JP2008103966A - Driving method of plane speaker, and plane speaker system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce steady generation of heat and power consumption of the conductor wire of a diaphragm. <P>SOLUTION: A drive pulse signal is outputted to the conductor wire 2 formed in a pair of the diaphragms 1 oppositely arranged from a switching amplifier, respectively. The output timing of at least one rising/falling edge of a drive pulse signal is made to change according to the level of an audio signal. Then, the electromagnetic force in correlation with the level of an audio signal is applied to the diaphragm 1, thus outputting power of sound by making the diaphragm 1 vibrate. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a planar speaker driving method and a planar speaker system.

  Many flat-type speakers are driven in the same manner as ordinary electrodynamic speakers, except that the diaphragm that hits the sound radiation surface is a flat plate. That is, when a current corresponding to an audio signal is supplied to a voice coil inserted in the magnetic gap, a driving force correlated with the audio signal is generated and connected to the voice coil via a bobbin, or a voice coil Electroacoustic conversion is performed by moving the diaphragm directly connected to the.

  However, in the above, the diaphragm needs to be strong enough to support the voice coil and the bobbin, and the diaphragm itself cannot be made extremely thin. Therefore, in order to vibrate the diaphragm, a corresponding force is required, and there is a problem that even delicate sounds cannot be reproduced faithfully.

  In order to solve this problem, the following apparatus using a force acting between two currents has already been proposed (see, for example, Patent Document 1). In this case, the diaphragm and the fixed plate are arranged opposite to each other, and a coil serving as a conductor line is arranged on both plates, and both coils are opposed to each other, and an audio signal supplied to the coil of the diaphragm Is positive, current flows in the same direction through the fixed plate coil, the diaphragm is displaced forward, and when the audio signal is negative, current in the reverse direction flows through the fixed plate coil. Flows, and the diaphragm is displaced backward.

  By the way, in the above, the use of a linear amplifier is assumed for the power amplification of the audio signal, but there is a problem that the efficiency of the linear amplifier is low and it is difficult to reduce the power consumption.

Japanese Patent No. 3349647

  An object of the present invention is to provide a planar speaker driving method and a planar speaker system that can reduce power consumption.

In order to achieve the above object, a driving method for a flat speaker according to the present invention is characterized in that a driving pulse signal is output from a switching amplifier to a conductor line formed on a pair of opposing diaphragms, and the driving pulse is output. The output timing of the rising and / or falling edge of at least one of the signals is changed according to the level of the audio signal, the duration of the attractive force acting on both conductor lines and the both conductor lines on the conductor lines of both diaphragms The ratio of the duration time of the repulsive force acting on the electromagnetic wave is that the electromagnetic force having a correlation with the level of the audio signal is applied, and the diaphragm is vibrated to output sound.
The flat speaker system of the present invention is characterized by A. A pair of opposing diaphragms formed with conductor lines; An audio signal is input, a drive pulse signal is output to the conductor line of each diaphragm, and the output timing of at least one rising and / or falling edge of the driving pulse signal is changed according to the level of the audio signal. A switching amplifier in which the electromagnetic force in which the ratio of the duration of the attractive force acting on both conductor lines and the duration of the repulsive force acting on both conductor lines is correlated with the level of the audio signal is applied to the conductor lines of both diaphragms It is in the point which has.
When the input audio signal is 0, the output timing of the rising and falling edges of each drive pulse signal may be shifted by 1/4.
The switching amplifier is a. Means for generating a sawtooth reference pulse signal; Means for comparing the level of the reference pulse signal and the audio signal and outputting a pulse width modulation signal in which the pulse width is modulated in accordance with the level of the audio signal; c. Means for converting the reference pulse signal to output a control pulse signal which is a rectangular wave and one of the drive pulse signals, the frequency of the control pulse signal being ½ of the reference pulse signal; When the other driving pulse signal is output and the levels of the pulse width modulation signal and the control pulse signal are different from each other, there may be provided means for setting the other driving pulse signal to a predetermined level.
Furthermore, the switching amplifier is a. Means for generating a reference pulse signal which is a rectangular wave and one drive pulse signal; Means for converting a reference pulse signal to output a control pulse signal having a triangular wave; c. Means for comparing the levels of the control pulse signal and the audio signal and outputting a pulse width modulation signal having a pulse width modulated in accordance with the level of the audio signal; There may be provided means for outputting the other driving pulse signal whose frequency is equal to the control pulse signal, triggered by the output of the rising edge of the pulse width modulation signal.
The switching amplifier is a. Means for generating a reference pulse signal having a rectangular wave and one drive pulse signal; Means for converting a reference pulse signal to output a control pulse signal having a triangular wave; c. Means for comparing the levels of the control pulse signal and the audio signal and outputting a first pulse width modulation signal having a pulse width modulated in accordance with the level of the audio signal; Means for inverting an audio signal and outputting an inverted audio signal; Means for comparing the levels of the control pulse signal and the inverted audio signal and outputting a second pulse width modulated signal having a pulse width modulated in accordance with the level of the inverted audio signal; The other drive pulse signal is output, the output timing of the rising edge of this drive pulse signal is made the same as the falling edge of the first pulse width modulation signal, and the output timing of the falling edge of the drive pulse signal is second pulse width modulated. It may have means for making it the same as the falling edge of the signal.
Furthermore, an amplification circuit and power amplification means for amplifying the drive pulse signal and outputting it to the conductor line may be provided.

  According to the present invention, a driving pulse signal correlated with an audio signal, that is, an alternating current is output from the switching amplifier to both conductor lines, but the frequency of the driving pulse signal of the switching amplifier is set to a relatively high frequency. Therefore, the impedance of the conductor line with respect to the alternating current is high, and therefore, when there is no audio signal input, the conductor line hardly generates heat, and the steady heat generation of the conductor line can be reduced. Moreover, since a highly efficient switching amplifier is used, power consumption can be reduced. Furthermore, since a magnetic circuit using magnets or metal parts is not used, the speaker can be reduced in weight.

  A first example of an embodiment of the present invention will be described below with reference to the drawings of FIGS. 1 to 4. The planar speaker system includes a planar speaker shown in FIGS. 1 and 2, and a switching amplifier (speaker drive) shown in FIG. Device).

  The flat speaker has a pair of flat diaphragms 1 made of ceramic or the like, for example, and these diaphragms 1 are arranged in parallel on the same projection surface and face each other. Normally, one diaphragm 1 is a fixed plate that is fixed to a frame or the like, and the other diaphragm 1 is held by the one diaphragm 1 via a spacer. The plate will be described as a functionally equivalent diaphragm 1. Each diaphragm 1 is formed with a conductor line (conductor, conductor, wiring) 2 in the same pattern, and both conductor lines 2 are opposed to each other. As shown in FIG. 1, when a reverse drive current flows through both conductor lines 2, a repulsive force due to Lorentz force (electromagnetic force) acts between the conductor lines 2 between both diaphragms 1. 2, when a drive current in the same direction flows through both conductor lines 2, an attractive force due to Lorentz force acts between the conductor lines 2 of both diaphragms 1, and this repulsive force and attractive force are It is made to substantially correspond to the target acoustic radiation direction. The conductor line 2 has a linear horizontal portion 2A disposed in the width direction of the diaphragm 1 and a curved connecting portion 2B that connects one end of the adjacent horizontal portion 2A. The conductor line 2 may be formed by adhering a conductor to the diaphragm 1, or may be formed on the diaphragm 1 by etching in the form of a transparent electrode. The material of the diaphragm 1 and the conductor line 2 is preferably lightweight.

  The switching amplifier converts the input analog audio signal into a digital audio signal, that is, a drive pulse signal, amplifies it, and outputs it to the two conductor lines 2 as a drive signal of the diaphragm 1. By changing the output timing of at least one rising and / or falling edge of the pulse signal in accordance with the potential (also referred to as voltage; hereinafter the same) level of the audio signal, the diaphragm 1 is vibrated. Yes. The driving force during a certain period is proportional to the on / off time ratio of the output stage of the switching amplifier. The switching amplifier performs the following operations. That is, when the input audio signal has a positive value, the potential of the pulse output of the switching amplifier connected to one conductor line 2 and the potential of the pulse output of the switching amplifier connected to the other conductor line 2 are The time of the same potential is set longer than the time of the reverse potential, and when the input audio signal has a negative value, the time of the two potentials being the reverse potential is set longer than the time of the same potential. Perform the action. The switching amplifier that performs such an operation includes a sawtooth wave generation circuit 4, a comparator 5, a D flip-flop 6, an exclusive OR gate 7, amplifier circuits 8, 9 and the like.

  The sawtooth wave generation circuit 4 is exemplified as a reference pulse signal generation circuit. As shown in FIG. 4, the sawtooth wave generation circuit 4 is a sawtooth wave having a frequency sufficiently higher than the frequency of the audio signal A input to the switching amplifier. A reference pulse signal B is generated. In this example, the rising edge of the waveform of the reference pulse signal B is loosened and the falling edge is steep.

  The comparator (comparator) 5 is exemplified as a pulse width modulation signal output circuit. An audio signal is input to one (plus side) input terminal and a sawtooth wave is generated to the other (minus side) input terminal. A circuit 4 is connected. As shown in FIG. 4, the comparator 5 compares the potential levels of the audio signal A and the reference pulse signal B, and the pulse width modulation signal D whose pulse width is modulated (PWM) according to the potential level of the audio signal A. Is output. When the level of the audio signal A is higher than that of the reference pulse signal B, the pulse width modulation signal D becomes high level.

  The D flip-flop 6 is exemplified as the rectangular wave generating circuit 4, the sawtooth wave generating circuit 4 is connected to the inverted clock input terminal bar CK, and the positive voltage + Vcc is applied to the data input terminal D. 4, the output of the falling edge of the reference pulse signal B is used as a trigger to output a control pulse signal C having a rectangular wave whose frequency is ½ of the reference pulse signal B from the output terminal Q, This is one drive pulse signal.

  The exclusive OR gate (EX-OR gate) 7 is exemplified as a drive pulse signal output circuit, and the output terminal of the comparator 5 and the output terminal Q of the D flip-flop 6 are connected to its input terminals. As shown in FIG. 4, the logical OR gate 7 outputs the other driving pulse signal E which is an exclusive OR (EX-OR) of the pulse width modulation signal D and the control pulse signal C. In other words, the output timing of the rising and / or falling edge of this drive pulse signal is controlled according to the potential level of the audio signal, and the potential levels of both the pulse width modulation signal D and the control pulse signal C are different. In this case, the drive pulse signal E is set to a predetermined level, that is, a high level.

  The output terminals of the exclusive OR gate 7 or the output terminal Q of the D flip-flop 6 are connected to the input terminals of the amplifier circuits (amplifiers) 8 and 9, and are used as the input drive pulse signal E and drive pulse signal. The control pulse signal C is amplified and output. The output terminal of each amplifier circuit 8 is connected to the conductor line 2 of each diaphragm 1.

  According to the above configuration example, the drive pulse signal E is input as the drive current to one of the conductor lines 2 of the two diaphragms 1 and the control pulse signal C that is the drive pulse signal is input as the drive current to the other. Is done. In this case, as shown in FIG. 1, when a reverse drive current flows through both conductor lines 2, a repulsive force due to Lorentz force acts between the conductor lines 2 of both diaphragms 1, and FIG. As shown, when a drive current in the same direction flows through both conductor lines 2, an attractive force due to Lorentz force acts between the conductor lines 2 of both diaphragms 1. The Lorentz force acting between the conductor lines 2 of both diaphragms 1 has a correlation with the exclusive OR of the drive pulse signal E and the control pulse signal C as the drive pulse signal as shown in FIG. (In reality, there is a correlation with the low frequency component included in this exclusive OR. The same applies hereinafter.) When the exclusive OR is at a high level, a repulsive force acts between the conductor lines 2 of both diaphragms 1. When the exclusive OR is at a low level, an attractive force is generated between the conductor lines 2 of both diaphragms 1. Works. The diaphragm 1 is vibrated by the repulsive force and the attractive force, and acoustic output is performed.

  5 and 6 show a second example of the embodiment of the present invention. As shown in FIG. 5, the switching amplifier includes a rectangular wave generating circuit 10, a triangular wave generating circuit 11, a comparator 12, It has a monostable multivibrator 13 and amplifier circuits 8 and 9.

  The rectangular wave generating circuit 10 is exemplified as a reference pulse signal generating circuit, and generates a reference pulse signal E having a rectangular wave as shown in FIG. This reference pulse signal E is one drive pulse signal, and the output terminal of the rectangular wave generation circuit 10 is connected to the input terminal of the triangular wave generation circuit 11.

  The triangular wave generation circuit 11 is exemplified as a control pulse signal output circuit. As shown in FIG. 6, the triangular wave generation circuit 11 converts the reference pulse signal E to generate a control pulse signal B having a triangular wave whose waveform is an isosceles triangle. Output. Note that the control pulse signal B becomes a high level when the reference pulse signal E rises and the control pulse signal B becomes a low level when the reference pulse signal E falls.

  The comparator 12 is exemplified as a pulse width modulation signal output circuit. The audio signal A is input to the plus side input terminal, and the triangular wave generating circuit 11 is connected to the minus side input terminal. The comparator 12 compares the potential levels of the audio signal A and the control pulse signal B, and as shown in FIG. 6, the pulse width modulation signal whose pulse width is modulated (PWM) according to the potential level of the audio signal A. C is output. When the level of the audio signal A is higher than that of the control pulse signal B, the pulse width modulation signal C becomes high level.

  The monostable multivibrator 13 is exemplified as a drive pulse signal output circuit, and outputs the other drive pulse signal D with the output of the rising edge of the pulse width modulation signal C as a trigger, as shown in FIG. The cycle of the drive pulse signal D is equal to the cycle of the control pulse signal B and is constant.

  The output terminal of the monostable multivibrator 13 or the output terminal of the rectangular wave generation circuit 10 is connected to the input terminals of the amplifier circuits 8 and 9.

  According to the above configuration example, the Lorentz force acting between the conductor lines 2 of both diaphragms 1 is the exclusive OR of the drive pulse signal D and the reference pulse signal E as the drive pulse signal as shown in FIG. And have a correlation.

  7 and 8 show a third example of the embodiment of the present invention. As shown in FIG. 7, the switching amplifier includes a rectangular wave generating circuit 15, a triangular wave generating circuit 16, and first and second. Comparators 17 and 18, a knot gate 19, an OR gate 20, a D flip-flop 21, and amplifier circuits 8 and 9 are included.

  The rectangular wave generating circuit 15 is exemplified as a reference pulse signal generating circuit, and outputs a reference pulse signal F having a rectangular wave as shown in FIG. This reference pulse signal F is one drive pulse signal, and the output terminal of the rectangular wave generation circuit 16 is connected to the input terminal of the triangular wave generation circuit 16.

  The triangular wave generating circuit 16 is exemplified as a first control pulse signal output circuit. As shown in FIG. 6, the triangular wave generating circuit 16 converts the reference pulse signal F into a triangular wave whose waveform is an isosceles triangle. The pulse signal C is output.

  The first comparator 17 is exemplified as a first pulse width modulation signal output circuit, and the audio signal A is input to the plus side input terminal, and the triangular wave generating circuit 16 is connected to the minus side input terminal. The first comparator 17 compares the potential levels of the audio signal A and the first control pulse signal C, and the pulse width is modulated (PWM) according to the potential level of the audio signal A as shown in FIG. The first pulse width modulation signal D is output. When the level of the audio signal A is higher than that of the first control pulse signal C, the first pulse width modulation signal D becomes high level.

  A knot gate (NOT gate, output inversion circuit, inverter) 19 is exemplified as an inverted audio signal output circuit. As shown in FIG. 6, the input audio signal A is inverted to generate an inverted audio signal B. Output.

  The second comparator 18 is exemplified as a second pulse width modulation signal output circuit, the output terminal of the knot gate 19 is connected to the positive input terminal, and the output of the triangular wave generation circuit 16 is connected to the negative input terminal. The terminal is connected. The second comparator 18 compares the potential levels of the inverted audio signal B and the control pulse signal, and the first comparator 18 is obtained by modulating (PWM) the pulse width according to the potential level of the inverted audio signal B as shown in FIG. A two-pulse width modulation signal E is output. When the level of the inverted audio signal A is higher than that of the first control pulse signal C, the second pulse width modulation signal E becomes high level.

  The OR gate (OR gate) 20 is exemplified as a second control pulse signal output circuit, and the output terminal of the second comparator 18 and the output terminal of the rectangular wave generation circuit 15 are connected to its input terminals. The second control pulse signal is output. When the potential levels of the second pulse width modulation signal E and the reference pulse signal F are different, the second control pulse signal is set to a predetermined level, that is, a high level.

  The D flip-flop 21 is exemplified as a drive pulse signal output circuit. The inverted clock input terminal bar CK is connected to the output terminal of the first comparator 17 and the data input terminal D is a rectangular wave generating circuit. The output terminal of the OR gate 20 is connected to the reset terminal R, and the other drive pulse signal G is output from the output terminal Q. The output timing of the rising edge of the drive pulse signal G is the same as the falling edge of the first pulse width modulation signal D, and the output timing of the falling edge of the drive pulse signal G is the same as that of the second pulse width modulation signal E. It is the same as the falling edge.

  The output terminal Q of the D flip-flop 21 or the output terminal of the rectangular wave generation circuit 15 is connected to the input terminal of each amplifier circuit.

  According to the above configuration example, the Lorentz force acting between the conductor lines 2 of both diaphragms 1 is the exclusive OR of the drive pulse signal G and the reference pulse signal F as the drive pulse signal as shown in FIG. And have a correlation.

  10 to 14 describe the operations of the above examples of the present invention more specifically. That is, when the sign of one diaphragm is A and the sign of the other diaphragm is B, as shown in FIG. 10, the drive currents (signals) in the same direction are applied to the conductor lines 2 of both diaphragms A and B. ) When I1 and I2 flow, magnetic lines of force in the same direction are generated around each conductor line 2 as shown by a one-dot chain line or a dotted line in FIG. Thereby, as shown by the one-dot chain line and the dotted line in FIG. 10, magnetic lines E1 and E2 in opposite directions due to the drive currents I1 and I2 flowing in the other conductor line 2 act on each conductor line 2. Due to electromagnetic induction by the drive currents I1 and I2 and the magnetic lines E1 and E2, an attractive force due to Lorentz force acts between the conductor lines 2 of both diaphragms A and B as shown by the thick lines in FIG.

  Further, as shown in FIG. 11, when reverse drive currents I1 and I2 flow through the conductor lines 2 of both diaphragms A and B, the one-dot chain lines and As indicated by the dotted line, magnetic field lines in the opposite direction are generated. As a result, as shown by the alternate long and short dash lines and dotted lines in FIG. Due to electromagnetic induction by these drive currents I1 and I2 and magnetic lines E1 and E2, repulsive force due to Lorentz force acts between the conductor lines 2 of both diaphragms A and B as shown by the thick lines in FIG.

Also, as shown in FIGS. 12 to 14, the input audio signal is V ₋ sig, the period of the drive current flowing through the conductor line 2 of the diaphragm A is τ, and the current flows through the conductor lines 2 of the diaphragms A and B. Deviation of the drive current rise (or fall) timing is τ ′, the repulsive force duration acting between the conductor lines 2 of both diaphragms A and B is T1, and between the conductor lines 2 of both diaphragms A and B. When the duration of the acting attractive force is T2, as shown in FIG. 12, when the input audio signal V _- sig is larger than 0, T1> T2 (τ ′> τ / 4). . As shown in FIG. 13, when the input audio signal V _- sig is 0, T1 = T2 (τ ′ = τ / 4). Further, as shown in FIG. 14, when the input audio signal V _- sig is smaller than 0, T1 <T2 (τ ′ <τ / 4).

  Thus, it is one of the features of the present invention that the period of each drive pulse is shifted by ¼ when the input audio signal is zero. Thereby, when the input audio signal is 0, T1 = T2, and the average of the force (exclusive logic) generated between the conductor lines 2 can be made 0.

  In the above embodiment, the period of one of the drive pulse signals is constant. However, as shown in FIG. 9, one of the drive pulse signals B and C rises according to the sign of the input audio signal A. And / or the falling output timing may be changed. In FIG. 9, when the audio signal A is negative, the output timing of one drive pulse signal C is changed, and when the audio signal A is positive, the other drive pulse signal B is changed. The output timing of the rise and / or fall of is changed. The exclusive OR of both drive pulse signals B and C as shown in FIG. 9 and the Lorentz force acting between the conductor lines 2 of both diaphragms 1 have a correlation.

It is explanatory drawing which shows the 1st example of embodiment of this invention. It is explanatory drawing which shows the operation state different from FIG. It is a block diagram which shows the 1st example of embodiment of this invention. FIG. 4 is a waveform diagram showing signal levels and the like at various parts in FIG. 3. It is a block diagram which shows the 2nd example of embodiment of this invention. FIG. 6 is a waveform diagram showing signal levels and the like at various parts in FIG. 5. It is a block diagram which shows the 3rd example of embodiment of this invention. FIG. 8 is a waveform diagram showing signal levels and the like at various parts in FIG. 7. It is a wave form diagram which shows the signal level etc. of the other example of embodiment of this invention. It is explanatory drawing explaining the specific operation | movement of each said example of this invention. It is explanatory drawing explaining the specific operation | movement of each said example of this invention. It is explanatory drawing explaining the specific operation | movement of each said example of this invention. It is explanatory drawing explaining the specific operation | movement of each said example of this invention. It is explanatory drawing explaining the specific operation | movement of each said example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, A, B Diaphragm 2 Conductor line 4 Saw wave generation circuit 5,12 Comparator 6,21 D flip-flop 7 Exclusive OR gate 8,9 Amplifier circuit 10,15 Rectangular wave generation circuit 11,16 Triangular wave generation circuit 13 Single Stable multivibrator 17, 18 First / second comparator 19 Not gate 20 OR gate

Claims (7)

Drive pulse signals are output from the switching amplifier to the conductor lines formed on the pair of opposed diaphragms,
The output timing of at least one rising and / or falling edge of the drive pulse signal is changed according to the level of the audio signal,
The electromagnetic force in which the ratio of the duration of the attractive force acting on both conductor lines and the duration of the repulsive force acting on both conductor lines is correlated with the level of the audio signal on the conductor lines of both diaphragms,
Vibrate the diaphragm,
A driving method of a flat speaker that outputs sound. A. A conductor line is formed and a pair of opposed diaphragms;
B. An audio signal is input, a drive pulse signal is output to the conductor line of each diaphragm, and the output timing of at least one rising and / or falling edge of the drive pulse signal is changed according to the level of the audio signal. Switching, in which the ratio of the duration of the attractive force acting on both conductor lines and the duration of the repulsive force acting on both conductor lines acts on the conductor lines of both diaphragms is correlated with the level of the audio signal. A flat speaker system with an amplifier.   3. The flat speaker system according to claim 2, wherein when the input audio signal is 0, the output timing of the rising and falling edges of each drive pulse signal is shifted by 1/4. Switching amplifier
I. Means for generating a sawtooth reference pulse signal;
B. Means for comparing the level of the reference pulse signal and the audio signal, and outputting a pulse width modulation signal in which the pulse width is modulated in accordance with the level of the audio signal;
C. Means for converting the reference pulse signal to output a control pulse signal which is a rectangular wave and one of the drive pulse signals, and sets the frequency of the control pulse signal to ½ of the reference pulse signal;
D. 4. The flat speaker system according to claim 2, further comprising means for outputting the other drive pulse signal and setting the other drive pulse signal to a predetermined level when both levels of the pulse width modulation signal and the control pulse signal are different. . Switching amplifier
I. Means for generating a reference pulse signal which is a rectangular wave and is one of the drive pulse signals;
B. Means for converting a reference pulse signal and outputting a control pulse signal in a triangular wave;
C. Means for comparing the level of the control pulse signal and the audio signal, and outputting a pulse width modulation signal in which the pulse width is modulated in accordance with the level of the audio signal;
D. 4. The flat speaker system according to claim 2, further comprising means for outputting the other drive pulse signal having a frequency equal to the control pulse signal, triggered by the output of the rising edge of the pulse width modulation signal. Switching amplifier
I. Means for generating a reference pulse signal which is a rectangular wave and one drive pulse signal;
B. Means for converting a reference pulse signal and outputting a control pulse signal in a triangular wave;
C. Means for comparing the levels of the control pulse signal and the audio signal and outputting a first pulse width modulation signal whose pulse width is modulated in accordance with the level of the audio signal;
D. Means for inverting the audio signal and outputting the inverted audio signal;
E. Means for comparing the levels of the control pulse signal and the inverted audio signal and outputting a second pulse width modulated signal whose pulse width is modulated in accordance with the level of the inverted audio signal;
F. The other drive pulse signal is output, the output timing of the rising edge of this drive pulse signal is the same as the falling edge of the first pulse width modulation signal, and the output timing of the falling edge of the drive pulse signal is the second pulse width. 4. The flat speaker system according to claim 2, further comprising means for making the same as a falling edge of the modulation signal.   The flat speaker system according to any one of claims 2 to 6, further comprising an amplifier circuit that amplifies the drive pulse signal and outputs the amplified signal to the conductor line.

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