt driven by the motor 30. Also in this
second embodiment, the same operation as that of the first embodiment can be performed.
[0019]
Although the noise reduction structure is provided on the wall or ceiling of the room in this
embodiment, the noise reduction structure may be provided in the compartment of a vehicle
such as a car or the room of another vehicle. The structure is suitable for reducing the noise of a
reverberant space. Further, in the present embodiment, the position of the membrane material is
changed by the motor, but it is also possible to use a solenoid type actuator, and the porous
sound absorbing material may be a film member, a flexible material, A perforated plate may be
used.
[0020]
As described above, according to the present invention, the position of the film material can be
appropriately changed so that the resonance frequency of the resonator is matched to the
frequency at which the sound pressure is maximum, and the sound absorption at the maximum
sound pressure frequency is achieved. Can be actively controlled, and an optimal sound
absorption characteristic can be obtained even for noise whose frequency at which the sound
pressure is maximum changes from moment to moment.
[0021]
Brief description of the drawings
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[0022]
1 is a schematic view showing a noise reduction structure based on the present invention.
[0023]
2 is a diagram showing the characteristics of the sound absorption coefficient against the
frequency in the noise reduction structure according to the present invention.
[0024]
3 is a flow chart showing control.
[0025]
4 is a perspective view of an essential part showing a first embodiment of the resonator.
[0026]
5 is a perspective view of an essential part showing a second embodiment of the resonator.
[0027]
Explanation of sign
[0028]
1 Wall 2 Sound Absorbing Body 3 Partition Plate 4 Resonator 5 Sound Absorbing Material 6
Movable Frame 7 Film Material 8 Motor 9 Membrane Position Detection Sensor 10 Sound Sensor
11 First Filter 12 CPU 13 Second Filter 14 Driver 15 Behind Air Layer 21 Fixed Part 22 Wires 23
Movable Frames 24a, 24b, 24c Pulleys 25 Motors 26 Winding Rollers 27 Movable Frames 28
Threaded Bars 29 Timing Belts 30 Motors
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