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JPH03196798

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DESCRIPTION JPH03196798
[0001]
The invention cooperates with an acoustic device connected to a general power amplifier to drive
a loudspeaker to improve its electro-acoustic reproduction characteristics, and the general power
amplifier, The invention relates to a drive for driving a loudspeaker to improve its electroacoustic reproduction characteristics. 2. Description of the Related Art Conventionally, a power
amplifier for driving a speaker (speaker unit or speaker system) generally has an output
impedance substantially zero and drives the speaker with a so-called constant voltage. On the
other hand, recently, so-called negative impedance drive in which a negative impedance
component is included in the output impedance, or so-called motional feedback (MFB) drive in
which the output of the speaker is detected and fed back in some way Sound systems have been
proposed which improve the reproduction characteristics and miniaturize the cabinet and the
speaker vibration system without deteriorating the sound reproduction characteristics (Japanese
Patent Application Laid-Open Nos. 1-229599 and 1-229598, Japanese Patent Publication No. 1 30358 etc.). However, these acoustic systems require the use of a special drive unit (power
amplifier) compatible with the speaker, so that a user who already possesses and uses a general
power amplifier tries to configure the system. In the case, there is a problem that the power
amplifier of favorite will be completely unavailable. In Japanese Patent Application Laid-Open No.
58-29295, a negative resistance circuit having a negative resistance at a predetermined
frequency or less is connected in series with a speaker, and a series circuit of the speaker and the
negative resistance is a general power amplifier. It is disclosed to drive to improve the bass
characteristic of the speaker. However, the negative resistance circuit disclosed only in the
embodiment of this Japanese Patent Application Laid-Open No. 58-29295 is a transistor class A
amplifier. Such a transistor class A amplifier is used for the speaker except for special purpose
such as when it is used for micro power such as earphones or headphones etc. or as a hobby in
terms of voltage utilization efficiency, power loss and cost etc. It is not used for such low
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impedance power supply. That is, the transistor class A amplifier is generally not included in the
scope of the power amplifier. Furthermore, in this negative resistance circuit, the emitter
resistance is also a detection resistance for detecting the speaker current, so this resistance is
simply replaced with an active element such as a transistor to form a 5 EPP configuration like a
general power amplifier. I can not do it either.
That is, although the said Unexamined-Japanese-Patent No. 58-29295 suggested that the
negative resistance drive of the speaker can be carried out using a general power amplifier by
connecting a negative resistance circuit in series with the speaker, It has not been disclosed or
suggested a practical negative resistance circuit configuration that can drive the speaker
practically without any problem. SUMMARY OF THE INVENTION The present invention has been
made in view of the above problems, and a conventional power amplifier can be used as it is, and
the same speaker characteristics as those in the acoustic system can be actually improved
without any problem. It is an object of the present invention to provide an acoustic device
capable of such driving and a driving device. [Means for Solving the Problems] In order to
achieve the above object, according to the present invention, a speaker is driven to improve the
electroacoustic reproduction characteristics of the speaker in cooperation with a general power
amplifier which normally drives the speaker. A driving device (second power amplifier) is
provided which generates an electric energy corresponding to an increase during normal
operation during characteristic improvement driving, and the normal operating energy, which is
other energy, is supplied from the general power amplifier I am trying to do it. [Operation and
Effect According to the above configuration, the energy for the normal drive is supplied from the
general power amplifier that is the normal power amplifier, so a user who uses the general power
amplifier can use the power amplifier Can be used to realize negative impedance driving, MFB
driving, etc., and improve the electroacoustic reproduction characteristics of a hand-held or
commercially available speaker. In addition, it is possible to realize a small-sized acoustic device
(speaker system) excellent in electro-acoustic reproduction characteristics, in which negative
impedance driving and MFB driving are automatically performed by driving by a general power
amplifier. Further, in the drive device of the present invention, since the second power amplifier
supplies the electric energy corresponding to the increase by the negative impedance drive, the
MFB drive, etc., the output of the general power amplifier cooperated with it. Can be used
without waste. Furthermore, since it is sufficient for the second power amplifier to supply only
the electric energy corresponding to the increase by the negative impedance drive, the MFB
drive, etc., the dedicated drive for the conventional negative impedance drive, the MFB drive, etc.
It can be configured smaller and less expensive than the device. The present invention will be
described in detail below with reference to the drawings. Note that common or corresponding
parts in the drawings are denoted by the same reference numerals or reference numerals with
the same suffix.
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2
FIG. 1 shows the structure of an acoustic device according to an embodiment of the present
invention. This acoustic device is driven by negative impedance to improve the characteristics of
the speaker, and the speaker unit 2 and the amplifier unit 3 which is a negative impedance
driving device according to the present invention are provided in the cabinet 1 having the
resonance tube boat 11. And a pair of external input terminals Pi and P2 for connecting this
acoustic device to the output end of the power amplifier 5, which is a general power amplifier.
The amplifier unit 3 includes a power amplification circuit 31, a positive feedback circuit 32, and
a transfer function application circuit 33. The positive feedback circuit 32 includes an impedance
element Zs for detecting the speaker current, and a feedback amplifier A1 having a
predetermined transfer function β given by the impedance elements Za and Zb. The impedance
value of the impedance element Zs is set to a negligible level compared to that of the speaker
unit 2. In the apparatus of FIG. 1, one external input terminal P1 is connected to one input
terminal P3 of the speaker unit 2 via the speaker current detection impedance element Zs, and
the other input terminal P4 of the speaker unit 2 is an amplifier It is connected to the operation
reference potential point of unit 3. Further, a detection output obtained by detecting the current
flowing through the speaker unit 2 with the impedance element Zs is positively fed back to the
input of the power amplification circuit 31 through the feedback amplifier A1, and a transfer
function having a predetermined transfer function is applied. The circuit 33 is configured to
supply a signal supplied to the one external input terminal pt. The various characteristics of this
amplifier unit 3 are the internal impedance of the speaker unit 2 as ZL, the transfer function
(gain) of the transfer function application circuit 33 as T (s), and the transfer gain of the positive
feedback circuit 32 as β-Z b / Z a Assuming that the transmission gain of the power
amplification circuit 31 with respect to the output voltage of the transfer function application
circuit 33 is α = Z f / Z c, and the transmission gain of the power amplification circuit 31 with
respect to the output voltage of the positive feedback circuit 32 is A = Z f / Z d (A) The transfer
characteristic G (s) is G (s) = "-Jω Vl 1 +-(1-α · β) Z L (1). (B) Also, the driving impedance Zo
viewed from the speaker unit 2 is Gzt = c. Z o = Z L (−−1)... (2) G Z L = 2 s = Z s (1−α · β)
Here, G 2 L 51: 1 and G 2 2 L are respectively ZL in the formula (1) It is a transfer characteristic
value when substituting = o: 1 and ZL = ZL.
Further, the output impedance AZ of the power amplifier 5 is O [Ω]. (C) The load impedance Zi
seen from the power amplifier 5 is ZL + Z. ”=1+A、□(5)・・・・(3)となる。 From
these equations, T (s) for setting the transfer characteristic to 1 (d), that is, for making the output
sound pressure of the speaker the same frequency characteristic as that during normal constant
voltage driving, is 20. (5) = A−ZL (e) negative impedance output end (in order to make the
voltage (v3) amplitude of the output end of the power amplification circuit 31 zero, ie, the
complete braking state (the speaker vibration system Q is O T (s) for making Vs zero when the
speaker is driven without reaction while maintaining the effect of state) is o-ZsT (S) "A (ZL + Zs) ...
(5) I understand that there is. However, since there is a reaction of the speaker in practice, even if
T (s) is set as in equation (5), ■, does not become zero. Next, the action of each variable in the
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acoustic device of FIG. 1 was examined. The results are as follows. (A) When α · β = 1, since Zo
= O according to equation (2), the device is in a constant voltage drive state, and according to
equation (1), the transfer characteristic is 1 + AT (s) Therefore, the frequency characteristics can
be controlled by controlling T (s). From (b) (2), the output impedance Zo is negative in the region
of α · β> 1. (C) When T (s) = O, it can be operated as a mere negative impedance circuit as
intended in the above-mentioned JP-A-58-29295. From (d) and (5), the amplitude of the output
of the negative impedance generation circuit, that is, the power amplifier 33 of the amplifier unit
3 can be reduced, and power saving can be achieved. (E) Optimal conditions can be set by setting
α, β, A and T (s). In this case, T (s) becomes a transmission system of a phase inversion system
(-17 (s)) for fishing. In FIG. 1, the amplifier unit 3 cooperates with the power amplifier 5 to drive
the speaker unit 2 in negative impedance. This negative impedance drive is performed in the
same manner as the acoustic device disclosed in JP-A-1-229599. FIG. 2 shows a second
embodiment of the present invention. This acoustic device more specifically represents the whole
circuit using the dynamic speaker as the speaker unit 2 with respect to that of FIG. 1, and the
speaker current detection is performed on the ground (GND) side.
Further, since the internal impedance of the dynamic speaker is mainly the resistance (Rv) of the
voice coil and slightly contains an inductance component, here, the output impedance ZO
represented by the equation (2) is the internal impedance Rv. Using resistance Rs as the speaker
current detection impedance element Zs so as to provide negative resistance (-Rv) that cancels
out, and using resistances also as impedance elements defining positive feedback gain α · β and
amplifier gain A ing. Further, in the apparatus of FIG. 2, the amplifier A3 constituting the transfer
function application circuit 33 is also used as an amplifier for DC servo. That is, the signal
supplied to the external input terminal P1 is non-inverted and amplified by the amplifier A3 of
the transfer function application circuit 33 and input to the non-inverted input terminal of the
amplifier (internal power amplifier) A2 constituting the power amplification circuit 31 The DC
variation of the internal power amplifier A2 is negatively feedback (NFB) compensated using the
inverting input of the amplifier A3. The acoustic device of FIG. 2 generates a negative resistance
(-Rv) that cancels the internal impedance Rv of the speaker 2 independently on the side of the
speaker 2 as shown in the equivalent circuit of FIG. 3A. . For this reason, the speaker 2 is
equivalent to the motional impedance ZM being directly connected to the voltage sources 5 and
31 without an impedance such as an internal impedance element. Since the voltage source has an
internal impedance of zero, the motional impedance ZM of the speaker 2 is short-circuited across
its both ends and the resonance Q becomes zero, and the speaker 2 is completely dead and is
extremely strongly driven and damped. . Then, in this acoustic device, by appropriately setting
the transfer function T (s) of the transfer function application circuit 33, the output voltage of the
power amplifier 31 for negative resistance generation is made small, and thereby the power from
the power amplifier 5 side. Power supply can be increased or frequency correction can be
performed during negative impedance driving. This acoustic device further has an advantage that
the conventional general amplifier can be used as it is and the characteristic unique to the
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amplifier can be sufficiently reflected. On the other hand, in the negative impedance driving
device disclosed in Japanese Patent Laid-Open No. 1-229599, as shown in the equivalent circuit
of FIG. 3B, the negative impedance is provided on the side of the amplifier 5 °. As the amplifier
5 °, it is necessary to use a special one including negative impedance in the output impedance,
and the amplifier is paired with the speaker, which has a disadvantage that the versatility is poor.
Further, as shown in the equivalent circuit of FIG. 3C, the speaker driving device disclosed in
Japanese Patent Application Laid-Open No. 58-29295 connects a negative resistance (-Rv) in
series with the speaker. When negative resistances are connected in this way, an equalizer circuit
such as the above-described transfer characteristic application circuit 33 is usually required to
adjust the output characteristics of the speaker. This equalizer circuit is considered to be
connected in series with the speaker as shown at 26 ° in FIG. 3C, in which case the effectiveness
of the negative resistance -Rv is reduced and the mossinal impedance ZM of the speaker 2 is
reduced. The braking force is reduced. Further, since this negative resistance (-Rv) is a transistor
class A amplifier having a speaker current detection resistance as an emitter resistance, this
transistor equivalently drives a parallel circuit of the speaker 2 and the emitter resistance.
Become. Therefore, if the emitter resistance is set to be sufficiently smaller than the impedance
of the speaker 2, the power consumption of the negative resistance transistor becomes so large
that it can not be practically used. On the other hand, when the emitter resistance is increased,
this is connected in series with the speaker 2 to the amplifier 5, so the output of the amplifier 5
is consumed by the emitter resistance and is reduced. In any case, the negative resistance circuit
disclosed in JP-A-58-29295 is not practical in terms of cooperation with a general amplifier. FIG.
4 shows a third embodiment of the present invention. In the acoustic device of FIG. 10, the
output of the transfer function application circuit 33 is shifted by the voltage across the speaker
current detection resistor Rs and amplified by the amplifier 31 based on the voltage on the right
end side of the resistor Rs in FIG. FIG. 5 shows a more specific circuit example of the acoustic
device of FIG. In the apparatus of FIG. 5, the transfer function application circuit 33 is composed
of only passive elements. FIG. 6 shows a fourth embodiment of the present invention. The
acoustic device of FIG. 6 is such that only the woofer of the two-way speaker system is driven by
the negative impedance which is the feature of the present invention. In the figure, the power
supply 7 is an AC power supply, for example, a 100 v commercial power supply and a DC power
supply + B and -B for the power amplification amplifier A2, and a current detection amplifier A1,
an amplifier A3 of the transfer function application circuit 33 and a protection circuit 8 DC
power supplies + 82 and -B of The protection circuit 8 is intended to prevent damage and
deterioration of the circuit and the speaker due to overload, transient or abnormal operation, and
turns off the relay contact ryl when a DC current of a predetermined value or more flows through
the part and part. DCC process 99 function, Current protection which turns off relay contact ryl
when excessive current flows to the speaker, Heat sink temperature protection which turns off
relay contact ryl when the temperature of the heat sink exceeds a predetermined value, and
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power switch When turning on 9, each function of the power supply muting to delay the
predetermined time delay and turn on the relay contact ryl is provided.
In addition, this device is also provided with protection means such as a partial fuse and a
transformer internal temperature fuse not shown. FIG. 7 shows a circuit diagram which more
specifically embodies the acoustic device of FIG. In FIG. 7, IC (STK 4040 V) 30 is each amplifier
AI of FIG. A2. It is a hybrid IC that integrates A3 and part of its peripheral circuits. The DC
power supply 7 is composed of a power transformer 71 having a center tap type secondary
winding voltage and a full wave rectification circuit 72, and generates two DC voltages of +81
and -B. These voltages are directly supplied to the amplifier A2 in the IC 30, and are also
supplied via the decoupling circuit 73 to a circuit consisting of the amplifiers AI, A3 and the like
as voltages B2 and -B. The speaker current detection resistor Rs is 0.2 [Ω]. In the protection
circuit 8, the DC component is passed to the signal generated at the external input terminal P1
by the resistor R81 and the capacitor Cat, and if this is +0.6 v or more, the transistor Qas is
turned on and the transistors Qaz and Qas are turned off. As a result, the relay solenoid RYI is deenergized and the relay contact ryl is turned off. If the DC component is -0, 6 v or less, the base
current of the transistor Q62 is bypassed through the diodes Dal and D62, and the relay solenoid
RYI is deactivated by turning off the transistors Q82 and Qas. By these operations, the DCC
process 99 function is realized. When an overcurrent flows through the speaker (woofer) 2, the
AC voltage across the current detection resistor Rs becomes high (high). This alternating voltage
is supplied to the base of the transistor Qa + via the diode D83. However, if this is more than SV,
as described above, the transistor Qa + is turned on, the transistors Qa2 and Q63 are turned off,
the relay solenoid RYI is de-energized, and the relay contact ryl is turned off. That is, the
overcurrent protection function is realized. When the heat sink temperature rises, the resistance
value of the positive characteristic thermistor PTH attached to the same heat sink (not shown) to
which the IC 30 is attached rises. When the temperature of the heat sink reaches a
predetermined value or more, the partial pressure value of the resistor R62 and the positive
characteristic thermistor PTH becomes 1.2 V or more. As a result, the transistor Qa + is supplied
with the base current through the diode Da4 to be turned on, the transistors Q82 and Q83 are
turned off, the relay solenoid RYI is turned off, and the relay contact ryl is turned off.
That is, the heat sink temperature protection function is realized. When the power supply switch
9 is turned on, the transistors Qaz and Q83 are not turned on until the capacitor ca2 is charged
via the resistor R83 and the terminal voltage thereof becomes 0.6 V or more. Therefore, during
this time, the relay contact ryl is off, and the signal to the woofer 2 and the amplifier unit 3 is cut
off. That is, the power supply muting function is realized. As the protection means of this device,
further, a next fuse FS is provided. In addition, a transformer temperature fuse not shown is also
provided in the power supply transformer 71. FIG. 8 shows a fifth embodiment of the present
invention. This acoustic device is such that MFB (motional feedback) driving similar to that of the
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acoustic device disclosed in Japanese Patent Application Laid-Open No. 1-229598 can be
performed by utilizing a general power amplifier 5, and a speaker unit 2 with a vibration sensor
21 and An amplifier unit 3 which is an MFB driving device according to the present invention is
disposed in a cabinet 1 having a resonance tube boat 11, and the acoustic device is connected to
an output end of a power amplifier 5 which is a general power amplifier. A pair of external input
terminals Pi and P2 for connection are provided. Here, one external input terminal P1 is
connected to one input terminal P3 of the speaker unit 2, and the other input terminal P4 of the
speaker unit 2 is connected to the operation reference potential point of the amplifier unit 3.
Furthermore, the vibration state detection output of the speaker unit 2 by the vibration sensor
21 is negatively fed back to the input of the power amplification circuit 31 of the amplifier unit 3
and the transfer function application circuit 33 having a predetermined transfer function is used.
A signal supplied to one external input terminal P1 is configured to be supplied. The vibration
sensor 21 detects the vibration state of the diaphragm 22 of the speaker unit 2 by any method,
and includes, for example, a velocity sensor, a displacement sensor, or an acceleration sensor. In
place of the vibration sensor 21, as described in Japanese Patent Laid-Open No. 1-229598, it is
possible to detect a vibration state using a bridge circuit. The amplifier unit 3 comprises a power
amplification circuit 31, a negative feedback circuit 32 and a transfer function application circuit
33. The negative feedback circuit 32 'amplifies the detection output of the vibration sensor 21 or
the vibration state detection bridge circuit with a predetermined transfer function β, and inputs
it to the inverting input terminal of the power amplification circuit 31. In the acoustic device of
FIG. 8, the amplifier unit 3 cooperates with a general power amplifier 5 to perform MFB driving
which is totally the same as that of the acoustic device of JP-A-1-229598 as a whole.
[0002]
Brief description of the drawings
[0003]
FIG. 1 is a circuit diagram showing the configuration of an acoustic device according to an
embodiment of the present invention, FIG. 2 is a circuit diagram showing the configuration of an
audio device according to a second embodiment of the present invention, FIG. 2 to C are
equivalent circuit diagrams of the acoustic device of FIG. 2, and equivalent circuit diagrams of the
acoustic device according to the first and second conventional examples, respectively, and FIG. 4
is an acoustic according to the third embodiment of the present invention. FIG. 5 is a circuit
diagram showing a more specific circuit example of the acoustic device of FIG. 4. FIG. 6 is a
circuit diagram of an acoustic device according to a fourth embodiment of the present invention.
FIG. 7 is a circuit diagram further embodying the acoustic device of FIG. 6, and FIG. 8 is a circuit
diagram of the acoustic device according to the fifth embodiment of the present invention.
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1: Cabinet 11: Resonant tube port 2 two-speaker uniform 21: Vibration sensor 3: Amplifier unit
31 double power amplifier circuit 32. 32 ': Feedback circuit 33: Transfer characteristic
application circuit 5; General power amplifier Pi, P2: External Input terminal P3. P4: Speaker
input end R8: Speaker current detection resistor
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