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DESCRIPTION JP2010136152

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DESCRIPTION JP2010136152
The present invention provides an acoustic device capable of reducing electromagnetic noise
radiated from the speaker cable to the atmosphere. An amplification unit amplifies an audio
signal. The speaker 11 reproduces the audio signal amplified by the amplifier. The speaker cables
8 h and 8 c transmit the audio signal amplified by the amplifier to the speaker 11. The ground
cable 8g is disposed along the speaker cables 8h and 8c, and absorbs the electromagnetic noise
radiated by the speaker cables 8h and 8c into the atmosphere. The inter-cable capacitance
adjustment capacitors 10h and 10c are disposed between a portion at the same potential as the
speaker cables 8h and 8c and a portion at the same potential as the ground cable 8g, and the
speaker cables 8h and 8c and the ground cable 8g Adjust the value of capacitance generated
between. [Selected figure] Figure 1
Sound equipment
[0001]
The present invention relates to an acoustic device capable of reducing electromagnetic noise
radiated from a speaker cable.
[0002]
In recent years, investigations have been made on the influence of electromagnetic noise emitted
from electronic devices.
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Along with this, standardization regarding the electromagnetic noise radiated from the electronic
device is spreading. Such a standard is generally called an EMC standard. The EMC standards are
defined internationally by the CISPR (International Special Committee on Radio Interference).
Also, in the United States, Federal Communications Commission (FCC) standards and European
Standard (EN) standards in Europe specify that electromagnetic noise radiated from the
electronic device to the atmosphere be suppressed. In addition, Korea, Taiwan, China, Canada,
and other countries are making progress in establishing and maintaining standards.
[0003]
On the other hand, a method of removing noise components mixed in an audio signal in an audio
device has been studied. For example, Japanese Patent Application Laid-Open No. 6-245294
(Patent Document 1) describes that the noise flowing into the speaker cable is released to the
ground by connecting the speaker cable and the ground via a capacitor. Japanese Patent LaidOpen No. 6-245294
[0004]
In an acoustic device such as a class D amplifier which needs to switch a DC signal at high speed,
a signal including a very high frequency component of a wide band flows to the speaker cable.
When a signal including such a very high and wide band frequency component flows into the
speaker cable, electromagnetic noise is radiated from the speaker cable itself to the atmosphere.
Such a very high-bandwidth frequency noise has a problem that it is difficult to remove the noise
by simply connecting the speaker cable and the ground via a capacitor and letting the noise go to
the ground as in the conventional method. there were.
[0005]
The present invention has been made in view of such problems, and it is an object of the present
invention to provide an acoustic device capable of reducing electromagnetic noise radiated from
the speaker cable itself to the atmosphere.
[0006]
In order to solve the problems of the prior art described above, the present invention amplifies
the audio signal, a speaker (11) for reproducing the audio signal amplified by the amplifier, and
the audio signal amplified by the amplifier. A ground cable (8 g) disposed along the speaker cable
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2
(8 h, 8 c) to be transmitted to the speaker (11) and the speaker cable (8 h, 8 c) and absorbing the
electromagnetic noise radiated to the atmosphere by the speaker cable (8 h, 8 c) Between the
speaker cable (8h, 8c) and the ground cable (8g), and the portion between the speaker cable (8h,
8c) and the portion of the same potential as the ground cable (8g) And an inter-cable capacitance
adjustment capacitor (10h, 10c) for adjusting the value of the capacitance generated in the
device. That.
[0007]
According to the acoustic device of the present invention, electromagnetic noise radiated from
the speaker cable to the atmosphere can be reduced.
[0008]
Hereinafter, the acoustic device of the present invention will be described with reference to the
attached drawings.
FIG. 1 is a diagram showing the configuration of the first embodiment of the present invention.
FIG. 2 is a diagram for explaining the operation of the class D amplifier of the first embodiment
of the present invention.
FIG. 3 is a view showing the effect of the first embodiment of the present invention. FIG. 4 is a
view showing the appearance of a second embodiment of the present invention. FIG. 5 is a
diagram showing the configuration of the second embodiment of the present invention.
[0009]
First Embodiment A sound device according to a first embodiment will be described with
reference to FIGS. 1 and 2. The class D amplifier 6 which is an amplification unit includes a PWM
(pulse width modulation) signal generation unit 2, a switching unit 3, an LPF (low pass filter) unit
4, and a bypass capacitor unit 5. An analog audio signal A is input to the PWM signal generator 2
through the audio signal input terminal 1. The PWM signal generator 2 compares, for example, a
predetermined triangular wave TW with the input analog audio signal A. The PWM signal
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generator 2 outputs low when the analog audio signal A is smaller than the predetermined
triangular wave TW, and outputs high when the analog audio signal A is larger than the
predetermined triangular wave TW. Thus, the PWM signal generator 2 generates the PWM signal
SW1.
[0010]
The PWM signal generation unit 2 inputs the PWM signal SW 1 to the switching unit 3. The
switching unit 3 is composed of four switches 31 to 34. The switches 31 to 34 are, for example,
MOSFETs.
[0011]
The switching unit 3 performs predetermined switching based on the input PWM signal SW1.
When the PWM signal SW1 is high, the switches 32 and 33 are turned on and the switches 31
and 34 are turned off. As a result, a voltage of + Vcc is generated at the rectangular wave output
terminal 3h, and a voltage of -Vcc is generated at the rectangular wave output terminal 3c. When
the PWM signal SW1 is low, the switches 31 and 34 are turned on and the switches 32 and 33
are turned off. As a result, a voltage of -Vcc is generated at the rectangular wave output terminal
3h, and a voltage of + Vcc is generated at the rectangular wave output terminal 3c. Thus, the
rectangular wave SW2 is output between the rectangular wave output terminal 3h and the
rectangular wave output terminal 3c.
[0012]
The rectangular wave SW 2 output from the rectangular wave output terminals 3 h and 3 c is
input to the LPF unit 4. The LPF unit 4 filters the input rectangular wave SW 2 into a continuous
audio signal and inputs the audio signal to the bypass capacitor unit 5. The bypass capacitor unit
5 absorbs noise of a relatively high frequency component such as spike noise of an audio signal.
The bypass capacitor unit 5 outputs the voice signal to the plus output terminal 7 h and the
minus output terminal 7 c. The configuration of the class D amplifier is not limited to this, and
various modifications are possible.
[0013]
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The positive output terminal 7h and the positive input terminal 9h of the speaker 11 are
connected by a speaker cable 8h. The negative output terminal 7c and the negative input
terminal 9c of the speaker 11 are connected by a speaker cable 8c. The positive input terminal 9
h is connected to a positive terminal (not shown) of the voice coil 13. The negative input terminal
9 c is connected to the unshown negative terminal of the voice coil 13. By connecting in this
manner, sound corresponding to the sound signal is reproduced from the diaphragm 14
connected to the voice coil 13. Note that, in FIG. 1, the portion of the speaker 11 is conceptually
shown to facilitate understanding.
[0014]
The ground terminal 7g and the speaker frame terminal 9g are connected by a ground cable 8g.
The speaker frame terminal 9g is connected to a speaker frame 12 made of metal (aluminum or
iron). The speaker frame 12 also includes a metal case or the like that covers a speaker drive unit
such as the voice coil 13 or the like. Further, the ground terminal 7g is connected to a housing of
an acoustic device (not shown). By being connected in this manner, the speaker frame 12 and the
casing of the acoustic device which is the ground have the same potential.
[0015]
In addition, three speaker cables 8h, eight speaker cables 8c, and three ground cables 8g are
installed along each other. The speaker cable 8 h, the speaker cable 8 c, and the ground cable 8 g
are wired in parallel or in a straight line or in a curve.
[0016]
In the speaker cables 8h and 8c, a signal including noise of a very high frequency of a wide band
which can not be removed even by the LPF unit 4 and the bypass capacitor unit 5 flows. Due to
the noise of this very high broadband frequency, high frequency electromagnetic noise above
200 MHz is radiated into the atmosphere. The ground cable 8g absorbs electromagnetic noise
radiated to the atmosphere from the speaker cables 8h and 8c, and escapes to the ground which
is a speaker housing.
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[0017]
A stray capacitance, which is a capacitance, is generated between the speaker cable 8 h and the
ground cable 8 g. The inter-cable capacitance adjustment capacitor 10 h is disposed between a
portion of the same potential as the speaker cable 8 h and a portion of the same potential as the
ground cable 8 g.
[0018]
The capacitance generated between the speaker cable 8h and the ground cable 8g is the sum of
the stray capacitance generated between the speaker cable 8h and the ground cable 8g and the
capacitance of the inter-cable capacitance adjustment capacitor 10h. become.
[0019]
The capacitance of the inter-cable capacitance adjustment capacitor 10 h is a value that the
ground cable 8 g most effectively absorbs the electromagnetic noise radiated from the speaker
cable 8 h.
[0020]
Similarly, a stray capacitance, which is a capacitance, is generated between the speaker cable 8c
and the ground cable 8g.
The inter-cable capacitance adjustment capacitor 10c is disposed between a portion of the same
potential as the speaker cable 8c and a portion of the same potential as the ground cable 8g.
[0021]
The capacitance generated between the speaker cable 8c and the ground cable 8g is the sum of
the stray capacitance generated between the speaker cable 8c and the ground cable 8g and the
capacitance of the inter-cable capacitance adjustment capacitor 10c. become.
[0022]
The capacitance of the inter-cable capacitance adjustment capacitor 10c is set to a value that the
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ground cable 8g most effectively absorbs the electromagnetic noise radiated from the speaker
cable 8c.
[0023]
In the present embodiment, the capacitance of the inter-cable capacitance adjustment capacitors
10h and 10c is 100 pF to 220 pF.
It is desirable to adjust the capacitance of the inter-cable capacitance adjustment capacitors 10h
and 10c according to the lengths of the speaker cables 8h and 8c and the ground cable 8g.
[0024]
Next, the effects of the present embodiment will be described using FIG.
The horizontal axis of FIG. 3 (A) and FIG. 3 (B) shows a frequency, and the vertical axis | shaft has
shown the level of the electromagnetic noise radiated | emitted from the acoustic apparatus.
FIG. 3A is a characteristic diagram when the ground cable 8g and the inter-cable capacitance
adjustment capacitors 10h and 10c are not provided. FIG. 3B is a characteristic diagram when
the present embodiment is applied. As for the characteristic 302 of FIG. 3A, it can be confirmed
that the level of the electromagnetic noise is high in a region 301 near 220 MHz surrounded by a
circle. On the other hand, in the characteristic 304 of FIG. 3B, compared to the characteristic
302, reduction of electromagnetic noise can be confirmed in a region 303 near 220 MHz
surrounded by a circle. In the vicinity of 220 MHz, generally, a strict upper limit is provided as
compared with a band of frequencies higher than that.
[0025]
The sound device of the present embodiment may be configured to store all the parts in the same
housing, or may be configured to store the speaker 11 and the circuit unit 15 in separate
housings and to connect them with a cable. It may be configured as follows.
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[0026]
Second Embodiment The configuration of the present embodiment will be described using FIGS.
4 and 5.
The present embodiment is a stereo type acoustic device using two acoustic devices of the first
embodiment.
[0027]
FIG. 4 is an external view of the invention of this embodiment. FIG. 4 shows an integrated
acoustic device 400 in which a left channel acoustic device and a right channel acoustic device
are housed in a housing 401. In such a configuration, the length of the cable often differs
between the left and right channels due to the wiring in the housing 401. Further, 11L and 11R
are speakers, and 14L and 14R are diaphragms.
[0028]
The upper part of FIG. 5 is the left channel acoustic device 50L, and the lower part is the right
channel acoustic device 50R. The acoustic device of the present embodiment is an acoustic
device in which these two acoustic devices are combined. The parts of the speaker 11L and the
speaker 11R are conceptually shown to facilitate understanding.
[0029]
In FIG. 5, 1L and 1R are audio signal input terminals. Reference numerals 6L and 6R denote class
D amplifiers which are amplification units. 7Lh and 7Rh are positive output terminals. 7Lc and
7Rc are negative output terminals. 7Lg and 7Rg are ground terminals. 9Lh and 9Rh are positive
input terminals. 9Lc and 9Rc are negative input terminals. 9Lg and 9Rg are speaker frame
terminals. 11L,11Rはスピーカである。 12L,12Rはスピーカフレームである。
13L,13Rはボイスコイルである。 14L and 14R are diaphragms. The configurations of the
acoustic device 50L and the acoustic device 50R other than the lengths of the ground cables 8Lg
and 8Rg and the speaker cables 8Lh, 8Lc, 8Rh and 8Rc, and the capacitance adjustment
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capacitors between cables 10Lh, 10Lc, 10Rh and 10Rc It is the same as the acoustic device of
one embodiment.
[0030]
The ground cable 8Rg and the speaker cables 8Rh and 8Rc of the right channel acoustic device
50R are longer than the ground cable 8Lg and the speaker cables 8Lh and 8Lc of the left channel
acoustic device 50L. As such, when the lengths of the speaker cable and the ground cable are
different, stray capacitances generated between the speaker cable and the ground cable are also
different.
[0031]
Therefore, in the present embodiment, the capacitance values are changed between the left
channel inter-cable capacitance adjustment capacitors 10Lh and 10Lc and the right channel
inter-cable capacitance adjustment capacitors 10Rh and 10Rc. As described above, by making the
values of the inter-cable capacitance adjustment capacitor different, electromagnetic noise
radiated from the speaker cable to the atmosphere can be more effectively reduced.
[0032]
The sound device according to the present embodiment may be configured to store all of the
parts in the same housing 401, or the speaker 11L, the speaker 11R, and the circuit unit may be
stored in separate housings and connected by a cable. It may be configured to do.
[0033]
The present invention is not limited to the above-described embodiments, and various
modifications can be made without departing from the scope of the present invention.
[0034]
It is a figure showing composition of a 1st embodiment of the present invention.
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It is a figure for demonstrating the operation | movement of the class D amplifier of 1st
Embodiment of this invention.
It is a figure which shows the effect of 1st Embodiment of this invention. It is a perspective view
which shows the external appearance of 2nd Embodiment of this invention. It is a figure which
shows the structure of 2nd Embodiment of this invention.
Explanation of sign
[0035]
6 Class D amplifier 8h, 8c Speaker cable 8g Ground cable 11 Speaker 10h, 10c Capacitance
adjustment capacitor between cables
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