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JPH05176388

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DESCRIPTION JPH05176388
[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 It has
been requested.
[0003]
Hereinafter, a conventional bass reproduction apparatus will be described with reference to the
drawings.
As shown in FIG. 14, the driver unit 41 is attached to the Kelton-type cabinet 42. Specifically, the
inside of the cabinet is divided into a first cavity 42c and a second cavity 42d by a cavity division
member 42b, and the driver unit 41 is attached to the cavity division member 42b. That is, the
rear portion of the driver unit 41 is sealed by the first cavity 42c. And, a port 42a is provided on
the side of the cavity 2; 42d, from which a low sound is emitted (this type of cabinet is generally
08-05-2019
1
called a Kelton-type cabinet).
[0004]
Further, the driver unit 41 is driven by the power amplifier 43, and a low pass filter 44 is
inserted in the front stage of the power amplifier 43.
[0005]
The operation of this conventional bass reproduction apparatus will be described with an
equivalent circuit of a Kelton-type speaker system shown in FIG.
[0006]
Resonances that make the phases of Vd and Vp become almost the same between Md and Mp
and Cd, Cc1 and Cc2 at a lower frequency f1, and Vd and Vp at Md, Mp and Cc2 at a higher
frequency f2 A resonance occurs in which the phases of the phases 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 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.
[0007]
Md, Cc1, Red, Cc2, and Mp are designed to have appropriate values (usually, Cd << Cc1, Rmd,
Rc1, Rc2, and Rp << Red, so the above parameters may be noted.
The in-port air mechanical resistance Rp is simply understood as a frictional resistance between
air moving by vibration in the port and the inside of the port pipe wall, and a resistance due to
air flow disturbance generated at the port outlet. (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 (the larger the Md and Mp, the more Cc1, Cc2 The smaller the, the higher
the Q of the resonance, and Red needs a larger value. The flat sound pressure frequency
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characteristics can be obtained in the 1.5 to 2.5 octave band between f1 and f2 by dumping each
resonance peak.
[0008]
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.
[0009]
Since this Kelton type speaker system utilizes resonance, it is more efficient than the closed type
speaker system, and has band-pass characteristics so that it is suitable for bass reproduction.
[0010]
By driving the Kelton-type speaker system with the power amplifier 43, a bass reproduction
apparatus for reproducing the ultra-low range is configured.
Note that if the frequency is about 200 to 300 Hz, air column resonance of air in the port 42a
may occur, or a standing wave may build up inside the cabinet, and the characteristics may be
disturbed. High frequencies are sufficiently attenuated.
[0011]
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.
[0012]
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 at a very low
frequency despite the small size. The driver unit and the air effective vibration mass in the port
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are increased to strengthen the magnetic circuit of the driver unit, and Cc1 = volume of first
cavity 41 / (air density × air velocity 2 × S12), Cc2 = second Since the volume of the cavity 42 /
(air density x air velocity 2 x S12), in order to increase Cc1 and Cc2 without enlarging the cavity,
the effective vibration area S1 of the driver unit has to be reduced. .
[0013]
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
unit and the magnetic circuit become large, which causes the driver unit to be difficult to realize.
[0014]
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
increase Md and Mp, the resonance Q of the above-mentioned two resonance frequencies f1 and
f2 becomes very high, and a large peak is generated that can not be dumped even if Red is
slightly increased. There is also a problem that a flat sound pressure frequency characteristic can
not be obtained.
[0015]
FIG. 14 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 ( In
general, the smaller the diameter of the speaker, the smaller the maximum amplitude of no
distortion). The minimum resonance frequency is 30 Hz, and the driver unit 41 is attached to the
cavity division member 42b of the Kelton cabinet 42.
The port 42a has an inner diameter of 80 mm and a length of 150 mm.
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The first cavity 42c has an inner volume of 35 liters, and the second cavity 42d has an inner
volume of 15 liters.
[0016]
The driver unit 41 is driven by a power amplifier 43 with an output of 100 W, and a low pass
filter 44 with a cutoff frequency of 250 Hz is inserted in its front stage.
[0017]
The measured sound pressure frequency characteristics of this conventional bass reproduction
apparatus are shown in FIG.
As is apparent from FIG. 12, substantially flat characteristics are obtained over about 30 Hz to
120 Hz, but 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.
[0018]
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.
13 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.
[0019]
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.
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[0020]
SUMMARY OF THE INVENTION In order to achieve the above object, a bass reproducing
apparatus according to the present invention comprises a driver unit, a Kelton cabinet to which
the driver unit is attached, a power amplifier for driving the driver unit, and the electric power. A
detection circuit inserted between an amplifier and the driver unit to detect a voltage
proportional to the vibration system speed of the driver unit, and fed back from the detection
circuit to the power amplifier to apply speed type feedback and acceleration type feedback And a
feedback circuit.
[0021]
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 the peak is
lowered. 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.
[0022]
An embodiment of the present invention will be described below with reference to the drawings.
[0023]
FIG. 1 shows a first embodiment of the bass reproducing apparatus according to the present
invention.
The 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 direct current 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 ohms), a speaker with a
diameter of 30 cm with no distortion maximum amplitude ± 6 mm, and a minimum resonance
frequency of 30 Hz, and this driver unit 1 is a Kelton type cabinet It is attached to two cavity
division members 2b.
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The port 2a has an inner diameter of 80 mm and a length of 150 mm.
The first cavity 2c has an inner volume of 35 liters, and the second cavity 2d has an inner volume
of 15 liters.
[0024]
The driver unit 1 is driven by a power amplifier 3 of 200 W output.
Detection circuit 4 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 3 and driver unit 1
Is inserted in the
[0025]
The output voltage of the bridge circuit, that is, the output voltage of the detection circuit 4 is in
direct proportion to the speed of the vibration system of the driver unit 1. Although this is well
known in electroacoustic theory, it will be described once with reference to FIG. 5, FIG. 6, and
FIG.
[0026]
FIG. 5 shows the impedance characteristics of a general speaker, but at a very low frequency, the
DC resistance Re of the voice coil is obtained, and the peak Zmax at the lowest resonance
frequency F0 (Zmax is 100 to 100 for powerful speakers of magnetic circuits It will be about
300Ω. It becomes), approaches Re again in the middle bass range, and has a curve that rises
gently in the high range.
[0027]
FIG. 6 shows the impedance component of the voice coil of the speaker. Ze is called the braking
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7
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 is E = BL × V (V is the speed of the voice coil), the dynamic impedance is in direct
proportion to the speed of the vibration system.
[0028]
That is, the impedance curve shown in FIG. 5 is obtained by superimposing dynamic impedance
on voice coil DC resistance and inductance. The impedance curve of the Kelton-type speaker
system is shown in FIG. 7, but this is also the same.
[0029]
Now, connect the speaker, that is, the voice coil of the driver unit to one side of the bridge circuit
as shown in the detection circuit 4 of FIG. 1, Re: R3 = R1: R2 and L = voice coil inductance × (R3
/ Re) By balancing the bridge by the following equation, the voltage due to the DC resistance and
inductance 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.
[0030]
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 value of each element of the bridge circuit of the detection circuit 4 of the present
embodiment is not exactly the same as that according to the above relation.
[0031]
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8
As described above, since the output voltage of the detection circuit 4 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 4 is applied 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 5 feeds back to the power amplifier 3 so that an
acceleration type feedback of a feedback amount is applied such that the effective vibrating mass
of the driver unit 1 is adjusted to 76 g equivalently. The amount of feedback is attenuated so as
not to become unstable at about 200 Hz or more.
[0032]
In addition, a low pass filter 6 having a cutoff frequency of 200 Hz is inserted in the front stage
of the power amplifier 3 to attenuate an unnecessary band.
[0033]
The effects of the MFB will be described in detail below with reference to FIGS. 8, 9 and 15.
[0034]
The speed of the vibration system of the driver unit is represented by Vd of the equivalent circuit
of FIG. 15, 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 will also be a
characteristic that attenuates at 6 dB / oct. .
[0035]
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.
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That is, when the sound pressure frequency characteristic is as shown in FIG. 8A, the velocity Vd
of the vibration system of the driver unit is as shown in FIG.
[0036]
Here, if a voltage proportional to the vibration system speed of the driver unit is detected and
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 at f1 and f2 peaks and
becomes as shown in FIG. 8 (D). That is, the sound pressure frequency characteristic becomes as
shown in FIG. 8C according to this, and the flat one with peaks f1 and f2 is obtained. This is just
equivalent to increasing the electromagnetic braking resistance Red of the driver unit of the
equivalent circuit of FIG. 15, 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.
[0037]
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.
8B 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.
[0038]
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.
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[0039]
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. 9A 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. Further, by increasing the in-port effective vibration mass Mp, the
two resonance frequencies f1 and f2 of (A) decrease to become as shown by (B).
[0040]
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.
[0041]
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).
[0042]
The bass reproducing apparatus configured as described above can apply MFB to the driver unit,
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
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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.
[0043]
The measured sound pressure frequency characteristics of the bass reproducing apparatus
configured as described above are shown in FIG. As apparent from FIG. 10, not only a
substantially 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
[0044]
Although L is inserted into the detection circuit 4 in this embodiment, the same effect as L can be
obtained even if L is eliminated and a capacitor is inserted in parallel to R 2 instead. Alternatively,
L may be omitted if the diameter of the voice coil is small or the inductance of the voice coil is so
small that it can be ignored because the copper short ring is attached to the magnetic circuit
yoke or the like.
[0045]
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), 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 Kelton type
cabinet 12 It is attached to the cavity division member 12b. The port 12a has an inner diameter
of 100 mm and a length of 580 mm, and bell mouth flanges are provided at both ends of the port
in order to suppress wind noise generated at the port end due to intense air movement. The port
12a is long and attached to the side of the second cavity 12d. The first cavity 12c has an inner
volume of 60 liters, and the second cavity 12d has an inner volume of 16 liters.
08-05-2019
12
[0046]
The driver unit 11 is driven by a power amplifier 13 with an output of 600 W. Further, a small
resistance R is inserted as a detection circuit 14 between the driver unit 11 and the power
amplifier 13. In this example, R = 0.1 Ω.
[0047]
The voltage across the resistor R is inversely proportional to the voice coil impedance curve (see
FIG. 7) 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.
[0048]
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 14 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.
[0049]
Therefore, the speed type feedback is applied by positively feeding back the detected voltage
without inverting the phase as it is. To explain the matter clearly, at two resonance frequencies f1
and f2, the detected voltage becomes minimum, and the output of the power amplifier 13 hardly
changes even if it is positively fed back. However, at the frequency outside the antiresonance
frequency Fr or f1 and f2, the detected voltage becomes large, and the output of the power
amplifier 13 increases because of positive feedback. 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.
08-05-2019
13
[0050]
Further, by passing the detected voltage through a differentiating circuit, a voltage inversely
proportional to the acceleration of the vibration system of the driver unit 11 can be obtained.
Therefore, an acceleration feedback is applied by positively feeding the voltage without inverting
the phase.
[0051]
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 15 feeds back to the power amplifier 13 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.
[0052]
Further, a low pass filter 16 having a cutoff frequency of 200 Hz is inserted in the front stage of
the power amplifier 13 to attenuate unnecessary bands.
[0053]
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.
[0054]
The measured sound pressure frequency characteristics of the bass reproducing apparatus
configured as described above are shown in FIG.
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As is apparent from FIG. 11, not only is an almost flat characteristic obtained from the super low
frequency of 20 Hz to about 100 Hz, but also the small cabinet of 76 liters in total volume, the
maximum distortion free output of about 100 dB at 20 Hz. A sound pressure level can be
obtained at 30 Hz as a powerful distortion-free maximum output sound pressure level of about
111 dB.
[0055]
Next, a third embodiment of the present invention will be described with reference to FIG.
The driver unit 21 is a speaker with a diameter of 30 cm, which is the same as that described in
the first embodiment. The same is true for the Kelton cabinet 22 as well. The inner diameter of
the port 22a is 80 mm, the length 150 mm, the first cavity 22c has an inner volume of 35 liters,
and the second cavity 22d has an inner volume of 15 liters.
[0056]
The driver unit 21 is driven by a power amplifier 23 of 200 W output. In addition, a piezoelectric
sensor 24 is attached to the center of the diaphragm of the driver unit 21 to detect the vibration
of the vibration system of the driver unit 21. Since this detection voltage is a voltage proportional
to the acceleration of the vibration system of the driver unit 21 in the case of the piezoelectric
sensor, the gain is adjusted as it is, and the feedback mass of the effective vibration mass of the
driver unit 21 equivalently becomes 76 g. If acceleration voltage feedback is applied and the
detection voltage of the sensor 24 is integrated through an integration circuit, a voltage
proportional to the speed of the vibration system can be obtained. After that, the gain is adjusted
and the electromagnetic of the driver unit 21 is adjusted. The feedback circuit 25 feeds back to
the power amplifier 23 so that a speed type feedback is applied such that the braking resistance
is equivalent to 51.2 mechanical ohms. The amount of feedback is attenuated so as not to
become unstable at about 200 Hz or more.
[0057]
In addition, a low pass filter 26 with a cutoff frequency of 200 Hz is inserted in the front stage of
the power amplifier 23 to attenuate unnecessary bands.
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[0058]
In the low-pitched sound reproducing apparatus configured as described above, the driver unit is
subjected to MFB, and the electromagnetic braking resistance and the effective vibration mass of
the driver unit can be made equivalently very large. Therefore, two resonance frequencies f1 and
f2 are set. Not only lowering the peak but also suppressing the peak, it is possible to obtain a flat
sound pressure frequency characteristic in a very low band in a state where the effective
vibration area of the driver unit is large.
[0059]
The measured sound pressure frequency characteristics of the bass reproducing apparatus
configured as described above are the same as those shown in FIG.
As apparent from FIG. 10, not only a substantially 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
[0060]
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.
08-05-2019
16
[0061]
Next, a fourth embodiment of the present invention will be described with reference to FIG. The
configuration is the same as that of the third embodiment of FIG. 3 except that the sensor
attached to the diaphragm is the microphone 34 and is provided inside the first cavity 32c, and
the others are exactly the same.
[0062]
The microphone 34 detects the sound pressure in the first cavity 32c, but the sound pressure in
the first cavity 32c is in the range where the wavelength of sound is sufficiently larger than the
length of each side of the first cavity 32c, that is, in the bass region , Is proportional to the
displacement of the vibration system of the driver unit. After the detection voltage of the
microphone 34 is passed through the differentiating circuit once by the feedback circuit 35, and
after passing through the differentiating circuit once more, voltages obtained in proportion to the
acceleration are obtained, and these are then adjusted by gain and fed back. The electromagnetic
braking resistance and the effective vibration mass are equivalently set to the same values as in
the third embodiment.
[0063]
Accordingly, the operation and effect are exactly the same as in the third embodiment, and the
same sound pressure frequency characteristics as those shown in FIG. 10 can be obtained.
However, by making the sensor a microphone, it is necessary to attach it to the vibration system
of the driver unit 31 This has the effect that the processing of the lead wire from the sensor
becomes easy and the assembly of the bass reproduction device becomes easy.
[0064]
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
speed of the vibration system of the driver unit, and the detected output The feedback control
circuit feeds back the speed type feedback and the acceleration type feedback to the power
amplifier to equivalently increase the electromagnetic braking resistance and the effective
vibration mass of the driver unit. Not only lowers the peak, but also flat low pressure sound
pressure frequency characteristics in a state where the effective vibration area of the driver unit
is large. It is possible to realize a bass reproduction apparatus that can reproduce.
08-05-2019
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[0065]
The same effect can be obtained even if the sensor detects the vibration of the vibration system
of the driver unit to generate a voltage, and the output voltage of the sensor is fed back to the
power amplifier by the feedback circuit to apply speed type feedback and acceleration type
feedback. Be
[0066]
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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