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BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
apparatus for reproducing speech from an IC storing speech. (Prior Art) FIG. 3 shows a
conventional synthetic sound reproduction apparatus. The readout signal from the speech
synthesis ICI storing the synthesized speech is high-frequency component cut by the filter 2,
amplified by the amplifier 3, and supplied to the dynamics beaker 4 '. The speech stored in the
speech synthesis ICI is a digital waveform as shown in FIG. 5 and therefore contains many high
frequency noises. The function of the filter 2 is to convert this into an audio waveform as shown
in FIG. In the example shown in FIG. 3, the dynamics beaker 4 'is used as a speaker, but it is
conceivable to replace this with the piezoelectric speaker 4 as shown in FIG. (Problems to be
Solved by the Invention) Although the sound quality shown in FIG. 3 can be changed to a good
sound quality, it consumes a large amount of current because it uses the dynamics beaker 4 'and
can not be adopted for a micro set using small batteries. . In the case shown in FIG. 4 using the
piezoelectric speaker 4, although the current consumption of the speaker itself is small, the
current consumption also increases due to the loss due to the step-up transformer 5 used to
improve the frequency characteristic. (Means for Solving the Problems) The present invention
has an object of using the piezoelectric speaker to scale the one without the above-mentioned
defect, which is driven by the read signal from the voice synthesis IC and the piezoelectric
speaker A coil is connected in series, and the series resonance frequency of the coil and the
piezoelectric speaker is selected as the frequency of the valley in the sound pressure frequency
characteristic. (Operation) The coil connected in series with the piezoelectric speaker raises the
valley of the frequency characteristic by series resonance and suppresses the high region.
(Embodiment) FIG. 1 shows an embodiment of the present invention. The read signal of the
speech synthesis ICI is directly amplified by the BTL-connected amplifier 3 and does not use a
conventional filter. The output signal of the amplifier 3 is supplied to a piezoelectric speaker 4 in
which a coil 6.6 'is connected in series. For example, when a 50 m H coil was connected to a
piezoelectric speaker 4 with a capacitance of 0.05 μF, its frequency characteristics were
improved as shown in FIG. That is, the solid line is the characteristic before connecting the coil,
while the dotted line is the characteristic after connecting the coil. As is apparent from these
characteristics, the valley is lifted and flat at the resonance frequency of 2.9 KIIz, and the sound
pressure level is suppressed in the high frequency band above 5 Kllz.
By both effects. Sound quality has been significantly improved. (Effects) As described above, the
capacitance of the piezoelectric speaker of the present invention is a simple configuration in
which only a series resonating coil is connected, and it is necessary to cut high-frequency noise
and mid-range noise necessary for synthetic sound reproduction. It is possible to flatten the
characteristics by lifting the resulting valleys, and the ultra-compact synthesized sound
reproducing device with extremely high sound quality can be obtained.
Brief description of the drawings
FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is a graph
showing its frequency characteristics, FIG. 3 and FIG. 4 are circuit diagrams showing the prior
art, and FIG. FIG. 6 is a graph showing the waveform of the signal, and FIG. 6 is a graph showing
the waveform of the reproduced sound after cutting the high frequency noise.
1 ··· Speech synthesis IC 3 · · Amplifier 4 · · Piezoelectric speaker 6.6 ′ · · · Coil Fig. 1