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JP2011015237

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DESCRIPTION JP2011015237
[PROBLEMS] A portable generator for outdoor use, capable of efficiently and stably generating
ultra low frequency sound of a specific frequency with high sound pressure, and generating low
frequency sound noise, etc. To provide an infrasound generator that can perform experiments
without moving the An ultra-low frequency sound generator (1) characterized by comprising a
diaphragm driven by compressed air includes a diaphragm (2), an air pressure servo actuator (3)
for driving the diaphragm (2), and An air tank for supplying compressed air to the actuator 3 is
provided, and diaphragms are respectively disposed on two opposing surfaces, and the two
diaphragms are configured to be driven in opposite phase. [Selected figure] Figure 1
Very low frequency sound generator
[0001]
The present invention relates to an apparatus for artificially generating an ultra low frequency
sound, and more particularly to an ultra low frequency sound generating apparatus suitable for
conducting experiments with low frequency sound outdoors where there is no power supply.
[0002]
Very low frequency sound components are included in the blast noise generated by construction
of mountain tunnel, roar by discharge of dam, sonic boom generated by aircraft flying at
supersonic speed, vibration when a large trailer crosses a bridge, etc. Therefore, it may cause
environmental problems such as rattling the fixtures of the house and giving a sense of
oppression to humans.
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[0003]
There are still many unexplained parts about the influence of ultra low frequency sound on
human bodies and buildings.
In order to elucidate these effects, a device for generating artificially similar low frequency sound
is necessary, but it was difficult to generate artificially the low frequency sound of 20 Hz or less
in particular.
So far, there has been developed a device capable of generating an ultra low frequency sound of
20 Hz or less at a large sound pressure, under the restricted condition of being in a sealed space.
However, in an experiment in which low-frequency sound is generated by such a device placed in
a room, it is difficult to collect probable data because it differs from the actual condition that
sound propagates from the outside.
[0004]
As a device for generating ultra low frequency sound in the above-mentioned enclosed space, for
example, a diaphragm is driven by a hydraulic actuator provided with a servo mechanism as
described in "low frequency sound source for joint test" of Patent Document 1 The method of
letting According to this method, it is possible to generate an ultra low frequency sound of 20 Hz
or less with a large sound pressure. However, it is not assumed to be used outdoors because it is
a method of generating low-frequency sound with high sound pressure by making use of the
characteristics of the enclosed space indoors. Therefore, when trying to use it outdoors, it is
necessary to operate the hydraulic compressor with the engine generator outdoors when there is
no power source for driving the hydraulic actuator, and the low frequency noise emitted by this
compressor becomes noise. In addition, since it is necessary to fix with a strong base in order to
suppress the vibration caused by the vibration of the compressor and the driving of the
diaphragm, the device can not be easily moved.
[0005]
Another means for generating infrasound may be to use a speaker that is usually used to
generate sound, but the speaker has a poor radiation efficiency of less than 20 Hz and is very low
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in the low frequency region. It is not suitable for outdoor use because it requires a large amount
of power. From the above circumstances, there has been a demand for a new device capable of
generating high sound pressure ultra low frequency sound outdoors.
[0006]
Japanese Patent Application Laid-Open No. 2004-147051
[0007]
The “low-frequency sound source for joint test” disclosed in Patent Document 1 is premised on
indoor use as described above, and is unsuitable for outdoor use.
The present invention is a portable type for outdoor use, which can efficiently and stably
generate very low frequency sound with high sound pressure, and without moving a generator or
the like that may generate low frequency noise. An object of the present invention is to provide
an ultra low frequency sound generator capable of carrying out experiments.
[0008]
In order to solve the above-mentioned subject, the ultra-low frequency sound generator of the
present invention is characterized by including a diaphragm driven by compressed air.
Preferably, the vibration of the apparatus itself can be prevented by arranging the diaphragms on
the two opposing surfaces and driving the two diaphragms in opposite phases.
[0009]
It is desirable that the above-mentioned ultra low frequency sound generator includes at least a
diaphragm, an air pressure servo actuator for driving the diaphragm, and an air tank for
supplying compressed air to the actuator. In addition, by disconnecting the air compressor at the
time of operation, the portable type suitable for outdoor use can be obtained.
[0010]
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According to the apparatus of the present invention, since a very low frequency sound is
generated by the diaphragm driven by the compressed air, it is possible to test the rattling
condition of the fixture due to the generation of the very low frequency sound even if the
compressed air can be prepared even outdoors. be able to. In addition, if the two diaphragms are
driven in opposite phase, vibration of the device itself can be prevented and stable ultra low
frequency sound can be generated.
[0011]
The apparatus according to the present invention comprises a diaphragm, a pneumatic servo
actuator for driving the diaphragm, and an air tank for supplying compressed air to the actuator.
It is not necessary to generate noise, noise vibration by a motor etc. can be prevented and stable
ultra low frequency sound can be generated.
[0012]
Since the device of the present invention can prevent the vibration of the device itself and noise
vibration due to the motor and the like, it is not necessary to attach a strong base or fix it on the
ground.
Therefore, it can be taken out outdoors, and can be easily moved frequently during an
experiment, and can be used as a portable experimental device.
[0013]
An example of the ultra-low frequency sound generator of this invention is shown, (a) is a side
view, (b) is an AA arrow sectional view of (a). The block diagram which shows an example of the
drive system of the ultra-low frequency sound generator of this invention. (A) Displacement of
diaphragm when generating a sine wave of 10 Hz according to the ultra low frequency sound
generating device of Table 1, (b) A diagram showing a time change of sound pressure measured
at a position 4 m away from the device . The figure which shows the frequency-analysis result of
the 10-Hz radiation sound measured in 4 m distance from the ultra-low frequency sound
generator of Table 1. FIG. The figure which shows the measurement result about 5 Hz radiation
sound which is an example of the distance attenuation | damping property of the low frequency
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sound radiated | emitted from the ultra-low frequency sound generator of Table 1. FIG.
Schematic which shows the positional relationship of the apparatus of an Example, a house, and
the measurement position of the ultra-low frequency sound in house inside and outside. (A), (b),
(c), (d) and (e) is a wave form diagram which shows the result of the outdoor experiment of an
Example.
[0014]
Hereinafter, embodiments of the present invention will be described in detail with reference to
the drawings. In FIG. 1, an ultra low frequency sound generator 1 includes a diaphragm 2, an air
pressure servo actuator 3, and an air tank 9 described later.
[0015]
The actuator 3 is coupled to the diaphragm 2 by an air cylinder 4 penetrating the center thereof.
Here, the number of diaphragms 2 may be one or more, and in the case of a plurality of
diaphragms 2, there is no upper limit if it is a practical number of sheets.
[0016]
However, as shown in FIG. 1, when two diaphragms 2 and 2 are vibrated in opposite phase with
each other using two actuators 3 and 3, a vibration form close to a breathing sphere can be
realized, and actuators 3 and 3 can be realized. Can be offset. For this reason, stable use can be
achieved without taking care of fixing the device or setting the base.
[0017]
If a plurality of actuators 3 such as 4 or 6 are used and the opposing actuators 3 are in opposite
phase, the same effect as in the case of using 2 above can be obtained. The reaction force applied
to the actuator 3 can also be canceled by combining a plurality of regular pentagonal diaphragms
2 having the same appearance as the breathing sphere speaker into a spherical shape.
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[0018]
The shape and material of the diaphragm 2 can be appropriately changed according to the scale
of the ultra low frequency sound generation experiment and the environmental conditions, but
for example, if one piece is a cube type generator of about 1 m, 1 m on two sides facing each
other The aluminum honeycomb diaphragms 2 and 2 of × 1 m are respectively installed. It is
preferable to attach a surround 5 formed of a flexible material such as rubber to the end edge
portions of the diaphragms 2, 2 so as not to hinder the operation of the diaphragms 2.
[0019]
The pneumatic servo actuator 3 according to the present invention is one in which an
electromagnetic air valve and an air cylinder 4 are integrated, and the air cylinder 4 can be
operated by the electromagnetic air valve to vibrate the diaphragm 2. Further, the duct 6
attached to the side is for relieving the pressure displacement generated inside the device 1, for
example, if the duct 6 capable of adding a volume of 15 m <3> or more with a diameter of 60 cm
is provided. A maximum displacement of ± 70 mm can be accommodated.
[0020]
Next, the procedure of ultra low frequency sound generation by the device 1 of the present
invention will be described using FIG. The very low frequency sound generator 1 is assumed to
be used outdoors without a power supply. Therefore, the compressed air is stored in the air tank
9 in advance using the generator 7 and the air compressor 8 before taking it to the experimental
site. In this way, there is no need to operate the generator at the outdoor test site, so there is no
need to secure a power source, and there is no concern about noise low frequency noise
generation by the generator.
[0021]
The apparatus 1 is placed at a predetermined position of the experimental site to start the
experiment. First, the compressed air in the air tank 9 is sent to the pneumatic servo actuator 3.
For that purpose, a control signal (voltage signal) is sent from the notebook PC or the like to the
electromagnetic air valve of the actuator 3 to move the air cylinder 4 connected to the valve. A
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battery for driving the electromagnetic air valve is separately prepared.
[0022]
The diaphragm 2 connected to the air cylinder 4 is driven in accordance with the control signal
in the above-mentioned procedure to generate an extremely low frequency sound. In order to
check whether the diaphragm 2 and the cylinder 4 are moving according to the control signal, it
is preferable to use the displacement gauge 10 to measure and feed back to the control signal
every moment.
[0023]
Table 1 shows an example of the basic specifications of the low frequency sound generator 1.
[0024]
Also, in FIG. 3, (a) displacement of the diaphragm 2 when generating a 10 Hz sine wave when
using the device 1 based on Table 1, and (b) measurement at a position 4 m away from the
device 1 Change in sound pressure over time.
[0025]
A low frequency sound level meter (RION XN-1G: frequency specification 1 to 500 Hz) was used
to measure the sound pressure.
Analysis of the displacement of the diaphragm 2 in (a) and the sound pressure waveform in (b)
shows a waveform that can be regarded as a sine wave, and the diaphragm 2 is properly
operated by the pneumatic servo system using displacement feedback. It turns out that control is
possible.
[0026]
FIG. 4 shows the frequency analysis result of the 10 Hz radiation sound measured at a distance
of 4 m from the device when the device 1 based on Table 1 is used.
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According to this figure, high frequency components other than 10 Hz (ultra low frequency
sound) are also observed, but the level is lower by 20 dB or more compared to 10 Hz
components, and it significantly affects the measurement results in the fixture test etc. It can be
judged that there is nothing to do.
[0027]
As an example of the distance attenuation characteristics of the low frequency sound emitted
from the device 1, FIG. The attenuation is gradual near the device 1, but after being separated
from the device by 3 to 4 m, an attenuation characteristic as a point source of 6 dB per double
distance is shown. Under no-wind conditions, the background noise of the 20Hz or less
infrasound component in the outdoor environment is 60 to 65 dB, so the test sound emitted from
this device 1 is of course suitable for use in fixture testing, Furthermore, it is speculated that it
can be used for propagation experiments several hundred meters away.
[0028]
(Example) The outdoor experiment with a simple house was conducted using the very low
frequency sound generation device 1 (the device based on Table 1) of the present invention.
[0029]
[Outline] An outdoor experiment was conducted using the ultra-low frequency sound generator 1
of the present invention to verify the practicability as a sound source for field test.
The apparatus 1 was installed at a position 3 m away from the simple house 11 manufactured
for this type of test, and the response of the house 11 was investigated by causing the house 11
to be exposed to ultra low frequency sound. FIG. 6 shows the positional relationship between the
device 1 and the house 11, and the measurement positions of the very low frequency sound
inside and outside the house.
[0030]
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The simple house 11 used in the test is a wooden 2 m × 4 m wide and 2 m high, and a 1.8 m ×
1.8 m sweep window (aluminum sash, glass thickness 5 mm) 12 is attached to the front. The
device 1 was arranged such that low frequency sound was incident on the window 12 from the
45 degree direction. The sound pressure was measured at two points, the front 13 of the window
glass (15 cm away from the window surface) and the center 14 in the house. In addition, in order
to confirm the occurrence of rattling of the window, the vibrations of the aluminum sash and the
window glass were respectively measured by the small vibration pickup and the laser
displacement meter.
[0031]
[Test Results] In FIG. 7A, the pure sound of 5 Hz is used as a test sound, and the displacement of
the diaphragm 2 is gradually increased, and the displacement of the diaphragm 2 when the rattle
of the window glass starts to be heard Indicates Also, (b) and (c) show the sound pressure
waveforms of the glass front surface 13 and the center 14 in the house, respectively. Further, (d)
shows the results of measurement of the vibration acceleration measured by the vibration
acceleration pickup attached to the window frame, and (e) the results of measurement of the
displacement of the center of the glass by a laser displacement meter.
[0032]
7 (b) and (c), when the sound pressure waveforms of the center 14 in the house and the front
surface 13 of the window glass are compared, it is apparent from the figure that the pressure in
the indoor 14 is smaller than that in the outdoor 13 It is also changing, and it is possible to
recognize the influence of the existence of a clear house even for the low frequency sound of 5
Hz.
[0033]
Next, looking at the condition of rattling of the window, the displacement (e) of the window glass
corresponds to the sound pressure waveform of the incident sound, and the sharp pulse seen in
the acceleration waveform (d) of the sash Correspondingly, rattling occurs, and it is understood
that this window is likely to be rattling at the time of positive pressure of the incident sound
(when the window glass is pushed inward from the outside).
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The sound pressure level on the front surface 13 of the window glass when rattling starts, that is,
the threshold value of rattling is 95 dB.
[0034]
Since the device 1 of the present invention can freely change the movement of the air cylinder 4
using a control signal (voltage signal) from a PC or the like, the frequency and the generation
level of the test sound can be freely controlled In addition, in the apparatus 1 used in this
example, the incident sound pressure level could generate a large sound pressure of up to 110
db.
[0035]
From the above results, using the device 1 of the present invention, it is possible to relatively
easily investigate the rattle threshold by frequency for aluminum sash, which is considered
relatively unlikely to rattle, and various other fixtures. It is presumed that
In particular, since the apparatus 1 can be used as a portable type, for example, it is possible to
obtain a rattling threshold in an actual house where rattling of a fixture is a problem, and
experiment such as grasping a reduction target value that does not generate this rattling It
becomes.
[0036]
Moreover, if the impulse sound source (see Japanese Patent Application No. 2008-263558)
developed by the present inventors and already filed a patent application is used in combination,
the steady sound and the impulsive sound in the sound insulation performance and rattling of
the house in the low frequency sound region. It is possible to consider the difference between
[0037]
The ultra-low frequency sound generation device of the present invention is a portable device
capable of generating ultra-low frequency sound of 5 to 20 Hz that could not be reproduced by a
speaker or the like. It is possible to inject ultra low frequency sound to objects such as fixtures in
free space close to the wave sound exposure conditions, and it becomes possible to investigate
the rattle threshold of fixtures and the like more in line with the actual situation.
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In addition, the device can reproduce not only the fixtures but also any shocking infrasound such
as a tunnel blasting sound or an artillery sound.
[0038]
DESCRIPTION OF SYMBOLS 1 ... Ultra-low frequency sound generator, 2 ... diaphragm, 3 ...
pneumatic servo actuator, 4 ... air cylinder, 5 ... surround, 6 ... duct, 7 ... generator, 8 ... air
compressor, 9 ... air tank, 10 ... displacement gauge, 11 ... simple house, 12 ... sweeping window,
13 ... front of window glass, 14 ... center of house.
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