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JP2006081117

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DESCRIPTION JP2006081117
An object of the present invention is to appropriately control the sound quality to be heard by a
listener in accordance with the relative position to the listener. A carrier frequency controller
controls a frequency of a carrier. By performing amplitude modulation in the modulator 3 using
this controlled carrier wave, the distance and directivity in which the acoustic output outputted
from the superdirective speaker system is demodulated by the nonlinearity of the medium are
controlled according to the carrier wave frequency Do. [Effect] By adjusting the demodulation
distance, the optimum demodulation distance can be adapted to the listener of the superdirective
speaker system, and a high quality sound field can be realized for the listener. [Selected figure]
Figure 1
Superdirectional speaker system
[0001]
The present invention relates to superdirective speaker systems, and more particularly to control
of distance and direction to be demodulated.
[0002]
Generally, the sound output reproduced from the sound speaker is diffusive.
For this reason, when the user, ie, the listener, listens to the sound output such as voice or music
reproduced through the sound speaker, the person other than the listener can hear the sound
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output and the problem of becoming noise and the leakage of the secret There was a problem. As
a means for solving this problem, a parametric speaker has been proposed as a superdirective
speaker for forming a highly directional sound field (e.g., Patent Document 1).
[0003]
A parametric speaker obtains high directivity by outputting high frequency sound waves as a
carrier wave. In order to obtain high directivity, the property of the sound wave is used that the
directivity angle decreases as the frequency of the sound wave increases. The parametric speaker
is realized, for example, in a configuration as shown in FIG. A high frequency sine wave
generated by the carrier oscillator 20 is used as a carrier, and the original sound 11 is amplitudemodulated with the carrier in the modulator, and input to the electroacoustic transducer 5
through the amplifier 4. The signal input to the electroacoustic transducer 5 is often amplified in
amplitude by the amplifier 4 in order to be output as a finite amplitude sound wave in the
medium.
[0004]
Next, the operation of such a superdirective speaker system will be described. The
electroacoustic transducer 5 is a so-called parametric array speaker, which radiates into the air a
carrier wave having an ultrasonic band frequency amplitude modulated by an audible sound
(voice signal), and can be utilized using non-linear characteristics of air. It is a speaker which
performs highly directional acoustic radiation by demodulating a listening sound. The modulator
3 amplitude-modulates the carrier wave of the ultrasonic band output from the carrier wave
oscillator 20 with the original sound 11 which is a voice signal. The frequency of the carrier
wave output from the carrier oscillator 20 is the frequency of the ultrasonic band, ie, 20 KHz or
more. Here, the frequency of the carrier wave is 40 KHz. The amplifier 4 amplifies the amplitude
of the modulated signal output from the modulator 3 to a level capable of driving the
electroacoustic transducer 5 according to a predetermined amplification factor, and outputs the
amplified signal to the electroacoustic transducer 5.
[0005]
The electroacoustic transducer 5 emits the modulated signal amplified by the amplifier 4 in a
specific direction as superdirective acoustic vibration. The acoustic vibration radiated into the air
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by the electroacoustic transducer 5 becomes a distorted wave due to the non-linear characteristic
of the air, and is demodulated to the original audible sound while propagating through the air.
The demodulated audible sound has superdirective characteristics of the original ultrasonic wave,
and thus can emit acoustic radiation only to a desired specific space.
[0006]
Here, superdirective acoustic radiation will be described with reference to FIG. The original
sound 11, which is an audio signal, is the transmission wave shown in FIG. FIG. 15 (b) shows the
waveform of the carrier wave generated inside the modulator 3. When this carrier wave is
amplitude-modulated by the original sound 11 which is a voice signal, an amplitude-modulated
wave as shown in FIG. 15C is obtained. The amplitude modulation wave x at this time is
expressed by equation (1), assuming that the carrier wave frequency is f1, the transmission wave
frequency is f2, the carrier wave amplitude is n1, and the transmission wave amplitude is n2.
x=(n1+nx)sinf1+n2sin(f1±f2)…(1)
[0007]
In equation (1), nx indicates the audio signal level when the transmission wave is zero. When the
amplitude modulation wave x is radiated into the air, the sound wave is shown in FIG. 15 (d)
because it travels faster when air vibrates in the forward direction due to nonlinear
characteristics of air and travels later when air travels in the reverse direction. It becomes a
distorted distortion wave, and the original audible sound is demodulated. The audible sound after
demodulation is shown in FIG. 15 (e). This demodulated wave has superdirective characteristics
of the original ultrasonic wave.
[0008]
Based on the above principle, the parametric speaker can output a directional acoustic signal. By
the way, as a technology to direct the sound field to a specific position using a parametric
speaker, the electroacoustic transducers of the parametric speaker are arrayed and arranged on a
curved surface, or the modulation wave subjected to the electroacoustic conversion is reflected
on a curved surface A method has been proposed in which the sound output is directed to a
certain point by doing this (for example, Patent Document 2 and Patent Document 3). However,
this method increases the volume required for the arrangement of the device by arranging the
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parametric speaker in space in space or requiring a reflection surface, and also increases the
space of the device for adjustment of the optimum demodulation position. There is a problem
that it is necessary to change the upper position.
[0009]
Further, as a technique for directing a sound field to a specific position using a parametric
speaker, a method of causing interference of sound fields from a plurality of electro-acoustic
transducers has been proposed (for example, Patent Document 4). However, in this method, it is
necessary to arrange a plurality of electroacoustic transducers at a distance, and it is difficult to
increase the number of electroacoustic transducers and to maintain high control accuracy
between devices. There's a problem.
[0010]
Furthermore, it is known that the original sound is demodulated from the modulated signal in the
process of the acoustic signal propagating through the medium, and the sound pressure to be
demodulated fluctuates according to the distance and depends on the frequency of the carrier
(for example, Non Patent Literature 1). However, the frequency of the carrier wave is fixed and
used after being set once, and there is a problem that it is not optimally used according to the
situation of use and the situation of the listener. Japanese Patent Application Laid-Open No. 58119293 Japanese Patent Application Laid-open No. 4-215399 Japanese Patent Application LaidOpen No. 2003-158788 Japanese Patent Application Laid-Open No. 11-145915 J76−A
No.8 pp.1127−1135、1993/ 8
[0011]
According to the above-mentioned prior art, when the listener listens to the sound output from
the superdirective speaker, the relative position between the superdirective speaker and the
listener degrades the sound quality heard by the listener. There is. The present invention has
been made to solve the above-mentioned problems of the prior art, and the purpose thereof is to
properly adjust the sound quality to be heard by the listener in accordance with the relative
position between the superdirective speaker and the listener. An object is to provide a
superdirective speaker system that can be controlled.
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[0012]
The superdirective speaker system according to claim 1 of the present invention is a
superdirective speaker system for emitting into the medium an acoustic output which is
demodulated at a predetermined distance by the non-linearity of the medium, wherein the carrier
wave in the ultrasound band An amplitude modulation means for amplitude-modulating a signal
with an original sound signal; a carrier frequency control means for varying and controlling the
frequency of the carrier signal according to a demodulation distance; and emitting an amplitude
modulation signal output from the amplitude modulation means into a medium And electroacoustic conversion means. By controlling the frequency of the carrier wave, it is possible to
control the distance and directivity in which the acoustic output outputted from the
superdirective speaker system is demodulated by the nonlinearity of the medium according to
the carrier frequency, and the demodulation distance is adjusted By doing this, the optimum
demodulation distance can be adapted to the listener of the superdirective speaker system, and a
high quality sound field can be realized for the listener.
[0013]
The superdirective speaker system according to claim 2 of the present invention further
comprises frequency band control means according to claim 1, wherein a filtering frequency
band is controlled in accordance with the frequency of the carrier signal and the frequency of the
original sound signal. The modulation means amplitude-modulates the carrier signal by the
output of the frequency band control means. With this configuration, the frequency band of the
original sound can be controlled, and a modulated wave obtained by amplitude-modulating the
original sound at the carrier frequency is output in the audio frequency band, particularly when
the carrier frequency is low or when the original sound includes high frequency amplitude. Can
be prevented.
[0014]
In the ultrasonic speaker system according to a third aspect of the present invention, in the first
or second aspect, the electro-acoustic conversion means includes a plurality of ultrasonic
transducers arranged in an array, and the electro-acoustic conversion means according to the
demodulation direction. It further comprises phase control means for controlling the output time
difference of the plurality of ultrasonic transducers. With this configuration, the acoustic outputs
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from the plurality of ultrasonic transducers are added, and the acoustic signal can be output from
the electroacoustic transducer at a high sound pressure. Further, by providing a phase difference
between the acoustic outputs outputted from the plurality of ultrasonic transducers constituting
the array, the wavefront of the acoustic output outputted from the electroacoustic transducer
constituted of the plurality of ultrasonic transducers is obtained. You will be able to control the
direction.
[0015]
The superdirective speaker system according to claim 4 of the present invention is characterized
in that, in any one of claims 1 to 3, it includes a number of electro-acoustic conversion means
corresponding to the number of channels of the original sound signal. Do. With this
configuration, the acoustic output of not only one channel but also two or more channels can be
output from the corresponding electroacoustic transducers. This configuration makes it possible
for the listener to listen to a stereo sound source or a binaural sound source.
[0016]
The superdirective speaker system according to claim 5 of the present invention further includes
a sensor for detecting the position of the listener according to any one of claims 1 to 4, and the
demodulation distance according to the detection result of the sensor To determine. With this
configuration, whenever the distance or direction of the listener is relatively changed with
respect to the superdirective speaker system, the change content can be measured by the sensor,
and based on the measured value, the sound can be detected. It is possible to calculate the
position at which the signal should be optimally demodulated, and to feed back the distance and
directivity angle at which the acoustic output outputted from the electroacoustic transducer is
demodulated with high quality based on the calculated position. As a result, it is possible to
adjust the distance to which the acoustic output reproduced from the superdirective speaker
system is directed and the directivity angle, and it is possible to form a sound field suitable for
the listener to listen to.
[0017]
The superdirective speaker system according to claim 6 of the present invention is characterized
in that in claim 5, the sensor detects the position of the listener by the reflected wave from the
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listener for the emitted sound wave. With this configuration, the superdirective speaker system
can use an acoustic device such as an electroacoustic transducer or a microphone for positioning,
so the number of devices configured for positioning use can be reduced. Thereby, since a
superdirective speaker can be used also as a positioning signal output means, the number of
devices configured for positioning applications can be reduced.
[0018]
The superdirective speaker system according to claim 7 of the present invention is characterized
in that in claim 6, the sensor detects the position of the listener by reflected light from the
listener for emitted light. With this configuration, an optical sensor can be used for positioning in
the superdirective speaker system. In the superdirective speaker system according to an eighth
aspect of the present invention, in any one of the first to seventh aspects, the amplitude
modulation means is configured to respond to at least one of the carrier signal and the original
sound signal. At least one of an amplitude of the carrier signal and a modulation degree in the
amplitude modulation is controlled. With this configuration, it is possible to reduce the sound
pressure of the carrier wave while appropriately setting the sound pressure of the multi-tone
sound, and it is possible to improve the efficiency of the sound output.
[0019]
As described above, according to the carrier frequency, the present invention controls the
distance and directivity in which the acoustic output outputted from the superdirective speaker
system is demodulated by the nonlinearity of the medium by controlling the carrier frequency. It
has the effect of being able to Then, by adjusting the distance to be demodulated, the optimum
demodulation distance can be adapted to the listener of the superdirective speaker system, and a
high quality sound field can be realized for the listener.
[0020]
Hereinafter, embodiments of the present invention will be described with reference to the
drawings. In the drawings referred to in the following description, the same parts as those in the
other drawings are indicated by the same reference numerals. FIG. 1 is a block diagram showing
an embodiment of the superdirective speaker system according to the present invention. As
shown in the figure, the superdirective speaker system is configured to include an input portion
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1, a carrier frequency controller 2, a modulator 3, an amplifier 4 and an electroacoustic
transducer 5. There is.
[0021]
The input unit 1 includes a distance input unit 1a and an original sound input unit 1b. To the
original sound input unit 1b, an original sound signal that the superdirective speaker system
demodulates at a listener's listening point is input. The distance input unit 1a receives a signal
relating to the distance or carrier frequency at which the superdirective speaker system
optimally demodulates the sound output. The carrier frequency controller 2 refers to the signal
relating to the distance or carrier frequency input from the input unit 1. The carrier frequency
controller 2 controls so as to lower the carrier frequency when the optimum demodulation point
is close to the present system, and to raise the carrier frequency when the optimum
demodulation point is separated from the present system. That is, the carrier frequency
controller 2 has a function of inputting to the modulator 3 a signal related to the carrier
frequency corresponding to the optimum demodulation distance.
[0022]
The modulator 3 amplitude-modulates the original sound signal input from the original sound
input unit 1 b at the carrier frequency input by the carrier frequency controller 2. The amplitude
modulation signal amplitude-modulated in the modulator 3 is input to the amplifier 4. The
amplifier 4 amplifies the amplitude of the input amplitude modulation signal and outputs the
amplified signal to the electroacoustic transducer 5. The electroacoustic transducer 5
electroacoustically converts the input amplitude modulation signal and outputs it into a medium.
As described above, by controlling the frequency of the carrier wave used for amplitude
modulation by the carrier wave frequency controller 2, the sound quality that the listener listens
to is appropriate according to the relative position between the superdirective speaker and the
listener. Can be controlled.
[0023]
A first embodiment of the present invention will be described with reference to FIGS. 2 and 3. As
shown in FIG. 2, in the present embodiment, two-channel original sound signals are input to the
original sound input unit 1b, and two electroacoustic transducers are mounted. That is, the
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number of electro-acoustic transducers corresponding to the number of channels of the original
sound signal is mounted. Then, for each of the left channel and the right channel, the distance
input unit 1a, the carrier frequency controller 2 and the modulator 3 are prepared, and are
configured to be able to process input signals of two channels. For example, input signals of two
channels are prepared in advance in the form of a database.
[0024]
The positional relationship between the superdirective speaker system 100 according to this
embodiment and the listener is shown in FIG. As shown in the figure, the electric-acoustic
transducer 5a is prepared corresponding to the left ear 10L of the listener 10 of the
superdirective speaker, and the electric-acoustic transducer 5b is prepared corresponding to the
right ear 10R. ing. In such a configuration, each channel of the original sound is demodulated at
each ear by outputting an acoustic signal from the electroacoustic transducer 5a and 5b.
Therefore, in this embodiment, a stereo sound source or a binaural sound source can be
reproduced as a two-channel original sound.
[0025]
A second embodiment of the present invention will be described with reference to FIGS. 4 and 5.
As shown in FIG. 4, in the present embodiment, the frequency band controller 6 is added to the
configuration of FIG. The frequency band controller 6 forms a band pass filter on the basis of the
frequency band of the original sound signal and the frequency designated by the carrier
frequency controller 2, and passes the band pass filter to input the original sound signal to the
modulator 3. Do. The frequency band controller 6 performs amplitude modulation on the original
sound signal having passed the band pass filter only when the frequency of the amplitude
modulation signal is lower than a predetermined value.
[0026]
The filtering characteristic of the band pass filter by the frequency band controller 6 is shown in
FIG. The horizontal axis of the figure is frequency, and the vertical axis is amplitude. Amplitude
modulation signals exist on both sides of the frequency of the carrier signal. As shown in FIG. 5
(a), when the frequency of the carrier wave 60 is low or the frequency band of the original sound
signal is wide and the band of the modulation wave is wide, the amplitude modulation signal
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becomes audible. That is, the lower frequency side of the amplitude modulation waves 61 and 62
is applied to the audible area 63, and the hatched portion in the figure becomes audible. In order
to make the amplitude modulation waves 61 and 62 have no audible amplitude, it is necessary to
narrow the frequency band of the original sound signal. If the original sound signal is amplitudemodulated after passing through a band-pass filter in order to realize this, the amplitudemodulated waves 61 'and 62' have no audible amplitude, as shown in FIG. 5 (b).
[0027]
Further, as shown in FIG. 5C, when the frequency of the carrier wave 60 is sufficiently high with
respect to the audible area 63, the amplitude of the modulated wave is audible even if the
frequency band of the amplitude modulation waves 61 and 62 is wide Have no In this case, it is
also possible to widely set the pass frequency band of the band pass filter or to adopt a
configuration in which the band pass filter itself is removed. As described above, by controlling
the frequency band of the original sound by the frequency band controller 6, a modulated wave
in which the original sound is amplitude-modulated at the carrier frequency, particularly when
the frequency of the carrier is low or when the original sound includes high-frequency amplitude.
Can be prevented from being output in the audio frequency band.
[0028]
A third embodiment of the present invention will be described with reference to FIGS. In this
embodiment, as shown in FIG. 7, by arranging a plurality of ultrasonic transducers 5-1, 5-2, 5-3,
5-4, ... in an array, an electroacoustic transducer is obtained. 5 is configured. Then, when the
ultrasonic transducers 5-i (i = 1, 2, 3, 4...) Are arranged in an array, it is necessary to adjust the
output timing between the transducers.
[0029]
That is, as shown in FIG. 8, considering the output wavefront radiated in the direction D to be
demodulated, the output signal from the ultrasonic transducer 5-2 is the signal from the
ultrasonic transducer 5-1. The output signal is delayed by a time corresponding to the distance d.
Similarly, the output signal from the ultrasonic transducer 5-3 has a time corresponding to the
distance d × 2 with respect to the output signal from the ultrasonic transducer 5-1, the output
signal from the ultrasonic transducer 5-4 is The time corresponding to the distance d × 3 is
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delayed with respect to the output signal from the ultrasonic transducer 5-1.
[0030]
Each ultrasonic transducer 5-i (as shown in FIG. 6) can be specified in order to enable oscillation
by designating an output time difference from each ultrasonic transducer 5-i in consideration of
this delay time. An input unit 1, a carrier frequency controller 2, a phase controller 7, a
modulator 3 and an amplifier 4 are provided corresponding to i = 1, 2, 3, 4. In addition to the
distance input unit 1a and the original sound input unit 1b, the input unit 1 is provided with a
direction input unit 1c, and information on the direction to be demodulated or the time
difference is input to the direction input unit 1c. The output timing of the ultrasonic transducers
5-1, 5-2, 5-3, 5-4..., That is, the phase difference is adjusted.
[0031]
The information on the direction or the time difference input to the direction input unit 1 c is
output to the phase controller 7. The phase controller 7 refers to the information input from the
direction input unit 1c, and outputs a signal for controlling the time difference to be provided to
the corresponding ultrasonic transducer 5-i to the modulator 3. The modulator 3 amplitude
modulates the carrier wave signal input from the carrier wave frequency controller 2 with the
original sound signal input from the original sound input unit 1 b. Then, the carrier frequency
controller 2 inputs the amplitude modulation signal to the corresponding ultrasonic transducer
5-i through the amplifier 4 with a time difference designated by the phase controller 7.
[0032]
As shown in FIG. 8, by providing a time difference between the ultrasonic transducers, the output
wavefront is inclined, and the direction of the acoustic output can be controlled, so the controlled
direction and the distance input unit 1a The original sound is demodulated at the distance input
to. Here, assuming that the distance between the ultrasonic transducers 5-i is P, and the angle of
the demodulation direction D with respect to the arrangement direction of the ultrasonic
transducers 5-i is θ, the distance d = P cos θ, so that the phase controller 7 The phase
difference is adjusted in accordance with the interval P between the ultrasonic transducers 5-i
and the demodulation direction D.
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[0033]
In short, the superdirective speaker system of the present embodiment includes a plurality of
ultrasonic transducers arranged in an array, and the output time difference of the plurality of
ultrasonic transducers is controlled by the phase controller according to the demodulation
direction. ing. With this configuration, the acoustic outputs from the plurality of ultrasonic
transducers are added, and the acoustic signal can be output from the electroacoustic transducer
at a high sound pressure. Further, by providing a phase difference between the acoustic outputs
outputted from the plurality of ultrasonic transducers constituting the array, the wavefront of the
acoustic output outputted from the electroacoustic transducer constituted of the plurality of
ultrasonic transducers is obtained. You will be able to control the direction.
[0034]
A fourth embodiment of the present invention will be described with reference to FIG. 9 to FIG. In
the present embodiment, as shown in FIG. 9, the sensor 8, the sensor input unit 8 a, and the
adjustment unit 9 are configured. The adjustment unit 9 is configured to include a distance
adjustment unit 9a. The distance adjustment unit 9a has a function of selecting information on
the distance input from the distance input unit 1a and information on the distance input from the
sensor input unit 8a and inputting the selected information to the carrier frequency controller 2.
There is. As to which of the input information is to be selected, the selection signal input from the
outside is followed. This selection signal is input, for example, by the operation of the key switch
by the listener.
[0035]
In such a configuration, the sensor 8 measures the position and orientation of the listener, and
the measured value is input to the adjustment unit 9 through the sensor input unit 8a. Then, the
adjusting unit 9 designates a distance at which the demodulation sound is to be demodulated
based on the value input from the distance input unit 1a and the value input from the sensor
input unit 8a, and the adjusting unit 9 relates to the specified distance. Information is input to
the carrier frequency controller 2. Here, for example, an acoustic sensor is used as the sensor 8.
An acoustic sensor usually consists of an oscillator and a receiver. Then, a sound wave is emitted
from the oscillator, the sound wave reflected from the listener is received by the receiver, and the
distance between the acoustic sensor and the listener is calculated from the time difference
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between the time of emission and the time of reception. Based on this calculation result, the
distance between the electroacoustic transducer and the listener is calculated.
[0036]
Also, if a plurality of sets of oscillators and receivers are prepared, the direction of the listener
with respect to the sensor can be determined by calculating the distances of the plurality of sets.
In this case, as shown in FIG. 10, the direction adjusting unit 9c is provided in the adjusting unit
9, and information on the direction input from the direction input unit 1c and information on the
distance input from the sensor input unit 8a , And may be input to the phase controller 7. The
direction adjustment unit 9c determines which of the input information is to be selected
according to the selection signal input from the outside. This selection signal is input, for
example, by the operation of the key switch by the listener.
[0037]
The configuration of FIG. 10 is a configuration in which the frequency band controller 6 and the
adjustment unit 9 are added to the configuration of FIG. Therefore, as described with reference to
FIG. 5, a modulation wave obtained by amplitude-modulating the original sound at the carrier
frequency is output in the audio frequency band, particularly when the carrier frequency is low
or when the original sound includes high frequency amplitudes. Can be prevented, and the
original sound can be optimally demodulated according to the distance and direction of the
listener detected by the sensor.
[0038]
By the way, instead of the oscillator, an electroacoustic transducer may be used. That is, as
shown in FIG. 11, the sensor 8 measures a reflected wave that the acoustic output from the
electroacoustic transducer 5 reflects from the listener 10, and listening based on the value
measured by the sensor 8 The position of the person 10 may be measured. By feeding back the
position of the listener 10 to the superdirective speaker system 100, the original sound can be
accurately demodulated to the listener 10. Since acoustic devices such as electro-acoustic
transducers and microphones originally mounted can be used for positioning, the number of
devices configured for positioning applications can be reduced. Thereby, since a superdirective
speaker can be used also as a positioning signal output means, the number of devices configured
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for positioning applications can be reduced.
[0039]
Besides, an optical sensor or a magnetic sensor may be used as the sensor 8. In the former case,
an infrared beam may be emitted toward the listener 10, and the distance and direction of the
listener 10 may be specified based on the reflected wave. Also in the latter case, the distance and
the direction can be detected. By adopting the configuration in which the sensor is added as
described above, whenever the distance or direction of the listener relative to the superdirective
speaker system is changed, the change can be measured by the sensor Based on the measured
values, the position at which the acoustic signal should be optimally demodulated is calculated,
and based on the calculated position, the distance and direction in which the acoustic output
outputted from the electroacoustic transducer is demodulated with high quality The angle can be
fed back. As a result, it is possible to adjust the distance to which the acoustic output reproduced
from the superdirective speaker system is directed and the directivity angle, and it is possible to
form a sound field suitable for the listener to listen to.
[0040]
A fifth embodiment of the present invention will be described with reference to FIGS. 1 and 12. In
this embodiment, in the modulator of FIG. 1 described above, as shown in FIG. 12, the amplitude
and modulation of the carrier wave can be controlled and output to the amplifier. Assuming that
the output to the amplifier, that is, the output of the modulator is p, the carrier amplitude is P,
the modulation degree is m, the original sound signal is a function s (t) of time t, and the carrier
frequency is fc, then p = P (1 + m · s ( t)) sin (2πfct) (2) In the equation (2), if the amplitude P
and the modulation degree m of the carrier wave are controlled to increase and decrease, the
output p of the modulator can be controlled as shown in FIG. Since the modulation degree m is
the ratio of the amplitude of the carrier signal to the amplitude of the original sound signal, an
amplifier is provided in front of the modulator to amplify the original sound signal and then
input it to the modulator. The output p can be controlled.
[0041]
As shown in FIG. 12A, when the amplitude of the carrier wave 60 is small and the degree of
modulation is small, the amplitudes of the modulation waves 61 and 62 become small. As a
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method of increasing the amplitudes of the modulated waves 61 and 62, there is a method of
increasing the amplitude of the carrier wave 60 while maintaining the degree of modulation as
shown in FIG. 12 (b). However, increasing the amplitude of the carrier wave 60 is also limited.
Therefore, the amplitudes of the modulation waves 61 and 62 can be increased by adjusting the
modulation degree as shown in FIG. That is, in this embodiment, at least one of the amplitude of
the carrier wave signal and the modulation degree in the amplitude modulation is controlled in
accordance with at least one of the carrier wave signal and the original sound signal. As a result,
it is possible to reduce the sound pressure of the carrier wave while appropriately setting the
sound pressure of the multi-tone sound, and it is possible to improve the efficiency of the sound
output.
[0042]
A sixth embodiment of the present invention will be described with reference to FIG. In the
present embodiment, as shown in FIG. 13, a superdirective speaker system is mounted on a
portable information device. The information device shown in the figure has a shape in which a
housing 101 a and a housing 101 b are connected by a hinge 102. An electroacoustic transducer
5a is provided at an end portion of the housing 101a, and an electroacoustic transducer 5b is
provided at an end portion of the casing 101b, and these electroacoustic transducers approach
each other around the hinge 102. Thus, the housing 101a is folded to close to the housing 101b
side.
[0043]
The housing 101 a is provided with a display 103 for displaying various information. Further, the
housing 101 b is provided with an operation key 104 and a dial key 105 for inputting various
information, and a mouthpiece 106. Since the electroacoustic transducer 5a and the
electroacoustic transducer 5b can oscillate ultrasonic waves, the stereo sound source and the
binaural sound source can be listened to by the listener if the configuration of FIG. 2 is adopted.
[0044]
(Summary) As described above, by controlling the frequency of the carrier wave, according to the
carrier wave frequency, control the distance and directivity in which the acoustic output
outputted from the superdirective speaker system is demodulated by the nonlinearity of the
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medium. Can. Also, by adjusting the demodulation distance, the optimum demodulation distance
can be adapted to the listener of the superdirective speaker system, and a high quality sound
field can be realized for the listener.
[0045]
The present invention can be used to control the demodulation distance in a superdirective
speaker system.
[0046]
FIG. 1 is a block diagram illustrating an embodiment of the superdirective speaker system
according to the present invention.
It is a block diagram which shows the structure of the super-directional speaker system by
Example 1 of this invention. FIG. 7 is a diagram showing the positional relationship between the
superdirective speaker system according to Embodiment 1 and a listener. It is a block diagram
which shows the structure of the super-directional speaker system by Example 2 of this
invention. FIG. 5 is a diagram showing an example of filtering characteristics of a band pass filter
by the frequency band controller in FIG. 4, where (a) shows a state where the carrier frequency is
low, the original sound band is wide, and the frequency band controller is not operating; (B)
shows that the frequency band controller operates to narrow the band of the original sound and
the modulation wave is not included in the audible area, and (c) shows that the carrier frequency
is sufficiently high and the band of the original sound is wide enough to control the frequency
band It is a figure which shows the state which can take the zone | band of the band pass filter of
the filter. It is a block diagram which shows the structure of the super-directional speaker system
by Example 3 of this invention. It is a figure which shows the electroacoustic transducer which
arrange | positioned several ultrasonic transducers in array form. When there is a time difference
between the oscillation waves of the respective ultrasonic transducers in FIG. 7, it is a diagram
showing that the oscillation wavefront is inclined. It is a block diagram which shows the structure
of the super-directional speaker system by Example 4 of this invention. It is a block diagram
which shows the structural example at the time of adding a direction adjustment part. It is a
figure which shows a mode that the reflected wave from the listener by the acoustic output from
a super-directional speaker system is measured, and the position with respect to the listener of a
super-directional speaker system is measured. It is a figure which shows the result of having
controlled the amplitude and the modulation degree of a carrier wave, (a) shows the case where
the amplitude of a modulation wave is small, (b) shows the case where the amplitude of a carrier
wave is enlarged by the same modulation degree as (a). (C) shows the case where the modulation
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degree is increased compared to (a). It is a block diagram which shows the structure of the superdirectional speaker system by Example 6 of this invention. It is a block diagram showing
composition of a basic super directivity speaker system. It is a figure for demonstrating superdirectional sound radiation.
Explanation of sign
[0047]
DESCRIPTION OF SYMBOLS 1 input part 1a distance input part 1b original sound input part 1c
direction input part 2 carrier frequency controller 3 modulator 4 amplifier 5, 5a, 5b
electroacoustic transducer 5-1, 5-2, 5-3, 5-4 or more Sound wave oscillator 6 Frequency band
controller 7 Phase controller 8 Sensor 8a Sensor input 9 Adjustment section 9a Distance
adjustment section 9c Direction adjustment section 10 Listener 10R Right ear 10L Left ear 11
Original sound 20 Carrier oscillator 60 Carrier 61, 62, 61 ', 62' amplitude modulation wave 63
audible range 100 super-directional speaker system 101a, 101b housing 102 hinge 103 display
104 operation key 105 dial key 106 mouthpiece
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