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JPH0879873

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DESCRIPTION JPH0879873
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
communication terminal, and more particularly to an audio output using a microphone unit for
feedback together with a headphone unit adapted to be able to perform feedback type noise
cancellation. It is something that can be done.
[0002]
2. Description of the Related Art In general, a headphone (earphone) device is known that can be
worn in the ear canal and used to hear the input voice. Using this headphone device, the speaker
of the wearer can There is something that can be output. This is shown in FIG. Reference numeral
50 denotes an earpiece attached to the ear canal, in which a sound path 51 is formed. A speaker
unit 52 is disposed at one end of the sound path 51, and an audio signal input from the input
terminal 53 is amplified by the amplifier 54 and supplied to the speaker unit 52 to output sound.
This is a normal earphone configuration.
[0003]
In addition to this, a vibration sensor 55 is provided in the earpiece portion 50. The vibration
sensor detects the vibration in the ear canal when the wearer utters, and the output of the
vibration sensor 55 is amplified by the amplifier 56 and output from the output terminal 57 as
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an audio signal emitted by the wearer. Is configured as. With this configuration, the user can
output voice without using a separate microphone simply by wearing the earphone, that is, the
earphone functions as a transmitting / receiving terminal for voice signals.
[0004]
However, in the detection by the vibration sensor, it has not been possible to obtain a satisfactory
degree of intelligibility in actual use as the output sound signal. For example, in the case of a
voice with a small amount of vibration in the head of the speaker, such as a consonant voice, the
output voice signal has become quite unclear.
[0005]
SUMMARY OF THE INVENTION In view of these problems, the present invention uses a
headphone (earphone) to be attached to the ear canal so that clear audio output can be realized,
which is sufficient for practical use. It is an object of the present invention to configure a
communication terminal with high performance.
[0006]
For this reason, the sound emitting surface of the headphone unit is formed on an acoustic tube
which is formed to have substantially the same inner diameter as the ear canal, one end is an
auricle mounting portion, and the other end is a non-reflection end of sound. Attach so as to face
the acoustic tube.
In addition, a microphone unit can be mounted so that the sound collecting surface faces the
acoustic pipe. Then, an audio signal from the microphone unit is fed back to an audio signal input
system from the input means to the headphone unit to form a noise cancellation type feedback
circuit means. Here, output means for outputting an audio signal from the microphone unit is
further provided.
[0007]
Also, the audio signal from the microphone unit is provided with a subtracting means for
subtracting the audio signal from the input means, and the output of the subtracting means is
supplied to the output means for output.
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[0008]
Also, the audio signal from the microphone unit is given a predetermined characteristic through
the equalizer means, and is then supplied to the output means for output.
[0009]
In the non-reflection type headphone device having an acoustic tube, in the case of forming the
noise cancellation type feedback circuit means, a microphone unit for feedback is provided facing
inside the acoustic tube.
The speaker's speech is transmitted through the head and vibrates the tympanic membrane and
the inner wall of the ear canal, whereby the sound wave of the speech is uttered in the attached
acoustic tube.
By extracting this sound wave using a microphone unit for feedback, an output sound signal with
high clarity can be obtained, and can be realized as a communication terminal. Further, in order
to further improve the output sound quality, the sound to be output from the sound collected by
the microphone unit is separated from the input sound signal by the subtraction means, or the
frequency characteristic is adjusted by the equalizer.
[0010]
Embodiments of the present invention will be described below with reference to FIGS. FIG. 1
shows the structure of the communication terminal of the embodiment, and FIG. 2 shows its
appearance. This communication terminal is used by connecting to a communication device (not
shown).
[0011]
In these figures, 1 is a voice input terminal. As seen in FIG. 2, the input terminal 1 is configured
as one terminal of a plug 20 having a three-pole structure, for example. As the input audio signal
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Sin, an audio signal received by a communication device (not shown) to which the plug 20 is
connected is supplied. 2 is an equalizer for adjusting the frequency characteristic of the input
audio signal Sin, 3 is a subtractor, 4 is an equalizer, 5 is an amplifier, and 6 is a speaker unit. The
audio signal Sin is supplied to the speaker unit 6 through the equalizer 2, the subtractor 3, the
equalizer 4 and the amplifier 5 and is output as an audio.
[0012]
Reference numeral 7 shown in FIGS. 1 and 2 denotes a long cylindrical acoustic tube, and the end
7b is an opening. In addition, a sound absorbing material 8 is filled inside. The speaker unit 6 is
attached to the sound tube 7 to constitute a so-called non-reflection type headphone. The
speaker unit 6 is attached to the sound tube 7 with its sound emitting surface 6a facing the
inside of the tube as shown in the drawing. The acoustic tube 7 is formed in a long tubular body
having an inner diameter W substantially the same as the inner diameter W0 of the ear canal A,
and an earpiece 9 is attached to one end 7a thereof. The other end 7 b is an opening as a nonreflection end of sound, and the sound absorbing material 8 is filled between the position near
the speaker unit 6 and the end 7 b.
[0013]
The earpiece 9 attached to the end 7a of the acoustic tube 7 is made of a flexible synthetic resin
or the like so that its tip can be inserted into the inlet portion C of the ear canal A. The inner
diameter of the earpiece 9 is set to W1 which is substantially the same as the inner diameter W
of the acoustic tube 7 and the inner diameter W0 of the ear canal.
[0014]
The sound emitting surface 6a of the speaker unit 6 is made to face the inside of the pipe in a
state substantially flush with the inner peripheral surface of the sound pipe 7. By doing this, the
acoustic impedance characteristic of the sound pipe 7 is obtained. The speaker unit 6 can be
mounted without disturbing the Then, in a state where the tip of the earpiece 9 is inserted into
the entrance portion C of the ear canal A and the acoustic tube 7 is attached, from the eardrum B
in the ear canal A to the end 7b as the non-reflection end between the sounds is substantially
constant. The sound tube 7 has a sound path with a constant acoustic impedance by having an
inner diameter of and being continuous.
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[0015]
With this configuration, the sound output from the speaker unit 6 is transmitted as a plane wave
to both sides (the end 7a and the end 7b) in the acoustic tube 7. Among them, the sound wave
that reaches the eardrum B and is reflected again returns to the acoustic tube 7 side, but since
the impedance matching is taken in the acoustic tube 7, the sound wave ends in the acoustic tube
7 without being reflected by the others. It is transmitted from the part 7a side to the end 7b side.
Then, it is gradually attenuated until reaching the end 7b, and becomes almost silent at the end
7b. With such an acoustic tube 7 and the speaker unit 6, the headphone itself is prevented from
generating a reflected sound. And in this non-reflection type headphone, flat characteristics can
be obtained in a wide frequency band.
[0016]
Reference numeral 10 denotes a microphone unit mounted toward the inner surface of the
acoustic tube 7. Of course, this microphone unit 10 is also mounted in the same manner as the
speaker unit 6 so as not to disturb the acoustic impedance characteristic of the acoustic tube 7.
The output of the microphone unit 10 is supplied to the subtractor 3 and becomes a subtraction
signal with respect to the input signal Sin.
[0017]
That is, the output of the microphone unit 10 is fed back to the signal input system to constitute
a feedback type noise cancellation circuit. In such a feedback noise cancellation type headphone,
the noise cancellation operation principle is based on the feedback theory by Board's theorem.
That is, the attenuation of the noise speech and the cancellation bandwidth are characterized by
the open loop characteristic.
[0018]
Considering the extraneous noise Pin, the sound pressure P0 reaching the tympanic membrane B
becomes PO ≒ (1 / loop gain) × Pin due to the nature of the feedback loop, that is, the noise is
reduced by the loop gain to the tympanic membrane B Reach.
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[0019]
FIG. 2 shows the active noise attenuation (dotted line) and the frequency characteristic of the
closed loop response (solid line).
The loop response to the input signal Sin is PO = {(E.A.H) / (1 + E.A.H.M)} × Sin ≒ (1 / M) × Sin.
Here, E is the characteristic of the equalizer 4, A is the characteristic of the amplifier 5, H is the
characteristic of the speaker unit 6, and M is the characteristic of the microphone unit 10. That
is, the loop response to the input signal Sin depends on the characteristic M of the microphone
unit 10 for feedback. When the microphone unit 10 is an electret condenser microphone, its
frequency characteristic is flat over a wide band, so that the closed loop characteristic is a
straight characteristic as seen in FIG.
[0020]
The equalizer 2 is for adjusting the fluctuation of the frequency characteristic due to the
influence of the feedback noise cancellation loop to make the output sound a flatter
characteristic.
[0021]
Here, in the present embodiment, the sound obtained by the microphone unit 10 is also used as
an output sound signal.
Therefore, a compensation circuit (equalizer) 11, a subtractor 12, an equalizer 13, and an output
terminal 14 are provided. The output terminal 14 is configured as one terminal of the three-pole
plug 20 as shown in FIG.
[0022]
The voice of the wearer wearing the communication terminal conducts in the head and vibrates
the tympanic membrane B and the wall of the ear canal A, whereby sound pressure due to the
speaking voice is generated in the ear canal A. Here, when the non-reflection type headphone
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having the above-described external auditory canal direct coupling closely coupled sound tube 7
is configured, a sound wave by the speaking voice is generated in the sound tube 7 and the
sound wave is picked up by the microphone unit 10 It will be That is, the audio signal picked up
by the microphone unit 10 is output as the signal Sout from the output terminal 14 through the
subtractor 12 and the equalizer 13 to supply the speech of the wearer to the connected
communication device, It can be sent to the outside.
[0023]
By the way, the transmitted sound Se generated in the ear canal A due to the vibration due to the
speaking voice transmitted in the head has a frequency characteristic as shown in FIG. For this
reason, even if it picks up with the microphone unit 10, when it outputs as it is, it will become a
thing with low intelligibility. In order to increase the clarity of the output audio signal, the abovedescribed noise cancellation feedback loop functions complementarily and is optimized by the
equalizer 13. Further, in order to perform two-way communication well and prevent howling,
etc., sufficient separation must be taken for the input signal Sin and the output signal Sout. That
is, although not only the transmitted sound Se but also the output sound of the speaker unit 6 is
picked up by the microphone unit 10, it is not preferable to use this as the output signal Sout as
it is. A compensation circuit 11 and a subtractor 12 are provided for this purpose.
[0024]
These points will be described below. First, the extraneous noise Pin is effectively attenuated by
the feedback noise cancellation loop as described above. As a result, the substantial S / N in the
ear canal A is improved by the reduction of the noise component, and the clarity of the
transmitted sound Se is also improved.
[0025]
Next, the separation by the compensation circuit 11 and the subtracter 12 is as follows. The
input signal Sin is output as an acoustic signal from the speaker unit 6 through the feedback
noise cancellation loop and reaches the eardrum B. The microphone unit 10 picks up the abovementioned transmission sound Se and the sound output from the speaker unit 6. Here, the closed
loop transfer characteristic of the feedback loop covers the voice band with a sufficiently flat
characteristic as shown in FIG. Therefore, separation can be ensured by subtracting the input
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signal Sin from the output of the microphone unit 10.
[0026]
Considering the characteristic MSe of the audio signal picked up by the microphone unit 10, MSe
= Se · M / (1 + G). なお、Gはイコライザ4、アンプ5、スピーカユニット6、マイクロホンユニ
ット10によるオープンループゲインである。 The sound signal of the characteristic of this MSe
is supplied from the microphone unit 10 to the subtractor 12. This characteristic MSe is
substantially the same as the active noise attenuation characteristic of FIG.
[0027]
A subtractor 12 is provided to separate the input signal Sin component from the voice signal of
this MSe characteristic. The input signal Sin is supplied to the subtractor 12 via the
compensation circuit 11 and is subtracted from the audio signal by the microphone unit 10 in
the subtractor 12. The compensation circuit 11 is an equalizer for making the frequency
characteristic of the input signal Sin substantially the same as that of the characteristic MSe.
[0028]
In other words, the input signal Sin has the same characteristics as the sound signal from the
microphone unit 10, and this is subtracted by the subtracter 12. As a result, the component of
the input signal Sin is good as the output of the subtractor 12. Will be canceled. As the
characteristics of the signal output from the headphone unit 6 and picked up by the microphone
unit 10, for example, the state of the solid line in FIG. 5 can be changed to the state of the broken
line by the operation of the subtractor 12, and good separation of 20 dB or more can get.
[0029]
Further, the output of the subtractor 12 is optimized by the equalizer 13 as the output signal
Sout. The equalizer 13 gives an inverse characteristic to the characteristic of MSe, that is, a
characteristic of (1 + G) / M. Furthermore, in order to correct the characteristic of the transfer
sound Se shown in FIG. As a result, the output of the equalizer 13 has high clarity that is easy to
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hear as an audio signal.
[0030]
As described above, in this embodiment, the transmitting / receiving terminal of the type worn
on the ear can be configured, and the received voice (input signal Sin) can be heard by the
wearer very clearly in the noise canceling loop. Also, the transmission voice (output signal Sout)
according to the speaker's speech can be a speech signal with high clarity. In other words, the
output signal Sout is also resistant to extraneous noise such as wind noise and environmental
sound by the complementary function of the noise cancellation loop, and the clarity can be
further improved by correcting with the equalizer 13 . Furthermore, the separation from the
input signal is good, and howling at the time of communication can be effectively prevented.
There is also an advantage that the propagation noise due to the vibration of the cord is also
attenuated.
[0031]
Although in the embodiment the communication terminal is used to transmit and receive
monaural sound, the communication terminal of the present invention may of course be applied
as a two-channel stereo headphone. In addition, the present invention can be widely implemented
as a transmission / reception unit in various communication devices such as a mobile phone, a
wireless device, and wire communication. And since it is particularly resistant to extraneous
noise, clear calls can be made even in noisy places such as on the street or in a factory. In
addition, since it is possible to make a hand-free call by attaching to only one ear, it is suitable
for, for example, a call during work at a factory or a work site, a call at a cockpit of an aircraft,
and the like.
[0032]
As described above, according to the communication terminal of the present invention, the
microphone unit for noise cancellation feedback is used to pick up and output the speaking voice
transmitted through the head of the wearer. Therefore, there is an effect that a hand-free
communication terminal can be realized. With regard to the received voice (input signal), the
noise cancellation loop can be clearly heard by the wearer, and for the transmitted voice (output
signal) by the speaker's speaking voice, wind noise is also generated by the complementary
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operation of the noise cancellation loop. It has the effect of being strong against external noises
such as noise and environmental noises and becoming clear.
[0033]
Furthermore, the clarity can be further improved by correcting the frequency characteristics of
the output sound by the equalizer means. Further, howling at the time of communication can be
effectively prevented by realizing separation of the input signal and the output voice by the
subtraction means.
[0034]
As a result, clear two-way communication can be performed even at places with large external
noise, and a very convenient communication terminal can be realized for carrying.
[0035]
Brief description of the drawings
[0036]
1 is a block diagram of an embodiment of the communication terminal of the present invention.
[0037]
It is explanatory drawing of the appearance example of the Example of the communication
terminal of the FIG. 2 Example.
[0038]
It is explanatory drawing of the active noise attenuation | damping characteristic of the FIG. 3
Example, and a closed loop characteristic.
[0039]
4 is an explanatory view of the frequency characteristics of the human head transmitted sound.
[0040]
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5 is an explanatory view of separation characteristics of the embodiment of FIG.
[0041]
6 is an explanatory view of a conventional audio output capable headphone device.
[0042]
Explanation of sign
[0043]
DESCRIPTION OF SYMBOLS 1 input terminal 2, 4, 13 Equalizer 3, 12 Subtractor 5 Amplifier 6
Speaker unit 7 Acoustic pipe 8 Sound absorption material 9 Earpiece 10 Microphone unit 11
Compensation circuit 14 Output terminal 20 Plug part
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