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DESCRIPTION JP2017152792

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DESCRIPTION JP2017152792
Abstract: The present invention provides an acoustic system that can demodulate a modulated
wave according to the position of a listener and reproduce an acoustic signal. The acoustic
system emits a modulated wave H whose amplitude is modulated by an acoustic signal of an
audible band to an acoustic space, and demodulates the modulated wave H in the acoustic space
to reproduce an acoustic signal. A parametric speaker 12 for generating the modulation wave H
and emitting it to the acoustic space, and a medium G2 containing the medium G2 having a
predetermined property different from the medium G1 filling the acoustic space; And a medium
container 14 for passing waves. [Selected figure] Figure 2
Acoustic system, medium container used therefor, and method of reproducing acoustic signal
[0001]
The present invention relates to an acoustic system using a parametric speaker, a medium
container used therefor, and a method of reproducing an acoustic signal.
[0002]
Conventionally, a parametric speaker that achieves high directivity using ultrasonic waves is
known (see, for example, Patent Document 1).
The parametric speaker emits a modulated wave obtained by modulating a carrier wave of an
ultrasonic band by an acoustic signal, and self-demodulates the modulated wave by non-linear
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characteristics in the air to transmit sound (demodulated sound). The audible area by the
parametric speakers is linear due to the high directivity of the ultrasound. Therefore, it is
possible to transmit a sound to the person present in the linear audible area.
[0003]
JP 2004-349816 A
[0004]
However, the demodulated sound obtained by demodulating the modulated wave has a
fluctuation in sound pressure depending on the distance from the parametric speaker, and can
sufficiently transmit the sound to the listener in the audible area where the sound pressure of the
demodulated sound is high. Even in areas where the sound pressure is low, sound may not be
transmitted sufficiently.
[0005]
The present invention is an acoustic system capable of demodulating a modulated wave
according to a desired position such as the position of a listener and reproducing an acoustic
signal, a medium container used therefor, and a method of reproducing an acoustic signal.
Intended to be provided.
[0006]
(1) The acoustic system according to the present invention radiates to an acoustic space a
modulated wave obtained by amplitude-modulating a carrier wave in an ultrasonic band with an
acoustic signal in the audible band, and demodulates the modulated wave in the acoustic space to
reproduce an acoustic signal. An acoustic system, the parametric speaker generating the
modulated wave and radiating into the acoustic space, and the medium filling the acoustic space
accommodating the medium having different predetermined properties from the parametric
speaker And a medium container for passing the emitted modulated wave.
[0007]
According to the acoustic system of the above configuration, the modulated wave radiated from
the parametric speaker passes not only through the medium that fills the acoustic space but also
through a medium that differs in predetermined characteristics from this, and is demodulated by
demodulation in that process Sound (sound signal) is reproduced.
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[0008]
The sound pressure of the demodulated sound depends on the degree of demodulation of the
modulated wave, and the sound pressure also becomes maximum at the position where the
degree of demodulation is maximum (the distance from the parametric speaker).
Also, the degree of demodulation changes in accordance with the predetermined property of the
medium through which the modulated wave passes.
Therefore, in the case where the modulated wave passes through only the medium that fills the
acoustic space and is demodulated, and in addition to the medium that fills the acoustic space,
the case where the modulated wave passes through a medium that has different predetermined
characteristics and is demodulated The position where the degree of demodulation is maximum
is different.
[0009]
The acoustic system of the above configuration includes a medium container that accommodates
a medium having a predetermined property different from that of the medium that fills the
acoustic space, so the position at which the degree of demodulation is maximized, that is, the
sound pressure of the demodulated sound is maximized. By setting the property of the medium in
the medium container so that the position is adjusted to the position of the listener etc., the
sound can be reliably transmitted to the listener.
[0010]
Note that "a medium having a predetermined property that differs from the medium that fills the
acoustic space" may be a medium of a type different from the medium that fills the acoustic
space, or may be the same type as the medium and only a predetermined property. It may be a
different medium.
Also, the "acoustic space" may be a closed space such as the inside of a room, or may be an open
space such as the outdoors.
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[0011]
(2) The predetermined property is preferably a factor that affects the density of the medium or
the velocity of sound in the medium.
The degree of demodulation of the modulated wave emitted from the parametric speaker varies
with the density of the medium and the speed of sound passing through the medium.
Therefore, by setting a factor that affects the density of the medium and the velocity of sound, it
is possible to adjust the position at which the degree of demodulation is maximum to a desired
position.
Note that factors that affect the speed of sound include the temperature, pressure, density and
the like of the medium.
[0012]
(3) A control device for adjusting the predetermined property of the medium in the medium
container so as to maximize the sound pressure of the demodulated sound at a desired position
away from the parametric speaker in the radiation direction of the modulated wave Preferably,
the According to this configuration, the degree of demodulation of the modulated wave is
controlled by adjusting the predetermined property of the medium in the medium container by
the control device, and the sound pressure of the demodulated sound at the desired position, for
example, the position of the listener Maximizing can ensure that the listener hears the sound. In
addition, adjustment of a predetermined | prescribed property includes converting to the
medium from which a predetermined | prescribed property differs in addition to adjustment of
the density, temperature, etc. of a specific medium.
[0013]
(4) The medium in the medium container is a mixed medium in which a plurality of types of
medium having different predetermined properties are mixed, and the control device adjusts the
mixing ratio of the mixed medium. It is also good. When the mixing ratio of a plurality of media is
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changed, the density or the like of the entire media also changes. Therefore, by adjusting the
mixing ratio of the medium, it is possible to control the degree of demodulation so that the
position at which the sound pressure of the demodulated sound is maximum is adjusted to the
desired position.
[0014]
(5) The control device may adjust a passing distance of the modulated wave with respect to the
medium in the medium container. The modulation wave also changes its degree of demodulation
depending on the distance through which the medium passes. Therefore, by adjusting the
distance, it is possible to control the degree of demodulation of the modulated wave so that the
position at which the sound pressure of the demodulated sound is maximum is adjusted to a
desired position.
[0015]
(6) The control device includes a detection unit that detects the position of the transmission
target of the demodulated sound, and adjusts the predetermined property so that the position of
the transmission target detected by the detection unit matches the desired position. It is
preferable to do. According to this configuration, the detection unit detects the transmission
target of the demodulated sound, for example, the position of the listener who is actually in the
acoustic space, and adjusts the predetermined property of the medium according to the detected
position of the transmission target. The position where the sound pressure of the demodulated
sound is maximum can be properly adjusted to the position of the transmission target.
[0016]
(7) Preferably, the parametric speaker includes a speaker main body having an ultrasonic wave
generating element for emitting the modulated wave, and the speaker main body is disposed in
the medium container. With such a configuration, the modulated wave passes through the
medium in the medium container immediately after being emitted from the speaker body.
Therefore, the modulation wave is largely influenced by the medium in the medium container,
and the degree of demodulation is efficiently controlled by the medium.
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[0017]
(8) The medium container may be detachably attached to the parametric speaker. With such a
configuration, for example, it is possible to replace a plurality of medium containers different in
the type of medium housed in the inside and in the size (passage distance of the modulation
wave) of the inside and attach to the parametric speaker. It is possible to control the degree of
demodulation of the modulated wave by replacing.
[0018]
(9) A medium container according to the present invention is detachably attached to a parametric
speaker that emits into an acoustic space a modulated wave obtained by amplitude-modulating a
carrier wave in an ultrasonic band with an audio signal in the audible band. The present
invention is characterized in that the modulation wave emitted from the parametric speaker is
allowed to pass through the medium containing the medium different in the predetermined
property from the medium. The medium container according to the present invention, by being
attached to the parametric speaker, can pass the modulation wave emitted from the parametric
speaker to the medium accommodated in the medium container as well as the medium in the
acoustic space. The degree of demodulation and the sound pressure of the demodulated sound
can be maximized at the desired position. Therefore, the sound can be reliably transmitted to the
transmission target at the desired position. In addition, the medium through which the modulated
wave passes can be easily changed by replacing the medium container.
[0019]
(10) A method of reproducing an acoustic signal according to the present invention is a method
of demodulating a modulated wave radiated from a parametric speaker into an acoustic space in
the acoustic space to reproduce an acoustic signal, and a medium filling the acoustic space The
modulation wave is demodulated by passing the medium having a predetermined property
different from that of the medium. In the method of reproducing an acoustic signal according to
the present invention, a position at which the degree of demodulation is maximized by passing
the modulated wave emitted from the parametric speaker between the medium in the acoustic
space and the medium in the medium container, ie, demodulation It is possible to set the position
at which the sound pressure of the sound is maximum as desired. Therefore, by setting the
position where the sound pressure of the demodulated sound is maximum to the position of the
listener or the like, it is possible to reliably transmit the sound to the listener.
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[0020]
According to the present invention, it is possible to demodulate the modulated wave in
accordance with the position of the listener, etc., and reproduce the acoustic signal.
[0021]
It is an explanatory view showing a usage pattern of a sound system concerning a 1st
embodiment.
It is a schematic block diagram of an acoustic system. It is a schematic block diagram of a
parametric speaker. It is an explanatory view showing a gas container. It is explanatory drawing
which shows the general relationship between the distance from a parametric speaker, and the
sound pressure level of a demodulation sound. It is explanatory drawing which shows the
relationship between the distance from a parametric speaker, and the sound pressure level of a
demodulation sound. It is explanatory drawing which shows the relationship between the
distance from a parametric speaker, and the sound pressure level of a demodulation sound. It is a
graph which shows the relationship between discontinuous distance (distance from which a
demodulation degree is the largest), the density of gas, and a sound pressure level. It is an
explanatory view showing a gas container of an acoustic system concerning a 2nd embodiment.
It is explanatory drawing which shows the experimental apparatus for conducting an evaluation
experiment. It is explanatory drawing which shows the experimental apparatus for conducting an
evaluation experiment. It is a graph which shows the change of the sound pressure level at the
time of accommodating carbon dioxide in a gas container. It is a graph which shows the change
of the sound pressure level at the time of accommodating helium in a gas container.
[0022]
Hereinafter, an acoustic system according to an embodiment will be described with reference to
the drawings. <First Embodiment> FIG. 1 is an explanatory view showing a usage form of the
sound system according to the first embodiment. The sound system 10 of the present
embodiment is for transmitting the sound emitted from the parametric speaker 12 to the listener
P who is present in the room 11 forming the sound space S. The parametric speaker 12 uses as a
carrier wave an ultrasonic wave that human beings can not perceive as sound at a high
frequency of 20 kHz or more as a carrier wave, and the modulated wave H amplitude-modulated
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by an acoustic signal such as voice is a large amplitude where nonlinearity occurs. Radiate to In
the process of propagating the air (atmosphere) G1 present in the acoustic space S, the
modulation wave H causes distortion due to the nonlinearity of the medium, and the distortion
causes the acoustic signal (demodulated sound), which is an audible sound, to self-demodulate. A
highly directional sound field is formed.
[0023]
FIG. 2 is a schematic block diagram of the sound system 10. FIG. 3 is a schematic block diagram
of the parametric speaker 12. The acoustic system 10 includes an acoustic signal generator 13
and a parametric speaker 12 or the like. The acoustic signal generation device 13 includes a
signal source 21 and a filter processing unit 22 as shown in FIG. The signal source 21 generates
an acoustic signal in the audible band, such as an audio signal or an audio signal, and outputs the
acoustic signal to the filter processing unit 22. The filter processing unit 22 outputs a
predetermined characteristic to the acoustic signal and then outputs the acoustic signal to the
parametric speaker 12.
[0024]
As shown in FIGS. 2 and 3, the parametric speaker 12 includes a speaker main body 26 and a
signal processing device 27. The speaker main body 26 includes a plurality of ultrasonic wave
generating elements for emitting ultrasonic waves, and the plurality of ultrasonic wave
generating elements are arrayed in an array along the emission surface in the longitudinal and
lateral directions.
[0025]
The signal processing device 27 includes a carrier wave generator 23, a modulator 24, and an
amplifier 25. The carrier wave generation unit 23 generates a carrier wave composed of
ultrasonic waves of a predetermined frequency and outputs the carrier wave to the modulation
unit 24. The carrier generation unit 23 includes, for example, a high frequency oscillator using a
quartz oscillator or the like. In the present embodiment, a 40 kHz carrier wave is generated and
output to the modulation unit 24.
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[0026]
The modulation unit 24 amplitude-modulates the carrier wave input from the carrier wave
generation unit 23 by the acoustic signal input from the signal generation device 13 and
generates a modulation wave H. The modulated wave H is emitted from the ultrasonic wave
generation element of the speaker main body 26 in a state of being amplified by the
amplification unit 25. The amplification unit 35 is configured using, for example, an operational
amplifier or the like that has a good amplification characteristic in the ultrasonic band.
[0027]
The carrier wave generation unit 23 and the modulation unit 24 are configured by, for example,
a computer including an operation unit such as a CPU, a storage unit such as a memory, and an
input / output interface. The carrier generation unit 23 and the modulation unit 24 are realized
by the arithmetic unit executing the computer program read into the storage unit.
[0028]
The modulated wave H radiated from the speaker body 26 of the parametric speaker 12 is selfdemodulated due to the non-linear phenomenon of air in the acoustic space S, and the
demodulated sound is reproduced. The self demodulation will be described. Assuming that the
carrier frequency is f c, time is t, and the maximum carrier amplitude is A c, the carrier W c (t)
can be expressed by the following equation (1).
[0029]
[0030]
Further, assuming that the frequency of the acoustic signal generated by the signal generation
device 13 is f s and the maximum amplitude of the acoustic signal is A s, the acoustic signal W s
(t) can be expressed by the following equation (2).
[0031]
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[0032]
Then, assuming that the modulation degree indicating the content of the acoustic signal is m (m
≦ 1) and the carrier wave W C (t) is amplitude-modulated by the acoustic signal W S (t), the
generated modulated wave W AM (t) is And can be expressed by the following equations (3) and
(4).
[0033]
[0034]
[0035]
The modulated wave W AM (t) represented by the equations (3) and (4) can be represented by
the following equation (5) using the trigonometric function addition theorem.
[0036]
[0037]
From equation (5), the modulation wave W AM (t) is the sum of the carrier frequency f c and the
audio signal frequency f s (f c + f s) in addition to the carrier of frequency f c ) And a sideband
having a frequency of difference (f c −f s).
Also, in general, when two sound waves in close proximity to each other in frequency are emitted
into the air, a secondary combined wave including a chord of the two sound waves and a
difference sound is generated.
Therefore, when a modulation wave is radiated from the parametric speaker 12 as a primary
wave, a secondary wave such as a difference sound between a carrier wave and a sideband wave
and a harmonic wave is generated in the propagation process.
The harmonics in the secondary wave are generated by the distortion of the waveform due to the
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emission of the amplitude modulation wave at high sound pressure and the generation of a
discontinuous wave front.
Also, in the secondary wave, the difference between the carrier wave and the sideband matches
the frequency of the original acoustic signal and is reproduced as an audible sound.
At this time, the self-demodulated acoustic signal includes not only the difference sound between
the carrier wave and the sideband but also the harmonic generated by the discontinuous wave
front.
Furthermore, since this demodulation phenomenon occurs only within the radiation range of the
amplitude modulated wave radiated as ultrasonic waves, the demodulated acoustic signal has
superdirectivity.
[0038]
The distance at which the discontinuous wavefront occurs in the process of self-demodulation is
derived as the “discontinuous distance x” by the following equation.
[0039]
[0040]
Here, c 0 is the velocity of sound in the gas, ρ 0 is the density of the gas, β is the nonlinear
coefficient of air, p 0 is the sound source sound pressure level of the modulation wave, and ω is
the angular frequency of the modulation wave.
Since the discontinuous wave front is generated in the section of the discontinuous distance x, it
is considered that the sound pressure of the demodulated sound becomes maximum at the
position of the distance x from the radiation plane of the parametric speaker 12.
[0041]
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FIG. 5 is an explanatory view showing a general relationship between the distance from the
parametric speaker and the sound pressure level of the demodulated sound.
In FIG. 5, it is assumed that the modulated wave H emitted from the parametric speaker 12 is
propagated in the air (atmosphere) G1.
The sound pressure level of the demodulated sound obtained by demodulating the modulated
wave H gradually increases with distance from the parametric speaker 12, and after being
maximized at a predetermined position, gradually attenuates.
When the modulation wave H is radiated into the air, the demodulated sound is sufficiently
transmitted to the listener who is at the position B where the sound pressure level is maximum.
[0042]
However, at a position A before the position B where the sound pressure level is maximum, the
modulated wave H is not sufficiently demodulated, and the sound pressure level is low. Also, at
position C, which has passed position B, the sound pressure level is lowered due to attenuation
due to distance. Therefore, at position A and position C, there is a possibility that sound can not
be sufficiently transmitted to the listener. In this embodiment, for example, the modulation wave
H emitted from the parametric speaker 12 is sufficiently demodulated at the position A or C so
that the demodulated sound can be sufficiently transmitted to the listener at the position A or C,
for example. , To maximize the sound pressure level. For that purpose, the acoustic system 10
has the following configuration.
[0043]
As shown in FIGS. 1 and 2, in addition to the acoustic signal generation device 13 and the
parametric speaker 12, the acoustic system 10 of the present embodiment includes a gas
container (medium container) 14, a gas supply device 15, and a controller It has 16 and. FIG. 4 is
an explanatory view showing the gas container 14. The gas container 14 is formed in a box
shape, and accommodates a gas (medium) inside. Specifically, a gas G2 (including a mixed gas
with air) different from the air (atmosphere) G1 in the acoustic space S is accommodated in the
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gas container 14.
[0044]
Further, the gas container 14 includes a box main body 31 with one side opened and a shielding
member 32 for closing the one side. The shielding member 32 blocks the passage of gas and
allows the passage of sound waves. The shielding member 32 is made of, for example, a film
having a thickness (for example, 2 μm) smaller than the wavelength of the modulation wave. For
example, as the shielding member 32, polyester film Diafoil (registered trademark) manufactured
by Mitsubishi Plastics, Inc. can be used. A gas supply device 15 is connected to the gas container
14.
[0045]
Further, in the present embodiment, the speaker body 26 of the parametric speaker 12 is
accommodated inside the gas container 14. The speaker body 26 is disposed such that the
radiation surface 26 a of the modulated wave H opposes the shielding member 32 with a space
w. The modulated wave H emitted from the speaker body 26 passes through the gas G2 in the
gas container 14 and the shielding member 32, is emitted to the acoustic space S, and is
demodulated to the listener P in the acoustic space S. Demodulated sound is transmitted.
Therefore, the modulated wave H passes through both the gas G2 in the gas container 14 and the
air G1 in the acoustic space S in the process of being demodulated into a demodulated sound.
[0046]
Further, the gas container 14 is configured to be able to increase or decrease the distance w from
the radiation surface 26 a of the speaker main body 26 to the shielding member 32, that is, the
distance w through which the modulation wave passes the gas in the gas container 14. ing.
Specifically, the side wall 31 a of the gas container 14 is configured to be extensible and
contractible along the radiation direction of the modulated wave H. In the example shown in FIG.
4, the side wall 31 a is formed in a telescopic structure. Further, the gas container 14 is provided
with an actuator 33 for contracting the side wall 31 a of the box body 31. Then, by extending the
side wall 31a of the box body 31, the distance w from the radiation surface 26a of the speaker
body 26 to the shielding member 32 can be increased, and the distance w can be shortened by
contracting the side wall 31a.
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[0047]
In addition, as the actuator 33, a fluid pressure drive or an electric cylinder, a motor, etc. are
employable. Further, as a structure for increasing or decreasing the distance w from the radiation
surface 26a of the speaker main body 26 to the shielding member 32, for example, a bellows
structure is incorporated in the side wall 31a of the gas container 14 and a structure for
expanding and contracting the side wall 31a is adopted. Alternatively, the speaker body 26 may
be moved along the radiation direction of the modulated wave.
[0048]
As shown in FIG. 2, the gas supply device 15 supplies a predetermined gas into the gas container
14. The gas supply device 15 includes a cylinder that contains a gas, a solenoid valve that
switches supply / stop of the gas, a switching valve, and the like. In addition, the gas supply
device 15 of the present embodiment is configured to switch a plurality of gases and supply the
gas to the gas container 14. Specifically, the gas supply device 15 switches to carbon dioxide,
which is a gas having a density higher than that of air, and helium, which is a gas having a
density lower than that of air, and supplies the gas to the gas container.
[0049]
The control device 16 performs operation control of the actuator 33 in the gas container 14,
supply control of gas by the gas supply device 15, and the like. The control device 16 includes a
detection unit 41, a distance calculation unit 42, and an adjustment unit 43 as its functional
units. The control device 16 is configured of, for example, a computer including an arithmetic
unit such as a CPU, a storage unit such as a memory, and an input / output interface. Then, the
calculation unit executes the computer program read into the storage unit, whereby the detection
unit 41, the distance calculation unit 42, and the adjustment unit 43 are realized.
[0050]
The detection unit 41 detects the position of the listener P (for example, the position of the
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listener's head) in the acoustic space S (see FIG. 1). Specifically, the detection unit 41 receives an
image from a camera (imaging device) 44 that captures the inside of the acoustic space S. The
detection unit 41 detects the position of the listener P in the acoustic space S by performing
image processing on the input image.
[0051]
The distance calculation unit 42 calculates the distance w between the position of the listener P
detected by the detection unit 41 and the radiation surface 26 a of the speaker main body 26 by
calculation. The adjustment unit 43 selects the type of gas contained in the gas container 14
according to the distance l from the radiation surface 26 a of the speaker main body 26 to the
position of the listener P, and the passing distance of the modulated wave in the gas container 14
Adjust w. The adjustment unit 43 will be specifically described below.
[0052]
In the above equation (6), the discontinuous distance x, that is, the distance at which the
demodulation degree of the modulated wave and the sound pressure of the demodulated sound
become maximum can be adjusted by changing the density ρ 0 or the speed of sound c 0 of the
gas. it can. The density 気 体 0 of the gas takes different values for each type of gas. Therefore,
the discontinuous distance x can be adjusted by changing the type of gas contained in the gas
container 14. In addition, the speed of sound c 0 changes with the temperature, pressure, density
and the like of the gas. Therefore, the discontinuous distance x can be adjusted by changing the
temperature or pressure of the gas contained in the gas container.
[0053]
The following Table 1 shows the relationship between density, sound velocity, and discontinuous
distance according to the type of gas. According to Table 1, it can be seen that when the
modulated wave propagates in a gas having a density lower than that of air, the discontinuous
distance becomes large, and the sound pressure of the demodulated sound becomes maximum at
a greater distance. Also, it can be seen that when the modulated wave propagates in a gas having
a density higher than that of air, the discontinuous distance becomes smaller, and the sound
pressure of the demodulated sound is maximized in the vicinity.
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[0054]
[0055]
In the present embodiment, the gas supply device 15 includes two types of gases, carbon dioxide
and helium, and adjusts the discontinuous distance x by switching these two types of gases and
supplying them to the gas container 14. .
Further, in the present embodiment, the expansion and contraction of the gas container 14 can
change the passing distance w of the modulation wave with respect to the gas inside. The
discontinuous distance x can also be adjusted by changing the passing distance w.
[0056]
In this embodiment, since the modulation wave passes through both the gas in the gas container
14 and the air in the acoustic space S, it is necessary to determine the discontinuous distance x in
consideration of both the gases. As shown in FIG. 2, assuming that the ratio of the passage
distance w of the modulation wave H to the gas G2 in the gas container 14 and the passage
distance of the modulation wave H to the gas G1 in the acoustic space S is γ, The distance d at
which the sound pressure is maximum can be expressed by the following equation (7).
[0057]
[0058]
Here, x gas is a discontinuous distance in the gas G2 in the gas container 14, and x air is a
discontinuous distance in the air G1 in the acoustic space S.
Further, γ can be expressed by the following equation (8) from the passage distance w of the
modulated wave in the gas container 14 and the distance 1 from the radiation surface 26 a of the
speaker main body 26 to the listener P.
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[0059]
[0060]
Further, the discontinuous distance x gas in the gas G 2 in the gas container 14 and the
discontinuous distance x air in air in the acoustic space S are expressed by the following equation
(9) using the equation (6) above: And equation (10).
[0061]
[0062]
[0063]
In the equations (9) and (10), gas gas is the density of the gas in the gas container 14, ρ air is
the density of the air in the acoustic space S, and c gas is the gas in the gas container 14. Sound
velocity, c air is the sound velocity in air.
FIG. 8 is a graph showing the relationship between the discontinuous distance (the distance at
which the degree of demodulation is maximum) in equation (6), the density of the gas, and the
sound pressure level.
In this graph, the horizontal axis indicates the density of the gas, the vertical axis indicates the
velocity of sound, and the back surface color (shade) in the graph indicates the discontinuous
distance.
According to the relationship shown in this graph, it is possible to determine the density and the
speed of sound of the required gas for any distance d where the degree of demodulation is
maximum.
Thereby, the gas closest to the calculated density and sound velocity can be determined as the
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medium from the above equation (9).
[0064]
The adjustment unit 43 maximizes the sound pressure of the demodulated sound at a distance l
from the radiation surface 26a of the speaker main body 26 to the position of the listener P
using the relationships of Equations (7) to (10) and FIG. The type of gas contained in the gas
container 14 is selected so as to match the distance d, and the passage distance w of the
modulated wave in the gas container 14 is set. As a result, at the position of the listener P, the
degree of demodulation can be controlled to maximize the sound pressure of the demodulated
sound, and the demodulated sound can be reliably transmitted to the listener P.
[0065]
6 and 7 are explanatory diagrams showing the relationship between the distance from the
parametric speaker and the sound pressure level of the demodulated sound. FIG. 6 shows an
example in which helium having a density lower than that of air is contained in the gas container
14, and FIG. 7 shows an example in which carbon dioxide having a density higher than that of air
is accommodated. In FIG. 6, the position B is the position where the sound pressure is maximum
when the modulation wave passes through the air as described in FIG. When helium is contained
in the gas container 14, the modulated wave emitted from the speaker body 26 passes through
the air G1 in the acoustic space S after passing through the helium G2 (He) in the gas container
14. . In this case, the sound pressure level is maximum at a position C farther from the speaker
main body 26 than the position B. Therefore, there is a possibility that the modulated wave H is
not sufficiently demodulated at the position B and the demodulated sound can not be sufficiently
transmitted to the listener, but the listener P at the position C is sufficiently demodulated. It can
transmit sound.
[0066]
As shown in FIG. 7, when carbon dioxide is stored in the gas container 14, the modulated wave H
emitted from the speaker main body 26 passes through the carbon dioxide G2 (CO 2) in the gas
container 14. , Through the air G1 in the acoustic space S. At this time, the sound pressure level
is maximum at a position A closer to the speaker main body 26 than the position B. Therefore, at
position B, the sound pressure level is lowered due to attenuation due to distance, and there is a
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possibility that the demodulated sound can not be sufficiently transmitted to the listener, but for
the listener P who is at position A, the demodulated sound is sufficiently Can be transmitted.
[0067]
The gas container 14 may not contain carbon dioxide or helium at a concentration of 100%, and
may be mixed with air. In this case, the concentration (mixing ratio) of carbon dioxide or helium
in the gas container 14 can be set to a predetermined value by controlling the supply amount of
carbon dioxide or helium supplied to the gas container 14 by the controller 16. it can.
Alternatively, a concentration sensor may be installed in the gas container 14 to supply each gas
to the gas container 14 such that carbon dioxide or helium is maintained at a predetermined
concentration. Also, by adjusting the concentration of carbon dioxide or helium, the degree of
demodulation of the modulated wave can be controlled, and the position at which the sound
pressure of the demodulated sound becomes maximum can be controlled.
[0068]
Further, the inside of the gas container 14 can be filled with the same air as the acoustic space S
by stopping the supply of gas to the gas container 14 and opening the inside of the gas container
14. In this case, the sound pressure can be maximized at position B, as described with reference
to FIG.
[0069]
The acoustic system 10 described above accommodates the modulated wave emitted from the
parametric speaker 12 in the gas G2 accommodating and accommodating the gas (medium) G2
having a predetermined property different from that of the air (medium) G1 filling the acoustic
space S. Since the gas container (medium container) 14 to be passed is provided, the modulated
wave emitted from the parametric speaker 12 passes through the gas G2 in the gas container 14
and the air G1 that fills the acoustic space S. It is demodulated and the demodulated sound is
reproduced. Therefore, the sound pressure of the demodulated sound becomes maximum at a
position different from the case where the modulation wave passes only the air G1 in the
acoustic space S, and the position depends on the property of the gas G2 in the gas container 14.
Therefore, by adjusting the property of the gas G2 in the gas container 14, it is possible to
control the degree of demodulation and to set the position at which the sound pressure of the
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demodulated sound becomes maximum according to the position of the listener P.
[0070]
Further, since the control device 16 is provided with the detection unit 41 for detecting the
position of the listener P, the control device 16 detects the actual position of the listener in real
time, and performs control of the optimum demodulation degree according to the position. Can.
Since the speaker body 26 of the parametric speaker 12 is disposed in the gas container 14, the
modulated wave emitted from the speaker body 26 passes through the gas G2 in the gas
container 14 in a high energy state. Therefore, the influence of the gas G2 in the gas container
14 is largely influenced, and the control of the degree of demodulation can be efficiently
performed by the gas G2.
[0071]
Second Embodiment FIG. 9 is an explanatory view showing a gas container of an acoustic system
according to a second embodiment. The gas storage device 14 is detachably attached to the
speaker body 26 of the parametric speaker 12. The gas container 14 includes a cylindrical side
wall 51 and a shielding member 52 that closes the opening on both sides of the side wall 51. The
shielding member 52 is a film that blocks the passage of gas and allows the passage of sound
waves as the shielding member 32 described above.
[0072]
The speaker body 26 is provided with a mounting tool 53 for mounting the side wall 51 of the
gas container 14. The mounting tool 53 can adopt, for example, a configuration in which the side
wall 51 is mounted using a fastener such as a bolt, or a configuration in which the side wall 51 is
mounted by a magnet. When the gas container 14 is mounted on the speaker body 26, one of the
shielding members 52 is in close contact with the radiation surface 26 a of the speaker body 26.
Therefore, the modulated wave passes through the gas G2 in the gas container 14 immediately
after being emitted from the speaker body 26.
[0073]
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In the present embodiment, a plurality of gas containers 14 having different types of stored
gases are prepared in advance, and the gas containers 14 are replaced and mounted according to
the position of the listener in the acoustic space S, etc. , It becomes possible to control the degree
of demodulation. In addition, by replacing and mounting the plurality of gas containers 14
having different widths w, it is possible to adjust the distance that the modulated wave passes
through the gas G2 in the gas container 14 and to control the degree of demodulation. Also, by
overlapping and mounting a plurality of gas containers 14 having the same width w, it is possible
to adjust the distance the modulated wave passes through the gas G2 in the gas container 14.
[0074]
<Evaluation Experiment> The inventor of the present application conducted an evaluation
experiment to confirm that the control of the degree of demodulation of the parametric speaker
can be effectively performed by the acoustic system as described above. For this evaluation
experiment, the experimental apparatus shown in FIGS. 10 and 11 was used. This experimental
apparatus radiates a modulated wave from outside to the inside of the gas container with one
side open by a parametric speaker, reflects on the bottom surface of the gas container, and emits
the demodulated sound of the modulated wave emitted to the outside, The sound pressure level
was measured by recording with a plurality of microphones at different locations at different
distances L from the gas container.
[0075]
The gas container shown in FIG. 10 was disposed with the opening directed upward to
accommodate carbon dioxide (CO 2) heavier than air. The gas container shown in FIG. 11 was
disposed with the opening directed downward to contain helium (He) lighter than air. Moreover,
in each experiment using the gas container of FIG.10 and FIG.11, the density | concentration of
the gas accommodated in a gas container was changed, and the sound pressure level was
measured.
[0076]
For parametric speakers, MSP-50E manufactured by Mitsubishi Electric Engineering Co., Ltd .;
ECM 88B manufactured by Sony Corporation for microphones; MICA-800A manufactured by
Hiratsuka Engineering Co. for microphone amplifiers; FireFace UFX manufactured by RME for
audio interfaces; NL-26 manufactured by Rion Co., Ltd. was used as a noise level meter.
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[0077]
The experiment shown in FIG. 10 was performed under the recording conditions shown in Table
2, and the experiment shown in FIG. 11 was performed under the recording conditions shown in
Table 3.
The concentration of gas in each experiment is the average concentration during the
measurement.
[0078]
[0079]
[0080]
FIG. 12 is a graph showing a change in sound pressure level when carbon dioxide is contained in
the gas container.
From the results shown in FIG. 12, it can be seen that the distance at which the sound pressure is
maximized is shortened by passing the carbon dioxide through the modulation wave as
compared with the case where the modulated wave passes through the air.
It can also be seen that the higher the carbon dioxide concentration, the shorter the distance at
which the sound pressure is at a maximum. Therefore, it can be said that the degree of
demodulation of the modulated wave can be maximized at a position closer to the parametric
speaker as the density of the gas contained in the gas container is higher than that of air.
[0081]
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FIG. 13 is a graph showing a change in sound pressure level when helium is contained in the gas
container. From the results shown in FIG. 13, it can be seen that the distance at which the sound
pressure is maximized is longer when the modulation wave passes through helium as compared
with the case where it passes through air. Also, it can be seen that the higher the helium
concentration, the longer the distance at which the sound pressure is maximum. Therefore, it can
be said that the degree of demodulation of the modulated wave can be maximized at a position
farther from the parametric speaker as the density of the gas contained in the gas container is
lower than that of air.
[0082]
The present invention is not limited to the above embodiment, and can be suitably modified
within the scope described in the claims. For example, the gas container (medium container) can
contain a gas different from carbon dioxide and air other than helium. In the above embodiment,
the degree of demodulation is controlled by changing the type of gas contained in the gas
container, but the degree of demodulation is controlled by changing factors that affect the speed
of sound, such as the temperature and pressure of one type of gas. You may control.
[0083]
Alternatively, the same air as the acoustic space may be accommodated in the gas container, and
the degree of demodulation may be controlled by changing the temperature or pressure of the
air in the gas container to a value different from that of the acoustic space. The acoustic space
may be filled with a gas different from air. The gas container may be formed into a bag shape
only with a film that can pass sound waves.
[0084]
The parametric speaker may be installed above or below the listener. In this case, it is possible to
set the transmission target of the demodulated sound as the head (ear) of the listener and to
control the degree of demodulation according to the height. Inside the gas container, a
temperature sensor for measuring the temperature of the gas or a pressure sensor for measuring
the pressure may be provided, and the speed of sound can be determined using these detected
values to control the degree of demodulation. .
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[0085]
The medium contained in the medium container is not limited to the gas, but may be liquid or
solid. The detection unit of the control device detects the position of the listener by analyzing the
image from the camera, but provides a position sensor such as a photoelectric sensor or an
infrared sensor provided in the acoustic space, and The position of the listener may be detected
based on the input signal.
[0086]
The speaker main body and medium container of the parametric speaker can be used, for
example, by being attached to the user's body. For example, by attaching the speaker body to the
head, face, neck, arms, etc. of the user and setting the audible area near the user's ear, the sound
can be delivered only to the user without using headphones etc. It becomes possible. Note that
"wearing" on the user's body includes carrying it in a pocket or the like of the user's clothes, for
example.
[0087]
10: sound system 12: parametric speaker 14: gas container (medium container) 16: control
device 26: speaker main body 41: detection unit G1: air (medium) G2: gas (medium) H:
modulation wave P: listener S: Acoustic space
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