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JPH05176389

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DESCRIPTION JPH05176389
[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. 12, the driver unit 21 is attached to a cavity division member 23c that divides
the inside of the cabinet 23 into two, and the passive radiator 22 is attached to the outside. The
driver unit 21 is driven by the power amplifier 24, and a low pass filter 25 is inserted in the front
stage of the power amplifier 24.
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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
08-05-2019
3
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. 12 shows an example of a conventional bass reproduction apparatus.
The driver unit 21 has an effective vibration radius of 78 mm, an effective vibration mass of 14.5
g, a magnetic circuit 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 is, the smaller the distortion-free maximum amplitude is), and
the lowest resonance frequency is 30 Hz. The driver unit 21 is attached to the cavity division
member 23c, and the effective vibration is 40 cm with a large amplitude. A passive radiator 22
having a radius of 165 mm and an effective vibration mass of 598 g is attached to the outside of
the cabinet 23.
The first cavity 23a has an inner volume of 35 liters and an inner volume of the second cavity
23b of 15 liters.
[0015]
The driver unit 21 is driven by a power amplifier 24 with an output of 100 W, and a low pass
filter 25 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 cabinet
mounted on the outside, a power amplifier for driving the driver unit, a detection circuit inserted
between the power amplifier and the driver unit to detect a voltage proportional to the vibration
system speed of the driver unit, And a feedback circuit for providing speed feedback and
acceleration feedback from the detection circuit to the power amplifier.
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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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Detection circuit 5 is a bridge circuit having R1 = 3.9 KΩ, R2 = 220 Ω, R3 = 0.33 Ω, L = 0.1 mH
and the voice coil of the driver unit as one side, and between power amplifier 4 and driver unit 1
Is inserted in the
[0024]
The output voltage of the bridge circuit, that is, the output voltage of the detection circuit 5 is in
direct proportion to the speed of the vibration system of the driver unit 1.
Although this is well known in electro-acoustic theory, it will be described once with reference to
FIG. 2, FIG. 3 and FIG.
[0025]
Fig. 2 shows the impedance characteristics of a general loudspeaker, but where the frequency is
extremely low, the DC resistance Re of the voice coil becomes the peak Zmax at the lowest
resonance frequency F0 (in the case of a powerful loudspeaker with a magnetic circuit, Zmax is
100 to It becomes about 300 ohms), approaches Re again in the middle bass range, and has a
curve that rises gently in the high range.
[0026]
FIG. 3 shows the impedance component of the voice coil of the speaker.
Ze is called the braking impedance of the voice coil (the impedance shown by the voice coil in a
fixed state so that the vibration system of the speaker does not move) Ze, and the direct current
resistance Re of the voice coil and the inductance are connected in series. (BL) 2 / Z m is called
the dynamic impedance of the voice coil, and is the impedance due to the back electromotive
force of the voice coil generated when the vibration system vibrates. Since the back electromotive
force of the voice coil E = BL × V (V is the velocity of the voice coil), the dynamic impedance is in
direct proportion to the velocity of the vibration system.
[0027]
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That is, the impedance curve shown in FIG. 2 is obtained by superimposing dynamic impedance
on voice coil DC resistance and inductance. FIG. 4 shows the impedance curve of the speaker
system of the conventional bass reproduction apparatus, which is also the same.
[0028]
Now, here, a speaker, that is, a voice coil of the driver unit is connected to one side of a bridge
circuit as shown in the detection circuit 5 of FIG. 1, Re: R3 = R1: R2, and L = voice coil inductance
× ( By balancing the bridge by the relation of R3 / Re), the voltage due to the DC resistance
component and the inductance component of the voice coil is not canceled out at the output of
the bridge circuit. Then, only the voltage due to the dynamic impedance comes out of the output
of the bridge circuit. That is, this bridge circuit can detect a voltage which is in direct proportion
to the speed of the vibration system of the driver unit 1.
[0029]
Actually, there is DC resistance of the lead wire for driver unit connection, and since the voice
coil braking impedance contains a slight capacity component, fine adjustment is necessary from
the value of each element according to the above relational expression. is there. For that reason,
the values of the respective elements of the bridge circuit of the detection circuit 5 of the present
embodiment are not exactly the same as those according to the above relation.
[0030]
As described above, since the output voltage of the detection circuit 5 is a voltage proportional to
the speed of the vibration system of the driver unit 1, the electromagnetic braking resistance of
the driver unit 1 is equivalently 51.2 mechanical Ω by adjusting the gain as it is. If the output
voltage of the detection circuit 5 is passed through a differentiating circuit so that a feedback
amount of speed feedback is applied, a voltage proportional to the acceleration of the vibration
system can be obtained. The feedback circuit 6 feeds back to the power amplifier 4 so that an
acceleration type feedback of a feedback amount is applied such that the effective vibrating mass
of the driver unit 1 is equivalently 72 g by adjustment. The amount of feedback is attenuated so
as not to become unstable at about 250 Hz or more.
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[0031]
In addition, a low pass filter 7 having a cutoff frequency of 250 Hz is inserted in the front stage
of the power amplifier 4 to attenuate unnecessary bands.
[0032]
The effects of the MFB will be described in detail below with reference to FIGS. 5, 6 and 13.
[0033]
The speed of the vibration system of the driver unit is represented by Vd of the equivalent circuit
of FIG. 13, 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.
[0034]
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 becomes minimal at the
antiresonance frequency fr.
That is, when the sound pressure frequency characteristic of the passive radiator is as shown in
FIG. 5A, the velocity Vd of the vibration system of the driver unit is as shown in FIG.
[0035]
Here, if a voltage proportional to the vibration system speed of the driver unit is detected and
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velocity type feedback (negative feedback) is applied as in the above configuration, servo is
applied in a direction to make the speed of the driver system vibration system constant. Because
of this, the speed of the vibration system of the driver unit becomes flat as shown by (D) in FIG.
That is, the sound pressure frequency characteristic of the passive radiator becomes as shown in
FIG. 5C 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. 13, 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.
[0036]
Further, 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. 5B 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 the direction in which this becomes constant, the flat band of the
vibration system acceleration spreads to lower frequencies, which is equivalent to just 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.
[0037]
Therefore, the electromagnetic braking resistance and the effective vibration mass of the driver
unit can be equivalently made extremely large by applying the velocity type and the acceleration
type feedback together as described above.
[0038]
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. 6A shows the sound pressure frequency characteristics without feedback when the effective
08-05-2019
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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).
[0039]
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.
[0040]
By further adding speed type feedback to this, the electromagnetic braking resistance of the
driver unit is equivalently increased, 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).
[0041]
In the bass reproducing apparatus of the present invention configured as described above, 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 extremely large (for example, the
electromagnetic braking resistance). Making 12.8 to 51.2 mechanical ohms is equivalent to
doubling the magnetic flux density of the magnetic circuit, and it is extremely difficult to realize
this in the magnetic circuit itself as in the prior art, and the tremendous cost It leads to the up.
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 with the effective vibration area of the driver unit being large.
[0042]
The measured sound pressure frequency characteristics of the bass reproducing apparatus
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configured as described above are shown in FIG. As apparent from FIG. 8, not only an almost flat
characteristic is obtained over about 30 Hz to 120 Hz, but also the compactness with a total
volume of 50 liters in the cabinet, the maximum distortion free output sound pressure level of
about 100 dB at 30 Hz You can get
[0043]
Although L is inserted in the detection circuit 5 in this embodiment, the voice coil has a small
diameter or a copper short ring is attached to the magnetic circuit yoke, so that the inductance of
the voice coil is small enough to be ignored. L may be omitted. Further, although the detection
circuit 5 is a bridge circuit in this embodiment, it may be a small resistance inserted between the
driver unit and the power amplifier as will be described later in the description of the second
embodiment.
[0044]
Next, a second embodiment of the present invention will be described with reference to FIG. The
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.) 40 cm diameter speaker with no distortion maximum amplitude ± 8 mm
and minimum resonance frequency 20 Hz, and this driver unit 11 is the cavity division member
13 c. , A passive radiator 12a with an aperture of 46 cm and an effective oscillation radius of 185
mm and an effective oscillation mass of 3.41 kg, and a passive radiator 12b with the same
effective oscillation area and effective oscillation mass. Are attached to the opposite surfaces of
the The first cavity 13a has an inner volume of 60 liters and an inner volume of the second
cavity 13b is 16 liters.
[0045]
The driver unit 11 is driven by a power amplifier 14 with an output of 600W. Further, a small
resistance R is inserted as a detection circuit 15 between the driver unit 11 and the power
amplifier 14. In this example, R = 0.1 Ω.
08-05-2019
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[0046]
The voltage across the resistor R is inversely proportional to the voice coil impedance curve (see
FIG. 4) of the driver unit 11. That is, the local minimum at the two resonance frequencies f1 and
f2 and the local maximum at the antiresonance frequency fr.
[0047]
As in the present embodiment, when the magnetic flux density B of the magnetic circuit and the
voice coil effective conductor length L are large and the product BL is sufficiently large, the voice
coil impedance becomes dominant in the bass region, and the braking is damped. The impedance
can be ignored. That is, the voltage across the resistor R, that is, the detection voltage of the
detection circuit 15 can be regarded as being inversely proportional to the dynamic impedance,
that is, inversely proportional to the speed of the vibration system of the driver unit 11.
[0048]
Therefore, speed feedback is applied by positively feeding back this detection voltage without
inverting the phase as it is. For the sake of simplicity, the detected voltage is minimized at the
two resonance frequencies f1 and f2, and the output of the power amplifier 14 hardly changes
even if it is positively fed back. However, at the frequency outside the antiresonance frequency Fr
or f1, f2, the detected voltage becomes large, and since the positive feedback is performed, the
output of the power amplifier 14 increases. That is, feedback is applied in the direction of
relatively suppressing the peaks of f1 and f2, and the same operation as the speed type feedback
described above is performed.
[0049]
In addition, by passing this detection voltage through a differentiation circuit, a voltage inversely
proportional to the acceleration of the vibration system of the driver unit 11 can be obtained.
Therefore, by positively feeding it without inverting the phase, acceleration type feedback is
applied. .
[0050]
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13
As described above, the effective vibration mass of the driver unit 11 is equivalent to 370 g so
that the speed type feedback of the feedback amount such that the electromagnetic braking
resistance of the driver unit 11 becomes equivalent to 180 machine Ω is applied. The feedback
circuit 16 feeds back to the power amplifier 14 so as to apply an acceleration type feedback of
such feedback amount.
The amount of feedback is attenuated so as not to become unstable at about 200 Hz or more.
[0051]
Further, a low pass filter 17 having a cutoff frequency of 200 Hz is inserted in the front stage of
the power amplifier 14 to attenuate an unnecessary band.
[0052]
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. It is
possible to suppress not the peak but to obtain a flat sound pressure frequency characteristic in
a very low frequency range in a state where the effective vibration area of the driver is large.
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 at the time of cancellation is canceled, and the
vibration of the cabinet at the time of high output is extremely reduced, so that unnecessary
resonance noise and noise are not generated.
[0053]
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 over an ultra-low frequency of 20 Hz to about 100 Hz, but also a
08-05-2019
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compact cabinet with a total volume of 76 liters and a distortion-free maximum output of about
100 dB at 20 Hz The sound pressure level can be obtained at 30 Hz as a powerful distortion-free
maximum output sound pressure level of about 111 dB.
[0054]
In addition, the vibration of the cabinet is about 1/100 of that when the passive radiators are
collectively attached to the outer surface of the cabinet, and even when the distortion-free
maximum output sound pressure level is output, almost unnecessary resonance noise and noise
occur do not do.
[0055]
Although the detection circuit is a resistor having a small value in this embodiment, it is needless
to say that a bridge circuit as described in the first embodiment may be used.
[0056]
As apparent from the above description, according to the present invention, the detection circuit
inserted between the power amplifier and the driver unit detects a voltage proportional to the
vibration system speed of the driver unit and detects the voltage. Since the speed feedback and
the acceleration feedback are applied by feeding back the output to the power amplifier by the
feedback circuit, the electromagnetic braking resistance and the effective vibration mass of the
driver unit can be equivalently made extremely large, so that the resonance Not only the
frequency can be lowered, but also the peak can be suppressed, and the ultra low frequency flat
sound pressure frequency characteristics can be obtained with the effective vibration area of the
driver unit being large, and the small size but the super bass with high maximum output sound
pressure level It is possible to realize a low-pitched sound reproduction apparatus that can
reproduce flat.
[0057]
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.
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