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[Outline] In the present invention, in the sampling period, the PGF-PAM conversion unit converts
a PCM signal converted from an analog audio signal which is an original signal into a PAM signal,
and then performs a predetermined processing on the PAM signal The switch unit is a speaker
drive circuit that switches the switch so that the capacitor is charged and discharged to the gap
of the speaker after charging, and the speaker can be nondirectional and miniaturized.
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
drive circuit of a speaker in an audio system. In recent years, in acoustic measurement such as
nondestructive inspection and medical ultrasound diagnostic apparatus, an impulse-like sound
wave of extremely short wavelength utilizing minute spark discharge is used. In particular, the
present invention refers to a single drive circuit utilizing micro spark discharge. PRIOR ART FIG.
4 is a view showing a conventional speaker structure. The configuration of a conventional
speaker will be described with reference to FIG. Cone 11 is a conical diaphragm, voice coil 12 is a
movable coil at the center of cone 11, damper 13 is a mechanism for correctly holding voice coil
12 in a magnetic field, and edge 14 is a cone. The supporting peripheral portions, which
constitute the vibration system of the speaker. The magnet 15, the yoke 16 and the center ball
17 constitute a magnetic circuit. Next, the operation will be described. When an analog voice
signal is input from the terminal, the voice coil 12 vibrates due to the electromagnetic force of
the magnetic field of the magnetic circuit and the current flowing to the voice coil 12. This
vibration is transmitted to the air through the cone 11 and is heard as a sound. [Problems to be
Solved by the Invention] However, since the conventional speaker vibrates the cone 11, which is
a diaphragm, back and forth according to the analog signal to emit sound, an audio signal
mediated by mechanical vibration Along with the reproduction, there are the following problems
of electroacoustic conversion. First, the first problem is that the high-pitched region becomes
sharper in directivity, and the snaking area becomes narrower. The second problem is the
presence of non-linear distortion and disturbance of the transfer characteristic due to the
difficulty of realizing a single resonance system. The third problem is that in the multiway
speaker, the acoustic center is less likely to be lost, and crossover distortion is likely to occur.
Furthermore, the fourth problem is that the speaker system becomes larger if emphasis is placed
on the low frequency range reproduction. Then, in view of the above-mentioned problems, the
present invention aims to provide a non-directional and compact speaker driving circuit.
[Means for Solving the Problems] FIG. 1 is a diagram showing the principle configuration of the
present invention. 0 In the present invention, in order to solve the above-mentioned various
problems, the PCM-PAM conversion unit 1 is an analog voice which is an original signal. The
PAM signal bias unit 2 adds a DC component of constant amplitude to the PAM signal Spa from
the PCM-PAM conversion unit 1 and converts the signal into a positive or negative signal. This is
a part that is level shifted so that it has only one amplitude, and is a part that amplifies the PAM
signal from the PAM signal signal part width part 3AM signal bias part 2 and charges the
capacitor C, and the switch part 4 is a PAM signal It is a switch connected between the signal
portion width portion 3 peaker 5 and performs charging and discharging of the capacitor C.
[Operation] In FIG. 1, the PCM signal Sin converted from the analog voice signal is converted by
the PCM-PAM conversion unit 1 into the PAM signal S. The PAM signal S, m is added with a
direct current component of a constant amplitude by the bias unit 2 of the PAM signal and level
shifted so that either positive or negative has only one amplitude. The PAM signal from the PAM
signal bias unit 2 charges the capacitor C by the PAM signal amplitude unit 3. The charged
capacitor C is discharged through the minute electrode gap g of the speaker 5 to emit an impulse
sound. The charge and discharge of the capacitor C are alternately repeated by the switch unit 4
every sampling period. Of the sound composed of the high frequency component and the direct
current component thus radiated, the sound of the high frequency component is smoothed by
human hearing and the direct current component is cut, so the impulse sound is reproduced to
the same degree as the analog sound. It will be done. EXAMPLE In recent years, in acoustics,
research on micro spark discharge sources has been advanced. The minute spark discharge
sound source is, for example, a sound source that instantaneously discharges, through a minute
electrode gap, electric energy charged in a direct current to a capacitance, and emits an impulselike sound wave. The minute spark discharge source injects an impulsive heat pulse into a minute
volume in the air and emits sound by causing a rapid expansion in a spherical shape, so it can be
regarded as a nearly omnidirectional point source. Furthermore, it is clear that the characteristics
of the charge voltage of the capacitance and the output sound pressure exhibit a linear
characteristic as described by Hakushita-Oh et al. In the 13th research presentation meeting of
the Doshisha University Institute of Science and Technology (1975, 12, 6). It is known for
"impulse source using air discharge". Since a minute spark discharge sound source is a point
sound source, if it can be used as a sound source of a speaker, it is nondirectional in an audio
band of 20 Hz to 20 kHz.
Furthermore, since this sound source unit can be made small and thermal energy is used, the
transient response is also superior to that of the conventional sound source unit using
mechanical vibration. Therefore, if the voice signal can be reproduced by continuously emitting
the impulse sound of the minute spark discharge sound source, the problems of the conventional
cone speaker etc. can be solved at once. The same effect can be obtained by applying a heat
impulse to one point in the air by laser focusing. Hereinafter, an embodiment of the present
invention will be described in detail with reference to the drawings. FIG. 1 is a view showing an
embodiment of the present invention. First, the configuration shown in the figure will be
described. The PCM-PAM conversion unit 1 converts the pulse code modulation PCM signal Sin
into a pulse amplitude modulation PAM signal S □. The bias unit 2 of the PAM signal applies a
DC positive or negative bias to the S □ signal from the PCM-PAM conversion unit 1. PAM signal
signal section width section 3 This is an amplifier for charging a capacitor. The switch 4
comprises switches SI and S2 for charging and discharging the capacitor C. The timing control
unit 6 receives the sampling signal Sc having a cycle of Δt, synchronizes with this signal,
performs control of the PCM-PAM conversion unit 1, the PAM signal bias unit 2, and the PAM
signal signal unit width unit 3 Control of the switches Sl and S2 contributing to the charging and
discharging of the The capacitor C is charged when the switch S2 is open and the switch S1 is
closed, and discharged when the switch S2 is closed and the switch S1 is open. The loudspeaker
5 has a discharge electrode gap (gap) g, and when a closed circuit Cg-R-3, -C is formed, the
capacitor C causes an air spark discharge in the gap g to generate a sound. FIG. 3 is a time chart
explaining the operation of the embodiment. 0 The operation of the embodiment will be
described using FIG. The PCM signal Si + s of (b) used in, for example, a CD or DAT, the original
analog signal of FIG. The sampling signal S shown in FIG. 6C is input to the timing control unit 5.
The signal 5A11 is converted by the PCM-PAM conversion 1 into a PAM signal S □ as shown in
FIG. The signal S pm is converted by a bias unit 2 of the PAM signal into, for example, a PAM
signal of positive polarity as shown in FIG. This is to make all positive impulses. On the other
hand, the timing control unit 6 causes the switches S1 and S!
Is alternately turned on and off within the sampling period Δ as shown in (f) and (g) of the
figure, the capacitor C is charged when S1 is on, and discharged reversely when S2 is on. Thus,
the capacitor is continuously charged and discharged. The voltage charged in the capacitor C is
proportional to the amplitude of the PAM signal shown in FIG. The sound pressure generated by
spark discharge in the gap g of the speaker 5 is a positive impulse sound with a peak value
proportional to the voltage of the capacitor C as a spherical wave, as shown in FIG. , To emit as a
digital signal. By the way, human hearing is sensitive to sounds in the band of 20 Hz to 20 kHz
but not to sounds above 20 kH, z and below 2011 z, so the sound from the speaker can not be
heard by humans. As shown in FIG. 1A, the sound of the high frequency component sounds as if
it were the envelope of FIG. 3H as if it were through a low pass filter, and it sounds as a sound
with the DC component cut. As a result, the impulse sound is reproduced as analog voice as in
the prior art as shown in FIG. In addition, you may use the mechanical filter which cuts the sound
whose frequency is 20 kHz or more. As described above in detail, according to the present
invention, the drive circuit for reproducing the voice input by the minute spark discharge sound
source in the discharge gap is provided. It can solve directivity, disturbance of transmission
characteristics due to resonance system, nonlinear distortion, acoustic center mismatch and
crossover distortion in multi-way speakers, speaker enlargement due to bass region
reproduction, jitter due to analog signal processing, and no directivity And it can be miniaturized.
Brief description of the drawings
1 shows the principle of the present invention, FIG. 2 shows an embodiment of the present
invention, FIG. 3 shows a time chart for explaining the operation of the embodiment, and FIG. 4
shows a conventional speaker structure. FIG.
In the figure, 1 ... PCM-PAM conversion unit, 2 ... PAM signal bias unit, 3 ... PAM signal
amplification unit, 4 ... switch unit, 5 ... speaker, g ... gap.
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