JPH0686382

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DESCRIPTION JPH0686382
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
speaker driving device for driving a speaker device.
[0002]
2. Description of the Related Art In recent years, with the spread of digital sources and AV
sources, there has been a demand for broadening the speaker apparatus (in particular, expanding
the frequency band in the low frequency direction). At the same time, with the spread of AV
devices, the number of channels has been increased, and downsizing of the speaker device has
also been required.
[0003]
Therefore, in order to obtain wider-band reproduced sound from the same speaker device, a
speaker drive device has been developed in which various signal processing circuits are added to
a power amplifier for driving the speaker device.
[0004]
By the way, in general, in the closed-type speaker device, the sound pressure in the low range
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decreases at the boundary of the lowest resonance frequency of the speaker cabinet.
Furthermore, as the cabinet is miniaturized, this minimum resonant frequency is increased. In
addition, the bass reflex type speaker device uses the principle of Helmholtz's resonator as the
drive source to resonate the port by using the vibration of air in the cabinet, and utilizes the
sound pressure radiated from the port to seal the same volume. The low-frequency reproduction
limit can be expanded compared to the speaker device. However, since the magnitude of the
sound pressure radiated from the port is determined by the volume of the cabinet and the
characteristics of the speaker unit, there is a limit to the expansion of the low frequency
reproduction band even if the port resonance frequency is set low.
[0005]
Therefore, MFB (Motional) as conventionally described in the magazine JAS Journal
(published by the Japan Audio Society) in September 1999 pp. 14 to 20 and in March 1991 pp.
25 to 33. There has been a speaker driving device using the Feed Back method.
[0006]
Hereinafter, a speaker driving device using a conventional MFB method will be described.
FIG. 6 shows a conventional speaker driving device using the MFB method. 61 is an amplifier for
driving a speaker, 62 is a speaker, 63 is a detector for detecting the vibration state of the speaker
62, and 64 is proportional to the vibration acceleration, velocity and amplitude of the diaphragm
of the speaker 62 based on the output of the detector 63 65 is an input signal, 66 is an equalizer
for manipulating the frequency characteristic of the input signal 65, and 67 is a subtracter for
calculating the difference between the output of the equalizer 66 and the output of the
characteristic correction circuit 64, The amplifier 61 receives the output of the subtracter 67 as
an input.
[0007]
As the detector 63, a method for mechanically, acoustically, optically or electrically detecting the
vibration state of the speaker 62 is known. FIG. 7 shows a bridge method in the case of using an
electrical method for the detector. Other current detection methods are also conceivable, but this
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will be described in an embodiment to be described later. In FIG. 7, 71 is the electric impedance
(Rv + sLv) of the voice coil of the speaker 61, 72 is the back electromotive force generated in the
voice coil, 73, 74, 75 and 76 are the resistors R1, R2, Rf and bridge circuits. Capacitors C2 and
77 are subtracters for calculating the difference between the voltages generated at resistors 74
and 75, respectively. Where Bl is the force coefficient of the speaker and vc is the vibration
velocity of the voice coil.
[0008]
The operation of the bridge-type detector will be described. The voltage Ef generated at both
ends of Rf is a combined current of the drive current by the amplifier 1 and the current by the
back electromotive force (−B1 · vc). In addition, R1, R2 and C2 have constants set so that the
voltage E2 generated at Rf when no back electromotive force is generated is generated at both
ends of R2, and the conditions are (Equation 1) and (Equation 2) Become.
[0009]
Therefore, by calculating the difference between E2 and Ef by the subtractor 77, the difference
voltage E0 becomes (Equation 3), and a voltage proportional to the vibration velocity vc of the
voice coil can be obtained.
[0010]
Next, the characteristic correction circuit 64 has a transfer function β (s) shown in (Equation 4),
and an acceleration signal and a velocity signal for correcting the characteristics of the speaker
62 from the velocity signal output from the detector 63 And output a voltage proportional to the
amplitude signal.
Here, βa is an acceleration coefficient, βv is a velocity coefficient, βx is an amplitude
coefficient, and s = jω.
[0011]
The input signal 65 is frequency-compensated (low-pass boost) by the equalizer 66. Then, the
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subtracter 67 calculates the difference from the signal output from the characteristic correction
circuit 64, and inputs the difference to the amplifier 61. The reason why the equalizer 66 is
necessary is that the speaker drive device of this conventional example is compared with a band
(middle high band) in which feedback is not performed in a band in which feedback is performed
for negative feedback operation (low band to improve characteristics). The sound pressure is
reduced by the amount returned. Therefore, the equalizer boosts the low range and compensates
so that the sound pressure equivalent to the middle high range can be obtained.
[0012]
Furthermore, as this MFB method using a current detection method, Yamaha Co., Ltd., such as
that described in the magazine "Radio and Experiment" (issued by Seibundo Shinkosha) April
1989, pp. 80-86. There has been a speaker drive device using active servo.
[0013]
Below, the speaker drive device using the conventional active servo is demonstrated.
[0014]
FIG. 8 shows a conventional speaker drive device using active servo.
In FIG. 8, 81 is a speaker (the impedance viewed from the input terminal is RS), 82 is an amplifier
for driving the speaker 81 at a constant voltage (amplification factor is A), 83 is a resistor (R0),
84 is a resistor ( RF), 85 is a detection resistor (pure resistor r) for detecting the current flowing
through the speaker 81, 86 is an amplifier for amplifying a voltage generated across the
detection resistor 85 (amplification factor is β), 87 is a resistor (R1) 88 is a resistor (R2), 89 is
an equalizer (EQ) that changes the frequency characteristics of the input signal input to the
speaker driver, and 810 is a resistor (R0).
[0015]
Next, the operation of this conventional example will be described.
The amplifier 82 (the amplification factor A is determined by the ratio of the resistors 83 and 84.
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When the speaker 81 is driven at a constant voltage, the current I (S) flows to the speaker 81.
The detection resistor 85 is connected in series to the speaker 81 in order to detect the current I
(S) flowing to the speaker 81. Therefore, if the output voltage of the amplifier 82 is EO and r <<
R2, then
[0016]
The following holds. Therefore, assuming that the voltage I generated at both ends of the
detection resistor 85 is Er, the current I (S) flowing to the speaker 81 is
[0017]
It is determined as: The detected voltage Er is determined by the amplifier 86 (the amplification
factor β is determined by the ratio of the resistors 87 and 88). Amplified). Here, since the
detection resistor 85 is a pure resistor, the waveform of the voltage Er is similar to the waveform
of the speaker current I (S). Further, the equalizer 89 changes the frequency characteristic of the
input signal input to the speaker driving device for the reason described later. The sum of the
output signal Ein of the equalizer 89 and the output of the amplifier 86 is determined by the
amplifier 82 and the resistors 83 and 810, and this sum is amplified (the amplification factor is
A). Here, assuming that the output voltage of the amplifier 86 is EF and the voltage applied to
both ends of the speaker 81 is ES, the equations (7) to (12) are satisfied.
[0018]
Therefore, according to (Equation 5) to (Equation 12)
[0019]
【００３２】となる。
From the above, it is assumed that the output impedance RO of this speaker driving device is Ein
= 0.
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[0020]
If A · β> 0, the open stable negative impedance is obtained. If A · β> 1 and both A and β have
flat frequency characteristics, negative resistance is obtained, and if A or β has frequency
characteristics, the output impedance can have frequency characteristics.
[0021]
In the conventional example, the speaker 81 is a bass reflex type speaker device having a
Helmholtz resonator port. Now, assuming that the resonance frequency of the port is fp, the
sound pressure from the port has a single peak characteristic of -6 dB / oct centered on fp, and
the phase of the sound pressure from the speaker unit and the port is in phase, In the band in
which the sound pressure characteristic of the speaker unit is -6 dB / oct, the sound pressure of
the speaker unit and the port is combined to be flat, but in the other bands, the combined sound
pressure is not flat. Therefore, by using the equalizer 89 to correct the frequency characteristics
of the input signal, flat sound pressure characteristics can be obtained in the whole area.
Therefore, by the above method, the impedance of the voice coil of the speaker unit is canceled
by the negative impedance of the speaker driving device, so that the driving ability of the speaker
in the low range is enhanced and sufficient sound pressure can be reproduced even at a port
having a low resonance frequency. Thus, a wide band (especially in the low frequency direction)
reproduction sound is obtained.
[0022]
That is, the current flowing to the voice coil of the speaker is detected by the detection resistor.
Since the detected current is proportional to the vibration speed of the voice coil, the speaker
bandwidth is expanded by performing so-called speed feedback in which the voltage generated at
both ends of the detection resistor is amplified and fed back to the input.
[0023]
However, in the above-mentioned conventional configuration, it is necessary to insert a resistor
in series between the amplifier and the speaker in order to detect the state of vibration of the
diaphragm of the speaker. Therefore, it is necessary to reduce the resistance value of the
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detection resistor in order to reduce the power loss due to the problem of power loss due to the
insertion of the resistor, and by reducing the resistance value, the detection voltage decreases
and the external noise In order to compensate for the low frequency range with the equalizer, a
large-output amplifier is required to obtain a sound pressure equivalent to the midrange from the
speaker, and the amplifier is large. Had the problem of becoming
[0024]
The present invention solves the above-mentioned conventional problems, and enables
downsizing of the amplifier by using a class D amplifier capable of high-efficiency power
amplification as the amplifier, and detects the state of vibration of the speaker unit. Since the
detector uses a coil of a low pass filter connected to the output of the pulse amplifier in the class
D amplifier, no detection resistor is required, and power loss due to the detection resistor can be
eliminated, and the detector The detection level can be optimized by increasing or decreasing the
number of turns of the detection coil by using a detection coil that detects the current flowing in
the coil of the low-pass filter connected to the output of the pulse amplifier. It is an object of the
present invention to provide a speaker drive device that enables
[0025]
SUMMARY OF THE INVENTION In order to achieve the object, a speaker driving apparatus
according to the present invention comprises binary state modulation means for converting an
analog signal into a binary state modulation signal, and power amplification of the binary state
modulation signal. Pulse amplification means, a first low pass filter which receives an output of
the pulse amplification means and passes only a necessary frequency band, and a signal between
both ends of a coil of the first low pass filter is an input only necessary frequency band A second
low pass filter to be passed, an amplification means for amplifying the output of the second low
pass filter, a first integrating means for integrating and amplifying an output of the second low
pass filter, and an output of the first integrating means A second integrating means for
amplifying, and an operating means for adding an input signal, an output of the amplifying
means, an output of the first integrating means and an output of the second integrator, and the
output of the operating means being binary It is obtained by a structure for inputting the state
modulation means.
[0026]
Further, the speaker driving device according to the present invention has binary state
modulation means for converting an analog signal into a binary state modulation signal, pulse
amplification means for power amplification of the binary state modulation signal, and an output
of the pulse amplification means as input. A first low pass filter for passing only a necessary
frequency band, a current detection coil for detecting a current value flowing in a coil of the first
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low pass filter, and an output of the current detection coil as an input to pass only a necessary
frequency band A second low pass filter, a first integrating means for integrating and amplifying
an output of the second low pass filter, a second integrating means for integrating and
amplifying an output of the first integrating means, an input signal and a second low pass The
arithmetic unit may be configured to add the output of the filter, the output of the first
integrator, and the output of the second integrator, and the output of the arithmetic unit may be
input to the binary state modulation unit. It is.
[0027]
The present invention operates as follows by the above-mentioned constitution.
That is, the binary state modulation means converts the analog signal into a binary state
modulation signal.
Pulse amplification means power amplifies this binary state modulated signal.
The first low pass filter processes the output of the pulse amplification means, passes signals in
the audio band, and drives the speaker. At this time, a current including the current flowing in
the speaker flows in the coil constituting the first low pass filter. Then, the second low pass filter
receives the voltage generated at both ends of this coil as an input, and passes the audio band
signal. The output of the second low pass filter is proportional to the vibration acceleration of the
voice coil of the speaker unit. The amplification means amplifies this acceleration signal. The first
integration means integrates and amplifies the acceleration signal to generate a velocity signal.
Furthermore, the second integration means integrates and amplifies the velocity signal to
generate an amplitude signal. The calculating means adds the outputs of the input signal, the
amplifying means, the first integrating means and the second integrating means, and inputs the
result to the binary state modulating means.
[0028]
Further, the present invention operates as follows by the above-described configuration. That is,
the binary state modulation means converts the analog signal into a binary state modulation
signal. Pulse amplification means power amplifies this binary state modulated signal. The first
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low pass filter processes the output of the pulse amplification means, passes signals in the audio
band, and drives the speaker. At this time, a current including the current flowing in the speaker
flows in the coil constituting the first low pass filter. The current is detected by a current
detection coil. Then, the second low pass filter receives a voltage generated at both ends of the
current detection coil as an input, and passes an audio band signal. The output of the second low
pass filter is proportional to the vibration acceleration of the voice coil of the speaker unit. The
first integration means integrates and amplifies the acceleration signal to generate a velocity
signal. Furthermore, the second integration means integrates and amplifies the velocity signal to
generate an amplitude signal. The calculating means adds the outputs of the input signal, the
second low pass filter, the first integrating means and the second integrating means, and inputs
the result to the binary state modulating means.
[0029]
An embodiment of the present invention will be described below with reference to the drawings.
[0030]
FIG. 1 is a block diagram of a speaker driving apparatus according to a first embodiment of the
present invention.
In FIG. 1, 1 is a binary state modulator that converts an analog signal into a binary state
modulation signal, 2 is a pulse amplifier that power-amplifies the output signal of binary state
modulator 1, 3 is audio from the output of pulse amplifier 2 A low pass filter for passing a band
signal, 4 is a coil constituting the low pass filter 3, 5 is a capacitor constituting the low pass filter
3, 6 is an output terminal of the present speaker driver, 7 is a speaker, 8 is a coil 4 at both ends
A low pass filter 9 receives an output of the low pass filter 8. An integrator 10 integrates and
amplifies an output of the low pass filter 11. An integrator 11 integrates and amplifies an output
of the integrator 10. 12 is an input terminal of the present speaker driver, 13 is an equalizer for
operating the frequency characteristic of an input signal inputted from the input terminal 12,
and 14 is an An adder for calculating the sum of the outputs of the integrator 11 output and the
integrator 10 and the output of the amplifier 9 of riser 13.
[0031]
FIG. 2 is an explanatory view for explaining the binary state modulator 1 and the pulse amplifier
2 of the speaker driving apparatus in the first embodiment, 21 is an input terminal for inputting
an analog signal, 22 is a comparator, 23 is a triangular wave generation The resistors R1, R2 and
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26 are drive amplifiers, 27 is a current amplifier, and 28 is an output terminal.
[0032]
FIG. 3 shows an example of a specific circuit of the first embodiment, wherein 31 is a power
amplifier, 32 is a coil, 33 is a capacitor, 34 is an output terminal, 35 is an input terminal, 36 is an
equalizer, 310 to 327 are Resistors 330-332 are capacitors, and 341-348 are amplifiers.
[0033]
The operation of the first speaker driving device of the present invention configured as described
above will be described below.
The binary state modulator 1 modulates the input analog audio signal to a binary state, and the
pulse amplifier 2 power-amplifies this binary state modulation signal.
The binary state modulator 1 and the pulse amplifier 2 constitute a class D amplifier which is a
high efficiency power amplifier. The operation of this class D amplifier will be described with
reference to FIG. FIG. 2 shows a PWM (Pulse Width Modulation) type power amplifier. The
analog audio signal input from the input terminal 21 is input to the inverting input of the
comparator 22 via the resistor 24. The triangular wave signal generated by the triangular wave
generator 23 is input to the non-inverted input of the comparator 23. The comparator 22
compares the amplitudes of the two types of input signals, and converts the analog audio signal
input to the inverting input into a 1-bit digital signal. The output Co of the comparator is as
follows. When audio signal 三角波 triangular wave signal Co = 0, when audio signal <triangular
wave signal Co = 1, ie, the audio signal is converted into a binary state modulation signal using
the frequency of the triangular wave signal as a carrier. The output of the comparator 22 is
power amplified by the drive amplifier 26 and the current amplifier 27. The output of the current
amplifier 27 is fed back via the resistor 25 to the inverting input of the comparator and the
voltage gain is the ratio R2 / R1 of the resistors 24 and 25.
[0034]
A low-pass filter 3 consisting of a coil 4 and a capacitor 5 removes the unnecessary frequency
components from the binary state modulation signal thus power-amplified, thereby extracting an
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audio band signal. That is, the audio signal input to the binary state modulator 1 is power
amplified and output from the output terminal 6. When the speaker 7 is connected to the output
terminal 6 as a load, current flows through the voice coil and the diaphragm vibrates to generate
a sound wave. The current flowing through the coil 4 is the sum of the current flowing through
the capacitor 5 and the current flowing through the voice coil of the speaker 7. However, since
the current having the component of the audio band does not flow in the capacitor 5, the current
having the component of the audio band in the current flowing in the coil 4 is equal to the
current flowing in the speaker 7. Further, the current flowing through the speaker 7 is
proportional to the vibration speed of the voice coil. Therefore, focusing on the current flowing
through the coil 4, the vibration state of the speaker 7 can be detected.
[0035]
As a current flows in the coil 4, a voltage is generated at both ends of the coil 4. When a voltage
generated at both ends of the coil 4 is input to the low pass filter 8 which passes the signal of the
audio band, a differential of the current flowing through the voice coil of the speaker 7, that is, a
voltage proportional to the vibration acceleration of the voice coil Output from 8 The amplifier 9
amplifies this output. This is feedback of the acceleration component, and the feedback
coefficient is determined by the inductance of the coil 4 and the voltage gain of the amplifier 9.
Also, the integrator 10 integrates and amplifies the output of the low pass filter 8 to generate a
signal proportional to the vibration velocity of the voice coil. This is feedback of the velocity
component, and the feedback factor is determined by the inductance of the coil 4 and the voltage
gain of the integrator 10. Furthermore, the integrator 11 integrates and amplifies the output of
the integrator 10 to generate a signal proportional to the vibration amplitude of the voice coil.
This is feedback of the amplitude component, and the feedback coefficient is determined by the
product of the inductance of the coil 4 and the voltage gain of the integrator 10 and the voltage
gain of the integrator 11.
[0036]
Next, the equalizer 13 performs frequency correction on the audio signal input from the input
terminal 12 for the reason described in the prior art. Then, the adder 14 calculates the sum of
the output of the equalizer, the output of the amplifier 9 which is a feedback signal, the output of
the integrator 10 and the output of the integrator 11, and outputs the sum to the binary state
modulator 1.
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[0037]
A description will now be given of FIG. The resistors 310 to 314, the capacitor 330 and the
amplifiers 341 and 342 constitute a low pass filter 8. The transfer function G1 (s) of the low-pass
filter 8 is expressed by Formula 15 when the cutoff angular frequency is ω1 (= 1 / C1 · R1).
[0038]
Further, assuming that the inductance of the coil 32 is L and the flowing current is I, the voltage
generated at both ends of the coil 32 is s · L · I, and the current I is differentiated. Then, the
output voltage E3 of the amplifier 342 is expressed by Equation 16.
[0039]
The resistors 315 to 318 and the amplifiers 343 and 344 constitute the amplifier 9, and the
voltage gain is R4 / R3. Assuming that the output voltage of the amplifier 344 is E2, the
following equation 17 is established.
[0040]
The coil 32 constitutes a low pass filter which limits the frequency band of the output signal of
the amplifier 31 together with the capacitor 33, and its inductance L is fixed. Therefore, the ratio
of the resistors 317 and 318 is changed to determine the constant of the acceleration feedback.
[0041]
The resistors 319 to 321, the capacitor 331, and the amplifiers 345 and 346 constitute the
integrator 10. The transfer function G2 (s) is (Expression 18), the output voltage E3 of the
amplifier 346 is (Expression 19), and the voice of the speaker 7 is It outputs a voltage
proportional to the vibration speed of the coil. The velocity feedback constant is determined by
the capacitor 331 and the resistor 319.
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[0042]
The resistor 322, the capacitor 332 and the amplifier 347 constitute an integrator 11, and the
output voltage E4 of the amplifier 347 becomes (Equation 20), and outputs a voltage
proportional to the vibration amplitude of the voice coil of the speaker 7. The amplitude
feedback constant is determined by the capacitors 331 and 332 and the resistors 319 and 322.
[0043]
The audio signal input from the input terminal 35 is corrected in frequency characteristic by the
equalizer 36.
[0044]
The resistors 323 to 327 and the amplifier 348 constitute the adder 14 and add the output of
the equalizer 36, the acceleration component that is the output of the amplifier 344, the velocity
component that is the output of the amplifier 346, and the amplitude component that is the
output of the amplifier 347 And the power amplifier 31 drives the speaker 7.
[0045]
As described above, in the first embodiment of the present invention, a small, high-power
amplifier is realized by using a class D amplifier for the power amplifier, and the vibration
acceleration of the voice coil of the speaker is connected to the output of the class D amplifier.
The voltage is generated from the voltage generated at both ends of the coil constituting the low
pass filter.
Then, this signal is integrated to generate the vibration velocity and vibration acceleration of the
voice coil, and acceleration, velocity, and amplitude combined feedback are performed to
improve the low frequency characteristic of the speaker.
[0046]
FIG. 4 shows a block diagram of a speaker driving apparatus in a second embodiment of the
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present invention.
In FIG. 4, 41 is a binary state modulator that converts an analog signal to a binary state
modulation signal, 42 is a pulse amplifier that power-amplifies the output signal of binary state
modulator 41, 43 is an audio from the output of pulse amplifier 42 A low pass filter for passing
signals in a band, 44 is a coil constituting the low pass filter 43, 45 is a capacitor constituting the
low pass filter 43, 46 is an output terminal of the present speaker driver, 47 is a speaker, 48 is a
current flowing in the coil 44 49 is a low pass filter that receives a voltage signal generated at
both ends of the coil 48, 410 is an integrator that integrates and amplifies the output of the low
pass filter 49, and 411 is an integrator that integrates and amplifies the output of the integrator
410 , 412 is an input terminal of the present speaker driver, and 413 is an input terminal
inputted from the input terminal 412. Equalizer to manipulate the frequency characteristic of the
signal, 414 is an adder for calculating the sum of the outputs of the low pass filter 49 of the
equalizer 413 and the output of the integrator 410 and the output of the integrator 411.
[0047]
FIG. 5 shows an example of a specific circuit of the second embodiment, 51 is a power amplifier,
52 is a coil, 53 is a capacitor, 54 is an output terminal, 55 is a coil for detecting the current
flowing in the coil 52, 56 is An input terminal 57 is an equalizer, 510 to 519 are resistors, 520 to
522 are capacitors, and 530 to 533 are amplifiers.
[0048]
The operation of the second speaker driving device of the present invention thus configured will
be described below.
4, the binary state modulator 41, the pulse amplifier 42, the low pass filter 43, the coil 44 and
the capacitor 45 that configure it, the output terminal 46, the speaker 47, the integrator 410, the
integrator 411, the input terminal 412, the equalizer 413, The adder 414 includes the binary
state modulator 1, the pulse amplifier 2, the low pass filter 3, the coil 4 and the capacitor 5
constituting the same, the output terminal 6, the speaker 7, the integrator 10, the integrator 11,
and the input in FIG. The terminal 12 performs exactly the same operation as the equalizer 13
and the adder 14.
[0049]
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First, the binary state modulator 41 modulates an input analog audio signal into a binary state
signal, and the pulse amplifier 42 power-amplifies the binary state modulation signal. Then, a
low-pass filter 43 consisting of a coil 44 and a capacitor 45 removes unnecessary frequency
components from the power-amplified binary state modulation signal, and a signal in the audio
band is extracted. That is, the audio signal input to the binary state modulator 41 is power
amplified and output from the output terminal 46. When a speaker 47 is connected to the output
terminal 46 as a load, current flows through the voice coil and the diaphragm vibrates to
generate a sound wave. The current flowing through the coil 44 is the sum of the current flowing
through the capacitor 45 and the current flowing through the voice coil of the speaker 47.
However, since a current having a component of the audio band does not flow in the capacitor
45, a current having a component of the audio band in the current flowing in the coil 44 is equal
to the current flowing in the speaker 47. Also, the current flowing through the speaker 47 is
proportional to the vibration speed of the voice coil. Therefore, paying attention to the current
flowing through the coil 44, the vibration state of the speaker can be detected.
[0050]
On the other hand, the current detection coil 48 wound around the coil 44 detects the current
flowing through the coil 44 by mutual induction, and outputs a voltage generated at both ends of
the coil proportional to the current as a detection signal. The low pass filter 49 passes a signal in
the audio band from this detection signal to generate a signal proportional to the vibration
acceleration of the voice coil of the speaker 47. Since the level of the detection signal generated
in the current detection coil 48 can be increased or decreased by increasing or decreasing the
number of turns of the current detection coil 48, the amplifier 9 is not necessary as in the first
embodiment of the present invention. This will be described later with reference to FIG.
[0051]
The integrator 410 integrates and amplifies the output of the low pass filter 49 to generate a
signal proportional to the vibration velocity of the voice coil of the speaker 47. Further, the
integrator 411 integrates and amplifies the output of the integrator 410 to generate a signal
proportional to the vibration amplitude of the voice coil of the speaker 47.
[0052]
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Also, the audio signal input from the input terminal 412 has its frequency characteristic
controlled by the equalizer 413 for the reason described in the prior art. The adder 414 adds the
input signal output from the equalizer 413, the acceleration signal output from the low pass filter
49, the velocity signal output from the integrator 410, and the amplitude signal output from the
integrator 411. The output of the adder 414 performs combined acceleration, velocity, and
amplitude feedback input to the binary state modulator 41.
[0053]
A description will be given of FIG. 5 which shows the above configuration as a specific circuit.
The resistor 510 and the capacitor 520 constitute a low pass filter 49. The transfer function of
the low pass filter 49 is the same as the low pass filter 8. Assuming that the inductance of the
coil 52 is L, the number of turns is N, the flowing current is I, and the number of turns of the
current detection coil 55 is M, the voltage across the current detection coil is E5 is Becomes
(Equation 22).
[0054]
The output of the low pass filter 49 is a signal proportional to the acceleration signal of the voice
coil. Therefore, the detection level can be changed by changing the number of turns M of the
current detection coil 55.
[0055]
The resistors 511 to 513, the capacitor 521, and the amplifiers 530 and 531 constitute an
integrator 410. The transfer function is the same as that of the integrator 10, and the output
voltage E7 is (Equation 23).
A voltage proportional to the vibration speed of the voice coil of the speaker 47 is output.
[0056]
The resistor 514, the capacitor 522 and the amplifier 532 constitute an integrator 411, and the
output voltage E8 of the amplifier 532 becomes (Eq. 24), and outputs a voltage proportional to
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the vibration amplitude of the voice coil of the speaker 47.
[0057]
The equalizer 57 corrects the frequency characteristics of the audio signal input from the input
terminal 56.
[0058]
The resistors 515 to 519 and the amplifier 533 constitute an adder 414, and an output of the
equalizer 57, an acceleration component which is a voltage across the capacitor 520, a velocity
component which is an output of the amplifier 531, and an amplitude component which is an
output of the amplifier 532 The signals are added and input to the power amplifier 51, and the
speaker 47 is driven by the power amplifier 51.
[0059]
As described above, in the second embodiment of the present invention, a compact, high-power
amplifier is realized by using a class D amplifier for the power amplifier, and the vibration
acceleration of the voice coil of the speaker is connected to the output of the class D amplifier.
The current flowing through the coil constituting the low pass filter is detected by the current
detection coil and processed and generated by the low pass filter.
Then, this signal is integrated to generate the vibration velocity and vibration acceleration of the
voice coil, and acceleration, velocity, and amplitude combined feedback are performed to
improve the low frequency characteristic of the speaker.
[0060]
As described above, according to the present invention, the vibration state (acceleration, velocity,
amplitude) of the voice coil is detected from the current flowing through the voice coil of the
speaker, and the MFB is performed based on this. By driving the speaker with a class D amplifier
that can perform power amplification with high efficiency, an effect of enabling downsizing of
the amplifier can be obtained.
[0061]
In addition, a detector that detects the state of vibration of the speaker unit uses a voltage
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generated at both ends of a coil that constitutes a low pass filter that passes audio band signals
connected to the output of the pulse amplifier in the class D amplifier. This eliminates the need
for the use of a resistor, thus providing the effect of eliminating the power loss due to the
detection resistor.
[0062]
Furthermore, using a detection coil that detects the current flowing through the coil of the lowpass filter connected to the output of the pulse amplifier in the detector, the detection level can
be optimized by increasing or decreasing the number of turns of the detection coil. The effect of
making it possible to omit is obtained.
[0063]
Brief description of the drawings
[0064]
1 is a block diagram showing the configuration of a speaker drive device according to a first
embodiment of the present invention.
[0065]
2 is a circuit diagram showing the configuration of the binary state modulator and the pulse
amplifier of the speaker driving device in the first embodiment.
[0066]
3 is a circuit diagram showing a specific configuration of the speaker drive device of the first
embodiment.
[0067]
FIG. 4 is a block diagram showing the configuration of a speaker driving device according to a
second embodiment of the present invention.
[0068]
5 is a circuit diagram showing a specific configuration of the speaker drive device of the second
embodiment.
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[0069]
Fig. 6 is a block diagram showing the configuration of a speaker driving device using the
conventional MFB method.
[0070]
Fig. 7 A circuit diagram showing the conventional bridge type detector
[0071]
FIG. 8 is a block diagram showing the configuration of a conventional speaker drive device using
active servo.
[0072]
Explanation of sign
[0073]
Reference Signs List 1 binary state modulator 2 pulse amplifier 3 8 low pass filter 4 coil 5
capacitor 6 output terminal 7 speaker 9 amplifier 10 11 integrator 12 input terminal 13
equalizer 14 adder
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