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JP2007251901

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DESCRIPTION JP2007251901
An object of the present invention is to provide a directional loudspeaker that allows a speaker to
confirm reproduced sound. SOLUTION: A microphone 2 for converting a speaker's voice into an
electric signal, a carrier oscillator 10 for generating a carrier wave of an ultrasonic frequency
band, and the carrier wave are modulated with an audio signal of an audio frequency band
outputted from the microphone 2. In a directional loudspeaker having a modulator 12 and an
ultrasonic transducer 15 driven by the modulation signal output from the modulator 12 to
reproduce a signal sound, the modulation sound signal is output from the modulation signal from
the modulator 12 A demodulation sound estimator 16 for estimating the waveform and level, a
filter 17 for filtering the demodulation sound estimation waveform output from the
demodulation sound estimator 16 and passing only the audio frequency band component signal,
and amplifying the output of the filter 17 And a loudspeaker 19 for reproducing the output of
the amplifier 18 with a small volume. [Selected figure] Figure 1
Directional loudspeaker
[0001]
The present invention relates to a loudspeaker capable of reproducing very directional sound.
[0002]
With the development and spread of information devices, modern society, especially public
spaces, are flooded with various sounds emitted from various information devices.
04-05-2019
1
However, unwanted voices and announcements cause great stress, such as confusion and
discomfort for individuals who do not need them. Under such circumstances, particularly in
public spaces, there is a growing demand for further improvement of the sound environment,
such as reducing noise to the surroundings.
[0003]
On the other hand, there is a loudspeaker system capable of reproducing sound having high
directivity (see Patent Document 1). This loudspeaker system includes a microphone, a low pass
filter (LPF), and a parametric speaker (ultrasonic speaker), and has a configuration aimed at
suppressing howling due to wall reflections of highly directional sound waves reproduced by the
parametric speaker. It is shown.
[0004]
By using such a super-directional speaker as a megaphone-type directional loudspeaker, voice
messages and instructions can be transmitted only to necessary individuals.
[0005]
In addition, since the directivity is very high, there is a feature that voice can be delivered far
without being attenuated so much, which is convenient as a loudspeaker.
Furthermore, it has a feature that it is difficult to cause a phenomenon such as how difficult it is
to hear due to the reflected sound or howling occurs, as in a conventional loudspeaker type
loudspeaker using a horn. JP, 2005-303533, A
[0006]
However, in the superdirective loudspeaker as described in Patent Document 1, the directivity of
the reproduced sound is very high, so when configuring as a loudspeaker such as a megaphone
type, the person who is speaking ( The speaker can not hear the playback sound. For this reason,
there is a problem that the speaker does not know whether the voice can be correctly output
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(provided).
[0007]
In the superdirective speaker using the parametric array phenomenon as described in Patent
Document 1, reproduced sound (demodulated sound) is easily distorted as compared with a
normal loudspeaker. Therefore, there is a risk that a very loud sound may be emitted without the
speaker being aware.
[0008]
The present invention has been made in view of such circumstances, and it is an object of the
present invention to provide a directional loudspeaker that allows a speaker to confirm
reproduced sound.
[0009]
In order to achieve the above object, the directional loudspeaker of the present invention
converts an input speaker's voice into an electrical signal, modulates a carrier wave of an
ultrasonic frequency band with the converted voice signal, and performs the modulation. In a
directional loudspeaker for driving an ultrasonic transducer by a signal and reproducing a signal
sound, the waveform and level of speech reproduced with directivity are estimated, and the
estimated speech is reproduced to the speaker It is characterized by having a means separately.
[0010]
In the directional loudspeaker having the above configuration, the voice of the input speaker is
converted into an electric signal, the carrier of the ultrasonic frequency band is modulated by the
converted voice signal, and the ultrasonic transducer is driven by the modulated signal. And the
directional sound is reproduced.
[0011]
At the same time, by estimating the waveform and level of this reproduced sound and
reproducing it separately to the speaker, the speaker confirms the sound corresponding to the
sound (self-demodulated sound) reproduced with directivity. can do.
[0012]
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Therefore, since the playback sound can be confirmed by the speaker while the speaker is talking
as it is, a very loud sound or a sound with a large distortion may be output without the speaker
being aware of it. Absent.
In addition, sound quality adjustment also becomes easy.
[0013]
Further, the directional loudspeaker according to the present invention comprises: voice input
means for converting a speaker's voice into an electrical signal; carrier generation means for
generating a carrier wave of an ultrasonic frequency band; and ultrasonic waves output from the
carrier generation means A pointing device comprising: modulation means for modulating a
carrier wave of a frequency band with an audio signal of an audio frequency band outputted
from the input means; and an ultrasonic transducer driven by the modulation signal outputted
from the modulation means to reproduce a signal sound Noise estimation means for estimating
the waveform and level of the demodulation sound from the modulation signal output from the
modulation means, filtering the demodulation sound estimation waveform output from the
demodulation sound estimation means, and processing the audio frequency band A filter that
passes only component signals, an amplifier that amplifies the output of the filter, and a
loudspeaker that reproduces the output of the amplifier at low volume Characterized in that it
has a.
[0014]
In the directional loudspeaker of the present invention having the above configuration, the voice
of the speaker is converted into an electric signal by the voice input means, and the carrier wave
of the ultrasonic frequency band outputted from the carrier wave generation means is generated
by the modulation means from the input means. The ultrasonic transducer is modulated by the
audio signal in the audio frequency band to be output, and the ultrasonic transducer is driven by
the modulated signal to reproduce a tone.
At the same time, the waveform and level of the demodulated sound are estimated from the
modulated signal by the demodulation sound estimation means, and the demodulation sound
estimation waveform output from the demodulation sound estimation means is filtered by a filter,
and only the audio frequency band component signal The signal is output to the amplifier, and
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the output of the amplifier is reproduced at low volume by the loudspeaker and monitored by the
speaker.
Therefore, the distortion condition and the magnitude of the superdirective sound to be
reproduced can be obtained by separately reproducing (monitoring) as an audible sound by the
loudspeaker after adding the distortion component after demodulation by the demodulation
sound estimator. You can easily check and adjust yourself.
[0015]
In the directional loudspeaker according to the present invention, as the frequency becomes
higher, the directional loudspeaker for equalizing the frequency characteristic of the
demodulated sound reproduced by the ultrasonic transducer between the voice input means and
the modulation means. It is characterized in that an equalization filter having a frequency
characteristic in which the attenuation amount of the signal becomes large is inserted.
[0016]
In the directional loudspeaker of the present invention having the above configuration, the
frequency characteristic of the demodulated sound reproduced by the ultrasonic speaker
becomes higher in principle as the frequency becomes higher, so that the demodulation
efficiency becomes higher, so the audio signal output from the audio input means On the other
hand, the frequency characteristic of the demodulated sound is equalized by outputting the audio
signal to the modulator through the equalizing filter having a characteristic that the attenuation
amount increases as the frequency characteristic of the demodulated sound becomes higher.
Therefore, the sound quality of the demodulated sound can be improved.
[0017]
In the directional loudspeaker according to the present invention, the ultrasonic transducer is an
electrostatic ultrasonic transducer.
[0018]
The directional loudspeaker of the present invention having the above configuration can
generate high sound pressure over a wide frequency band from the ultrasonic frequency band to
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the audio frequency band by using the electrostatic ultrasonic transducer, so that demodulation
is performed. The sound quality of the sound can be improved.
[0019]
Hereinafter, embodiments of the present invention will be described in detail with reference to
the drawings.
The directional loudspeaker of the present invention converts the voice of the input speaker into
an electrical signal, modulates the carrier wave of the ultrasonic frequency band with the
converted voice signal, and drives the ultrasonic transducer with the modulated signal. In a
directional loudspeaker that reproduces a highly directional signal sound, it has a function of
estimating the waveform and level of the speech reproduced with directivity and reproducing the
estimated speech to the speaker, ie reproduction It has a built-in function of monitoring sound.
[0020]
The configuration of a directional loudspeaker according to an embodiment of the present
invention is shown in FIG.
In the figure, a directional loudspeaker according to an embodiment of the present invention
includes a microphone 2, a preamplifier 4, a low pass filter (LPF 1) 6, an equalization filter 8, a
carrier oscillator 10, a modulator 12, and an amplifier. 14, an ultrasonic transducer 15, a
demodulation sound estimator 16, a low pass filter (LPF 2) 17, an amplifier 18, and a
loudspeaker 19.
[0021]
A mouse hood 2A is attached to the microphone 2.
This mouse hood is intended to prevent the monitor sound reproduced from the loudspeaker 19
from entering the microphone and prevent howling by bringing the mouth close to each other
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when the speaker speaks.
[0022]
The low pass filter (LPF1) 6 has a function of filtering the output signal of the preamplifier 4 and
passing only the audio frequency band component.
[0023]
The equalization filter 8 is a filter for equalizing (flattening) the frequency characteristics of the
demodulated sound.
In principle, the parametric array phenomenon exhibits a characteristic that the higher the
frequency, the higher the demodulation efficiency. Therefore, for example, the filter can be
configured as a low-pass filter-like frequency characteristic in which the amount of attenuation
increases as the frequency becomes higher. .
[0024]
The carrier oscillator 10 has a function of generating and outputting a carrier in an ultrasonic
frequency band.
The modulator 12 modulates the carrier wave output from the carrier wave oscillator 10 with the
voice signal after passing through the low pass filter 6, and outputs a modulation signal. The
amplifier 14 (for ultrasonic transducer) power-amplifies the modulation signal output from the
modulator 12 to a predetermined level.
[0025]
The ultrasonic transducer 15 is driven by the modulation signal and outputs the modulation
wave in the ultrasonic frequency band at high sound pressure.
[0026]
Further, the demodulation sound estimator 16 has a function of estimating a demodulation
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sound waveform including demodulation distortion from a drive signal (modulation signal) for
driving the ultrasonic transducer 15.
[0027]
The low pass filter (LPF 2) 17 has a function of filtering the estimated demodulated sound
waveform output from the demodulated sound estimator 16 and passing only the audio
frequency band component.
The amplifier 18 (for loudspeakers) amplifies the estimated demodulated audio signal after
passing through the low pass filter 17 to a predetermined level.
The loudspeaker 19 reproduces the estimated demodulated voice amplified by the amplifier 18
at a small volume.
[0028]
The microphone 2 is a voice input means of the present invention, the carrier wave oscillator 10
is a carrier generation means of the present invention, the modulator 12 is a modulation means
of the present invention, and the demodulation sound estimator 16 is a demodulation sound
estimation means of the present invention. The low pass filter 17 corresponds to the filter of the
present invention.
[0029]
In the above configuration, when the speaker brings the mouth close to the mouse hood and the
microphone 2 utters the voice, the voice is converted to a voice signal (electric signal) by the
microphone 2 and the voice signal is amplified by the preamplifier 4 to obtain a low pass filter. It
is input to 6.
The low pass filter 6 filters the output signal of the preamplifier 4, passes only the audio
frequency band component, and outputs it to the equalizing filter 8. The equalization filter 8 has,
for example, a pass characteristic such that the amount of attenuation increases as the frequency
increases, and is input so that the frequency characteristic of the demodulated sound reproduced
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from the ultrasonic transducer 15 becomes flat. After the audio signal is subjected to filtering
processing, it is output to the modulator 12.
[0030]
The modulator 12 modulates the carrier wave of the ultrasonic frequency band output from the
carrier wave oscillator 10 with the audio signal of the audio frequency band output through the
equalizing filter 8, and outputs the modulated signal to the amplifier 14. The modulated signal
power-amplified by the amplifier 14 to a predetermined level is output to the ultrasonic
transducer 15 and the demodulation sound estimator 16.
[0031]
The ultrasonic transducer 15 is driven by the modulation signal to reproduce a signal sound.
[0032]
At the same time, from the drive signal (modulated signal) for driving the ultrasonic transducer
15, the demodulated sound estimator 16 generates a response waveform (hereinafter referred to
as demodulated sound) including demodulation distortion that occurs when propagating through
the air. Estimate and output to the low pass filter 17.
[0033]
The demodulation sound estimator 16 is composed of, for example, a digital signal processor
(DSP) or the like.
Here, the modulation wave (drive signal of the ultrasonic transducer) output from the amplifier
14 is taken in, the response distortion of the ultrasonic transducer 15 and nonlinear distortion
when the sound wave propagates in the air are added to the modulation waveform, Output in real
time.
[0034]
Assuming that the input signal waveform (drive waveform) to the transducer is x, the response
waveform y after a predetermined time has elapsed in the far-field can be approximated by the
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following equation (1).
[0035]
y = a0 + a1x + a2x <2> + a3x <3> + a4x <4> + (1) where an is a coefficient, the term of a0 is a DC
component (DC offset component), the term of a1x is no distortion component, anx < The term
n> corresponds to an nth-order distortion component.
[0036]
The superdirective speaker utilizing the parametric array effect according to the present
invention outputs from the transducer a modulated wave obtained by modulating an ultrasonic
carrier wave with an audio band signal, and utilizes propagation distortion in the air to obtain a
modulated wave frequency spectrum. By generating a difference sound component, an audible
sound (self-demodulated sound) having high directivity is reproduced.
This highly directional audible sound (self-demodulated sound) corresponds to part of the
difference component of intermodulation distortion (intermodulation distortion).
That is, it is a component that appears in the audio frequency band in the differential component
of the intermodulation distortion of the modulation waveform (difference sound component of
the modulation wave frequency spectrum).
[0037]
In Equation (1), the difference sound component (difference component of intermodulation
distortion) of the modulation wave frequency spectrum is contained in the output signal y with
respect to the input signal x of the modulation wave, and there is an even order distortion
component (The values of the coefficients a2, a3, a4,... Are not 0).
That is, even-order distortion, in particular, the second-order distortion (coefficient a2)
component predominantly contributes to the components of the self-demodulated sound
(including the distortion component) due to the parametric array effect.
04-05-2019
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[0038]
On the other hand, odd-order distortion is caused by non-linear response (such as amplitude
saturation) of the ultrasonic transducer, and these are mainly harmonic distortion components.
[0039]
From the above, the estimated characteristics of the demodulation sound estimator 16 can be
described, for example, as in equation (2).
[0040]
y = a0 + a1x + a2x <2> + a3x <3> + a4x <4> (2) Here, a1 >> a2> a4, and each coefficient value is
set according to the specification of the ultrasonic transducer and the radiation environment
conditions Ru.
By adjusting each coefficient value, distortion condition or reproduction condition of estimated
demodulation sound (monitor sound) reproduced by the loudspeaker 19 described later with
respect to distortion condition and reproduction level (magnitude) of sound actually
demodulated. The levels can be adjusted to match.
[0041]
The demodulated sound estimation output output from the demodulated sound estimator 16 is
input to the low pass filter 17.
Since an estimated signal in a state in which a large ultrasonic wave (carrier wave) frequency
component is included as it is output from the demodulation sound estimator 16, after the
ultrasonic frequency component is cut by the low pass filter 17, only the audio frequency band
component is output. The signal is output to the loudspeaker 19 via the amplifier 18. The
estimated demodulated voice is reproduced at a small volume by the loudspeaker 19 and
monitored by the speaker.
[0042]
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As described above, according to the directional loudspeaker according to the embodiment of the
present invention, after the distortion after demodulation is taken into consideration by the
demodulation sound estimator 16, the signal is separately reproduced (monitored) as an audible
sound by the loudspeaker. Thus, the speaker can easily confirm and adjust the distortion of the
superdirective sound to be reproduced.
[0043]
In addition, voice messages and instructions can be delivered only to the required individuals.
[0044]
In addition, it is difficult for the reflected sound to make it difficult to hear or for howling to
occur.
[0045]
Next, an example of the structure of an electrostatic ultrasonic transducer suitable for use as an
ultrasonic transducer in a directional loudspeaker according to an embodiment of the present
invention is shown in FIG.
[0046]
FIG. 2A shows a cross section of the electrostatic ultrasonic transducer 15, which is provided so
as to face the respective surfaces of the vibrating membrane 22 having the conductive layer
(vibrating membrane electrode) 221 and the vibrating membrane 22. It has a pair of fixed
electrodes consisting of the front side fixed electrode 20A and the back side fixed electrode 20B
(When both the front side fixed electrode 20A and the back side fixed electrode 20B are referred
to, it is called the fixed electrode 20).
As shown in FIG. 2A, the vibrating film 22 may be formed so that the conductive layer (vibrating
film electrode) 221 forming the electrode is sandwiched by the insulating film 220, or the whole
vibrating film is formed of a conductive material. You may do so.
[0047]
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Further, a plurality of through holes 24A are provided in the front side fixed electrode 20A
sandwiching the diaphragm 22, and a position opposite to each through hole 24A provided in
the front side fixed electrode 20A in the back side fixed electrode 20B. The through holes 24B of
the same shape are provided in the same (in the case where both the through holes 24A and the
through holes 24B are referred to as the through holes 24).
The front side fixed electrode 20A and the back side fixed electrode 20B are supported by the
supporting member 21 with a predetermined gap from the vibrating membrane 22, respectively,
and as shown in FIG. 2A, the vibrating membrane 22 and the fixed electrode 20 The support
member is formed such that the two members face each other via a gap.
[0048]
FIG. 2 (B) shows the one-side planar appearance of the electrostatic ultrasonic transducer 15 (in
a state where a portion of the fixed electrode 20 is cut away), and the plurality of through holes
24 are arranged in a honeycomb shape There is.
FIG. 2C is a plan view of the fixed electrode to which the support member is joined, and shows a
state where the fixed electrode 20 side is just seen from the vibrating film 22 side of the
electrostatic ultrasonic transducer.
The support member 21 is made of an insulating material, and can be formed, for example, by
pattern-printing the insulating material on the surface of the fixed electrode 20 (the side facing
the vibrating film 22) in the same manner as resist printing on a printed substrate.
[0049]
With the above-described configuration, alternating-current signals 28A and 28B having the
same amplitude and opposite phases to each other are applied to the front fixed electrode 20A
and the back fixed electrode 20B of the electrostatic ultrasonic transducer 15. Further, a DC bias
voltage is applied to the diaphragm electrode 221 by the DC power supply 26. Thus, the
diaphragm 22 is applied by applying a DC bias voltage to the diaphragm electrode 221 and
applying drive signals (AC signals) whose phases are inverted to each other on the front fixed
electrode 20A and the back fixed electrode 20B. Electrostatic attraction and electrostatic
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13
repulsion simultaneously act in the same direction. Every time the polarity of the drive signal (AC
signal) is reversed, the vibrating film 22 is push-pull driven because the direction in which the
electrostatic attraction force and the electrostatic repulsion force act is changed. As a result, the
sound waves generated by the diaphragm are emitted to the outside through the through holes
24 provided in the front fixed electrode 20A and the back fixed electrode 20B.
[0050]
The electrostatic transducer as described above has a wide band sound pressure-frequency
characteristic in the ultrasonic frequency band, as shown in FIG. Therefore, since the sound
pressure-frequency characteristic to be reproduced (demodulated) can be flattened over a wide
band by using the above equalization filter, a piezoelectric type having a steep (narrow band)
sound pressure-frequency characteristic can be obtained. It has the feature of being easier to
improve the reproduction sound quality than the ultrasonic transducer of
[0051]
1 is a block diagram showing the configuration of a directional loudspeaker according to an
embodiment of the present invention. FIG. 1 shows an example of the construction of an
electrostatic ultrasonic transducer suitable for use as an ultrasonic transducer in a directional
loudspeaker according to an embodiment of the present invention. The figure which shows an
example of the frequency characteristic of an electrostatic ultrasound transducer.
Explanation of sign
[0052]
Reference Signs List 2 microphone, 4 preamplifier, 6 17 17 low pass filter 8 equalization filter 10
carrier oscillator 12 modulator 14 18 amplifier 15 ultrasonic transducer 16 demodulation sound
estimator 19 ... Loudspeaker
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