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DESCRIPTION JP2005323027

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DESCRIPTION JP2005323027
PROBLEM TO BE SOLVED: To provide a speaker unit capable of stable operation even when
connected to a digital amplification circuit. SOLUTION: A first voice coil (voice coil 50a) to which
an audio signal is inputted, and a detection means (detection circuit 13) for detecting the
movement of the vibration system driven by the first voice coil or the sound by the vibration
system And a second voice coil (voice coil 50b) independent of the first voice coil, and a vibration
system by controlling a voltage applied to the second voice coil according to the detection result
of the detection means. Control means (variable resistor 51) for controlling the movement of
[Selected figure] Figure 2
Speaker unit, acoustic device, and control method of speaker unit
[0001]
The present invention relates to a speaker unit, an audio device, and a control method of the
speaker unit.
[0002]
Various MFB (Motional Feed Back) type loudspeakers have been conventionally proposed for the
purpose of improving the reproduction characteristics of the loudspeakers (see Patent
Documents 1 to 3).
[0003]
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1
In the MFB speaker, the motion of the vibration system is detected as an electric signal, and the
electric signal is fed back to the amplification circuit in the reverse phase to form a feedback loop
as a whole including the mechanical system.
By driving the vibration system with such a feedback loop, distortion in the piston vibration
region of the vibration system can be reduced.
[0004]
FIG. 8 is a view showing an example of a conventional MFB type speaker.
In this figure, a sound source 10 is, for example, a sound source such as a CD (Compact Disc)
playback device or a DVD (Digital Versatile Disc) playback device, and plays back and outputs, for
example, an audio signal recorded on a recording medium. The analog amplification circuit 11 is
formed of, for example, a semiconductor amplification element such as a transistor or a field
effect transistor (FET), and amplifies and outputs an audio signal (analog signal) supplied from
the sound source 10 with a predetermined gain. Further, the analog amplification circuit 11
receives feedback of the electric signal corresponding to the movement of the vibration system
output from the detection circuit 13 of the MFB speaker 12, and the vibration system of the MFB
speaker 12 faithfully corresponds to the audio signal. Control to vibrate.
[0005]
The MFB speaker 12 converts an audio signal supplied from the analog amplification circuit 11
into a corresponding sound pressure and outputs it, and the detection circuit 13 detects the
movement of the vibration system and feeds it back to the analog amplification circuit 11.
[0006]
FIG. 9 is a diagram for explaining the operation of the MFB loudspeaker 12 shown in FIG.
FIG. 9A shows a single sine wave output from the sound source 10. When such a sine wave is
input, in the state where MFB is not applied, since the vibration system has a constant mass, as
shown in FIG. 9B, the vibration system gradually attenuates in amplitude due to inertia. Indicates
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damped oscillations. On the other hand, when MFB is applied, as shown in FIG. 9C, the vibration
is rapidly attenuated, and a vibration close to the input audio signal can be obtained.
[0007]
JP-A-5-183978 (claims, abstract) JP-A-5-183980 (claims, abstract) JP-A-6-62487 (claims,
abstract)
[0008]
By the way, in recent years, an amplifier circuit for amplifying a signal based on a digital system
such as PCM (Pulse Code Modulation), PWM (Pulse Width Modulation), PDM (Pulse Density
Modulation), PAM (Pulse Amplitude Modulation) is widely distributed in the market. doing.
[0009]
In such a digital type amplifier circuit (hereinafter referred to as "digital amplifier circuit"), not an
analog signal but a digital signal as a pulse train is output. Therefore, in order to obtain an output
close to an analog signal, The digital signal needs to be smoothed by a low pass filter (LPF) or the
like.
[0010]
FIG. 10 is a diagram showing an example of the configuration when the MFB speaker 12 is
connected to the digital amplification circuit 20. As shown in FIG.
In addition, in this figure, since the same code | symbol is attached | subjected to the part
corresponding to the case of FIG. 8, the description is abbreviate | omitted.
In the example of this figure, the analog amplifier circuit 11 is replaced with a digital amplifier
circuit 20 as compared with the case of FIG.
Further, the MFB speaker 12 and the digital amplification circuit 20 are connected via a low pass
filter constituted by a coil 21 and a capacitor 22.
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[0011]
However, when the digital amplification circuit 20 and the MFB speaker 12 are connected via the
low pass filter in this way, the phase changes in this low pass filter, so that the operation of the
digital amplification circuit 20 becomes unstable. There is a point.
[0012]
The present invention has been made based on the above-described circumstances, and an object
thereof is to provide a speaker unit, an audio apparatus, and a control method of the speaker unit
that can operate stably even when connected to a digital amplifier circuit. The purpose is
[0013]
In order to achieve the above-mentioned object, the speaker unit of the present invention detects
a first voice coil to which an audio signal is input, a motion of a vibration system driven by the
first voice coil, or a voice by the vibration system The movement of the vibration system is
controlled by controlling the voltage applied to the second voice coil according to the detection
result of the detection means, the second voice coil independent of the first voice coil, and the
detection result of the detection means Control means for
[0014]
In the speaker unit according to another invention, in addition to the above-mentioned invention,
the control means applies an electric signal for braking the vibration system to the second voice
coil based on the detection result of the detection means.
[0015]
In addition to the above-mentioned invention, the speaker unit of the other invention further
includes an adjusting means for adjusting the signal level of the electric signal applied to the
second voice coil.
[0016]
In addition to the above-described invention, the speaker unit of the other invention further
includes setting means for setting the frequency characteristic or phase characteristic of the
electric signal applied to the second voice coil.
[0017]
In addition to the above-described invention, the speaker unit according to another invention
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further includes feedback means for feeding back the detection result of the detection means to a
digital amplification circuit for supplying an audio signal.
[0018]
A speaker unit according to the present invention includes a first voice coil to which an audio
signal is input, detection means for detecting a motion of a vibration system driven by the first
voice coil or a sound due to the vibration system, A second voice coil capable of driving the
vibration system independently of the voice coil of the above, and a control means for applying
the signal detected by the detection means to the second voice coil to control the movement of
the vibration system doing.
[0019]
A speaker unit according to the present invention includes a first voice coil to which a voice
signal is input, a second voice coil capable of driving a vibration system independently of the first
voice coil, and a second voice coil. And an element connected and serving as a load of the second
voice coil.
[0020]
Further, according to the sound device of the present invention, the speaker unit detects a first
voice coil to which a voice signal is input, a motion of a vibration system driven by the first voice
coil, or a sound by the vibration system. And feedback means for feeding back the detection
result of the detection means to the digital amplification circuit, a second voice coil independent
of the first voice coil, and the second voice coil according to the detection result of the detection
means. Control means for controlling the movement of the vibration system by controlling the
voltage of the vibration system, wherein the digital amplification circuit controls an audio signal
to be supplied to the first voice coil in response to feedback by the feedback means have.
[0021]
Further, according to the control method of the audio device of the present invention, the
movement of the vibration system of the speaker unit driven by the first voice coil to which the
audio signal is input or the sound by the vibration system is detected, and the speaker is detected
according to the detection result. The movement of the vibration system is controlled by
controlling the voltage applied to the second voice coil of the unit.
[0022]
The present invention can provide a speaker unit, an audio device, and a control method of the
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speaker unit that can operate stably even when connected to a digital amplification circuit.
[0023]
Hereinafter, embodiments of the present invention will be described based on the drawings.
[0024]
FIG. 1 is a diagram showing a configuration example of an acoustic device according to a first
embodiment of the present invention.
In this figure, the sound source 10 is composed of, for example, a CD reproducing device, a DVD
reproducing device, an FM / AM tuner, an MD (Mini Disc), etc., and is conveyed while being
superimposed on an audio signal or radio wave recorded on a recording medium. Play and
output the voice signal that has been sent.
[0025]
The digital amplification circuit 20 modulates the audio signal supplied from the sound source
10 by, for example, PCM, PWM, PDM, PAM or the like, amplifies it with a predetermined gain,
and outputs it.
[0026]
The coil 21 and the capacitor 22 form a low pass filter (LPF), and among the pulse signals output
from the digital amplification circuit 20, only the low frequency component is allowed to pass to
correspond to the original analog signal. Output an audio signal.
[0027]
The speaker unit 50 has two independent voice coils as described later, and has connection
terminals t1 and t2 connected thereto.
The terminals of the coil 21 and the capacitor 22 are connected to the connection terminal t1,
and one terminal of the variable resistor 51 is connected to the connection terminal t2.
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The side from which the sound of the speaker unit 50 is radiated (the side opposite to the side
attached to the enclosure) is provided with a detection circuit 13 as detection means and
feedback means, and the vibration of the diaphragm which is a component of the vibration
system And an electrical signal corresponding to the sound generated thereby.
The detection circuit 13 has a microphone or the like for converting vibration and sound into an
electric signal, and is connected to the other end of the variable resistor 51 and the digital
amplification circuit 20.
Therefore, the output of the detection circuit 13 is supplied as a feedback signal to the digital
amplification circuit 20 and connected to the connection terminal t2 of the speaker unit 50
through the variable resistor 51.
The variable resistor 51 as the control means and the adjustment means steps down the output
voltage from the detection circuit 13 and supplies it to the connection terminal t2.
[0028]
FIG. 2 is a diagram showing a detailed configuration example of the speaker unit 50 and the
detection circuit 13 shown in FIG.
As shown in this figure, the speaker unit 50 has two voice coils 50a and 50b which are
independent of each other.
One of the voice coils 50a, which is the first voice coil, is connected to the LPF, and the other is
grounded.
One end of the voice coil 50 b as the second voice coil is grounded, and the other end is
connected to the variable resistor 51.
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The input to the voice coil 50a and the input to the voice coil 50b are in a relationship in which
the positive and negative are reversed.
That is, a positive input to the voice coil 50a has the same effect as a negative input to the voice
coil 50b.
[0029]
The detection circuit 13 is a dynamic microphone in this example, and is configured of a coil 13a
and a magnet 13b.
The coil 13a is attached directly or indirectly to a diaphragm (not shown).
The detection circuit 13 generates an electrical signal according to the sound pressure of the
sound by vibrating in the magnetic field according to the diaphragm that vibrates according to
the sound pressure of the sound.
[0030]
In the embodiment of the present invention, the feedback amount from the detection circuit 13
to the digital amplifier circuit 20 is set to be a feedback amount that does not cause the digital
amplifier circuit 20 to oscillate.
[0031]
The operation of the first embodiment of the present invention will now be described with
reference to FIG.
[0032]
When a single sine wave shown in FIG. 3A is output from the sound source 10, the digital
amplification circuit 20 converts this into a digital signal and amplifies it.
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For example, when the modulation system of the digital amplification circuit 20 is PWM
modulation, a pulse signal having a width corresponding to the amplitude at each time of an
input signal (analog signal) is generated and output.
[0033]
The LPF constituted by the coil 21 and the capacitor 22 passes audio band signals from the
digital signal output from the digital amplification circuit 20 and blocks other signal components.
As a result, the LPF constituted by the coil 21 and the capacitor 22 outputs an analog signal
corresponding to the original audio signal.
[0034]
The audio signal that has passed through the LPF in this manner is supplied to the voice coil 50 a
of the speaker unit 50.
The voice coil 50a vibrates according to the audio signal that has passed through the LPF.
FIG. 3B is a diagram showing a temporal change of displacement of the vibration system
including the voice coil 50a. As shown in this figure, the voice coil 50a exhibits a gently damped
oscillation despite the input of a single sine wave.
[0035]
When the voice coil 50a vibrates, a diaphragm (not shown) vibrates and a sound wave is emitted.
The sound wave vibrates the coil 13 a of the detection circuit 13, so that an electric signal
corresponding to the vibration is output. FIG. 3C shows an example of the audio signal output at
this time. In this example, a signal corresponding to the displacement of the voice coil 50a shown
in FIG. 3B is output.
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[0036]
The audio signal output from the detection circuit 13 is supplied to the voice coil 50 b via the
variable resistor 51 and is also supplied to the digital amplifier circuit 20. Here, the voice signal
supplied to the voice coil 50b is reverse in direction to the current flowing into the voice coil
50a, as indicated by the arrow in the circuit diagram of FIG. Since the winding directions of the
voice coils 50a and 50b are the same, as shown in FIG. 3D, a force in the opposite direction to
the voice coil 50a acts on the voice coil 50b. Therefore, a force in the direction of braking the
diaphragm is generated in the voice coil 50b. On the other hand, the voice signal fed back to the
digital amplification circuit 20 becomes motional feedback, and is controlled so that the
operation of the diaphragm is faithful to the voice signal inputted to the digital amplification
circuit 20, so attenuation The braking is performed in the direction in which the vibration is
suppressed. As a result, the vibration by the diaphragm becomes as shown in FIG. 3E by the
action of the braking by the voice coil 50b and the braking by the motional feedback, and the
operation becomes similar to the input waveform shown in FIG. .
[0037]
In the first embodiment of the present invention, as described above, the feedback amount from
the detection circuit 13 to the digital amplification circuit 20 is suppressed to such an extent that
the digital amplification circuit 20 does not oscillate. The digital amplifier circuit 20 is prevented
from oscillating.
[0038]
As described above, in the first embodiment of the present invention, the digital amplifier circuit
is supplied with the signal from the detection circuit 13 in reverse phase to the voice coil 50b to
damp the vibration of the diaphragm. Since the amount of feedback to 20 can be reduced,
oscillation of the digital amplification circuit 20 can be prevented while realizing motional
feedback.
[0039]
In the above embodiment, the detection signal is directly fed back from the detection circuit 13
to the digital amplification circuit 20. However, as shown in FIG. 4, for example, between the
detection circuit 13 and the digital amplification circuit 20 A variable resistor 52 may be inserted
in the circuit to adjust the amount of feedback.
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According to such an embodiment, it is possible to adjust the feedback amount to the voice coil
50b by adjusting the variable resistor 51 and adjust the feedback amount to the digital amplifier
circuit 20 by adjusting the variable resistor 52. It will be possible.
Therefore, for example, the variable resistor 52 can be adjusted to adjust the feedback amount so
that the digital amplification circuit 20 does not oscillate, and the variable resistor 51 can be
adjusted to set the braking amount appropriately. Further, by adjusting these, the low-pass
resonant frequency f0 of the speaker unit 50 or the sharpness Q0 of resonance can be set to a
desired value.
[0040]
Alternatively, the output of the detection circuit 13 may be amplified by an amplification circuit
(not shown) to obtain a predetermined braking force.
[0041]
Next, a second embodiment of the present invention will be described with reference to FIG.
[0042]
FIG. 5 is a view showing an example of the configuration of an acoustic device according to the
second embodiment of the present invention.
In addition, in this figure, since the same code | symbol is attached | subjected to the part
corresponding to FIG. 1, the description is abbreviate | omitted.
In FIG. 5, the variable resistor 51 is excluded and the resistor 60 and the capacitor 61 are newly
added, as compared with the case of FIG. The other configuration is the same as that of FIG.
[0043]
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11
Here, the capacitor 61 which is the setting means as well as the resistor 60 which is the setting
means constitutes an LPF, and only the low frequency component is supplied to the voice coil
50b. Therefore, in the second embodiment, the low frequency component of the output of the
detection circuit 13 is mainly supplied to the voice coil 50b. As a result, the lower frequency
components are more strongly braked. By adjusting the time constant by the resistor 60 and the
capacitor 61, it is possible to set the frequency characteristic and / or the phase characteristic of
the braking to the voice coil 50b.
[0044]
As described above, in the second embodiment of the present invention, since the output of the
detection circuit 13 is supplied to the voice coil 50b via the LPF, it is possible to strongly apply
braking to a desired band. become.
[0045]
In the above embodiment, although the case of the LPF has been described as an example, for
example, a high pass filter (High Pass Filter) HPF, a band pass filter (Band Pass Filter) BPF, a band
elimination filter (Band Elimination Filter) It is also possible to apply other filters such as BEF).
It is also possible to set not the frequency characteristic but the phase characteristic.
Furthermore, in the above embodiment, although the example of the passive LPF by RC was
mentioned and demonstrated, it is also possible to apply the passive filter by LCR, and an active
filter.
[0046]
Next, a third embodiment of the present invention will be described with reference to FIG.
[0047]
FIG. 6 is a view showing an example of the configuration of an acoustic device according to the
third embodiment of the present invention.
In addition, in this figure, since the same code | symbol is attached | subjected to the part
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corresponding to FIG. 1, the description is abbreviate | omitted. 6, the variable resistor 51 is
excluded and the grounded variable resistor 70 is newly added as compared with the case of FIG.
The other configuration is the same as that of FIG. That is, one end of the variable resistor 70 is
electrically connected to one end of the voice coil 50b, and the other end of the variable resistor
70 is electrically connected to the other end of the voice coil 50b. The voice coil 50b and the
variable resistor 70 form a closed circuit. Do.
[0048]
In this embodiment, the output of the detection circuit 13 is fed back only to the digital
amplification circuit 20. The variable resistor 70 serves as a load of the voice coil 50 b to brake
the voice coil 50 b. That is, since the electromotive force is generated in the voice coil 50b by the
operation of the diaphragm, and the electromotive force is consumed by the variable resistor 70,
the braking force acts on the voice coil 50b. Therefore, by adjusting the variable resistor 70, it is
possible to make the damping oscillation converge early, reduce the feedback amount to the
digital amplification circuit 20, and prevent oscillation from occurring.
[0049]
As described above, in the third embodiment of the present invention, since the variable resistor
70 is connected to the voice coil 50b as a load, adjustment to the variable resistor 70 allows
adaptation to motional feedback. It is possible to obtain a desired braking force.
[0050]
Next, a fourth embodiment of the present invention will be described with reference to FIG.
[0051]
FIG. 7 is a view showing an example of the configuration of an acoustic device according to the
fourth embodiment of the present invention.
In addition, in this figure, since the same code | symbol is attached | subjected to the part
corresponding to FIG. 2, the description is abbreviate | omitted.
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In FIG. 7, the detection circuit 13 is replaced with a capacitor microphone 80 and an
amplification circuit 81 as compared with the case of FIG. 2. The other configuration is the same
as that of FIG.
[0052]
Here, the condenser microphone 80 which is a part of the detection means and a part of the
feedback means is, for example, an electret condenser microphone etc., and the distance between
the plates of the condenser displaced by receiving the sound pressure is an electric signal Output
as The amplification circuit 81 which is a part of the detection means and a part of the feedback
means has, for example, a high input impedance element such as a FET at its input, and amplifies
the output of the capacitor microphone 80 with a predetermined gain. The purpose is to perform
impedance conversion.
[0053]
In this example, the operation of the circuit is the same as that of FIG. 2, but since an inexpensive
capacitor microphone can be used compared to the dynamic microphone shown in FIG. 2, the
manufacturing cost can be reduced. . In this example, although the amplifier circuit 81 is
required, since the amplifier circuit 81 can use an inexpensive IC chip or the like, the cost can be
reduced as a whole.
[0054]
Although the above-described embodiments are preferred examples of the present invention, the
present invention is not limited to these, and various modifications and changes can be made
without departing from the scope of the present invention. It is.
[0055]
For example, although the case where the speaker unit 50 is connected to the digital
amplification circuit 20 is described as an example in each of the above embodiments, it is also
possible to connect the speaker unit 50 to an analog amplification circuit.
[0056]
Further, in the above embodiments, the pressure detection type dynamic and condenser type
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microphones have been described as an example, but it is also possible to use a speed detection
type microphone (for example, a ribbon type microphone).
[0057]
Furthermore, the acoustic device according to each of the above-described embodiments can be
applied to an on-vehicle speaker device or an amplifier.
The acoustic device in each of the above embodiments is suitable for a woofer device that
requires a relatively large output and a drive device therefor.
[0058]
The present invention can be used, for example, in a speaker unit used in connection with a
digital amplification circuit.
[0059]
It is a figure showing an example of composition of an acoustic device concerning a 1st
embodiment of the present invention.
It is a figure which shows the detailed structural example of the speaker unit of 1st Embodiment
shown in FIG. 1, and a detection circuit.
It is a figure for demonstrating the operation | movement of 1st Embodiment shown in FIG.
It is a modification of the 1st embodiment of the present invention. It is a figure which shows the
structural example of the audio equipment based on the 2nd Embodiment of this invention. It is a
figure which shows the structural example of the audio equipment based on the 3rd Embodiment
of this invention. It is a figure which shows the structural example of the acoustic apparatus
based on the 4th Embodiment of this invention. It is a structural example of the conventional
MFB type | mold speaker. It is a figure for demonstrating the operation | movement of the MFB
type | mold speaker shown in FIG. It is a figure which shows the state which connected the
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conventional MFB type | mold speaker to the digital amplification circuit.
Explanation of sign
[0060]
13 detection circuit (detection means, feedback means) 50a voice coil (first voice coil) 50b voice
coil (second voice coil) 51 variable resistance (control means, adjustment means) 60 resistance
(part of setting means) 61 Condenser (part of setting means) 70 Variable resistance (load means)
80 Condenser microphone (part of detection means, part of feedback means) 81 Amplifier circuit
(part of detection means, part of feedback means)
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