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JP2007028419

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DESCRIPTION JP2007028419
[Object] To provide a speaker drive device provided with a correction filter circuit of
transmission characteristics for flattening a peak of a low-pass resonance peak. A peak waveform
PK2 of low-pass resonance generated at a lowest resonance frequency f when an effective Q of a
speaker system 5 comprising a cabinet 1 and an electrodynamic speaker unit 2 accommodated
therein exceeds 1 On the other hand, correction filter circuit 7 of transmission characteristic of
frequency characteristic waveform A1 having peak waveform PK1 of valley for flattening this is
provided, and bass reproduction of good sound quality is realized, and lowest resonance
frequency f of speaker unit Since the speaker unit Q and diaphragm aperture can be set without
considering the occurrence of a peak in the above, the degree of freedom in the speaker system
design can be expanded and the cost can be reduced. [Selected figure] Figure 1
Speaker drive device
[0001]
The present invention relates to a speaker driving apparatus suitable for a speaker system with
high Q0 such as a subwoofer or the like in which an electrodynamic speaker is housed in a
cabinet having a relatively small volume, and particularly to the technical field of flattening of
low frequency characteristics. .
[0002]
In the design of a speaker system comprising an electrodynamic speaker unit, the frequency
characteristic of the electrical impedance is such that the amplitude of the voice coil increases as
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the frequency decreases and the back electromotive force is generated, so that the electrical
impedance is rapidly increased.
Then, it reaches a peak at a certain frequency, and after that there is a sharp drop and the sound
pressure also drops. The frequency at which this electrical impedance shows the maximum value
is called f0 at the lowest resonance frequency. This f0 is also called a cabinet (enclosure). As the
volume of) becomes smaller, the frequency shifts to a higher frequency, and from this peak
shape, the effective Q0 of the speaker system can be calculated. This Q0 is a constant
representing the sharpness of resonance around the lowest resonance frequency f0 of the
speaker unit or the speaker system (referred to as the sharpness or resonance sharpness. )であ
る。
[0003]
As shown in the low-pass characteristic graph of the conductive speaker unit in FIG. 9, Q0 is
closely related to the low-pass frequency characteristic (sound pressure level (dB) vs. frequency (f
/ f0) semi-logarithm graph) of the speaker unit Relatedly, the flattest characteristic is obtained
when Q0 = 0.7. Then, Q0 of the speaker unit becomes large when it is put in the cabinet as with
f0. Therefore, it is said that the basics of cabinet design is to put a speaker unit with Q0 of 0.6 or
less in a cabinet, and in that case, the effective Q0 is 1 or less, preferably 0.7.
[0004]
However, in order to obtain flat frequency characteristics in low frequency reproduction of a
speaker system such as a subwoofer using an electrodynamic speaker unit, a cabinet with a
sufficient volume and a low minimum resonance frequency f0 and a moderate value of 1 or less
At present, it is necessary to have an effective Q0, which inevitably results in a large-scaled
system with a large amount.
[0005]
On the other hand, what is considered as a problem of the conventional speaker system is the
sound in the low band near the low cut-off frequency fc in the speaker system having a sufficient
volume of 1 or less effective Q0 made by the above design concept Mainly was the construction
of boost means to compensate for pressure level drops.
[0006]
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For example, in the following [patent document 1], a low band characteristic improvement circuit
provided with means for lifting low band shoulder characteristics is proposed, and in the
following [patent document 2], a 12 dB / oct low pass filter of a completely enclosed speaker
system A means of second-order correction using the above has been proposed.
[0007]
Japanese Patent Application Laid-Open No. 58-063289
[0008]
Japanese Patent Application Laid-Open No. 04-030698
[0009]
Due to the trend of downsizing and price reduction of speaker systems in recent years, the
capacity allowed for cabinets used in speaker systems including subwoofers is rapidly reduced,
and drive systems such as magnets of electrodynamic speaker units Cost is also reduced.
[0010]
On the other hand, in order to perform bass reproduction in a small cabinet, it is necessary to
make the diaphragm mass heavier, but a small magnet with low cost can not obtain the
electromagnetic braking force necessary for driving, resulting in an increase in Q0.
[0011]
Under such conditions, when housed in a cabinet having a volume too small from the
conventional design concept without reducing the diaphragm area of the electrodynamic speaker
unit, low frequency resonance of the speaker system at the lowest resonance frequency f0 The
problem is that the peak becomes very large (Q0 large), and the frequency characteristic
fluctuates to deteriorate the sound quality.
[0012]
In this respect, the low-pass characteristic improvement technique described in the above [Patent
Document 1] and [Patent Document 2] is effective to reduce the volume of the cabinet so that no
peak appears at the lowest resonance frequency f0. .7 was made for the purpose of boosting and
improving the drop of the sound pressure level in the vicinity of the low cut-off frequency fc on
the premise of the speaker system made to be about .7. It is not a measure.
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[0013]
In the case of a relatively small speaker system based on a relatively small speaker system in
which an electrodynamic speaker unit is placed in a small-volume cabinet in which a large peak
of the effective Q0 exceeds 1 at the lowest resonance frequency f0 appears. From the design
concept of the speaker system, under the condition that is not preferable for low-frequency
reproduction, the speaker drive device is still focusing on the correction to flatten the large peak
of the low-frequency resonance at the lowest resonance frequency f0 Absent.
[0014]
However, there is a method to reduce the resistance of the speaker unit by making the negative
resistance electrically and adding it from the outside, thereby making the damping effective and
equivalently reduce the Q0 of the speaker, but this method is The complexity of the circuit to
create negative resistance (oscillating element comes in), or if the effect is increased, problems
such as increase in distortion and instability with temperature change of voice coil resistance are
observed. You
[0015]
The present invention has been made in view of the above circumstances, and generates a
minimum resonance frequency f0 for a speaker system in which an electrodynamic speaker unit
is housed in a cabinet of a small volume in which the effective Q0 exceeds 1 An object of the
present invention is to provide a speaker drive device provided with a correction filter circuit of a
frequency characteristic (transmission characteristic) which cancels so as to flatten a peak of a
low-pass resonance peak.
[0016]
The present invention is a peak waveform PK2 of low-pass resonance peaks generated at the
lowest resonance frequency f0 when the effective Q0 of the speaker system 5 comprising the
cabinet 1 and the electrodynamic speaker unit 2 accommodated therein exceeds 1 On the other
hand, the above problem is solved by providing a speaker driving device 10 having a frequency
characteristic correction filter circuit 7 having a peak waveform PK1 of a valley for flattening the
above.
[0017]
The speaker drive device according to the present invention is configured as described above. (1)
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Low frequency resonance for a speaker system having an effective Q0 of more than 1 formed by
housing an electrodynamic speaker unit in a relatively small cabinet It is possible to obtain flat
frequency characteristics by canceling out the peaks of the mountain, and to realize bass
reproduction with good sound quality.
(2) The output near the lowest resonance frequency f0 is suppressed and the required output of
the amplifier is reduced.
(3) Since Q0 and diaphragm diameter of the speaker unit can be set without considering peak
generation at the lowest resonance frequency f0 of the electrodynamic speaker unit, the degree
of freedom in speaker system design can be expanded and cost can be reduced. .
[0018]
An embodiment of a speaker drive device according to the present invention will be described
based on the drawings.
[0019]
FIG. 1 is a block diagram of a speaker drive device according to the present invention.
FIG. 2 is a circuit diagram showing a first embodiment using a twin T circuit of the correction
filter circuit of the speaker driving device according to the present invention.
FIG. 3 is a circuit diagram showing a second embodiment using the band pass filter (BPF) of the
correction filter circuit of the speaker driving device according to the present invention.
FIG. 4 is a circuit diagram showing the second embodiment in which a state variable type is used
as the band pass filter (BPF).
FIG. 5 is a circuit diagram for simulation of the correction filter circuit of the first embodiment
using a twin T circuit. FIG. 6 is an amplitude characteristic waveform of the correction filter
circuit for simulation and sound of the speaker output after correction. It is a graph which shows
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the frequency characteristic waveform of a pressure level, the frequency characteristic waveform
of the sound pressure level of the speaker output without correction | amendment, and a group
delay (group delay) characteristic.
FIG. 7 is a graph of measured data of the case (waveform A) and without (waveform B) of the
correction filter circuit of the frequency characteristic of the sound pressure level of the
prototype.
FIG. 8 is a graph of measurement of frequency characteristics of a correction filter circuit using a
state variable type band pass filter.
[0020]
In FIG. 1 or FIG. 6, the speaker driving device 10 corrects (for example, +6 dB) the drop of the
sound pressure level in the low region near the low region cutoff frequency fc (for example, 35
Hz) provided in the conventional speaker driving device. In the frequency characteristic
waveform A3 of the sound pressure level of the speaker system 5 including the cabinet 1 and the
electrodynamic speaker unit 2 accommodated in the cabinet 1 in addition to the boost circuit 8,
the main amplifier 9, and other known additional circuits not shown. With respect to the peak
waveform PK2 of the low-pass resonant peak that occurs at the lowest resonance frequency f0
(about 65 Hz) when the effective Q0 exceeds 1, the peak waveform PK1 of the valley that flattens
this (for example, f0 = 65 Hz, -15 dB And a correction filter circuit 7 of the transmission
characteristic of the frequency characteristic waveform A1.
[0021]
The cabinet 1 is not only completely sealed but also bass reflex type, flat baffle (rear surface
open) type, etc., and its shape (book shelf type, flow type, column type etc) and configuration (full
range single, subwoofer, multi) -There is no limitation on units, multi ways, etc.
[0022]
Next, as a specific example of the correction filter circuit 7, the correction filter circuit 7A of FIG.
2 uses a so-called twin T circuit.
In the figure, f0 is set by the resistors R1, R2 and R3 and the capacitors C1, C2 and C3, and Q is
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set by the resistors R5 / R6.
[0023]
The resistor R4 adjusts the dip amount at f0, but can be adjusted by changing the balance of the
R1 to C3 and therefore can be omitted.
Although it is difficult to change the characteristics of f0, it is suitable for fixed circuit
implementation because it is stable even at high Q.
[0024]
The circuit constants are, for example, R1 = 18 kΩ, R2 = 20 kΩ, R3 = 8.2 kΩ, R4 = 150 kΩ, R5
= 470 Ω, R6 = 1 kΩ, C1 = C2 = 0.15 μF, C3. It is 0.33 μF.
[0025]
Next, the correction filter circuit 7B of FIG. 3 is an NFB type correction filter circuit using a band
pass filter (BPF), and is also widely used as a graphic equalizer.
The BPF to be used may be any circuit as long as an appropriate Q can be obtained.
[0026]
The correction filter circuit 7C of FIG. 4 is a circuit example using a state variable BPF.
In FIG. 4, f0 is set by the capacitors C1 and C2 and the resistor Rf, Q is set by the resistor RQ, and
gain (dip amount) is set by the resistor RA.
Since each value can be varied independently and the value of Q can be set in a wide range, it is
suitable for applications in which the transmission characteristics are varied.
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[0027]
Preferred examples of the circuit constants in FIGS. 3 and 4 are: R1 = R3 = R = 33 kΩ, R2 = 15
kΩ, C1 = C2 = 0.1 μF, Rf = 3.9 kΩ + VR50 kΩ (f0 = 30 to 200 Hz variable), RQ = 15 kΩ + VR
300 kΩ (Q = 0.5 to 3.5 variable), RA = VR 10 kΩ (dip amount: 0 to 2 Q variable).
[0028]
The frequency characteristics of the correction filter circuits 7A, 7B and 7C are inverse functions
with respect to the peak waveform PK2 of the low band resonance peak generated at the lowest
resonance frequency f0 of the target speaker system 5 (effective Q0> 1). The frequency
characteristic of is desirable for the purpose of flattening, but if it is not a perfect inverse
function, if the frequency characteristic effective for flattening (peak waveform PK1 of valley of
approximately the same size) can be achieved .
[0029]
Next, with the correction filter circuit 7D shown in the circuit diagram for simulation of FIG. 5
(using the above-mentioned twin T circuit), the speaker unit with f0 = 32 Hz and Q0 = 2.0 is one
of Vas (equivalent volume) A simulation result when the bass reflex type speaker system is tuned
to 32 Hz by putting it in a cabinet with a volume of 2 and 2 is shown in FIG.
[0030]
V3 in FIG. 5 is an input signal source, P1 is an output point of the correction filter circuit, P2 is a
speaker output point after correction, and P3 is a speaker output point without correction.
[0031]
The graph of FIG. 6 shows the amplitude characteristic A1 of the point P1, the amplitude
characteristic A2 of the point P2, and the group delay (group delay) characteristics of the
amplitude characteristics A3 of the point P3, the points P2 and P3.
In addition, the amplitude of A2 and A3 is based on the -40 dB line on account of the sound
pressure detection of simulation.
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[0032]
The response of the speaker output P3 point without correction in FIG. 5 has a large sound
pressure peak of +14 dB near 60 Hz, and the group delay also has a peak of 24 ms at 60 Hz,
which shows that the sound quality is adversely affected.
[0033]
On the other hand, in the response at point P2 after passing through the correction filter circuit
7D, the peak PK2 of the peak due to low frequency resonance near 60 Hz is canceled by the peak
PK1 waveform of the valley of the amplitude characteristic A1 of the correction filter circuit 7D.
The amplitude characteristic A2 is flattened, and both group delay characteristics show a
straightforward response.
The large peak of the group delay around 17 Hz is due to the anti-resonance of the bass reflex
duct, and since it is out of the reproduction band, there is almost no adverse effect.
[0034]
Next, actual measurement values of sound pressure characteristics of a prototype of the speaker
driving device of the present invention are shown in FIG. 7 and the effects thereof will be
described below.
[0035]
The speaker system to be driven contains an electrodynamic speaker unit with a diameter of 30
cm, f0 = 35 Hz, Q0 = 1.3, Vas = 50 L (liter) in a 30 L cabinet, and the bass reflex tuning is 33 Hz
Since it is put in a small cabinet of 30L with a somewhat poor magnet as the aperture of 30cm, a
large peak of 13dB at the lowest resonance frequency f0 of about 70Hz like the upper
characteristic curve F1 of the graph without correction It has occurred.
A correction filter circuit 7C (f0 and Q0 are set as shown in FIG. 8) using the state variable BPF of
FIG. 4 for this.
Flat frequency characteristics can be obtained as indicated by the characteristic curve F2 on the
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lower side of the graph by adding.
[0036]
It is a block diagram of a speaker drive concerning the present invention.
FIG. 6 is a circuit diagram showing a first embodiment using a twin T circuit of a correction filter
circuit of the speaker driving device according to the present invention.
It is a circuit diagram showing the 2nd example of a form using a band pass filter (BPF) of a
amendment filter circuit of a speaker drive concerning the present invention.
It is a circuit diagram showing the above-mentioned 2nd example of a form which used a state
variable type as said band pass filter (BPF).
FIG. 6 is a circuit diagram for simulation of the correction filter circuit of the first embodiment
using a twin T circuit.
The amplitude characteristic waveform of the correction filter circuit for simulation, the
frequency characteristic waveform of the sound pressure level of the speaker output after
correction, the frequency characteristic waveform of the sound pressure level of the speaker
output without correction, and the group delay (group delay) characteristic Is a graph showing
It is a graph of the measurement data in the case with and without the correction filter circuit of
the frequency characteristic of the sound pressure level of a prototype. It is a measurement
graph of the frequency characteristic of the correction filter circuit which used the state variable
type band pass filter. It is a graph which shows the low-pass characteristic of a conduction type
speaker unit, and the relation of Q0.
Explanation of sign
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[0037]
DESCRIPTION OF SYMBOLS 1 cabinet 2 electrodynamic-type speaker unit 5 speaker system 7,
7A, 7B, 7C, 7D correction filter circuit 8 boost circuit 9 main amplifier 10 speaker driver fc lowpass cutoff frequency f0 lowest resonance frequency PK2 low-pass resonance mountain Peak
waveform PK1 Peak waveform of valley Q0, Q resonance sharpness
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