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JPH0349399

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DESCRIPTION JPH0349399
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
speaker driving circuit suitable for a multiway speaker system. SUMMARY OF THE INVENTION
The present invention relates to a voltage feedback means for controlling a feedback amount in a
predetermined frequency band of a voltage proportional to each terminal voltage of a plurality of
speakers and a current proportional to each applied current in a speaker drive circuit. It is
possible to set the output impedance of the power amplifier in each frequency band arbitrarily
while eliminating the shadow noise of the characteristics of the band division network by feeding
back to the input side of the power amplifier through and the current feedback means. It is a
thing. 2. Description of the Related Art Heretofore, it has been general to drive an electrodynamic
(dynamic) speaker by a constant voltage system. For example, as shown in FIG. 4A, a single-band
speaker (12) of all band type (so-called full range type) is connected to a constant voltage signal
source (11). In the case of two-way, as shown in FIG. B, the high frequency speaker (tweeter) (13)
and the low frequency speaker (woofer) (14) respectively include a high frequency filter (15) and
a low frequency filter It is connected in parallel to the signal source (11) and driven via the band
division network consisting of 16). Although illustration is omitted, in the case of 3-way using a
midrange speaker (squaker), they are connected in parallel via a band pass filter. In the case of
constant voltage driving, since the output impedance of the signal source (11) is zero, the
damping factor (damping factor) becomes infinite and substantially sufficient damping is applied
to the vibration system of the speaker. As is well known, according to Fleming's left-hand rule, a
force proportional to the current flowing through the voice coil is applied to the vibration system
of the dynamic speaker. For this reason, it is supposed that driving should be performed by the
constant current method originally. For example, as shown in FIG. 5A, a single-range speaker (22)
of full range type with constant current signal source (21) with infinite output impedance. Are
connected, and in the case of two ways, as shown in the same figure B, the tweeter (23) and the
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woofer (24) respectively transmit the signal source (high pass filter (25) and low pass filter (26)).
In some cases, they are connected in parallel to 21) and driven at constant current. In this case,
the speaker units (22) to (24) and the filters (25) and (26) are used for constant current. In the
case of a normal direct radiation type speaker, the electrical impedance takes a local maximum
value at the low resonance frequency f0 and gradually increases in the high region as shown by a
solid line in FIG. 6B.
Therefore, when such a speaker is driven at a constant voltage, the drive current has a local
minimum value at the bass resonance frequency f0 and gradually decreases at a high frequency,
as shown by a broken line in FIG. Then, the output sound pressure frequency characteristic as
shown in FIG. However, when the above-mentioned speaker is driven at a constant current, the
output sound pressure level corresponding to the increase of the electrical impedance is
generated in the vicinity of the frequency f0 and the high region, and the fidelity of the
reproduced sound is impaired. There was a problem. Furthermore, there is a problem that
sufficient damping can not be applied to a vibration system in which the damping factor becomes
zero and the amplitude increases in the low range. In order to solve such a problem,
conventionally, a speaker or system for constant current driving has been configured by adding
an appropriate braking resistance to a mechanical system or an acoustic system. However, in this
case, there is a problem that the mechanical configuration of the speaker or the system becomes
complicated. Therefore, in order to solve such a problem, the applicant controls a voltage
proportional to the terminal voltage of the speaker device and a voltage proportional to the
current applied to the speaker device to control the feedback amount in a predetermined
frequency band. We have already proposed a speaker drive circuit in which the output
impedance of the power amplifier in each frequency band can be arbitrarily set by feeding back
to the input side of the power amplifier through the feedback means and the current feedback
means ( See patent application filed July 13, 1991). First, with reference to FIG. 7, the case where
the previously proposed speaker drive circuit is applied to a two-way speaker device will be
described. The configuration of the previously proposed example is shown in FIG. In FIG. 7, parts
corresponding to those in FIG. 4 are given the same reference numerals. In FIG. 7, the audio
signal inputted from the terminal (1) is supplied to the non-inverting input terminal of the power
amplifier (31), and the output terminal of this amplifier (31) and one terminal of the band
division network (17) 17a) is connected, and a resistive voltage divider (32) is connected
between the terminal (17a) and the ground, and a resistor (33) with a small resistance value
between the other terminal (17b) and the ground. ) Is connected. The band division network (17)
is comprised of a high pass filter (15) and a low pass filter (16) as shown in FIG. 4 mentioned
above, and the output of the network (17) is a tweeter (13) and a woofer (14). Supplied. A voltage
proportional to the terminal voltage of the network (17) is taken out to the voltage dividing point
A of the voltage divider (32), and a voltage proportional to the applied current is taken out to the
resistor (33) to detect the applied current.
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(40) is a voltage feedback circuit, and the input sides of the high pass filter (41), the band pass
filter (42) and the low pass filter (43) are commonly connected to the voltage dividing point A of
the voltage divider (32) And the output sides of the filters (41), (42) and (43) are commonly
connected to one end B of the resistor (47) via the resistors (44), (45) and (46), The other end of
the resistor (47) is grounded. In the example of FIG. 7, the cut-off frequencies of the filters (41)
and (43) and the cut-off frequencies above and below the filter (42) are set to fz and f + (fz> f +),
and the audio band is divided into three. Be done. Further, the cutoff (crossover) frequency fco of
each filter of the network (17) is the cutoff frequency f of the high pass filter (41) of the feedback
circuit (40) and the cutoff frequency f of the low pass filter (43). And is set in between. f, <fco <fz
The connection midpoint B of the resistors (44) to (47) whose resistance values are appropriately
set is connected to the inverting input terminal of the amplifier (31) via the adder (34). Thus, a
required amount of voltage negative feedback is applied to each of the component .delta.I bands.
The voltage divider (32) may be omitted by reducing the resistance value of the resistor (47) by
the voltage dividing ratio of the voltage divider (32). (50) is a current feedback circuit, and the
input sides of the high pass filter (51), the band pass filter (52) and the low pass filter (53) are
commonly connected to one end C of the resistor (33), The connection point between the
resistors (54), (55) and (56) and the resistor (57) on the output side of the filters (51), (52) and
(53) is the adder (34). It is connected to the inverting input terminal of the amplifier (31). The
cut-off frequencies of the filters (51) to (53) and the resistance values of the resistors (54) to (56)
are set in the same manner as the voltage feedback circuit (40). A return is given. For example,
the cutoff frequency of both paper band filters (43) and (53) is set to be larger than the bass
resonance frequency of woofer (14) and set to ro <r, and the voltage feedback amount through
filter (43) is set large. When the amount of current feedback through the filter (53) is set small,
the output impedance of the power amplifier (31) is close to zero in the low range, and the
woofer (14) is driven at a constant voltage in the low range. Then, when setting the amount of
voltage feedback through the high pass filter (41) and the band pass filter (42) small and setting
the amount of current feedback through the high pass filter (51) and the band pass filter (52)
large, The output impedance of the amplifier (31) is close to infinity in the middle high band, and
the tweeter (13) is constant current driven in the middle high band.
As a result, in the low band, the rise in the output sound pressure near f 0 of the woofer is
suppressed, and the vibration system is sufficiently braked. Further, in the middle and high
frequencies, current distortion due to the non-linear reaction of the magnetic circuit of the
tweeter is removed, and the influence of the remarkable increase in resistance due to the heat
generation of the voice coil does not appear. However, in the previously proposed example of
FIG. 7, the feedback voltage and the feedback current through both feedback circuits (40) and
(50) are obtained based on the terminal voltage and the applied current at the input end of the
network (17). Therefore, the problem of being affected by the characteristics of the network itself
arises. In view of the above, it is an object of the present invention to provide a speaker drive
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circuit capable of arbitrarily setting the output impedance of the power amplifier in each
frequency band while removing the influence of the characteristics of the band division network.
. [Means for Solving the Problems] The present invention supplies an input signal to a power
amplifier Fi (31) and divides the output of this amplifier into a plurality of frequency bands via
filter circuits (15) and (16). A plurality of current detection means (33), (36) for respectively
detecting the currents applied to the plurality of speakers in the speaker drive circuit for driving
the plurality of speakers (13), (14); Voltage feedback means (40) for controlling the feedback
amount of current, and current feedback means (50) for controlling the feedback amount of
current in a predetermined frequency band, and a plurality of loudspeakers via voltage feedback
means and current feedback means The speaker drive circuit is configured to feed back each
divided voltage proportional to the terminal voltage of each and each detection current by the
plurality of current detection means to the input side of the power amplifier. According to the
present invention, the output impedance of the power amplifier in each frequency band is
arbitrarily set while eliminating the influence of the characteristics of the band division network.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which a
speaker drive circuit according to the present invention is applied to a two-way speaker
apparatus will be described below with reference to FIG. The configuration of one embodiment of
the present invention is shown in FIG. In this FIG. 1, parts corresponding to those in FIG. 4 and
FIG. 7 are given the same reference numerals. In FIG. 1, the audio signal inputted from the
terminal (1) is supplied to the non-inverting input terminal of the power amplifier (31), and the
output of this amplifier (31) is a high pass filter (15) and a low pass filter (16). And divided into
two and supplied to the tweeter (13) and the woofer (14), respectively. A resistor divider (32) is
connected between one terminal (13a) of the tweeter (13) and the ground, and a resistor (33) of
small resistance value between the other terminal (13b) and the ground Is connected.
Similarly, a resistive voltage divider (35) is connected between one terminal (14a) of the woofer
(14) and the ground, and a resistor with a small resistance value between the other terminal
(14b) and the ground (36) is connected. Thereby, a voltage proportional to the terminal voltage
of the tweeter (13) is taken out to the voltage dividing point A of the voltage divider (32), and a
voltage proportional to the applied current is taken out to the resistor (33) to detect the applied
current Be done. Similarly, a voltage proportional to the terminal voltage of the woofer (14) is
taken out at the voltage dividing point E of the voltage divider (35), and a voltage proportional to
the applied current is taken out to the resistor (36) to detect the applied current Be done. (40A)
is a voltage feedback circuit, and the input sides of the high pass filter (41) and the low pass filter
(43) are connected to voltage dividing points A and E of the voltage dividers (32) and (35)
respectively, Both voltage dividing points A and E and the input side of the band pass filter (42)
are connected via an adder (48). The remainder is configured in the same manner as the voltage
feedback circuit (40) of FIG. (50A) is a current feedback circuit, and the input sides of the high
pass filter (51) and the low pass filter (53) are connected to one end C and F of the resistors (33)
and (36), respectively, Each end C, F of (33), (36) and the input side of the band pass filter (52)
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are connected via an adder (58). The remainder is configured in the same manner as the current
feedback circuit (50) of FIG. In the embodiment of FIG. 1, the voltage of each terminal of tweeter
(13) and woofer (14) and each applied current are suitably fed back to amplifier (31) through
both feedback circuits (40 ^) and (50A). Thus, in addition to the above-described effects exhibited
by the previously proposed example shown in FIG. 7, the influence of the characteristics of both
filters (15) and (16) themselves constituting the network can be eliminated. Next, with reference
to FIG. 2, another embodiment in which the speaker drive circuit according to the present
invention is applied to a two-way speaker device will be described. The configuration of another
embodiment of the present invention is shown in FIG. In FIG. 2, the parts corresponding to those
in FIG. In FIG. 2, the amount of voltage feedback and the amount of voltage feedback based on
the terminal voltage of both speakers and the applied current are bounded by the crossover
frequency fco of the high pass filter (15) and the low pass filter (16) constituting the band
division network. The amount of current feedback is set. Therefore, as shown in FIG. 1, the
feedback circuit (40A). It is not necessary to provide high pass filters (41), (51) to low pass filters
(43), (53) of (50A).
Therefore, in FIG. 2, both the voltage feedback circuit (40R) and the current feedback circuit
(50R) are composed of only resistors, and the negative end of the resistors (44) and (46) of the
feedback circuit (40R) is The resistors (54) of the feedback circuit (50R) are connected to the
voltage dividing points A and E of the voltage divider (32) and (35) respectively. One end of (56)
is connected to one end C, F of the resistors (33), (36) respectively. The rest of the configuration
is the same as the embodiment shown in FIG. The embodiment of FIG. 2 also operates in the
same manner as the above-described embodiment, exerts the same effect, and has a very simple
structure. Next, with reference to FIG. 3, still another embodiment in which the speaker driving
circuit according to the present invention is applied to a two-way speaker device will be
described. The configuration of still another embodiment of the present invention is shown in
FIG. In FIG. 3, the parts corresponding to those in FIG. In FIG. 3, the voltage divider (35) is moved
to the input side of the low pass filter (16), and the rest of the configuration is the same as the
embodiment of FIG. This causes the low pass filter (16) to be out of the voltage feedback loop in
the embodiment of FIG. 3 so that there is no phase shift of the feedback voltage by the filter (16)
and thus the amplifier (31) is positive. It is prevented that the feedback takes place and operates
stably. In the embodiment shown in FIGS. 1 and 3, the voltage feedback amount and the current
feedback amount are made different in the middle region and the high region, and either one is
driven as a constant voltage, and the other is a constant current. It may be driven in the same
manner. Further, the number of speakers to be used can be increased, and the number of band
divisions of the feedback circuit can be increased or decreased, and the degree of freedom in
setting conditions is large. [Effects of the Invention] As described above, according to the present
invention, the amount of feedback in a predetermined frequency band is controlled for the
voltage proportional to each terminal voltage of a plurality of speakers and the current
proportional to each applied current. Is fed back to the input side of the power amplifier via the
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voltage feedback means and the current feedback means, so that the output impedance of the
power amplifier in each frequency band can be arbitrarily selected while eliminating the
influence of the characteristics of the band division network. The speaker drive circuit which can
be set to
[0002]
Brief description of the drawings
[0003]
FIG. 1 is a block diagram showing the configuration of an embodiment of a speaker drive circuit
according to the present invention, FIG. 2 is a block diagram showing the configuration of
another embodiment of the present invention, and FIG. 3 is another embodiment of the present
invention. FIG. 4 is a block diagram showing the configuration of an example, FIGS. 4 and 5 are
block diagrams showing a configuration example of a conventional speaker drive circuit, FIG. 6 is
a characteristic curve diagram for explaining the present invention, and FIG. It is a block diagram
which shows the example of a structure of the speaker drive circuit by this.
(13), (14) are speakers, (15) is a high pass filter, (16) is a low pass filter, (31) is a power
amplifier, (32). (35) is a voltage divider, (33), (36) is a current detection means, (40). (40A), (40R)
are voltage feedback means, and (50), (50A), (50R) are current feedback means.
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