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JP2005286579

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DESCRIPTION JP2005286579
PROBLEM TO BE SOLVED: To provide a modulator for superdirective speaker which enables
optimum bias and modulation output matched to an audio signal without becoming
overmodulation. SOLUTION: An envelope unit 11 for outputting a DC value according to the level
of an audio signal, a coefficient unit 15 for adjusting the level of the audio signal according to a
given coefficient, and a DC value from the envelope unit 11 An adder 19 for DC-shifting the
audio signal after level adjustment by the coefficient unit 15; a multiplier 18b for multiplying the
audio signal DC-shifted by the adder 19 by the carrier of the ultrasonic band and outputting a
modulation signal; And a variable multiplier 13 which changes the coefficient of the coefficient
unit 15 and the level of the carrier wave output from the ultrasonic band oscillator 14 in
accordance with the DC value from the envelope unit 11. [Selected figure] Figure 1
Modulator for superdirective speaker
[0001]
The present invention relates to a modulator for superdirective loudspeakers which directionally
radiates audible sound.
[0002]
FIG. 2 is a block diagram showing the configuration of a conventional superdirective speaker
device.
03-05-2019
1
As shown in the figure, the conventional superdirective speaker device comprises a modulation
signal source 1, a coefficient unit 2, a direct current source 3, an adder 4, a square root converter
5, an ultrasonic band oscillator 6, and a multiplier 7. A modulator, a power amplifier 8 and a
radiator 9 are provided.
[0003]
The modulation signal source 1 outputs an audio signal s (t) and supplies it to the coefficient unit
2. The coefficient unit 2 multiplies the audio signal s (t) by m to obtain m · s (t) and supplies the
same to the adder 4. m · s (t) is added by the adder 4 by the bias of the direct current source 3 to
be 1 + m · s (t). Subsequently, the square root converter 5 square-roots the output signal 1 + m · s
(t) of the adder 4. The signal 11 + m · s (t) thus obtained is multiplied by the carrier wave which
is the ultrasonic wave from the ultrasonic band oscillator 6 by the multiplier 7. Amplitude
modulation is performed by this multiplication processing to obtain a modulation signal.
[0004]
The above-described processing from the coefficient unit 2 to the multiplier 7 is processing in
which the sound signal m · s (t) having the modulation degree m is subjected to square root
processing and amplitude modulation . The output of the multiplier 7 is amplified by a power
amplifier 8 and supplied to a radiator 9 provided with a plurality of ultrasonic transducer arrays
for generating ultrasonic waves. The radiator 9 radiates the acquired signal into the air as a
directional sound wave.
[0005]
In the superdirective speaker modulator having such a configuration, there is a problem that the
carrier frequency signal from the ultrasonic band oscillator 6 is output from the radiator 9 as it is
when no sound source signal is output from the modulation signal source 1. there were.
Therefore, in order to solve such a problem, a modulator having the following configuration has
been considered.
[0006]
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2
FIG. 3 is a block diagram showing another configuration of the conventional superdirective
speaker modulator. As shown, this modulator comprises an enveloper 30 in addition to the
modulator of FIG. The audio signal s (t) output from the modulation signal source 1 is supplied to
an enveloper 30 and a coefficient unit 2. Upon acquiring the audio signal s (t), the enveloper 30
extracts and outputs an envelope bias value a (0 <a ≦ 1). When acquiring the audio signal s (t),
the coefficient unit 2 multiplies it by m and outputs a signal of m · s (t). The adder 4 adds the
output of the envelope unit 30 and the output of the coefficient unit 2 to obtain a + m · s (t). The
operations of the square root converter 5, the ultrasonic band oscillator 6, and the multiplier 7
are the same as those shown in FIG. In the modulator configured as shown in FIG. 3, since the
enveloper 30 does not output the envelope bias value when there is no input of an audio signal
from the modulation signal source 1, the excitation signal from the modulation signal source 1 as
shown in FIG. The carrier wave is never output when the signal is not output.
[0007]
The modulated signal obtained by the processing by the circuit of FIG. 3 is amplified by a power
amplifier and emitted as a sound wave from a plurality of ultrasonic vibration elements that
generate an ultrasonic wave. This sound wave causes a non-linear interaction in the process of
being propagated through the air as a finite amplitude sound wave which is a strong ultrasonic
wave, and is self-demodulated into superdirective speech consisting of low frequency
components etc. Become.
[0008]
JP-A-4-58758
[0009]
The conventional superdirective speaker modulator is configured as described above. Since
amplitude modulation is adopted as the modulation method, the modulation rate is lowered when
an audio signal of a small level is input.
Therefore, there is a problem that the demodulated sound radiated from the ultrasonic vibration
element into the air and generated by itself can not obtain a desired sound pressure level.
03-05-2019
3
[0010]
In addition, since the input audio signal is over-modulated when it is over-input, there is a
problem that the sound to be output is distorted.
[0011]
The present invention has been made to solve the above-described problems, and a modulator for
superdirective speaker that enables optimum bias and modulation output matched to an audio
signal without being overmodulated. The purpose is to get.
[0012]
The superdirective speaker modulator according to the present invention comprises: level
detection means for outputting a DC value according to the level of the audio signal; coefficient
means for adjusting the level of the audio signal according to the given coefficient; and level
detection means DC shift means for DC shifting the audio signal after level adjustment by the
coefficient means according to the DC value of the coefficient means, multiplying the audio signal
DC shifted by the DC shift means by the carrier wave of the ultrasonic band, and outputting a
modulation signal , And variable multiplier means for changing the coefficient of the coefficient
means and the level of the carrier wave output from the ultrasonic band oscillator in accordance
with the direct current value from the level detection means.
[0013]
According to the present invention, the level detecting means for outputting a DC value
according to the level of the audio signal, the coefficient means for adjusting the level of the
audio signal according to the given coefficient, and the DC value from the level detecting means
DC shift means for DC shifting an audio signal after level adjustment by coefficient means,
multiplication means for multiplying an audio signal DC shifted by the DC shift means by a
carrier wave of an ultrasonic band, and outputting a modulation signal, level detection Since the
variable multiplier means for changing the coefficient of the coefficient means and the level of
the carrier wave output from the ultrasonic band oscillator according to the direct current value
from the means is provided, modulation according to the level of the audio signal There is an
effect that it is possible to obtain a superdirective speaker modulator capable of outputting a
modulation signal without reducing the rate.
[0014]
03-05-2019
4
Embodiment 1
FIG. 1 is a block diagram showing the configuration of a superdirective speaker modulator
according to a first embodiment of the present invention.
As shown in the figure, the superdirective speaker modulator comprises a modulation signal
source (audio sound signal source) 10, an enveloper (level detection means) 11, a DC shift value
generator (DC shift means) 12, a variable multiplier Unit (variable multiplier unit) 13, ultrasonic
band oscillator 14, coefficient unit (coefficient unit) 15, limiter unit (limiter unit) 16, square root
converter 17, multiplier 18a, multiplier (multiplication unit) 18b, and multiplier 18c , Adder (DC
shift means) 19.
[0015]
The modulation signal source 10 outputs an audio signal.
When an audio signal is output from the modulation signal source 10, the enveloper 11 performs
envelope detection according to the level to extract an envelope level value (DC value).
The envelope level value to be output is 0 to 1. The DC shift value generator 12 changes the DC
shift value which is a bias based on the envelope level value output from the envelope unit 11.
The multiplier 18 a multiplies the output value from the DC shift value generator 12 by the
envelope level value from the envelope 11. The direct current shift value generator 12 can set an
output value obtained by multiplying the output value of the direct current shift value generator
12 by the multiplier 18a to an arbitrary value, with the envelope level values 0 to 1 output from
the envelope unit 11 It is a thing. For example, the output value of the multiplier 18a is set to be
always 1 so that 100% amplitude modulation can be realized. That is, when the equation of the
amplitude modulation wave is input signal f (t) = As cos ω st Carrier f (t) = Accos (ω ct + θ c), [fc
(t)] AM = Ac mAM = As / Ac) Therefore, if the envelope level value is 1 (Ac), 100% modulation
can be realized. Thus, the DC shift value generator 12 adjusts the envelope level value to obtain
the desired degree of modulation.
[0016]
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5
The ultrasonic band oscillator 14 outputs a carrier wave in the ultrasonic band. The coefficient
unit 15 adjusts the level of the audio signal from the modulation signal source 10 by the given
coefficient m. The variable multiplier 13 adjusts the level of the carrier wave output from the
ultrasonic band oscillator 14 and the coefficient of the coefficient unit 15 based on the envelope
level value output from the envelope unit 11. For example, when the envelope level value output
from the envelope unit 11 is 0.5, the output level from the coefficient unit 15 is adjusted to 1 and
the output level from the ultrasonic band oscillator 14 to 0.5. Do. The multiplier 18 c multiplies
the carrier wave from the ultrasonic band oscillator 14 by the output value from the variable
multiplier 13 and outputs the result.
[0017]
The adder 19 DC shifts the audio signal after level adjustment by the coefficient unit 15
according to the DC shift value generated by the DC shift value generator 12. The limiter 16
functions to suppress overmodulation. That is, in accordance with the level of the DC-shifted
audio signal output from the adder 19, in the case of excessive input, it is adjusted to a value
smaller than 0 or the carrier level. The square root converter 17 square-roots the output from
the limiter 16. The multiplier 18 b multiplies the output from the square root converter 17 by
the output from the multiplier 18 c and outputs the result.
[0018]
Next, the operation will be described. When an audio signal is output from the modulation signal
source 10, the enveloper 11 extracts an envelope level value according to the level of the audio
signal. Subsequently, the variable multiplier 13 adjusts the coefficient m of the coefficient unit 15
and the output level of the carrier wave from the ultrasonic band oscillator 14 according to the
envelope level value. The coefficient unit 15 adjusts the level of the audio signal from the
modulation signal source 10 by the adjusted coefficient m. The level adjusted audio signal is DC
shifted by the adder 19 by the DC shift value generated by the DC shift value generator 12 based
on the envelope level value from the envelope unit 11. The DC-shifted audio signal is subjected to
the square root processing by the square root converter 17 after the overmodulation is
suppressed by the limiter 16. The carrier whose output level has been adjusted by the variable
multiplier 13 and the output from the square root converter 17 are multiplied by the output from
the multiplier 18 c and output. This is output as a modulation signal to a power amplifier,
superdirective speaker or the like. The sound waves emitted from the superdirective speaker
have superdirectivity.
03-05-2019
6
[0019]
As described above, according to the first embodiment, the coefficient of the coefficient unit 15
and the output level of the carrier wave from the ultrasonic band oscillator 14 are adjusted based
on the envelope level value output from the envelope unit 11. Since the variable multiplier 13 is
provided, it is possible to obtain the superdirective speaker modulator capable of outputting a
modulation signal without lowering the modulation rate in accordance with the level of the audio
signal. Further, since the limiter 16 for suppressing overmodulation is provided according to the
level of the audio signal, an effect of preventing overmodulation can be obtained.
[0020]
It is a block diagram which shows the structure of the modulator for superdirective speakers by
Embodiment 1 of this invention. It is a block diagram which shows the structure of the
conventional super-directional speaker apparatus. It is a block diagram which shows another
structure of the conventional modulator for superdirective speakers.
Explanation of sign
[0021]
1, 10 modulation signal source (audible sound signal source), 2, 15 coefficient unit (coefficient
means), 3 direct current source, 4, 19 adder (direct current shift unit), 5, 17 square root
converter, 6, 14 ultrasonic wave Band oscillator, 7, 18a, 18b, 18c multiplier (multiplication
means), 8 power amplifier, 9 radiator, 11, 30 envelope (level detection means), 12 DC shift value
generator (DC shift means), 13 Variable multiplier (variable multiplier means), 16 limiter (limiter
means).
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