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JP2006311101

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DESCRIPTION JP2006311101
PROBLEM TO BE SOLVED: To provide a superdirective acoustic device in which the conversion
efficiency from electricity to sound is improved. SOLUTION: An audio signal from an audio
source is pulse width modulated to a signal in a frequency band higher than at least an audio
band, and a carrier level and a gain of a modulation signal according to an envelope processed
value of the audio signal level from the audio source. Set [Selected figure] Figure 1
Superdirectional sound device
[0001]
The present invention relates to a superdirective acoustic device that directionally radiates
audible sound.
[0002]
As a superdirective acoustic device, for example, there is one disclosed in Patent Document 1.
This speaker device is composed of a coefficient unit, a DC source adder, a square root converter,
a multiplier, a power amplifier and an ultrasonic transducer array (hereinafter referred to as a
radiator). To explain the operation briefly, an audio signal generated by a modulation signal
source or the like is input to a coefficient unit in the apparatus. The coefficient unit multiplies the
value of the audio signal by a predetermined coefficient, and outputs the result to the DC source
adder.
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[0003]
In the direct current source adder, the bias voltage from the direct current source is added to the
audio signal voltage from the coefficient unit and output to the square root converter. The square
root converter performs square root processing on the input signal from the direct current
source adder and outputs the processing result to the multiplier. In addition to the input signal
from the square root converter, the ultrasonic carrier wave signal from the ultrasonic band
oscillator is input to this multiplier.
[0004]
Thus, the multiplier multiplies the carrier signal of the ultrasonic wave by the input signal from
the square root converter to perform amplitude modulation of the input signal. After this, the
modulation signal from the multiplier is output to the power amplifier. In the power amplifier,
the power of the modulation signal from the multiplier is amplified and supplied to the radiator.
Thereby, the radiator emits the modulation signal derived from the audio signal as a sound wave.
This sound wave causes a non-linear interaction in the process of propagating through the air as
a finite amplitude sound wave which is a strong ultrasonic wave, and it self-demodulates to a
superdirective sound composed of low frequency components etc. and becomes audible to a
listener .
[0005]
In such a conventional device, when driving the capacitive element, the capacitive element can be
driven most efficiently by resonating the load of the capacitive element with the carrier
frequency. However, since the linear amplifier system is generally adopted for the power
amplifier, there is a problem that the efficiency is not good for driving the capacitive element.
[0006]
In order to eliminate the above-mentioned problems, the inventor of the present invention can
improve the driving efficiency by resonating the load of the radiator, which is a capacitive
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element, with the carrier frequency, and further configure using an operational amplifier. We
have proposed a superdirective acoustic device with a pulse width modulator that can Briefly,
this device comprises an audio source, a DC source, an ultrasonic band oscillator for sawtooth
generation, a level comparator, a signal controller, an amplifier and a radiator.
[0007]
In operation, the audio signal generated by the audio source is first shifted up by the bias of the
DC source. As a result, the signal shifted up is compared in voltage level with the sawtooth wave
generated by the ultrasonic band oscillator for sawtooth wave generation by the level
comparator. Pulse width modulation is performed by this voltage level comparison process, and a
pulse modulation signal (PWM signal) is obtained.
[0008]
Subsequently, the output of the level comparator is subjected to polarity inversion processing
every arbitrary cycle of the PWM signal by the signal controller. The amplifier performs
switching in accordance with the signal subjected to the above-mentioned polarity inversion
processing, and is made up of an ultrasonic transducer of a piezoelectric element and resonates
and amplifies with a capacitive radiator. Thereby, the signal is emitted from the emitter as a
sound wave. This sound wave is self-demodulated into superdirective sound in the process of
propagating through the air as a high intensity sound wave of 120 dB or more as a finite
amplitude sound wave, and can be heard by a specific listener.
[0009]
Tokuhei 4-58758
[0010]
In the conventional superdirective acoustic device, since pulse modulation is adopted as the
modulation method, there is a problem that the modulation rate is lowered when a low level
audio signal is input.
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For this reason, the demodulated sound that is self-generated by emitting from the ultrasonic
transducer to air can not obtain a desired sound pressure level.
[0011]
The present invention has been made to solve the above problems, and controls the carrier wave
level in accordance with the audio signal level, and at the same time controls the modulation
wave level, thereby improving the conversion efficiency from electricity to sound. It is an object
of the present invention to obtain a superdirectional acoustic device that
[0012]
The superdirective acoustic device according to the present invention is driven by a modulation
processing unit that pulse width modulates an audio signal from an audible sound source to a
signal in a frequency band higher than at least an audible band, and a pulse width modulation
signal modulated by the modulation processing unit. It has an ultrasonic vibration element, and it
has a signal output part which outputs the superdirective sound wave according to an audio
signal.
Further, an envelope processing unit for obtaining a value obtained by subjecting an audio signal
level from an audible sound source to an envelope processing by a modulation processing unit,
and a carrier level setting processing unit for setting a carrier level according to the value
obtained by the envelope processing unit. And a gain setting processing unit configured to set
the gain of the modulation signal according to the value obtained by the envelope processing
unit.
[0013]
According to the present invention, a modulation processing unit that pulse width modulates an
audio signal from an audible sound source to a signal in a frequency band higher than at least an
audible band, and an ultrasonic vibration element driven by a pulse width modulation signal
modulated by the modulation processing unit An envelope processing unit including: a signal
output unit configured to output a superdirective sound wave according to an audio signal, the
modulation processing unit calculating a value obtained by performing envelope processing on
an audio signal level from an audible sound source; A carrier level setting processing unit that
sets a carrier wave level according to a value obtained by the envelope processing unit, and a
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gain setting processing unit that sets the gain of the modulation signal according to the value
obtained by the envelope processing unit. As a result, the degree of modulation can be made
variable, the conversion efficiency from electricity to sound can be improved, and enlargement of
the device itself can be suppressed, and it is possible to easily listen to the sound corresponding
to the audio signal. There is an effect that it can be provided.
[0014]
Embodiment 1 FIG. 1 is a block diagram schematically showing a configuration of a
superdirective acoustic device according to a first embodiment of the present invention. The
superdirective acoustic device according to the present embodiment includes an audio sound
source 1, an envelope (envelope processing unit) 2, a coefficient unit 3, an adder 4, a level
comparator (modulation processing unit) 5, and a multiplier (carrier level). Setting processor 6),
ultrasonic band generator 7 for sawtooth wave generation, multiplier 8, gain variable device
(gain setting processor) 9, signal controller (signal output unit) 10, pulse width modulation
amplifier (signal output unit And 11) and a radiator (signal output unit) 12. The audible sound
source 1 outputs an audio signal which is an audio signal. The envelope 2 inputs an audio signal
from the audio sound source 1, performs envelope processing, and obtains and outputs an
envelope level for causing a direct current shift according to the level. Further, the coefficient
unit 3 inputs an audio signal from the audible sound source 1 and multiplies it by m. The adder 4
adds the outputs of the envelope unit 2 and the coefficient unit 3.
[0015]
The multiplier 6 inputs the envelope levels from the envelope unit 2 and further inputs sawtooth
carrier waves having a constant frequency higher than the audio signal of at least the audible
band generated by the ultrasonic band oscillator 7 and outputs these. Multiply. The level
comparator 5 compares the voltage of the multiplied carrier wave output from the multiplier 6
with the audio signal output from the adder 4 to generate a pulse width modulation signal. The
gain variable unit 9 receives the envelope level from the envelope unit 2 and changes the level of
the modulation signal based on this level. Specifically, the multiplier 8 is adjusted to a desired
level by multiplying the modulation signal output from the level comparator 5 by the level
determined by the gain variable unit 9.
[0016]
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The signal controller 10 executes polarity inversion processing every arbitrary cycle of the pulse
width modulation signal (PWM signal) whose level is adjusted via the multiplier 8 and the gain
variable device 9. The pulse width modulation amplifier 11 performs switching in accordance
with the signal subjected to the polarity inversion processing described above, and is amplified
by resonating with the radiator 12 having a capacitive property, which is configured of an
ultrasonic transducer of a piezoelectric element. Thereby, the signal is emitted from the radiator
12 as a sound wave. Here, the envelope level of the envelope 2 is set to 0 <envelope level ≦ 1
according to the audio signal level output from the audible sound source 1. In general, when the
envelope level is 1, the modulation rate is 100%. This indicates that the smaller the audio signal
level, the smaller the envelope level.
[0017]
Next, level control processing by the superdirective acoustic device of the first embodiment will
be described. FIG. 2 is a diagram for explaining an example of level control, in which (a) shows an
example of control by the above-described conventional superdirective acoustic device which
performs pulse width modulation, and (b) shows superdirecting of the first embodiment. It shows
an example of control by the dynamic sound device. In the conventional example shown in FIG.
2A, the sawtooth signal level is fixed, but in the first embodiment shown in FIG. 2B, the sawtooth
signal level is reduced according to the audio signal level. . From this, it can be seen that the
pulse width of the PWM signal shown in FIG. 2B is clearer in magnitude than the pulse width of
the PWM signal of the conventional example shown in FIG. 2A. This indicates that the pulse
width modulation can be performed faithfully regardless of the audio signal level, and the
modulation rate is improved.
[0018]
Such modulation wave gain adjustment processing is performed by the gain changer 9 based on
the envelope level from the envelope 2. The gain variable unit 9 can set, for example, an arbitrary
value of X, and substitutes the envelope level output from the envelope 2 into a relational
expression of 1 / (X + envelope level). Thereby, when the level of the audio signal is small, the
gain of the modulation signal can be increased. For example, when the envelope level of the
audio signal is 0.3, the value of X approaches 0.7. By multiplying this value by the PWM signal
output from the level comparator 5 by the multiplier 8, it becomes possible to raise the
modulation signal level of a small audio signal level.
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[0019]
FIG. 3 is a view showing an example of the configuration of the signal controller peripheral
portion in FIG. 1, and shows an example of a specific configuration of a portion surrounded by a
broken line in FIG. The pulse width modulation amplifier 11 includes a gate driver 13, a MOSFET
14 constituting switches S 1 to S 4, and two coils L 1 and L 2 connected to the radiator 12.
Radiator 12 is hereinafter also referred to as LOAD. In the following, an example in which the
radiator 12 is configured by a capacitive ultrasonic transducer is shown. The same components
as in FIG. 1 are assigned the same reference numerals and redundant explanations will be
omitted.
[0020]
The gate driver 13 applies a switching signal, which is a pulse width modulation signal input
from the signal controller 10, to the gates of the four MOSFETs 14 to control on / off of the
switches S1 to S4 composed of the MOSFETs 14.
[0021]
As the connection of four MOSFETs 14, a unit in which two MOSFETs 14 are connected in series
is connected in parallel, one end of each unit is connected with the variable power supply voltage
15 represented by the voltage VDC, and the other end is connected with the ground (GND) Do.
The MOSFETs 14 connected in series in each unit are connected to the radiator 12 via the coils
L1 and L2.
[0022]
The pulse width modulation amplifier 11 turns on / off the switches S1 to S4 by a switching
signal which is a pulse width modulation signal input from the signal controller 10. A system
consisting of the LOAD 12 and the coils L 1 and L 2 can perform resonance and amplification in
accordance with this switching, and the pulse waveform supplied to the LOAD 12 can be
smoothed. The number of coils L1 and L2 may be one in theory. It also has a function as a filter
for suppressing the high frequency component of LOAD12.
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[0023]
Next, the operation will be described. FIG. 4 is a timing chart showing the operation of the
superdirective acoustic device according to the first embodiment, which will be described with
reference to this figure. In the figure, Vcarrier represents the output voltage waveform of the
carrier wave signal of the ultrasonic frequency band from the ultrasonic band oscillator 7. The
period A of this output waveform is the frequency of the pulse width modulation signal output
from the level comparator 5. Here, it is assumed that the carrier frequency is 80 kHz, which is
twice the frequency when the carrier frequency is 40 kHz. Vpwm is a voltage signal waveform of
a pulse width modulated signal and can be obtained by comparing the voltage level of the audio
signal from the audio sound source 1 with the voltage level of the carrier signal Vcarrier from the
ultrasonic band oscillator 7.
[0024]
The broken line portion in the voltage waveform of Vpwm shows the waveform when the period
in which the voltage level of the audio signal from the audible sound source 1 is higher than that
of the carrier wave signal is longer than that of the solid line portion. That is, the rising edge of
the pulse in the solid line portion is located in the broken line portion indicated by the arrow, and
the pulse width is wide. Also, the reverse arrow in the solid line portion shows the waveform
when the period in which the voltage level of the audio signal from the modulation signal source
1 is higher than that of the carrier signal is shorter than the solid line portion.
[0025]
V1 (S1), V2 (S2), V3 (S3), and V4 (S4) are voltage waveforms of signals input to the gates of the
MOSFETs 14 constituting the switches S1 to S4. VL (L1, L2) is a voltage waveform applied to the
coils L1, L2 by the power supply voltage 15. The broken line portion in the voltage waveform of
VL (L1, L2) shows the voltage waveform of VL (L1, L2) when the pulse width of the voltage
waveform of Vpwm is in the state of the broken line portion. In this case, the edge of the pulse in
the solid line portion is located in the broken line portion indicated by the arrow. Also, the
reverse arrow in the solid line portion shows the waveform when the period in which the voltage
level of the audio signal from the modulation signal source 1 is higher than that of the carrier
signal is shorter than the solid line portion.
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[0026]
VLOAD is the voltage waveform applied to LOAD12, and the curve of the solid line portion shows
the waveform when the voltage waveform of VL (L1, L2) is the solid line portion, and the curve of
the broken line portion shows the voltage waveform of VL (L1, L2) as a broken line It represents
the waveform of the part. That is, the curve of the broken line portion of VLOAD corresponds to
the case where the voltage waveform pulse width of Vpwm is wider than the solid line portion.
When the voltage waveform pulse width of Vpwm is shorter than the solid line portion, the
amplitude is lower than that of the solid line waveform of VLOAD. The voltage wave VLOAD is
generated by filtering the coils L1 and L2 and the radiator 12.
[0027]
When the signal controller 10 receives a pulse width modulation signal as shown in FIG. 4 from
the level comparator 5 via the multiplier 8, the signal controller 10 always generates a switching
signal having a polarity inversion every two cycles. In the example of FIG. 4, the voltages of V1
(S1), V2 (S2), V3 (S3) and V4 (S4) always have polarity inversion once in two cycles based on the
voltage waveform of the solid line portion of Vpwm. A four mode switching signal having a
waveform is generated.
[0028]
These switching signals are output from the signal controller 10 to the gate driver 13. The gate
driver 13 inputs switching signals to the gates of the corresponding switches S1 to S4,
respectively.
[0029]
At this time, by performing switching in the above-described four modes, VL (L1, L2) having
twice the cycle A of the carrier signal is applied to the coils L1, L2 in one cycle. As a result, the
LOAD 12 is charged and discharged, and as a result, the LOAD 12 is supplied with a smooth
waveform voltage as indicated by VLOAD in FIG. Specifically, the four modes of switching are
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configured by (1) to (4) below.
[0030]
(1) When both V1 (S1) and V4 (S4) applied to the switches S1 and S4 are in the on state (H level),
the power supply voltage 15 passes through the switch S1, coil L1 and LOAD12, coil L2 and
switch S4 And the ground (GND) is connected. As a result, the power supply voltage 15
(hereinafter referred to as VDC) is applied to the LOAD 12 to charge the charge.
[0031]
(2) Following (1), both V2 (S2) and V4 (S4) applied to the switches S2 and S4 are turned on (H
level). At this time, the LOAD 12 is short-circuited via the switches S2 and S4. As a result, the
charge stored in the LOAD 12 is discharged.
[0032]
(3) Subsequently to (2), both V2 (S2) and V3 (S3) applied to the switches S2 and S3 are turned on
(H level). At this time, the ground (GND) is connected from the power supply voltage 15 via the
switch S3, the coil L2, the LOAD 12, the coil L1, and the switch S2. As a result, VDC is applied to
the LOAD 12 to charge the charge.
[0033]
(4) Subsequent to (3), both V2 (S2) and V4 (S4) applied to the switches S2 and S4 are turned on
(H level). At this time, the LOAD 12 is short-circuited via the switches S2 and S4. As a result, the
charge stored in the LOAD 12 is discharged.
[0034]
The VLOAD obtained in this manner is a curve corresponding to the pulse width of the pulse
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width modulation signal Vpwm as shown in FIG. 4, and for example, an amplitude difference B
occurs between the dashed curve and the solid curve in FIG. . The amplitude difference B in the
voltage waveform VLOAD increases or decreases in proportion to the pulse width of the voltage
waveform VPWM. That is, a voltage having an amplitude corresponding to the voltage level of
the audio signal is applied to the LOAD 12, and an acoustic signal having an intensity
corresponding to the voltage level of the audio signal is output. This output voltage can be
adjusted by changing the value of the variable power supply voltage 15.
[0035]
As described above, according to the first embodiment, the value obtained by pulse width
modulating the audio signal from the audible sound source to a signal in a frequency band higher
than at least the audible band and performing envelope processing on the audio signal level from
the audible sound source Setting the carrier wave level and the gain of the modulation signal
accordingly, so that the conversion efficiency from electricity to sound can be improved, the
enlargement of the device can be suppressed, and the easy-to-listen sound corresponding to the
audio signal can be provided. Can.
[0036]
FIG. 1 is a block diagram schematically showing a configuration of a superdirective acoustic
device according to Embodiment 1 of the present invention.
It is a figure explaining the example of level control. It is a figure which shows the structural
example of the broken line part in FIG. 5 is a timing chart showing the operation of the
superdirective acoustic device according to the first embodiment.
Explanation of sign
[0037]
DESCRIPTION OF SYMBOLS 1 audible sound source, 2 enveloper (envelope processing unit), 3
coefficient unit, 4 adder, 5 level comparator (modulation processing unit), 6 multiplier (carrier
level setting processing unit), 7 super generation for sawtooth wave Sound wave band oscillator,
8 multiplier, 9 gain variable unit (gain setting processing unit), 10 signal controller (signal output
unit), 11 pulse width modulation amplifier (signal output unit), 12 radiator (signal output unit),
13 Gate driver, 14 MOSFETs, 15 supply voltages.
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