JPH05176390

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DESCRIPTION JPH05176390
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
bass reproducing apparatus utilizing MFB (motional feedback), which is small in size and
reproduces super bass at a high maximum output sound pressure level.
[0002]
2. Description of the Related Art In recent years, it has been regarded as important to reproduce
the ultra bass contained in music sources and AV sources at a sufficient volume even in ordinary
homes, and a bass player capable of reproducing ultra bass at a high sound pressure level Is
being requested.
[0003]
A conventional bass reproduction apparatus will be described below with reference to the
drawings.
As shown in FIG. 10, the driver unit 41 is attached to the cavity division member 43c which
divides the inside of the cabinet 43 into two, and the passive radiator 42 is attached to the
outside. Further, the driver unit 41 is driven by the power amplifier 44, and a low pass filter 45 is
inserted in the front stage of the power amplifier 44.
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[0004]
The operation of this conventional bass reproduction apparatus will be described using an
equivalent circuit of the speaker system of the conventional bass reproduction apparatus shown
in FIG.
[0005]
Resonances that make the phases of Vd and Vp become almost the same between Md and Mp
and Cd, Cc1, Cc2 and Cp at a lower frequency f1, Md, Mp and Cc2 and Cp at a higher frequency
f2 The resonance occurs such that the phases of Vd and Vp are opposite to each other, and in the
band outside the two resonance frequencies, the characteristic that the sound pressure is
attenuated at 12 dB / oct or more is obtained.
In addition, resonance occurs between Mp and Cp and Cc2 at a frequency fr (generally called an
antiresonance frequency) approximately at the middle of f1 and f2, and at this time, Vd becomes
a minimum.
[0006]
Md, Cc1, Red, Cc2, and Mp are designed to have appropriate values (usually, Cd << Cc1, Cp <<
Cc2, Rmd, Rc1, Rc2, and Rp << Red, so the above parameters may be noted. (Ie, the values of Md,
Cc1, Cc2, and Mp are balanced appropriately to equalize the heights of the resonance peaks of f1
and f2), and Red is made sufficiently large (as Md and Mp are larger, Cc1 , Cc2 is smaller, the
resonance Q is higher, and Red needs a larger value. The flat sound pressure frequency
characteristics can be obtained in the 1.5 to 2.5 octave band between f1 and f2 by dumping each
resonance peak.
[0007]
In order to shift the reproduction frequency band to the very low frequency side, f1 and f2 may
be lowered by increasing Mp, Md, Cc1 and Cc2. However, if only Md and Mp are increased, the
resonance Q is increased, so Cc1 and Cc2 also need to be increased.
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[0008]
This speaker system is more efficient than a closed speaker system because it uses resonance,
and has band-pass characteristics so that it is suitable for bass reproduction.
[0009]
By driving the speaker system with the power amplifier 24, a bass reproducing apparatus for
reproducing the ultra low frequency band is configured.
When the frequency reaches several hundreds Hz, standing waves may be generated inside the
cabinet and the characteristics may be disturbed, and a low pass filter 25 is inserted to
sufficiently attenuate unnecessary high frequencies.
[0010]
The electromagnetic braking resistance Red means an electromagnetic brake based on the back
electromotive force of the voice coil generated when the vibration system of the driver unit
vibrates, and the electromagnetic braking resistance Red = (magnetic flux density of magnetic
circuit × voice coil effective conductor length 2) Since it is 2 / voice coil direct current
resistance, Red is generally larger as a powerful driver unit of a magnetic circuit.
[0011]
However, in the above-described conventional configuration, it is necessary to increase Md, Mp,
Cc1, Cc2, and Red in order to obtain a flat sound pressure frequency characteristic in an ultralow range, so the driver unit And increase the effective vibration mass of the passive radiator and
strengthen the magnetic circuit of the driver unit, and Cc1 = volume of first cavity / (air density
× air velocity 2 × S12), Cc2 = volume of second cavity / (Air density × air speed of sound 2 ×
S12). Therefore, in order to increase Cc1 and Cc2 without enlarging the cavity, the effective
vibration area S1 of the driver unit has to be reduced.
[0012]
Therefore, despite the fact that a power amplifier with a large output can be easily realized these
days, the maximum output sound pressure level can not be increased in the ultra-low range
because the effective vibration area of the driver unit is small. Since the amplitude of the
diaphragm is very large, distortion is large, and both the effective vibration mass of the driver
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unit and the magnetic circuit become large, which causes the driver unit to be difficult to realize.
[0013]
Or, conversely, if the effective vibration area of the driver unit is made excessively large in order
to raise the maximum output sound pressure level in the ultra low range, not only Cc1 and Cc2
will be reduced but also the resonance frequency will not be increased. Since it is necessary to
make Md and Mp large, the resonance Q of the above-mentioned two resonance frequencies f1
and f2 becomes very high, and a large peak occurs that can not be dumped even if Red is made a
little large, There is also a problem that flat sound pressure frequency characteristics can not be
obtained.
[0014]
FIG. 10 shows an example of a conventional bass reproduction apparatus.
The driver unit 41 has an effective vibration radius of 78 mm, an effective vibration mass of 14.5
g, a magnetic circuit magnetic flux density of 0.8 Tesla (= 8000 gauss), a voice coil effective
conductor length of 8 m, a DC resistance of 5 Ω, no distortion maximum amplitude ± 4 mm (
Generally speaking, the smaller the aperture, the smaller the distortion-free maximum
amplitude), and the lowest resonance frequency is 30 Hz. The driver unit 41 is attached to the
cavity division member 43c, and the effective vibration is 40 cm with a large amplitude. A
passive radiator 42 having a radius of 165 mm and an effective vibration mass of 598 g is
attached to the outside of the cabinet 43.
The first cavity 43a has an inner volume of 35 liters and an inner volume of the second cavity
43b of 15 liters.
[0015]
The driver unit 41 is driven by a power amplifier 44 with an output of 100 W, and a low pass
filter 45 with a cutoff frequency of 320 Hz is inserted in its front stage.
[0016]
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The measured sound pressure frequency characteristics of this conventional bass reproduction
apparatus are shown in FIG.
Although a substantially flat characteristic is obtained over about 30 Hz to 120 Hz, the maximum
distortion free output sound pressure level at 30 Hz is only about 89 dB.
The reason why the maximum output sound pressure level is low is not because the output of the
power amplifier is insufficient but because it is limited by the amplitude of the driver unit.
[0017]
Effective vibration radius 125 mm, effective vibration mass 46 g, magnetic circuit flux density
0.8 Tesla, voice coil effective conductor length 10 m, DC resistance 5 Ω, distortion-free
maximum amplitude ± 6 mm, in order to raise the maximum output sound pressure level FIG.
11 shows the sound pressure frequency characteristics in the case where a speaker of 30 cm in
diameter having a minimum resonance frequency of 30 Hz is attached instead of the speaker of
20 cm in diameter.
It can be seen that even if the magnetic circuit is slightly strong, peaks high enough to cause
dumping occur at around 30 Hz and 140 Hz, which is not practical.
[0018]
An object of the present invention is to solve the above-mentioned conventional problems, and to
provide a bass reproduction apparatus which is compact and reproduces super bass flat at a high
maximum output sound pressure level.
[0019]
SUMMARY OF THE INVENTION In order to achieve the above object, according to a bass
reproducing apparatus of the present invention, the driver unit is attached to a driver unit, a
passive radiator, and a cavity division member which divides the inside into two. , A power
amplifier for driving the driver unit, a sensor for detecting a vibration of a vibration system of the
driver unit to generate a voltage, and an output voltage of the sensor by feeding it back to the
power amplifier. It has a feedback circuit which applies a mold feedback and an acceleration type
feedback.
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[0020]
With this configuration, MFB is applied to the driver unit, and the electromagnetic braking
resistance and the effective vibration mass of the driver unit can be equivalently made very large.
Therefore, not only the two resonance frequencies f1 and f2 are lowered but also A peak can be
suppressed, and a flat sound pressure frequency characteristic in an ultra-low range can be
obtained in a state where the effective vibration area of the driver unit is large.
[0021]
Embodiments of the present invention will be described below with reference to the drawings.
[0022]
FIG. 1 shows a first embodiment of the bass reproducing apparatus according to the present
invention.
Driver unit 1 has an effective vibration radius of 125 mm, an effective vibration mass of 46 g, a
magnetic flux density of 0.8 tesla of a magnetic circuit, an effective conductor length of 10 cm of
a voice coil, and a DC resistance of 5 Ω (electromagnetic braking resistance = (flux density ×
effective conductor length) 2 / Because this is a DC resistance, the electromagnetic braking
resistance of this driver unit is 12.8 mechanical Ω.) A speaker with a diameter of 30 cm with a
maximum amplitude of no distortion ± 6 mm and a minimum resonance frequency of 30 Hz.
The passive radiator 2 attached to the member 3c and having a diameter of 40 cm capable of
large amplitude, an effective vibration radius of 165 mm, and an effective vibration mass of 598
g is attached to the outside of the cabinet 3.
The first cavity 3a has an inner volume of 35 liters and an inner volume of the second cavity 3b
of 15 liters.
[0023]
The driver unit 1 is driven by a power amplifier 4 with an output of 200W.
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In addition, a piezoelectric sensor 5 is attached to the center of the diaphragm of the driver unit
1 to detect the vibration of the vibration system of the driver unit 1.
Since this detection voltage is a voltage proportional to the acceleration of the vibration system
of the driver unit 1 in the case of a piezoelectric sensor, a feedback amount such that the
effective vibration mass of the driver unit 1 equivalently becomes 80 g by adjusting the gain as it
is If the voltage detected by the sensor 5 is integrated through an integration circuit, a voltage
proportional to the speed of the vibration system can be obtained. The feedback circuit 6 feeds
back to the power amplifier 4 so that a speed type feedback is applied such that the resistance is
equivalent to 51.2 mechanical ohms. The feedback amount is attenuated so as not to be unstable
at about 400 Hz or more.
[0024]
In addition, a low pass filter 7 having a cutoff frequency of 320 Hz is inserted in the front stage
of the power amplifier 4 to attenuate an unnecessary band.
[0025]
Hereinafter, the effects of the MFB will be described in detail with reference to FIG. 2, FIG. 3 and
FIG.
[0026]
The speed of the vibration system of the driver unit is represented by Vd of the equivalent circuit
of FIG. 11, but when the frequency is very low, the reactance component of Cc1 of the equivalent
circuit becomes dominant, and when the frequency is halved, Vd is 1 It becomes the relation of
becoming / 2 times, it becomes the characteristic which attenuates with 6dB / oct.
Conversely, if the frequency is very high, the reactance component of Md in the equivalent circuit
will be dominant, and if the frequency is doubled, Vd will be halved, and this is also a
characteristic that attenuates at 6 dB / oct. Become.
[0027]
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On the other hand, at frequencies near f1 and f2, when there is a peak in the sound pressure
frequency characteristic, Vd also has peaks at f1 and f2 and is minimized at the antiresonance
frequency fr.
That is, when the sound pressure frequency characteristic of the passive radiator is as shown in
FIG. 2A, the velocity Vd of the vibration system of the driver unit is as shown in FIG.
[0028]
Here, when the vibration of the vibration system of the driver unit is detected and velocity type
feedback (negative feedback) is applied as in the above configuration, the servo is applied in a
direction to make the speed of the vibration system of the driver unit constant. The velocity of
the vibration system of the unit becomes as shown in FIG. 2D, with the peaks of f1 and f2
becoming flat. That is, the sound pressure frequency characteristic of the passive radiator
becomes as shown in FIG. 2C according to this, and becomes flat with peaks of f1 and f2. This is
just equivalent to increasing the electromagnetic braking resistance Red of the driver unit of the
equivalent circuit of FIG. 11, and corresponds to strengthening the magnetic circuit of the driver
unit. By increasing the feedback amount, the electromagnetic braking resistance Red of the driver
unit can be equivalently made very large.
[0029]
When acceleration type feedback (negative feedback) is applied, servo is applied in a direction to
make the vibration system acceleration of the driver unit constant. The acceleration is obtained
by differentiating the velocity by the angular frequency, so that the entire characteristic of FIG.
2B falls to the left by about 6 dB / oct. That is, the vibration system acceleration has a
characteristic such as (E) which is flat at f2 or more and 12 dB / oct at f1 or less. Since servo is
applied in a direction in which this becomes constant, a flat band of vibration system acceleration
is expanded to a lower frequency, which is equivalent to increasing the effective vibration mass
Md of the driver unit of the equivalent circuit of FIG. , Which corresponds to making the
vibration system of the driver unit heavier. By increasing the feedback amount, the effective
vibration mass Md of the driver unit can be equivalently made very large.
[0030]
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Therefore, by applying the velocity type and acceleration type feedback in combination as
described above, the electromagnetic braking resistance and the effective vibration mass of the
driver unit can be equivalently made extremely large.
[0031]
Hereinafter, it will be described that, even when the effective vibration area of the driver unit is
large, flat sound pressure frequency characteristics in an ultra low range can be obtained by
using both speed type and acceleration type feedback with reference to FIG.
FIG. 3A shows the sound pressure frequency characteristics without feedback when the effective
vibration area of the driver unit is large, but the frequencies f1 and f2 have high peaks. If an
acceleration type feedback is applied to this, the effective vibration mass of the driver unit
becomes equivalently large. Furthermore, by increasing the passive radiator effective vibration
mass Mp, the two resonance frequencies f1 and f2 of (A) decrease and become as shown by (B).
[0032]
In practice, if the feedback is applied to a very high frequency, the operation becomes unstable
and oscillation may occur, so the feedback amount is reduced at a certain frequency fc or more.
Therefore, as shown in (B), the gain rises at fc or more.
[0033]
By further adding speed type feedback to this, the electromagnetic braking resistance of the
driver unit becomes equivalently large, and the peaks of f1 and f2 can be suppressed.
Furthermore, by attenuating unnecessary fc or more with the low-pass filter, finally, a flat sound
pressure frequency characteristic can be obtained in an ultra low band as shown in (C).
[0034]
The bass reproducing apparatus configured as described above can apply MFB to the driver unit,
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and can equivalently increase the electromagnetic braking resistance and the effective vibration
mass of the driver unit (for example, the electromagnetic braking resistance is 12.8). To 51.2
mechanical Ω corresponds to doubling the magnetic flux density of the magnetic circuit, which is
extremely difficult to realize with the magnetic circuit itself as in the prior art, resulting in a
tremendous cost increase. . Therefore, not only the two resonance frequencies f1 and f2 can be
lowered but also peaks can be suppressed, and a flat sound pressure frequency characteristic in
an ultra low range can be obtained in a state where the effective vibration area of the driver unit
is large.
[0035]
The measured sound pressure frequency characteristics of the bass reproducing apparatus
configured as described above are shown in FIG. As apparent from FIG. 6, not only a substantially
flat characteristic is obtained over about 30 Hz to 120 Hz, but also a small-sized cabinet with a
total volume of 50 liters and an undistorted maximum output sound pressure level of about 100
dB at 30 Hz. You can get it.
[0036]
Although in the present embodiment the sensor is of the piezoelectric type, it goes without
saying that a moving coil type, a light quantity detection type, an electrostatic type or the like
may be used. For example, in the case of a moving coil type sensor, a voltage proportional to the
speed of the driver unit vibration system can be obtained, so that a voltage proportional to the
acceleration of the vibration system can be obtained by passing the differentiation circuit in the
feedback circuit. Alternatively, in the case of a light amount detection type or electrostatic type
sensor, a voltage proportional to the displacement of the vibration system can be obtained.
Therefore, by passing the differentiation circuit once in the feedback circuit, the speed is
obtained by passing the differentiation circuit one more time. A voltage proportional to the
acceleration can be obtained. In addition, although the sensor is attached to the center of the
diaphragm of the driver unit, it may be attached to an outer peripheral portion of the diaphragm,
or any part of the vibration system such as a voice bobbin.
[0037]
Next, a second embodiment of the present invention will be described with reference to FIG. The
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driver unit 11 has an effective vibration radius of 176 mm, an effective vibration mass of 85 g, a
magnetic circuit flux density of 1 Tesla, a voice coil effective conductor length of 14 m, a DC
resistance of 5 Ω (electromagnetic braking resistance = (flux density × effective conductor
length) 2 / DC resistance Therefore, the electromagnetic braking resistance of this driver unit is
39.2 mechanical Ω), a speaker with a diameter of 40 cm with no distortion maximum amplitude
± 8 mm, and a minimum resonance frequency of 20 Hz, and this driver unit 11 is a cavity
division member 13c. Relative to the outside of the cabinet 13, the passive radiator 12a mounted
with 46 cm diameter capable of large amplitude, 185 mm effective vibration radius and 3.63 kg
effective vibration mass, and passive radiator 12 b with the same effective vibration area and
effective vibration mass It is attached to the facing side respectively. The first cavity 13a has an
inner volume of 62 liters and an inner volume of the second cavity 13b of 14 liters.
[0038]
The driver unit 11 is driven by a power amplifier 14 with an output of 600W. Further, a
piezoelectric sensor 15 is attached to the back side of the diaphragm of the driver unit 11,
detects the vibration of the vibration system of the driver unit 11, and processes the driver unit
11 in the same process as the first embodiment. Acceleration type feedback of feedback quantity
such that effective vibration mass of the driver unit 11 is equivalent to 350 g is applied so that
feedback of feedback quantity is applied such that the electromagnetic braking resistance is
equivalent to 218 mechanical Ω. As such, the feedback circuit 16 feeds back to the power
amplifier 14. The feedback amount is attenuated so as not to be unstable at about 400 Hz or
more.
[0039]
In addition, a low pass filter 17 having a cutoff frequency of 320 Hz is inserted in the front stage
of the power amplifier 14 to attenuate unnecessary bands.
[0040]
In the bass reproducing apparatus configured as described above, MFB is applied to the driver,
and the electromagnetic braking resistance and the effective vibration mass of the driver can be
equivalently made very large, so only the two resonance frequencies f1 and f2 are lowered. In
addition, the peak can be suppressed, and a flat sound pressure frequency characteristic in an
ultra low range can be obtained in a state where the effective vibration area of the driver is large.
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Not only that, but in the present embodiment, the passive radiators having the same effective
vibration mass and effective vibration area are respectively attached to the opposing surfaces on
the outside of the cabinet, so that the passive radiator having a very large effective vibration
mass vibrates. The reaction force that is generated when canceling out is canceled, the vibration
of the cabinet at the time of high output is extremely small, and unnecessary resonance noise and
noise are not generated.
[0041]
The measured sound pressure frequency characteristics of the bass reproducing apparatus
configured as described above are shown in FIG. As is apparent from FIG. 9, not only a nearly flat
characteristic is obtained from the super low frequency of 20 Hz to about 100 Hz, but the total
volume inside the cabinet is as small as 76 liters, and the maximum output noise of
approximately 100 dB at 20 Hz. A pressure level can be obtained at 30 Hz, a strong undistorted
maximum output sound pressure level of about 111 dB.
[0042]
In addition, the vibration of the cabinet is about 1/100 of that when the passive radiators are
collectively attached to the outside of the cabinet, and even when the distortion-free maximum
output sound pressure level is output, most unnecessary resonance noise and noise are
generated. It does not occur.
[0043]
Although in the present embodiment the sensor is of the piezoelectric type, it goes without
saying that a moving coil type, a light quantity detection type, an electrostatic type or the like
may be used.
In addition, although the sensor is attached to the back side of the diaphragm of the driver unit, it
may be attached to the surface of the diaphragm, or any part of the vibration system such as a
voice bobbin.
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[0044]
Next, a third embodiment of the present invention will be described with reference to FIG. The
configuration is the same as that of the first embodiment of FIG. 1 except that the sensor
attached to the diaphragm is the microphone 25 and is provided inside the first cavity 23a, and
the others are exactly the same.
[0045]
The microphone 25 detects the sound pressure inside the first cavity 23a, but the sound pressure
inside the cavity 1 is a driver unit in a range where the wavelength of the sound is sufficiently
larger than the length of each side of the first cavity 23a Proportional to the displacement of the
vibration system of The detected voltage of the microphone 25 is passed through the
differentiating circuit once with the feedback circuit 26, and after passing through the
differentiating circuit once more, voltages obtained in proportion to the acceleration are
obtained, and these are adjusted for gain and fed back. The electromagnetic braking resistance
and the effective vibration mass are equivalently set to the same values as in the first
embodiment.
[0046]
Therefore, although the operation and effect are exactly the same as in the first embodiment, by
making the sensor a microphone, it is not necessary to attach it to the vibration system of the
driver unit 21, and the processing of the lead wire from the sensor becomes easy As a result, it
has the effect of facilitating the assembly of the bass reproduction device.
[0047]
As is apparent from the above description, according to the present invention, the sensor detects
the vibration of the vibration system of the driver unit to generate a voltage, and the output
voltage is fed back to the power amplifier by the feedback circuit. Since the electromagnetic
braking resistance and the effective vibration mass of the driver unit can be equivalently made
extremely large by the configuration of applying the speed type feedback and the acceleration
type feedback, it is possible to suppress not only the resonance frequency but also the peak. It is
possible to realize a bass reproduction device that can obtain a flat sound pressure frequency
characteristic in a very low frequency range with a large effective vibration area of the driver
unit and reproduce a super low sound flat at a high maximum output sound pressure level
although being small. is there.
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[0048]
Furthermore, the reaction force generated when the passive radiator having a very large effective
vibrating mass vibrates is canceled by respectively attaching the passive radiators having the
same effective vibrating mass and effective vibrating area on the opposite surfaces of the outside
of the cabinet. Thus, it is possible to realize a low-pitched sound reproducing apparatus which
does not generate unnecessary resonance noise or noise due to extremely small vibration of the
cabinet even at high output.
[0049]
Furthermore, by making the sensor a microphone, it is not necessary to attach the sensor to the
vibration system of the driver unit, processing of the lead wire from the sensor is easy, and a bass
reproducing apparatus easy to assemble can be realized.
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