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JP2016086382

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DESCRIPTION JP2016086382
Abstract: The present invention provides a stable and easily realized driving circuit that improves
the frequency characteristics of a speaker by a feedback signal. Kind Code: A1 A mixer including
a combiner for combining a first feedback signal and a second feedback signal into an input
signal, a mixer including an inverting circuit for inverting the signal combined by the mixer to a
reverse phase, and an output signal of the mixer An amplifier for amplification, a speaker load to
which a signal amplified by the amplifier is input, a voltage detection unit for detecting a voltage
of the speaker load, and a signal detected by the voltage detection unit are band-passed to
generate a first feedback signal. An L component correction unit that outputs, an element
according to an ohmic rule connected in series with a speaker load, a current detection unit that
detects a current flowing to the element, and a signal detected by the current detection unit is
inverted in reverse phase , And an inverting circuit that outputs the second feedback signal.
[Selected figure] Figure 1
Drive circuit
[0001]
The present invention relates to a drive circuit for driving a speaker.
[0002]
Various improvements have been made to drive circuits to improve the frequency response of
the speaker.
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1
For example, in the sound reproduction band expansion device of Patent Document 1, a voltage
signal corresponding to the drive current of the low band drive speaker unit is positively fed back
to the amplifier input side to equalize the inherent internal impedance of the low band drive
speaker unit. The resonance frequency of the bass reflex Helmholtz resonator is lowered by
reducing or nullifying the speaker unit substantially as a factor that responds only to the drive
signal input from the drive amplifier, thereby reducing the resonance Q factor. Is maintained at a
sufficiently high value to ensure sufficient acoustic radiation capability as a resonator.
[0003]
Patent No. 2751190
[0004]
When the current positive feedback is applied to the drive circuit of the speaker as in Patent
Document 1, oscillation easily occurs, and the quality of the speaker becomes unstable.
In order to prevent oscillation from occurring in the method of Patent Document 1, the negative
impedance component can not be set to a large value, and there are cases in which the
characteristics of the speaker can not be sufficiently improved. Therefore, it is an object of the
present invention to improve the frequency characteristics of a speaker by a feedback signal and
to provide a stable and easily realized driving circuit.
[0005]
The drive circuit of the present invention includes a mixer, an amplifier, a speaker load, a voltage
detection unit, an L component correction unit, an element, a current detection unit, and an
inversion circuit.
[0006]
The mixer includes a combiner that combines the first feedback signal and the second feedback
signal with the input signal, and an inverting circuit that reverses the signal combined by the
combiner in reverse phase.
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The amplifier amplifies the output signal of the mixer. The signal amplified by the amplifier is
input to the speaker load. The voltage detection unit detects the voltage of the speaker load. The
L component correction unit passes the signal detected by the voltage detection unit in a band
and outputs the signal as a first feedback signal. The elements are connected in series with the
speaker load and obey the Ohm's law. The current detection unit detects the current flowing
through the element. The inverting circuit inverts the signal detected by the current detection
unit in reverse phase and outputs the inverted signal as a second feedback signal.
[0007]
According to the drive circuit of the present invention, the frequency characteristic of the
speaker is improved by the feedback signal, and the high frequency band in which the phase
margin can not be obtained is not fed back.
[0008]
FIG. 2 is a block diagram showing an electrical configuration of a drive circuit of Embodiment 1.
FIG. 2 is a block diagram showing an electrical configuration of a drive circuit of Embodiment 1.
The figure showing the result of having simulated the frequency characteristic in each point of a
drive circuit. The figure showing the result of having simulated the frequency characteristic in
each point of a drive circuit. FIG. 6 is a diagram showing an example of frequency characteristics
of a conventional small bass reflex speaker and an example of frequency characteristics of a
miniature bass reflex speaker using the drive circuit of the first embodiment. The figure
explaining the process of the change of a frequency characteristic. The circuit diagram of the
current detection part connected with a single end type amplifier. The circuit diagram of the
current detection part connected with a bridge connection load type amplifier. FIG. 7 is a block
diagram showing an electrical configuration of a drive circuit of a modification of the first
embodiment. FIG. 7 is a block diagram showing an electrical configuration of a drive circuit of a
modification of the first embodiment. FIG. 6 is a diagram for explaining correction in an L
component correction unit of the drive circuit of the first embodiment.
[0009]
Hereinafter, embodiments of the present invention will be described in detail. Note that
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components having the same function will be assigned the same reference numerals and
redundant description will be omitted.
[0010]
Hereinafter, the drive circuit according to the first embodiment of the present invention will be
described with reference to FIG. FIG. 1 is a block diagram showing the electrical configuration of
the drive circuit 10 of this embodiment. As shown in FIG. 1, the drive circuit 10 is connected to
the high pass filter 105 for suppressing the low frequency component of the input signal and the
output side of the high pass filter 105, and selects the band of the input signal band-passed by
the high pass filter 105. A band pass filter 110 for passing the signal, a VCA 113 for adjusting
the output level of the band pass filter 110, and an input signal subjected to the band pass by the
band pass filter 110 for the input signal subjected to the band pass by the high pass filter 105; A
mixer 115 that synthesizes first to third feedback signals to be described later, a single end
amplifier 120 connected to the output side of the mixer 115 and amplifying a composite signal
output from the mixer 115, and a single end amplifier 120 Speaker load (ZL) 145 to which the
amplified signal is input, speed In order to detect the current IL flowing to the load (ZL) 145, a
current detection resistor (ZS) 150 connected in series to the output side of the speaker load (ZL)
145 and having the secondary side connected to ground, Voltage detection unit 125 connected
to the connection point X of the differential amplifier 120 and the speaker load (ZL) 145 for
detecting the voltage (voltage of the speaker load) at the connection point X, and the output side
of the voltage detection unit 125 Middle band Q correction unit 130 which selectively passes the
band of the signal detected by detection unit 125, and the output side of voltage detection unit
125 are connected, and the band of the signal detected by voltage detection unit 125 is
selectively selected. The L component correction unit 135 to be passed, the resistor 140
connected to the output side of the L component correction unit 135, and the current detection
unit 15 that detects the current flowing in the current detection resistor (ZS) 150 When a
configuration including an inverting circuit 160 for inverting the signal detected by the current
detecting section 155 in the opposite phase, the resistor 165 connected to the output side of the
inverting circuit 160. Here, the mixer 115 is configured to include a synthesizer 1150 and an
inverting circuit 1155. The inverting circuit 1155 inverts the signal synthesized by the
synthesizer 1150 in reverse phase. The single-ended amplifier 120 is configured to include an
operational amplifier 1205. The current detection resistor (ZS) 150 is an element according to
Ohm's law, and the current detection is performed by the voltage drop of the resistance, but the
present invention is not limited to this and may be another current detection element. For
example, the current detection resistor (ZS) 150 may be a current probe or the like.
Note that the VCA 113 receives an input signal that exceeds a preset level so that the sound in
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the frequency band amplified by the band pass filter 110 does not distort earlier than the sound
in the other band in the speaker output. In this case, the signal level of the band pass filter 110
applied to the combiner 1150 is instantaneously attenuated.
[0011]
In the synthesizer 1150, the input signal band-passed by the high pass filter 105, the signal
passed through the high pass filter 105 and the band pass filter 110, and feedback signals from
the three paths (first, second and third feedback Signal) is input. The first feedback signal is a
signal of which the high frequency band is suppressed by the L component correction unit 135
among the signals whose voltages are detected by the voltage detection unit 125 and which
passes through the resistor 140. The second feedback signal is a signal that is detected by the
current detection unit 155, inverted in reverse phase by the inverting circuit 160, and passed
through the resistor 165. The third feedback signal is a signal that has selectively passed through
the mid-range band by the mid-range Q correction unit 130 among the signals whose voltages
are detected by the voltage detection unit 125. When the sign of the input signal passing only
through the high pass filter 105 is positive, the input signal passing through the band pass filter
110 and the second feedback signal are input to the combiner 1150 with a positive sign (second
feedback signal Is inverted twice by the inverting circuit 1155 and the inverting circuit 160). The
first and third feedback signals are input with a negative sign (these signals are inverted by an
inverting circuit 1155).
[0012]
<L Component Correction Unit 135> Hereinafter, how to determine the feedback amount and L
component correction will be described with reference to FIG. FIG. 11 is a diagram for explaining
the correction in the L component correction unit 135 of the drive circuit of this embodiment.
FIG. 11A is a graph showing each characteristic before the correction by the L component
correction unit 135 is performed. FIG. 11B is a graph showing each characteristic after the
correction by the L component correction unit 135 is performed. In FIGS. 11A and 11B, the
voltage detected by the voltage detection unit 125 is indicated by a solid line, the current
detected by the current detection unit 155 is indicated by a broken line, and the feedback
amount (voltage-current) is indicated by an alternate long and short dash line. As shown in FIG.
11, while the voltage detected by the voltage detection unit 125 is constant regardless of the
impedance and the frequency characteristic is constant, the current detected by the current
detection unit 155 is attenuated as the frequency becomes higher. There is a tendency (area 8 in
FIG. 11A). This is because the inductance component of the voice coil influenced the current
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detection. Thereby, the feedback amount in the high frequency band as shown in the area 9 is
recognized. If the amount of feedback in the high frequency band remains, the drive circuit may
become unstable. Therefore, by performing correction on the voltage detection side so as to
cancel out the inductance component of the voice coil, it is necessary to devise a mechanism for
not returning the band which is an unstable operation. As shown in FIG. 11B, the L component
correction section 135 can substantially eliminate the feedback amount in the high frequency
band by correcting the voltage detection amount in the high frequency band so as to match the
slope of the current detection amount.
[0013]
The drive circuit 10 described above has a configuration in the case of using a single end
amplifier. Next, with reference to FIG. 2, the configuration of the drive circuit in the case where
the amplifier is of the BTL type (bridge connection load type) will be described. FIG. 2 is a block
diagram showing the electrical configuration of the drive circuit 20 of this embodiment. As
shown in FIG. 2, the drive circuit 20 of the present embodiment is configured to include a bridge
connection load type amplifier 220 instead of the single end amplifier 120 in the drive circuit 10.
Further, the drive circuit 20 of the present embodiment includes a voltage detection unit 225
and a current detection unit 255 instead of the voltage detection unit 125 and the current
detection unit 155 in the drive circuit 10. The bridge connection load type amplifier 220 is
configured to include a positive phase signal operational amplifier 2205, an inverting circuit
2210, and a negative phase signal operational amplifier 2215. The voltage detection unit 225
detects a potential difference between a connection point Y of the positive phase signal
operational amplifier 2205 and the speaker load (ZL) 145 and a connection point Z of the
negative phase signal operational amplifier 2215 and the current detection resistor (ZS) 150. The
other elements of the drive circuit 20 are common to the drive circuit 10. The speakers mounted
with the drive circuits 10 and 20 are bass reflex (bus reflex) type speakers and have a relatively
small enclosure.
[0014]
The frequency characteristics of the drive circuit 20 will be described below with reference to
FIGS. 3 and 4. FIGS. 3 and 4 are diagrams showing the simulation results of the frequency
characteristics at each point of the drive circuit 20. FIG. 3 and 4 are graphs in which the vertical
axis represents the amplification factor [dB] and the horizontal axis represents the frequency
[Hz]. The simulated points were 7 points A to G shown in FIG. 2, and the portions shown by x in
FIG. 2 were separated on the circuit in the simulation. In addition, at the time of simulation of the
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point F, X marks separating the first feedback signal and the second feedback signal were
connected. . In this simulation, it is assumed that the speaker load (ZL) 145 is attached to a bass
reflex structure enclosure having a resonance frequency of 80 Hz and an inner volume of 1 L.
The high pass filter 105 is provided to suppress useless amplitude of the very low frequency
band in the input signal. For example, the cutoff frequency of the high pass filter 105 can be 90
Hz, and the attenuation slope can be 12 dB / oct. The frequency characteristic at point A in FIG. 2
is as shown in FIG. 3A. The band pass filter 110 is a band pass filter that passes a band
equivalent to a band attenuated by feedback, and can have, for example, a peak frequency of 100
Hz and an attenuation slope of 6 dB / oct. The frequency characteristic at point B in FIG. 2 is as
shown in FIG. 3B. As described above, the voltage detection unit 225 detects the potential
difference between the connection point Y and the connection point Z. The frequency
characteristic at point C in FIG. 2 is as shown in FIG. 3C. As the signal passing through point C in
FIG. 2 becomes higher in frequency, there is a possibility that the phase margin disappears and
the operation becomes unstable. Therefore, the L component correction unit 135 suppresses the
high band of the signal passing through point C in FIG. Therefore, it can be said that the L
component correction unit 135 is a low pass filter. For example, the cutoff frequency of the L
component correction unit 135 can be 3 to 4 kHz, and the attenuation slope can be 3 dB / oct.
The frequency characteristic at point D in FIG. 2 is as shown in FIG. 3D. Note that the first
feedback signal is inverted to a negative sign by the inverting circuit 1155 of the mixer 115.
Next, the current detection unit 255 detects the current IL flowing through the speaker load (ZL)
145. The frequency characteristic at point E in FIG. 2 is as shown in FIG. 4E. As shown in FIG. 4E,
the signal passing through point E in FIG. 2 is suppressed to −10 dB or less in the vicinity of 50
Hz and 200 Hz, and amplified to about 15 dB in the vicinity of 100 Hz.
Although the signal passing through point E in FIG. 2 is previously inverted to a negative sign by
the inverting circuit 1155 of the mixer 115, the signal is inverted again in the inverting circuit
160 and becomes a second feedback signal of the positive sign.
[0015]
The frequency characteristic of point F in FIG. 2 is as shown in FIG. 4F. As shown in FIG. 4F, at
point F in FIG. 2, the amplification factor is about −20 dB near 50 Hz and about −10 dB near
200 Hz, while the amplification factor is about −55 dB near 80 Hz. Thus, at point F in FIG. 2, two
peaks of amplification factor are included, and these are local distortion (accumulation) of
amplification factor at the lowest resonance frequency due to the bass reflex duct resonance, and
the enclosure is made compact It contributes to the flattening of local distortion (swelling) of the
amplification factor near the lowest resonance frequency.
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[0016]
On the other hand, the frequency characteristic at point G in FIG. 2 is as shown in FIG. 4G. The
mid-range Q correction unit 130 is configured to compensate for the degradation of the midrange frequency characteristics caused by the correction of the frequency characteristics by the
first and second feedback signals and the like, for example, a frequency band of 100 to 500 Hz. It
can be said that it is a band pass filter that passes The third feedback signal is inverted by the
inverting circuit 1155 of the mixer 115 to a negative sign.
[0017]
Hereinafter, an example of the frequency characteristic of the conventional speaker and the
frequency characteristic of the speaker improved by the drive circuit 10 (20) of the present
embodiment will be described with reference to FIG. FIG. 5 is a diagram showing an example of
the frequency characteristic of the conventional small bass reflex speaker and an example of the
frequency characteristic of the miniature bass reflex speaker using the drive circuit 10 (20) of
this embodiment. As shown in FIG. 5A, in the conventional small bass reflex type speaker, the
frequency characteristic tends to be uneven in the vicinity of the lowest resonance frequency
(around 50 Hz in the figure) due to the duct resonance of the bass reflex, and downsizing of the
enclosure It is often a problem that frequency characteristics become non-uniform near the
lowest resonance frequency (around 200 Hz in the figure). Therefore, as in the present invention,
the band-selected signal (negative sign) and the current-detected signal (positive sign) are bandselected and fed back, and the band pass filter 110 and the mid band Q correction unit 130 By
performing the correction, as shown in FIG. 5B, it is possible to realize a small bass reflex type
speaker having flat frequency characteristics from the low band to the high band.
[0018]
This will be described in more detail with reference to FIG. FIG. 6 is a diagram for explaining the
process of change of the frequency characteristic. FIG. 6A is a graph simulating a frequency
characteristic of an infinite baffle type speaker or a speaker in which a speaker unit is stored in a
huge closed box. f0 is the lowest resonance frequency of the unit alone. In the infinite baffle type
speaker, the frequency characteristic almost equivalent to a single unit can be obtained. FIG. 6B
is a graph simulating a frequency characteristic when the speaker unit in FIG. 6A is stored in a
small sealed box. fc is the lowest resonant frequency of the closed box. In this simulation result,
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since the internal volume of the closed box is small, the lowest resonance frequency f0 of the unit
alone also rises to the position of fc, and Q rises to 0.7 or more which is the most flat condition.
FIG. 6C is a graph simulating the frequency characteristics when the closed box of FIG. 6B has a
Helmholtz resonance structure (Bass reflex type). fp is the lowest resonance frequency due to
duct resonance. As shown in FIG. 6C, in the frequency region near fp, although the operation of
the speaker unit is reduced, it can be seen that the sound pressure of the port and the overall
characteristics become complicated. FIG. 6D is a graph showing a simulation of frequency
characteristics in a state where velocity feedback is applied to the speaker unit in the state of FIG.
6C (the state where the speaker unit is stored in a small bass reflex type enclosure). More
specifically, FIG. 6D is a simulation result of frequency characteristics in the configuration
excluding the band pass filter 110 and the mid band Q correction unit 130 in the drive circuit 10
(20). That is, FIG. 6D is a simulation result in which the correction to suppress the frequency of
the very low band by the high pass filter described above and the correction by the first and
second feedback signals are added. As shown in FIG. 6D, even when the internal volume of the
enclosure is small, Q can be set to 0.7 or less, which is the most flat condition, so that the
frequency characteristics can be easily flattened. Further, in the case of the simulation result of
FIG. 6D, the sound pressure of the port also has a single-peak characteristic, so the overall
characteristic also has a relatively straightforward characteristic. FIG. 6E is a graph simulating
the frequency characteristic in the state where the frequency characteristic optimization
correction is performed in the state of FIG. 6D. More specifically, FIG. 6E is a simulation result in
the case where the frequency characteristic is corrected by all the constituent requirements of
the drive circuit 10 (20) including the band pass filter 110 and the mid band Q correction unit
130.
Even when the internal volume of the enclosure is small as shown in FIG. 6E, it is possible to
obtain low-pass regeneration equivalent to an infinite baffle. The operation of the speaker unit is
reduced by the output of the resonator, and in the frequency range near fp, the diaphragm
almost stops.
[0019]
Next, the configuration of the current detection unit 155 of the drive circuit 10 will be described
in detail with reference to FIG. FIG. 7 is a circuit diagram of the current detection unit 155
connected to the single end amplifier 120. As shown in FIG. 7, the current detection unit 155
includes an operational amplifier 1555. The output end of the operational amplifier 1205 of the
single-ended amplifier 120 is connected to the speaker load (ZL) 145. The secondary side of the
speaker load (ZL) 145 is connected to the current detection resistor (R1) 150. In the present
embodiment, R1 can be set to, for example, 0.22 [Ω]. The secondary side of the current detection
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resistor (R1) 150 is connected to the ground in the single-ended amplifier 120. The input
terminal of the current detection resistor (R1) 150 and the negative input terminal of the
operational amplifier 1555 are connected via the resistor R3. The output terminal of the current
detection resistor (R1) 150 and the positive input terminal of the operational amplifier 1555 are
connected via the resistor R2. R2 and R3 can be, for example, 1 k [Ω]. The connection point
between the resistor R2 and the operational amplifier 1555 is connected to ground via a resistor
R4. The connection point between the resistor R3 and the operational amplifier 1555 is
connected to the output side of the operational amplifier 1555 via the resistor R5. R4 and R5 can
be, for example, 10 k [Ω]. In addition, in FIG. 7, although it was set as the structure which detects
an electric current by measuring the voltage between a speaker and resistance, not only this but
using a differential amplifier enables resistance between a power amplifier output and a speaker.
It is also possible to detect the current by inserting it and measuring the potential difference
between both ends of the resistor.
[0020]
Next, the configuration of the current detection unit 255 of the drive circuit 20 will be described
in detail with reference to FIG. FIG. 8 is a circuit diagram of the current detection unit 255
connected to the bridge connection load type amplifier 220. As shown in FIG. As shown in FIG. 8,
the current detection unit 255 is configured to include an operational amplifier 1555. The output
terminal of the positive phase signal operational amplifier 2205 (an operational amplifier that
amplifies the positive phase signal) is connected to the primary side of the speaker load (ZL) 145.
An output end of the negative phase signal operational amplifier 2215 (an operational amplifier
that amplifies the negative phase signal) is connected to the secondary side of the speaker load
(ZL) 145. In parallel with the speaker load (ZL) 145, a series circuit of voltage dividing resistors
R4 and R3 for dividing the driving voltage of the speaker and a series circuit of voltage dividing
resistors R5 and R2 are provided. The primary side of the resistor R1 is connected to the
secondary side of the series circuit of the voltage dividing resistors R4 and R3, and the secondary
side of the resistor R1 is connected to the secondary side of the series circuit of the voltage
dividing resistors R5 and R2 There is. R2 to R5 can be set to, for example, 2.2 k [Ω]. The
connection point of the voltage dividing resistors R4 and R3 is connected to the negative input
terminal of the operational amplifier 1555. The connection point of the voltage dividing resistors
R5 and R2 is connected to the positive input end of the operational amplifier 1555. The positive
input terminal of the operational amplifier 1555 is connected to the ground via a resistor R7 and
a voltmeter V1. The negative input terminal of the operational amplifier 1555 is connected to the
output side of the operational amplifier 1555 via the resistor R6. R6 and R7 can be, for example,
10 k [Ω].
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[0021]
The principle of the current detection circuit of FIG. 8 is as follows. The outputs of the two
amplifiers of the BTL output are at the same potential (DC 1/2 Vcc) and have the same amplitude
and phase opposite relationship, so connect two equal resistances between both outputs, and the
middle point is from GND As seen, the signal portion is canceled and only DC (1/2 Vcc) is
obtained. Therefore, if the same connection is made before and after the current detection
resistor and the midpoint potentials of the both are calculated by the subtractor, the output
voltage is removed from the subtracter, and only the current detection component is handled.
Thus, the dynamic range is broadened, and the element sensitivity can be lowered.
[0022]
[Modification] Hereinafter, a modification of the first embodiment will be described with
reference to FIG. 9 and FIG. FIG. 9 is a block diagram showing an electrical configuration of a
drive circuit 10A which is a modification of the drive circuit 10 of the first embodiment. FIG. 10
is a block diagram showing an electrical configuration of a drive circuit 20A which is a
modification of the drive circuit 20 of the first embodiment. As shown in FIGS. 9 and 10, the midrange Q correction unit 130 may be between the high pass filter 105 and the mixer 115. In this
case, the mid-range Q correction unit 130 selectively passes and outputs the mid-range band
among the bands of the input signal band-passed by the high-pass filter 105. The combiner 1150
combines the first and second feedback signals with the input signal band-passed by the midrange Q correction unit 130.
[0023]
The above-described drive circuits 10 and 20 (10A and 20A) are not limited to the electrical
configurations disclosed in FIGS. 1 and 2 (FIGS. 9 and 10), and other electrical configurations are
also conceivable. For example, any of the drive circuits 10 and 20 (10A and 20A) to the high pass
filter 105, the band pass filter 110, and the mid-range Q correction unit 130 described above or
any two or more of them may be omitted. It is also good. For example, when the band pass filter
110 and the mid band Q correction unit 130 are omitted, the characteristics are as disclosed in
FIG. 6D, and sufficient flatness for practical use can be secured as a drive circuit used for a small
bass reflex type speaker. .
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[0024]
As described above, according to the drive circuit of the first embodiment and its modification, by
applying current feedback and voltage feedback only to a specific band, oscillation hardly occurs,
and the speaker characteristics are stably and easily improved with high accuracy. I can do it. In
addition, since the drive circuit of the first embodiment and its modification improve the
frequency characteristic by combining a plurality of filters, it is possible to flatten the frequency
characteristic over a wide band even if it is a speaker of a small enclosure. it can.
[0025]
DESCRIPTION OF SYMBOLS 10 Drive circuit 105 High pass filter 110 Band pass filter 113
VCA115 Mixer 1150 Mixer 1155 Reversing circuit 120 Single-ended amplifier 1205 Op amp
125 Voltage detection part 130 Mid-range Q correction part 135 L component correction part
140 Resistance 145 Speaker load 150 For current detection Resistor 155 Current detection unit
1555 Op amp 160 Inverting circuit 165 Resistor 20 Drive circuit 220 Bridge connection load
type amplifier 2205 Positive phase signal operational amplifier 2210 Inverting circuit 2215
Reverse phase signal operational amplifier 225 Voltage detection part 255 Current detection unit
10A Drive circuit 20A Drive circuit
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