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JPH0595597

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DESCRIPTION JPH0595597
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
reproduction band in which distortion of a sound is reduced by restricting a reproduction signal
band at large volume using MFB (motional feedback) in an audio reproduction apparatus using a
speaker. It relates to an adjustment device.
[0002]
2. Description of the Related Art A conventional MFB circuit is constructed as shown in FIG. 4. In
FIG. 4, 1 is an amplifier whose frequency characteristic can be changed, 2 is a speaker connected
to the amplifier 1, 3 is a vibration of the speaker 2. A detection coil for detecting the amplitude,
and a feedback circuit 4 for feeding back a detection signal from the detection coil 3 to the
amplifier 1.
[0003]
FIG. 5 is a simplified cross-sectional view showing the configuration of the speaker 2 and the
detection coil 3.
The detection coil 3 is wound around the bobbin 2a of the voice coil of the speaker 2, and the
speaker 2 side and the detection coil 3 side are configured in a pair of voice coil structures with
the bobbin 2a in common. When the speaker 2 converts an acoustic signal into a sound, the
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bobbin 2a vibrates in the axial direction. Along with the vibration of the bobbin 2a, the detection
coil 3 also vibrates, and a current flows in the detection coil 3 by the electromagnetic induction
action.
[0004]
Next, the operation will be described with reference to FIG. The output obtained by the detection
coil 3 as described above is converted into a control signal through the feedback circuit 4 and
then fed back to the control input side of the amplifier 1 to change the frequency characteristic
of the amplifier 1. Thereby, by improving the frequency characteristic with respect to the input
sound signal, the reproduction capability of the sound signal transmitted from the amplifier 1 to
the speaker 2 at a low frequency is improved.
[0005]
Since the conventional MFB circuit is configured as described above, it is necessary to use a
dedicated amplifier, a speaker having a complex structure in the form of a pair of voice coil
structure, and its amplitude detection system. It has to be complicated and expensive.
[0006]
In addition, since the voice coil bobbin of the speaker is commonly used for the detection coil, the
vibration system of the speaker is affected, and there is a problem that the design is complicated
and distortion occurs in the low range at high volume. there were.
[0007]
The present invention has been made to solve the above-mentioned problems, and the amplitude
detection system of the speaker is a simple structure to form a feedback system, and the
reproduction band is inexpensive and does not adversely affect the characteristics of the speaker.
The aim is to obtain a regulating device.
[0008]
A reproduction band adjusting device according to the present invention projects a light beam to
a light reflecting portion and a light non-reflecting portion provided on a bobbin of a voice coil of
a speaker, and reflects the light beam from the light beam. A high-pass filter circuit is connected
to the light amplitude detector that detects the large amplitude of the speaker by receiving a
change in the speaker, and a high-pass filter circuit to the amplifier connected to the speaker for
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the large amplitude, and a switching unit that bypasses the high-pass filter circuit for the small
amplitude. It is
[0009]
In the reproduction band adjusting device according to the present invention, when an excessive
low frequency signal is input to the speaker, the vibration of the speaker becomes large in
amplitude, and this large amplitude is detected contactlessly by the light amplitude detector and
detected. The signal is transmitted to the switching means, and the switching means inserts a
high pass filter circuit.
By inserting the high pass filter circuit, the low frequency band of the acoustic signal input to the
speaker is cut, so the speaker is suppressed in large amplitude and distortion is reduced.
[0010]
An embodiment of the present invention will be described hereinbelow with reference to the
drawings.
In FIG. 1, 10 is a high pass filter circuit (hereinafter referred to as HPF circuit), 11 is a switching
circuit switched to the A terminal side bypassing the HPF circuit 10 or the B terminal side
connected to the output terminal of the HPF circuit 10; An existing amplifier 12 amplifies the
acoustic signal from the switching circuit 11, and a speaker 13 converts the acoustic signal from
the amplifier 12 into sound.
[0011]
14 is a light amplitude detector for detecting vibration amplitude of a predetermined width of the
speaker 13 with light, 15 is a detection sensitivity adjuster for adjusting detection sensitivity of
the light amplitude detector 14, and 16 is a detection signal from the light amplitude detector 14
It is a control circuit that outputs a control signal for switching the switching circuit 11
depending on whether or not it has been received.
[0012]
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FIG. 2 is a simplified cross-sectional view of the speaker 13 and the light amplitude detector 14.
The speaker 13 is disposed around the light non-reflecting bobbin 13a of the voice coil, the coil
13b wound around one end of the bobbin 13a, the cone 13c attached to the other end of the
bobbin 13a, and the coil 13b It is a well-known thing comprised from the permanent magnet 13d
etc. which comprise these.
[0013]
A pair of light reflecting portions 14a is provided on the outer surface of the middle portion of
the bobbin 13a of the voice coil of the speaker 13 at a predetermined interval in the axial
direction.
Then, at the neutral position of the speaker 13, the light emitting element and the light receiving
element for receiving the reflected light of the projected light and converting it into an electric
signal so as to project the light beam to the intermediate position between the light reflecting
portions 14a Is mounted on the frame of the speaker 13.
[0014]
Therefore, the light amplitude detector 14 projects light on the light reflecting portion 14a
provided on the bobbin 13a of the voice coil of the speaker 13 and the light non-reflecting
portion (part of the bobbin 13a) between them, and this reflection By receiving the change of
light, the vibration amplitude of the predetermined width or more of the speaker 13 is detected.
[0015]
Next, the operation will be described with reference to FIGS. 1 and 2.
The acoustic signal amplified by the amplifier 12 is converted into sound by the speaker 13 and
output.
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When the vibration amplitude of the speaker 13 is relatively small within the predetermined
width, the photo reflector 14 b emits light to the bobbin 13 a and does not receive the reflected
light, and therefore does not output a pulse. Therefore, the switching circuit 11 is switched to the
A terminal side under the control of the control circuit 16. In this state, the acoustic signal
bypasses the HPF circuit 10 and is input to the amplifier 12. At this time, since the input signal is
input to the speaker 13 with the characteristic of the amplifier 12, high sound quality can be
maintained.
[0016]
Next, when an excessive low frequency signal is input to the speaker 13 and the speaker 13
vibrates with an amplitude of a predetermined width or more, the bobbin 13a of the speaker 13
largely vibrates in its axial direction, and the photo reflector 14b The light reflecting portion 14a
is intermittently located at the light projection position. As a result, the photo reflector 14b that
has received the intermittent reflected light from the light reflecting portion 14a outputs a pulse.
This pulse is given to the control circuit 16 via the detection sensitivity adjuster 15. Thus, the
control circuit 16 controls the switching circuit 11 to switch to the B terminal side.
[0017]
When the switching circuit 11 is switched to the B terminal side, the acoustic signal is input to
the amplifier 12 via the HPF circuit 10, and the low frequency band is cut by the HPF circuit 10
to pass via the amplifier 12 Since the sound is input to the speaker 13, distortion of the sound of
the speaker 13 due to the excessive vibration amplitude is reduced.
[0018]
FIG. 3 shows the frequency characteristic, 20 shows the frequency characteristic of the amplifier
12, 21 shows the frequency characteristic of the combination of the HPF circuit 10 and the
amplifier 12, and the low frequency is in a cut state.
[0019]
Further, in the above embodiment, the detection sensitivity adjuster 15 can be operated so that
the listener sounds like a favorite sound while actually listening to the reproduced sound.
[0020]
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In the above embodiment, the light reflecting portions are separated by a predetermined
distance, but the light nonreflecting portions between the light reflecting portions in the above
embodiment are formed by reversing the positional relationship between the light reflecting
portions and the light non-reflecting portions. It goes without saying that the same effect as that
of the above embodiment can be obtained in the light reflecting portion.
[0021]
As described above, according to the present invention, when the light amplitude detector detects
a change in the reflection of the projection light to detect the vibration amplitude of a
predetermined width or more of the speaker and detects this, the HPF circuit is activated. Since
insertion is performed to cut the low band, there is no adverse effect on the vibration of the
speaker at the time of amplitude detection, which saves time and effort in design, and the entire
circuit configuration is also simplified and inexpensive. There is.
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