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DESCRIPTION JPH10341492

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DESCRIPTION JPH10341492
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
bass amplifier of a speaker system for use in an audio system, a personal computer or the like.
[0002]
2. Description of the Related Art Since it is desirable that an audio system reproduces an original
sound more faithfully, various ideas have been made for high-fidelity reproduction without
making it a simple amplification circuit. One of them is the NFB (negative feedback) circuit
usually applied to the amplification circuit. This NFB circuit was initially implemented only in the
amplification circuit, but is gradually implemented including the speaker system. The reason is
that the speaker system is the worst in the audio system, so this speaker does not take any
measures (of course, research and improvement of the speaker itself has been made) and driving
it This is because there is a limit to improving only the circuit.
[0003]
By the way, in order to faithfully reproduce the sound quality, especially the low frequency
sound, a speaker with a large diameter will inevitably be used. This is because the cone paper
must be vibrated with a large amplitude to reproduce the low-range sound. However, in practical
applications, large diameter speakers can not often be used. For example, a compact audio
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system is such, and a speaker for audio monitor of a personal computer corresponds to this.
Although both are small in diameter, it is because reproduction | regeneration of low-pass is
strongly demanded.
[0004]
Therefore, as a measure to reproduce lower-range sound with a speaker having a fixed aperture,
a bass boost device called a passive radiator has been devised and put into practical use. In this
case, another speaker (this speaker may have only a cone for vibration and may not have a
magnetic circuit) is disposed at the place where the sound pressure of the main speaker (active
speaker) driven by the output of the amplifier is received. The speaker resonates with the sound
pressure emitted by the main speaker to generate a sound (low frequency sound). This resonant
speaker is called a passive radiator.
[0005]
This technology is also researched and various patent applications have been made. Among
them, those described in JP-A-5-176389 and JP-A-5-176390 are drivers driven by an amplifier
to a first cavity in a box (an enclosure) which divides the inside into two. In the structure where
the unit (speaker) is attached and the passive radiator is attached to the second cavity
independent of the first cavity, a sensor for detecting the vibration of the driver unit is provided,
and feedback is made to the amplifier according to the output of this sensor. The
[0006]
Another prior art is disclosed in JP-A-3-232399. In this system, the passive radiator is provided
with means for detecting the vibration, and the amplifier for driving the main speaker is fed back
according to the output.
[0007]
SUMMARY OF THE INVENTION All of these inventions can exhibit excellent effects in the
reproduction of the low range. In the present invention, the signal system of the main speaker is
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independent without giving feedback to the drive amplifier system of the main speaker as
described in the above [0005] and [0006] according to the idea totally different from these
techniques. With the above compensation method, we have developed a technology that can
satisfy low frequency compensation and try to provide it.
[0008]
SUMMARY OF THE INVENTION As means for solving the above-mentioned problems, according
to the present invention, in the invention described in claim 1, the magnetic pressure is applied
to the portion receiving the sound pressure of the main speaker driven by the amplifier. A
passive radiator comprising a speaker having a circuit is disposed, and a motional feedback
circuit independent of a drive circuit of the main speaker is connected to the passive radiator.
[0009]
The invention described in claim 2 is characterized in that, in the invention described in claim 1,
the main speaker and the passive radiator are attached to a sealed box.
[0010]
The invention described in claim 3 is characterized in that, in the invention described in claim 1,
the main speaker and the passive radiator are attached to a bass reflex type box.
[0011]
The cone paper of the passive radiator vibrates with the operation of the main speaker.
This vibration is captured by the magnetic circuit of the passive radiator and becomes an audio
current.
This audio current is signal-processed by the differential input buffer amplifier, the integral MFB
amplifier, the speed MFB amplifier and the summing amplifier, and then power amplified and
again added to the magnetic circuit of the passive radiator.
Thus, the passive radiator continues to operate.
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[0012]
The above circuit causes the passive radiator to be servo-controlled, and the stiffness of the
passive radiator is canceled. If the main speaker and the passive radiator are attached to a closed
type or bass reflex type box, the effect of the above-mentioned servo control and the effect
peculiar to these boxes synergy, and the reproduction of the low range is further excellent.
[0013]
A loudspeaker unit having a magnetic circuit as a passive radiator is used, and a motional
feedback loop (MFB loop) closed only by the passive radiator is configured independent of the
main unit, and MFB effectively cancels the stiffness acting on the passive radiator . As a result,
the operating band of the passive radiator is expanded to the low frequency range, the bass
reproduction limit frequency of the speaker system is greatly lowered, and the reproduction of
the super bass can be performed with the small system.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be
described below with reference to the drawings. In FIG. 1, 1 is a main speaker, 2 is cone paper,
and 3 is a voice coil serving as a magnetic circuit. The voice coil 3 is connected to the output side
of the main amplifier 4. A passive radiator 5 is disposed in the vicinity of the main speaker 1 to
receive the sound pressure when the main speaker 1 is activated. The passive radiator 5 is
composed of a speaker having cone paper 6 and a voice coil 7 serving as a magnetic circuit, and
when the main speaker 1 is activated, an audio current is generated in the voice coil 7.
[0015]
The output side of the power amplifier 8 and one end of the resistor 9 are connected to one end
(positive side) of the voice coil 7 of the passive radiator 5. The other end of the resistor 9 is
connected to the positive input end of the differential input buffer amplifier (balanced input
buffer amplifier) 10 and one end of the resistor 11. The other end of the resistor 11 is connected
to the ground circuit together with the other end of the resistor 12 whose one end is connected
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to the other end (negative side) of the voice coil 7 and the negative input end of the differential
input buffer amplifier 10 . The differential input buffer amplifier 10 eliminates the difference
between the input levels at both input terminals, and the amplification level is 0 dB.
[0016]
The output side of the differential input buffer amplifier 10 is connected to the input ends of the
integral MFB amplifier 13 and the speed MFB amplifier 14. The integrating MFB amplifier 13
attenuates the high frequency region at an attenuation rate of -6 dB / oct through the built-in
integrating circuit and produces a signal having a phase difference of 90 degrees. Since the
stiffness acting on the diaphragm of the passive radiator 5 is equivalently canceled by feeding
back this signal, the lowest resonance frequency of the passive radiator 5 is lowered, and the
bass reproduction limit frequency is lowered. The velocity MFB amplifier 14 amplifies and feeds
back a signal proportional to the diaphragm velocity of the passive radiator 5, and a state in
which the electromagnetic braking resistance of the passive radiator 5 is equivalently reduced is
obtained, and the stiffness by the integral MFB is obtained. The Q factor of the vibration of the
passive radiator 5 which has become equivalently smaller due to the reduction of the V.sub.0 is
increased to compensate for the reduction of the bass reproduction level.
[0017]
The output terminals of these two amplifiers 13 and 14 are connected to the input terminal of
the summing amplifier 15 with flat characteristics with an amplification factor of 0 dB, the
integrated MFB signal and the velocity MFB signal are added by this summing amplifier 15, and
the added signal is It is output. The output terminal is connected to the input side of the power
amplifier 8 with an amplification factor of 26 decibels.
[0018]
Since this circuit configured in this manner reduces the voice current generated in the voice coil
7 of the passive radiator 5, it reduces the electromagnetic braking force generated by the voice
current flowing through the electrical resistance of the voice coil 7 itself, thus causing vibration.
It is proved by drawing a Nyquist diagram that it operates as a positive feedback circuit to work
to increase. Therefore, in this state, the voice coil 7 is damaged by self-oscillation. Therefore,
Nyquist's stability determination method is applied to determine the gain of velocity MFB and the
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gain of integral MFB by an exact and practical method so as to be an optimal value within the
range where the stability is obtained in advance, and prevent this It is.
[0019]
As shown in FIG. 2, the main speaker 1 and the passive radiator 5 are attached to a closed box
16, or attached to a bass reflex box 17 as shown in FIG. In any of these cases, the passive
radiator 5 is driven by the sound pressure at the back of the main speaker. In the closed type box
16, the opposite phases of the front and rear surfaces of the cone 2 of the main speaker 1 and
the cone 6 of the passive radiator 5 are blocked, so that the sound pressure attenuation due to
the interference does not occur. [0016] The advantages of the feedback described in the section
above are added. On the other hand, in the bass reflex type, the vibration amplitude of the cone
paper 6 of the main speaker 1 and the passive radiator 5 is limited in the vicinity of the
antiresonance frequency where Helmholtz resonance of air in the box body and air in the port
body occurs. For this reason, by setting the antiresonance frequency lower than the resonance
frequency of the passive radiator 5 to which feedback is applied, the sound pressure in the super
bass region where the vibration amplitude of the cone paper 6 is increased without substantially
affecting the sound pressure. Distortion can be reduced.
[0020]
When the circuit of FIG. 1 operates, the passive radiator 5 will not only make a sound by
resonating with the main speaker 1 but will make a positive sound at the output of the power
amplifier 8. Therefore, even in the case where both the main speaker 1 and the passive radiator 5
use small-aperture speakers, and these are attached to a box with a small capacity, the low band
can be sufficiently covered.
[0021]
The graph in Fig. 4 shows an example, in a semi-infinite space where a main speaker unit with a
diameter of 100 mm and a minimum resonance frequency of 80 Hz and a passive radiator with a
diameter of 160 mm are attached to a 7.5-liter box. It is a reproduction sound pressure
characteristic view. In this figure, it is a passive radiator type with servo control according to the
present invention, and for comparison, the characteristics when a speaker unit with the same
diameter of 100 mm is used in a closed type with a 7.5 liter box body are shown. In this example,
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the bass reproduction threshold frequency is about 160 Hz when used in a closed form, but can
be extended to about 40 Hz in the arrangement according to the invention. In this example, since
the bass reproduction limit frequency is about 80 Hz or more when the speaker unit being used
is used in the usual closed type, bass reflex type and passive radiator type, the bass reproduction
capability of the speaker system is It can be seen that the scheme according to the invention is
greatly enhanced. In FIG. 4, the impedance characteristic of the main speaker unit is shown,
which corresponds to the one or the one. In an ordinary passive radiator speaker system, the
impedance characteristic has two peaks, but in the method according to the present invention,
only high frequency peaks appear due to MFB, low frequency peaks disappear and the
impedance is reversed there. It can be seen that it has decreased from the specified value.
[0022]
The one shown in FIG. 1 is merely an example, and it is possible to detect and use the vibration of
the passive radiator with a sensor for displacement, vibration, acceleration, etc. as a signal for
MFB, and it is possible to obtain a more desirable result. it can.
[0023]
As another example, in the case where a main speaker of 160 mm in diameter and a passive
radiator of 180 mm in diameter are used in the configuration shown in FIG. 1 in a sealed 16 liter
box, in this case, FIG. As shown in 1, it was possible to extend the sound pressure characteristics
to the super bass region of 30 Hz or less.
Note that FIG. 5 shows the characteristics when the same main speaker unit is used in the same
box and in a closed type. Also, in the figure, the impedance characteristic of the main speaker
unit is shown, which corresponds to the one or the one. In an ordinary passive radiator speaker
system, the impedance characteristic has two peaks, but in the method according to the present
invention, only high frequency peaks appear due to MFB, low frequency peaks disappear and the
impedance is reversed there. It can be seen that it has decreased from the specified value.
[0024]
As described above, since the present invention is a bass enhancing apparatus for a speaker
system in which only motional feedback (MFB) is applied to passive radiators, the following
effects can be obtained.
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[0025]
Since the MFB loop is closed only by the passive radiator, the MFB loop can enhance the bass
without impairing the sound quality of the main unit, and the choice of the drive amplifier of the
main unit is free.
[0026]
By using a servo-controlled-passive radiator, the stiffness acting on the passive radiator can be
canceled by the MFB, and the passive band can be broadened in the low frequency direction. It
was possible.
[0027]
As the volume of the box required by the main unit is sufficient, passive radiator operation in the
super low frequency range is possible with a small box, and ultra low frequency reproduction is
possible with the small-diameter main unit of lightweight vibration mass and the ultra small box.
it can.
And there is no need to divide the cavity for bass reproduction.
[0028]
Since the main unit does not contribute to bass reproduction, intermodulation distortion is
greatly reduced as compared to a general small speaker system.
[0029]
Brief description of the drawings
[0030]
1 is a circuit diagram showing an example of the implementation of the present invention.
[0031]
2 is a partial cross-sectional view showing the main speaker and the passive radiator attached to
a sealed box.
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[0032]
3 is a partial cross-sectional view showing the main speaker and the passive radiator attached to
the bass reflex type box.
[0033]
4 is a characteristic diagram showing the effect of the present invention using the circuit of FIG.
1 and the box of FIG.
[0034]
5 is a characteristic diagram showing the effect of another embodiment of the present invention.
[0035]
Explanation of sign
[0036]
DESCRIPTION OF SYMBOLS 1 Main speaker 4 Main amplifier 5 Passive radiator 7 Voice coil 8
Power amplifier 10 Differential input buffer amplifier 13 Integral MFB amplifier 14 Speed MFB
amplifier 15 Summing amplifier 16 Sealed box 17 Bass reflex box
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