JP3091834B2 - Remotely located transmitter and hands-free two-way voice terminal using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a remote-installed transmitter capable of clearly picking up only the voice of a caller even if it is installed away from the mouth, and a hands-free type two-way transmitter using the transmitter. The present invention relates to a voice terminal device.

[0002]

2. Description of the Related Art In recent years, the spread of portable telephones has been remarkable. It is common to carry this mobile phone into a car and make a call while traveling. However, since a mobile phone is usually carried in a hand for making a call, it is not preferable for safe driving.

[0003] Therefore, a communication device has been developed in which a call is made using a mobile phone without using hands. In this case, a transmitter is mounted at a position about 30 to 60 cm away from the driver, such as a sun visor of a car, and a speaker is installed below a driver's seat.

When two-way simultaneous communication is performed using such a transmitter and a speaker, since the transmitter is at a considerable distance from the mouth of the talker, a normal handset-type microphone that picks up sound at the mouth is used. The voice level of the caller is about 1 /
Since it is 3 or less, it was easy to pick up ambient noise, and hands-free communication under high noise was difficult. Further, in order to perform a two-way communication, the sound from the speaker must be heard at the same time, and howling and echo occur unless the acoustic coupling between the transmitter and the speaker is reduced.

[0005] For this purpose, the above-mentioned communication device is provided with a circuit for lowering the sensitivity of the transmission circuit during reception and lowering the volume of the reception circuit during transmission. This allows
The occurrence of howling and echo during two-way communication was prevented.

[0006]

However, in the above-mentioned conventional hands-free communication device, when the volume of the radio in the vehicle is high, or when the vehicle speed increases and the ambient noise at high speed increases, or When high-level external noise that is almost the same as or higher than the speech voice level enters the transmitter, such as when ambient noise rises due to driving with the window opened, the circuit incorrectly determines that the telephone is in a transmitting state. As a result, a malfunction such as lowering the volume of the receiving circuit is performed, and there is a problem that voice communication is remarkably obstructed.

In addition, the switching between the transmission sound volume and the reception sound volume is generally adjusted by detecting the average value of the transmission sound level or the reception sound level, and involves a certain switching delay.
During that time, there has been a problem that the voice call may be interrupted.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and an object of the present invention is to make it possible to clearly hear only the voice of a caller even when the speaker is installed away from the mouth, and howling can be achieved even if the sensitivity is increased. It is an object of the present invention to provide a remote-installed transmitter that is free from the risk of occurrence, and a hands-free two-way audio terminal device configured using the transmitter.

[0009]

The present invention employs the following means in order to solve the above-mentioned problems. That is, the remote-installed transmitter according to the present invention has a microphone that becomes bidirectional at the center of a pipe having a predetermined length, and has sound collecting ports formed at least at appropriate positions on both left and right ends of the pipe. Two sound collecting chambers are formed in the pipe, one on each of the left and right sides of the microphone, and the two sound collecting chambers are filled with a sound absorbing material, and the two sound collecting chambers when not filled with the sound absorbing material.
One of with minimum sound resonance frequency of the sound receiving chamber together define a shape and size of the used sound upper-limit frequency above and so as the voice pickup chamber transmitter, that put the speech upper limit frequency above audio frequency band for said use as voice frequency characteristic is monotonic attenuation characteristic is obtained by adjusting the amount of sound absorbing material.

[0010] The shape and size of the sound collecting room are determined so that the lowest sound resonant frequencies of the two sound collecting rooms when the sound absorbing material is not filled are both equal to or higher than the upper limit frequency of the sound used by the transmitter. with sensitivity at the lowest sound resonance frequency of the sound receiving chamber after filling the sound absorbing material to adjust the amount of such sound absorbing material to be less than twice the sensitivity in 1 KHz, further pre
The voice frequency characteristics of the handset are monotonic attenuation characteristics in the high frequency range.
Starting frequency is 2/3 times or more of upper limit frequency of used voice
In addition, the length from the end of the pipe to the center of the microphone is １ ／ or less, or か つ and １ ／ of the wavelength of the upper limit sound frequency of the transmitter. It was done.

Preferably, an ambient noise suppression circuit having an amplification characteristic whose amplification gain increases with an increase in the output level of the microphone is connected to the output terminal of the microphone. A gain controller that amplifies and outputs an output signal of the microphone;
A band amplifier that passes only a signal of a specific frequency band in an output signal of the bidirectional microphone, a peak detector that detects a peak value of a signal that has passed through the band amplifier, and a peak that is output from the peak detector And a hold circuit for holding the value for a predetermined time and controlling the amplification gain of the gain controller according to the held peak value.

Further, the hands-free type two-way voice terminal device according to the present invention is a hands-free type two-way voice terminal device provided with one transmitter and one receiver which can be used without using hands. A remote-installed transmitter according to any one of claims 1 to 4, wherein the receiver is attached to a first fixed part with the receiver facing the ear of the talker, and the transmitter is connected to the talker of the talker. The pipe is attached to a second fixed portion at a predetermined distance from the other end of the pipe so that one end of the pipe faces the caller.

[0013] Further, the receiver and the transmitter are arranged in a vehicle. And the receiver may be mounted on a center pillar, and the transmitter may be mounted on a sun visor, or the receiver may be mounted on one side of a headrest of a seat, and the transmitter may be The headrest may be attached to the other side surface, and the receiver and the transmitter may be attached to a belt-like member detachably mounted on a headrest of a seat, and the receiver and the transmitter may be attached to the left and right sides of the headrest. They may be arranged so as to be divided on both sides.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 4 show one embodiment of a remote installation type microphone according to the present invention. 1 is a diagram showing the structure of the entire transmitter, FIG. 2 is a diagram showing the structure of a bidirectional microphone, FIG. 3 is a diagram showing the structure of a pipe, and FIG. 4 is a diagram showing the structure of packing.

Reference numeral 1 denotes a transmitter, and two pipes 1a, 1
a, and an electret-type bidirectional microphone 1b built in a joint position between the two pipes 1a, 1a
And a sound absorbing material 1c filled in the pipes 1a, 1a.
And nets 1d, 1d constituting sound pickup surfaces attached to both end openings of the pipes 1a, 1a. The two pipes 1a, 1a sandwich a cut ring-shaped packing 1d made of rubber or the like. And are integrally fixed with an adhesive or the like. 1e is an electrode plate 1i of the bidirectional microphone 1b.
Lead wires connected to the positive and negative electrodes 1j, 1k of
The plug 1f is connected to the tip. 2 is I to be described later.
This is a case in which a C-shaped ambient noise suppression circuit 5 is accommodated.

Although the transmitter 1 has been described as being composed of one bidirectional microphone, two unidirectional microphones are integrated back to back, and a difference signal between the two microphones is extracted. It is also possible to do so. In the transmitter thus configured, the maximum direction of sensitivity is substantially the axial direction of the pipe, and the minimum direction of sensitivity is a direction perpendicular to the axial direction of the pipe. Therefore direct the axial direction of the pipe in the direction of the harvested want sound source, when the relative ambient noise source to place the transmitter so as to be perpendicular to the pipe axis, to take out a good transmission signal most SN ratio Can be.

Here, the sensitivity of the present transmitter in the axial direction of the pipe is proportional to the difference between the sound pressure levels of the two sound holes from the sound source, and the sound pressure level is substantially equal to the distance between the sound source and the sound hole. Since it is proportional, the sensitivity increases substantially in proportion to the length of the pipe. Utilizing this fact, the present transmitter can have higher sensitivity than a single bidirectional microphone, and even if installed far away, sufficiently high sensitivity can be obtained for practical use.

FIG. 5 shows the sensitivity characteristics of the transmitter 1 using the pipe 1a. A characteristic curve a is a characteristic when the pipes 1a, 1a having a pipe length = 2.0 cm and a pipe inner diameter = 6.0 mm are used, and a characteristic curve b is a characteristic when only the bidirectional microphone 1b is used. As is apparent from FIG. 5, by incorporating the bidirectional microphone 1b in the pipes 1a, 1a, it is possible to prevent a decrease in sensitivity of the sound to be picked up.
In the case of FIG. 5, by attaching pipes 1a, 1a having a pipe length of 2.0 cm to both sides of the bidirectional microphone 1b, the microphone alone realizes a sound pressure of 3 cm from the mouth and 14 cm from the mouth.

However, the sound pickup room in the pipe of the present transmitter becomes a cavity resonator when the sound absorbing material is not filled, and has a unique sound resonance mode determined by the shape and size of the sound pickup room. The diameter of the bidirectional microphone is usually 6 to 9 mm, and the cross-sectional area of the sound-acquisition room in the pipe axis direction is usually sufficiently short with respect to the sound wavelength to be used. It will be substantially determined by the length of the sound pickup room, that is, the length of the pipe. Therefore, if the length of the pipe 1a is simply increased in order to increase the sensitivity of the transmitter, the following problem occurs.

(1) When the length of the pipe becomes longer, the inherent sound resonance frequency of the sound pickup room becomes lower. When the lowest sound resonance frequency becomes lower than the upper limit frequency of the used sound, the sound absorbing material 1c is selected and the filling amount is reduced. Even if the adjustment is made, the sound frequency characteristics of the transmitter sound sensitivity within the used sound band cannot be flattened, the sound quality deteriorates, and howling tends to occur near the sound resonance frequency.

(2) This transmitter has a canceling effect on ambient noise from a distant place in which the sound pressure levels at the two sound pickup openings are substantially the same and cancels each other, but the ambient noise coming from the axial direction of the pipe , The distance between the two sound holes (almost twice the length of the pipe 1a) is Ld, and the sound speed is V (344 m at 20 ° C.).
/ S), where f is a specific frequency of ambient noise,
A phase difference represented by d occurs between the two sound holes. θd = 360 ° × (f · Ld / V) (degree)

Therefore, as the distance Ld between the sound pickup ports increases, the phase difference increases, and the canceling effect in the axial direction decreases at a position where f is large, that is, at the high frequency side.
Ambient noise suppression effect is reduced. Therefore, in order to realize a transmitter with good sound quality, suppression of howling, and excellent suppression of ambient noise, it is necessary to select an optimal pipe length. The method for determining the optimum pipe length will be described below.

To obtain the optimum pipe length means to realize a sound frequency characteristic whose characteristics are flat up to the upper limit frequency of the voice used as the transmitter and whose sensitivity is monotonously attenuated when the frequency exceeds the upper limit frequency of the voice used. Nothing else. This is
Around use speech upper frequency f _uL, to a high-frequency cut-off frequency f _c
This is equivalent to realizing a monotonically attenuated low-pass filter characteristic.
You.

Let us consider that this low-pass filter characteristic is realized by a first-order Butterworth type which has a monotonic attenuation characteristic of 6 dB / oct and has the highest practicality. The sound frequency is f, the microphone sensitivity is P (f), and the center sound frequency is f
_{If o} (around 1 KHz), the microphone sensitivity at f = f _o is P _o = P (f _o ), and the frequency at which the sensitivity is lower by −3 dB than P _o is the high cutoff frequency f _C , the following equation is established.

(Equation 1)

[0000] reduction half sensitivity f _C, i.e., the P _o -1.
If the frequencies of 5dB sensitivity and f _FL, sensitivity characteristic without knowing f ≦ f little practical sensitivity reduction in _FL is substantially flat and regarded practically f _FL it can be said monotonic attenuation start frequency sensitivity. In equation (a)

(Equation 2) _FFL is obtained as follows. _{f FL = 0.642 · f c ≒} 3 / 2f c formula (b)

[0000] The decrease in sensitivity with the use audio upper limit frequency f _uL is desirable to be within -3dB to practice P _o, the following equation is established. f _uL ≦ f _C ≒ 3 / 2f _FL Equation (c) Therefore, f _FL ≧ 2 / _3fuL Equation (d) This is because the frequency at which the audio frequency characteristic starts a monotone attenuation characteristic in a high frequency region is 2 which is the upper limit of the used audio frequency. / 3 times or more.

For example, in the case of a transmitter for a telephone, the upper limit frequency of the used voice is 3.3 KHz, and in the case of a transmitter for voice recognition combined with a computer or the like, the upper limit frequency of the used voice is about 5.5 KHz. is there. Usually, in the range that we use, the upper limit frequency of the used voice is 2 KHz or more and 10 KHz or less.

As shown in FIG. 6, the sound resonance mode in the case where the shape of the sound collection chamber constituted by the pipe 1a is cylindrical is such that the diaphragm of the microphone is terminated and the tip of the pipe is opened. The open mode of the column is in vibration mode, and the sound pressure is maximum at the end and minimum at the open end.

Here, assuming that the open pipe length (the distance from the pipe tip surface to the diaphragm of the microphone) is L ₀ and the sound velocity is V (344 m / s at 20 ° C.), the sound frequency is V / 4L ₀ , 3.
Resonate at V / 4L ₀ , 5V / 4L ₀ ,..., An odd multiple of V / 4L ₀ . Therefore, the lowest voice resonance frequency is V / 4L _0.

[0027] Then the transmitter is, the distance from the signal source is installed sufficiently distant from the degree of signal source 20 times the pipe length L _p, and the axial direction of the pipe is oriented in the direction of the sound source Let's assume the case.

Here, the distance between the two sound holes (approximately pipe 1
double length) of L _d of a, at the speed of sound in air V (20 ° C. 34
4m / s), when the phase difference for a specific frequency f between the specific frequency of the signal source f, 2 two sound collecting port and _{θd, θ d = 2πf · L} d / V (radian) L d ≒ 2L p ≒ 2L ₀

Assuming that the sound pressures for the frequency f at the two sound inlets are P ₁ and P ₂ , it can be considered that the sound pressure levels are the same and there is only a phase difference at a sufficiently distant place, so that P ₁ = k sin (2πft) ( k is a proportional constant) P ₂ = k sin (2πft + θ _d ) Therefore, the difference P between the sound-collecting ports of the sound pressure level is P = P ₂ −P ₁ = (2 k · sin θ _d / 2) · cos (2π
ft + θ _d / 2)

Therefore, since the transmitter sensitivity Q is proportional to the absolute value of P,

(Equation 3) This expression is

(Equation 4) That is,

(Equation 5) It shows that the sensitivity Q is maximized each time と, which is consistent with the conclusion derived from the above-described resonance theory. When the signal source is in a direction perpendicular to the pipe axis, P ₁ ,
Since there is no phase difference between P _2, P = 0, that is, the sensitivity is theoretically zero.

Assuming that the diaphragm 1 _o of the microphone is located substantially at the center of the microphone, the open tube length L ₀ is substantially equal to the distance L _C between the pipe tip surface and the center of the microphone. Thus, the lowest sound resonance frequency f _{1 is, f 1 = V / 4L 0} ≒ V / 4L C ≧ f u However, f _u: the design conditions be used speech upper limit frequency of the transmitter.

Therefore, L _C ≦ ・ · V / _fu = λ _u / 4 where λ _u = V / _fu (the wavelength of the upper limit frequency of the used voice), and the distance between the tip of the pipe and the center of the microphone is obtained. L
_C needs to be 以下 or less of the wavelength λ _u of the upper limit frequency of the used voice.

The sensitivity of the transmitter thus obtained is
If the length of L _C is shortened, the sensitivity at the time of remote installation is significantly reduced (see FIG. 5), so it is not advisable to reduce L _C too much. Therefore, it is preferable that the lower limit of L _C is also limited. By the way, recently, it has become possible to analyze the voice frequency to estimate words and individuals. In such a case, the frequency range of the transmitter is set to about twice the upper limit frequency _fu of the voice used. If you do, there will be almost no inconvenience in analysis. Therefore, a length corresponding to the frequency of the 2f _u L _C
May be considered as the lower limit value. Therefore, if L _C is in the range of λ _u / 8 ≦ L _C ≦ λ _u / 4, practically most cases can be handled.

By the way, as shown in FIG.
₀ , the length of the pipe is L _p , the length of the sound collection chamber is L _r , the thickness of the microphone is L _M, and assuming that the diaphragm 1 _o of the microphone is located substantially at the center of the microphone, L ₀ ≒ L _C = L _r + L _M / 2 ≒ L _p > L _r (1)

[0035] In the above equation, L if _M / 2 is sufficiently smaller than L _r is, L ₀ ≒ regarded as L _r, vibrating membrane 1 _o position above slightly offset from the microphone center portion formula (1) Suffices to hold. The electret-type bidirectional microphone widely used at present has a diameter of 6 to 9 m.
m, the thickness L _M is as small as 2~6mm, voice pickup Office L _r
Is more than 10 times L _M / 2, the approximation of the above equation (1) is very well established.

FIG. 7 shows theoretical values and actual measurement data of the sound resonance frequency based on the above theory. This FIG. 7 shows that L ₀ = L _c under the assumption of the equation (1) by the measurement circuit as shown in FIG.
The primary sound resonance frequency (f ₁ = V / 4L ₀ ), the secondary sound resonance frequency (f ₂ = 3V / 4L ₀ ), and the third sound resonance frequency (f ₃ = 5V / 4L ₀ ) are measured. is there.

As is apparent from FIG. 7, the measured data of the sound resonance frequency agrees very well with the theoretical values.
It can be seen that all measured data fall within the range of ± 5% of the theoretical value. Further, as is apparent from a comparison between the measured data of the bidirectional microphone and the measured data of the omnidirectional microphone, the sound resonance frequency is irrelevant to the microphone characteristics and is related only to the open tube length L ₀ (≒ L _c ). It is understood that.

[0038] From the results of FIG. 7, the transmitter used for the phone, so use audio upper limit frequency f _u is 3.3 KHz, in order to avoid resonance in this use the audio upper limit frequency, the pipe length L _p It must be 2.6 cm or less. Further, 1 the transmitter to be used for voice recognition, when approximately 7KHz use speech upper limit frequency f _u, in order to avoid resonance in the use audio upper frequency, the pipe length L _p.
It needs to be 2 cm or less.

Next, with reference to FIGS. 9A to 9D, a description will be given of a method for flattening the voice frequency characteristics in the transmitter of the present invention. FIG. 9A shows the sound frequency characteristics of the transmitter 1 when the sound absorbing material 1c is not filled. From this figure, it is understood that the resonance mode affects the sound quality of the transmitter. FIG. 9B shows a sound frequency characteristic of the sound absorbing material 1c. From this figure, it can be seen that the sound frequency characteristics, particularly the characteristics in a high frequency region, can be changed by the filling density of the sound absorbing material.

As the sound absorbing material 1c, for example, a fibrous filter developed for tobacco can be used. By changing the fiber density of this filter,
Controls high frequency attenuation characteristics. As a result of the experiment, the fiber density was 1
Filters from 5,000 denier to 20,000 denier were preferred.

FIG. 9C shows audio frequency characteristics when FIG. 9A and FIG. 9B are combined. This figure is
An audio frequency characteristic when the lowest sound resonance frequency f ₁ is greater than the use sound upper-limit frequency f _u, by selecting the type and loading of the sound absorbing material 1c appropriately, the overall audio frequency response of the transmitter 1 , almost flat up to the vicinity using sound upper-limit frequency f _u, and it can be seen that can achieve an ideal sound frequency characteristic substantially monotonously attenuated by using speech upper limit frequency f _u more.

The conditions for satisfying such characteristic is greater than the minimum sound resonance frequency f ₁ is used sound upper-limit frequency f _u, and the sensitivity in the lowest voice resonance frequency f ₁ after filled with sound absorbing material 1c , Which is less than twice the sensitivity at 1 KHz, which is the central voice frequency of human voice. Varies depending on the intended use, typically, the lowest sound resonance frequency f ₁ is 2KHz or more, in the range of less 10 KHz.

[0043] For reference, in FIG. 9 (D), shows an audio frequency characteristic when the lowest sound resonance frequency f ₁ is smaller than the used sound upper-limit frequency f _u. In this case, when to the vicinity using sound upper-limit frequency f _u to be obtained equivalent transmitter output and the low frequency, it will be the peak occurs due to the resonance in the vicinity of the lowest sound resonance frequency f _1, using voice upper limit frequency f _A flat characteristic cannot be obtained over the entire working frequency range up to _u . Since the gain is high near the peak, howling tends to occur. In addition, it becomes the lowest voice resonance frequency f ₁ nearby emphasized unnatural sound.

The transmitter 1 of the present invention configured as described above is used as follows. That is, the transmitter 1 is placed at least 10 cm away from the talker's mouth with the open end of one pipe 1a facing the talker. With this arrangement, there is a large level difference between the voice of the caller entering through the opening of the pipe 1a facing the mouth of the caller and the voice of the caller entering through the opening of the pipe 1a located on the opposite side. Yes, even if the difference is obtained by the bidirectional microphone 1b, the signal is output from the transmitter 1 as a sound signal of a sufficiently large level.

On the other hand, the surrounding noise also enters the transmitter 1 together with the voice of the caller, but the source of the ambient noise is usually farther than the distance between the transmitter 1 and the talker's mouth. This ambient noise is input from the two pipes 1a, 1a on the left and right sides of the transmitter 1 at substantially the same level. For this reason, the bidirectional microphone 1b
In, the difference is taken and canceled each other, and the ambient noise is output as a signal of an extremely small level. Therefore, the voice of the caller is output from the transmitter 1 as a signal level much higher than the ambient noise, and only the call voice is clearly transmitted to the other party.

FIG. 10 shows an example of a circuit configuration of the ambient noise suppression circuit 5 built in the case 2 in FIG. Even if only the transmitter 1 having the above-mentioned pipe structure is used, the ambient noise can be suppressed and only the voice of the caller can be clearly picked up. The connection prevents howling and allows the voice of the caller to be transmitted more clearly.

In FIG. 10, reference numeral 1 denotes the transmitter, 5
Reference numeral 1 denotes a band amplifier that allows sound in a frequency band of 0.2 to 1 KHz or 0.2 to 2 KHz to pass, 52 denotes a peak hold circuit, and 53 denotes a gain controller that controls an amplification gain by an output from the peak hold circuit 52. is there. The peak hold circuit 52 includes a peak detector 52a for detecting a peak value of a sound passing through the band amplifier 51, and a hold circuit 52b for holding the peak value detected by the peak detector 52a.

As described above, the band width of the band amplifier 51 is 0.2
It is designed to pass sounds in a frequency band of １1 KHz or 0.2 to 2 KHz. The reason is that most human speech is speech, and most of the time and energy of speech is vowels. For example, taking a Japanese vowel as an example, as shown in FIG. 11, it is a synthesized sound of a specific frequency spectrum called first, second, and third formants,
Above all, the first and second formants occupy most of the energy.

The first formant is approximately 0.2-1.
KHz, the second formant is about 0.75 to 2KHz
Are distributed. Therefore, when the pass band is set to 0.2 to 1 KHz, the first formant having the highest energy can be selectively extracted. When the pass band is set to 0.2 to 2 KHz, the first and second formants of the vowel are selected. Can be extracted.

The ambient noise contains a lot of low frequency components (50 to 150 Hz) such as a rotating sound of a car or a train, and many high frequency components (2 KHz or more) such as a fricative noise. By setting the band to 0.1 to 2 KHz or 0.2 to 2 KHz as described above, it is very effective to identify and extract the conversation voice uttered by the caller.

The peak hold circuit 52 detects the peak value of the output of the band amplifier 51 by the peak detector 52a, and holds the peak value by the hold circuit 52b.
Gain controller 5 according to the magnitude of the held peak value
3 is controlled as shown in FIG. 12, and the input / output characteristics as shown in FIG. 13 are realized. As a result, continuous and smooth gain control is realized so that the transmission level of the talker's utterance section and the talker's non-utterance section do not have a sense of incompatibility.

When the ambient noise suppression circuit 5 having the circuit configuration of FIG. 10 is connected to the transmitter 1, the overall sensitivity characteristic is as shown in FIG.
As shown by the dotted line in Fig. 4, the torso of the gourd-shaped sensitivity curve becomes narrower and narrower over a wider range than the case of the transmitter alone shown by the solid line, and howling to the side by that much Margins are improved.
Therefore, even when combined with a receiver such as a mobile phone, the howling margin can be further improved as compared with the case without the ambient noise suppression circuit 5 as long as the direction of the sound directly entering from the receiver is the angle direction of the constriction.

As a specific circuit example of the gain controller 53, as shown in FIG. 15, the result of multiplication of the gain control signal V _C from the peak hold circuit 52 and the output signal V _I from the transmitter 1 is shown. An analog multiplier configured to output the output signal V ₀ is suitable. 15, the output signal V _{0 is, V 0 = K (X 1} -X 2) (Y 1 -Y 2) = K · V I · V
_C = G · V _I where K is given by a proportional constant G = K · V _C (amplification gain).

In the above equation, since V _C is the magnitude of the peak hold value, that is, the input level of the voice, the relationship between the input level and the amplification gain is as shown in FIG.
The relationship between the input level and the output level has characteristics as shown in FIG. Note that an FET multiplier (which utilizes a change in the channel resistance of the FET) or the like can be used instead of the analog multiplier.

The hold time of the peak value of the hold circuit 52b may be determined in consideration of the duration of the vowel occupying most of the linguistic speech. Considering that the lower limit of the spectrum of the first formant of the vowel is approximately 200 Hz, The longest period T _m is considered to be about 5 ms. Accordingly, the hold circuit 52b is to hold a certain time the peak value of the 5ms periodic waveform may be set to the hold time T _h.

As described above, when the gain control circuit 53 is controlled by the output of the hold circuit 52b in which the hold time _Th is set, as shown in FIG. 12, the gain during the conversation is proportional to the volume of the talker's voice. Therefore, the gain does not change suddenly during the conversation and the sound is not interrupted. Further, since the rising response of the entire peak hold circuit 52 including the peak detection note 52a and the hold circuit 52b is very fast, a high gain operation, that is, a sufficient volume can be transmitted from the beginning of the conversation.

[0057] When the attenuation of the peak hold circuit 52 in this embodiment is examined at time T _f from practically almost hold range up may 99% attenuation thought out, and T _f = 13T _h. According to the above-mentioned relational expression, the time _Tf is 1 second or less, which is a sufficiently short decay in practical conversation. Therefore,
When the speech communication is over, the hold circuit 52 holds the peak value in the non-speech interval within a sufficiently short time, so that the ambient noise can be suppressed quickly.

If the hold time in the hold circuit 52b is defined as the time during which the decay rate from the peak value stops within 30%, the hold time is 5 to 65 ms when the peak detector 52a is of the one-way detection type. In the case of the two-way detection type, by setting the hold time to 2.5 to 32.5 ms, it is possible to prevent the transmission from being interrupted unnaturally due to too short a hold time, and to terminate the transmission due to being too long. Nevertheless, it is possible to prevent the ambient noise suppression effect from weakening while the transmission output is still large.

That is, in conclusion, when the hold time is set to 1 to 13 times the time period 5 ms corresponding to the lowest frequency 200 Hz of the first formant of the vowel, which is the largest component of the transmission energy, the transmission becomes smoother. The gain after the end of the transmission can be quickly reduced without any loss, and practically optimal control can be performed. When the peak detector 52a has the bidirectional detection type, the peak detection is performed in a half cycle as compared with the one-way detection type.
1 to 13 times the optimum holding time.

FIGS. 16 to 19 show a telephone 1 according to the present invention.
5 shows another example of the shape. 16 shows a pipe 1a having a spindle shape, FIG. 17 shows an L-shaped pipe 1a, and FIG. 18 shows a sound pickup having a diameter of about 1 to 2 mm on a side surface of the pipe 1a by closing an outer end face thereof. FIG. 19 shows a pipe 1a in which the outer end face is opened and a plurality of small holes 1p having a diameter of about 1 to 2 mm are formed in the outer end side face. The shape of the pipe and the positions of the small holes are not limited to those shown in the figures, but can be freely changed according to the purpose of use, thereby changing the sensitivity characteristics of the transmitter.

FIG. 20 shows an example of a portable telephone (or PHS) constructed using the transmitter 1 of the present invention. In this example, the receiver 21 is arranged on the upper side of the case main body, and the transmitter 1 is embedded in the lower side of the case horizontally. Windshields 22 for preventing wind noise are provided on the left and right sides of the transmitter 1. The ambient noise suppression circuit 5 is built in the case body.

FIG. 21 shows an example of a laptop computer configured using the transmitter 1 of the present invention. In this example, the handset 2 is located at the upper left corner on the keyboard body 23 side.
4 and a liquid crystal display screen 2 provided inside the opening / closing lid.
5, a transmitter 1 is vertically arranged at the upper right corner.
The transmitter 1 is rotatably attached to the opening / closing lid, and is vertically erected as shown in the drawing when used, and is rotated to lie down when the lid is tightened.

FIGS. 22 and 23 show a first example in which the transmitter 1 of the present invention is mounted in a vehicle. In the case of the first example, as shown in FIG. 22, a stopper 1g for attaching the transmitter 1 to a sun visor or the like is provided on the outer peripheral surface of the pipe of the transmitter 1. Transmitter 1, as shown in FIG. 3, this stop 1g, attached as pipe longitudinal transmitter 1 in such sun visor A ₁ of the driver's seat of the vehicle A is directed to the mouth side of the driver Have been. Further, the center pillar A ₂ of the vehicle, the receiver 3 is speaker, the sound output port is mounted so as to face towards the ear of the driver.

FIGS. 24 and 25 show a second example in which the transmitter 1 is mounted in a vehicle. In this second embodiment, as shown in FIG. 24, located on one side of the strip-shaped elastic fabrics 4 attached headrest A ₃ wound of the driver's seat of the vehicle A (passenger side), transmitter 1 is mounted so that the tip of one pipe faces the driver's mouth, and as shown in FIG. 25, the receiver 3 is mounted on the other side (window side) so as to protrude toward the ear of the driver. It is a thing.

[0065] The elastic fabrics 4 described above are those can be mounted from above the headrest A ₃ in a ring shape, and, although that detachably formed with respect to the headrest A _3, Rights may be provided with attachment means such as hook and loop fastener to allow clamping in the end portion in the band-like cloth, it may also incorporate the previously receiver 3 the headrest a ₃ and transmitter 1.

Next, in the examples of FIGS.
The operation when a call is made using a mobile phone will be described. During a call, the sound from the other party is emitted from the receiver 3 toward the driver's ear. However, since the receiver 3 is arranged near the driver's ear, even if the ambient noise is large, the receiver 3 outputs the voice from the receiver 3. Is clearly transmitted to the driver.

On the other hand, the voice uttered by the driver is
, And an output proportional to the difference between the two input audio levels is extracted from the bidirectional microphone 1b. At this time, ambient noise such as engine sound heard inside the vehicle, wind noise from outside the vehicle, and fricative noise generated between the tire and the road also enter the transmitter 1. Since the distance from the microphone 1b is sufficiently large, the ambient noise is reduced by the two pipes 1a and 1 of the transmitter 1.
The input is made at substantially the same level from both ends of a. As a result, the ambient noise cancels each other and is attenuated, and the ambient noise is output as a sufficiently low level signal. Therefore, the driver's voice is output from the transmitter 1 at a level sufficiently higher than the ambient noise, and is transmitted clearly to the other party.

By the way, in the case of the transmitter 1 installed in the vehicle, both the driver's voice and ambient noise are converted into electric signals and output. In the receiver 3, a part of the signal from the transmitter 1 is added to the audio signal transmitted from the other party, and then the sound is emitted as voice. In other words, the driver can talk with confidence by talking while confirming the voice uttered by the receiver with the receiver 3, so that a part of the transmission signal is added to the reception signal.

For this reason, when a call is made under a large ambient noise, even if the user is not talking and only the other party is talking, the ambient noise from the own transmitter is added to the other party's call. It becomes difficult to hear. On the other hand, since the ambient noise from the own transmitter is transmitted to the other party and reproduced by the other receiver, the other party is very uncomfortable and confirms his / her own voice. Difficulties and hinder the conversation.

Therefore, according to the present invention, the ambient noise suppressing circuit 5 shown in FIG. 10 is connected to the transmitter 1 to reduce the amplification gain of the output signal of the transmitter when the caller is not speaking. This prevents ambient noise from being transmitted from the own transmitter 1 at a large level. For this reason, the ambient noise emitted from the own receiver 3 is suppressed, and the ambient noise transmitted to the other party is also suppressed. Therefore, SN
The ratio is improved, the call becomes easier to hear, and howling can be prevented.

[0071]

As described above, in the transmitter according to the first aspect of the present invention, a bidirectional microphone is attached to a center position of a pipe having a predetermined length, and at least appropriate positions at both left and right ends of the pipe. Forms a sound pickup opening, two sound pickup chambers are formed in the pipe, one on each of the left and right sides of the microphone, and the two sound pickup chambers are filled with a sound absorbing material,
The shape and size of the sound collecting room are determined so that the lowest sound resonance frequencies of the two sound collecting rooms when not filled with the sound absorbing material are both equal to or higher than the upper limit sound frequency of the transmitter. Since the amount of sound absorbing material was adjusted so that the voice sound frequency characteristics in the above voice frequency band became monotonic attenuation characteristics, even when talking under high noise, ambient noise was attenuated and the voice of the talker was good. Is transmitted at an appropriate SN ratio.

Further, the transmitter according to the third aspect has a voice frequency.
Use the start frequency at which the characteristic shows a monotonic attenuation characteristic.
2/3 times or more of the maximum frequency
Smooth audio frequency characteristics can be obtained in all frequency bands.
The sound quality becomes even better.

Further, in the transmitter according to the fourth aspect, the length from the end face of the pipe to the center of the microphone may be set to １ ／ or less of the wavelength of the upper limit frequency of the voice used by the transmitter, or 1 /
Since the number is not less than 8 and not more than 1/4, practically, the input sensitivity of the voice uttered from the mouth of the sender can be sufficiently secured, and a clear call can be made.

[0073] Also, 5 SL placing of transmitter claims, since the connecting ambient noise suppression circuit to the output terminal of the microphone, it is possible to prevent the howling suppressing ambient noise, to increase the SN ratio Call quality can be improved.

A hands-free two-way voice terminal device according to claim 7 is a hands-free two-way voice terminal device provided with one transmitter and one receiver that can be used without hands. 5. A remote-installed transmitter according to any one of claims 1 to 4 as a transmitter, wherein the receiver is mounted on a first fixed part with the receiver facing the ear of the talker, and the transmitter is connected to the talker. Since the one end of the pipe is attached to the second fixed portion at a predetermined distance from the mouth so that the front end face of the pipe faces the talker, even when performing two-way simultaneous communication under high noise,
Without having to hold the transmitter and the receiver by hand, it is possible to suppress ambient noise and perform a good call with a good SN ratio.

Further, in the hands-free type two-way voice terminal device according to the eighth aspect , since the receiver and the transmitter are arranged in the cabin of the vehicle, it is necessary to make a call without using a hand in a seated state. However, it is possible to make a call without using a hand, and it is possible to make a good call even under high noise in the traveling vehicle.

According to a ninth aspect of the present invention, in the hands-free type two-way audio terminal device, the receiver is mounted on a center pillar.
Further, since the transmitter is mounted on the sun visor, the receiver and the transmitter do not obstruct the driver, and the operability and the safety are excellent.

According to a tenth aspect of the present invention, the handset is mounted on one side of a headrest of a seat, and the transmitter is mounted on the other side of the headrest. Therefore, the transmitter is closer to the talker's mouth and the receiver is closer to the talker's ear, so that a clearer call is possible. In addition, the receiver and the transmitter do not obstruct the driver, and the operability and the safety are excellent.

Further, in the hands-free type two-way audio terminal device according to the eleventh aspect , the receiver and the transmitter are attached to a belt-like member detachably mounted on a headrest of a seat, and the receiver and the transmitter are connected to each other. Since the headrest is arranged so as to be separated on the left and right sides, the transmitter and the receiver can be easily arranged near the mouth and ears of the caller when necessary, and the handling becomes excellent. In addition, the receiver and the transmitter do not obstruct the driver, and the operability and the safety are excellent.

[Brief description of the drawings]

1A and 1B show the entire structure of a remote installation type transmitter according to the present invention, wherein FIG. 1A is a longitudinal sectional view and FIG. 1B is a right front view.

FIG. 2 shows the structure of a bidirectional microphone.
(A) is a left front view, (B) is a side view, and (C) is a right front view.

FIG. 3 shows a structure of a pipe, in which (A) is a sectional view,
(B) is a side view.

4A and 4B show the structure of the packing, wherein FIG. 4A is a front view and FIG. 4B is a side view.

FIG. 5 is a sensitivity characteristic diagram with respect to a distance between a bidirectional microphone and a sound source.

FIG. 6 is an explanatory diagram of a sound resonance state of a sound collection room in a pipe.

FIG. 7 is a diagram showing measured data of a voice resonance frequency.

FIG. 8 is a diagram showing a circuit for measuring actual measurement data in FIG. 7;

FIG. 9 is a diagram illustrating the principle of a remote installation type transmitter according to the present invention.

FIG. 10 is a block diagram of an ambient noise suppression circuit.

FIG. 11 is a speech frequency characteristic diagram showing a formant of a Japanese vowel.

FIG. 12 is a gain characteristic diagram with respect to an input level of the ambient noise suppression circuit.

FIG. 13 is an input / output characteristic diagram of an ambient noise suppression circuit.

FIG. 14 is a sensitivity characteristic diagram of the remote installation type transmitter of the present invention.

FIG. 15 is a configuration diagram of a gain controller using an analog multiplier.

FIG. 16 is a cross-sectional view showing a second example of the remotely located transmitter of the present invention.

FIG. 17 is a cross-sectional view showing a third example of the remote installation type microphone of the present invention.

FIG. 18 is a cross-sectional view showing a fourth example of the remote installation type microphone of the present invention.

FIG. 19 is a cross-sectional view showing a fifth example of the remotely located transmitter of the present invention.

FIG. 20 is an external perspective view of a mobile phone (or PHS) configured by applying the remote installation type microphone of the present invention.

FIG. 21 is an external perspective view of a laptop computer configured by applying the remote installation type microphone of the present invention.

FIG. 22 is a cross-sectional view of a remotely located transmitter used in the hands-free two-way audio terminal device of the present invention.

FIG. 23 is a side view showing the use state of the remote installation type transmitter and receiver of FIG. 22;

FIG. 24 is a perspective view seen from the transmitter in another use state.

FIG. 25 is a perspective view as viewed from the receiver of the above.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Transmitter 1a Pipe 1b Microphone 1c Sound absorbing material 1d Net 1h Packing 1i Electrode plate 2 Case 3 Handset 4 Band member 5 Ambient noise suppression circuit 51 Band amplifier 52 Peak hold circuit 53 Gain controller

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04M 1/02-1/23 H04M 1/00 H04M 1/24 H04M 1/58-1/62 H04M 1 / 66-1/78

Claims (11)

(57) [Claims] 1. A microphone having bidirectional characteristics is attached to a center position of a pipe having a predetermined length, and sound collecting holes are formed at appropriate positions at least on both right and left ends of the pipe. Two sound-acquisition chambers are formed in the pipe, and the two sound-acquisition chambers are filled with a sound-absorbing material, and the lowest sound resonance frequencies of the two sound-acquisition chambers when the sound-absorbing material is not filled are transmitted together. The shape and size of the sound collection room are determined so as to be equal to or higher than the use sound upper limit frequency of the speaker, and the amount of the sound absorbing material is set so that the sound frequency characteristics in the sound frequency band equal to or higher than the use sound upper limit frequency become monotonic attenuation characteristics. Distant microphone. 2. The remote installation type transmitter according to claim 1, wherein the lowest sound resonance frequencies of the two sound collection rooms when the sound absorbing material is not filled are both equal to or higher than the upper limit sound frequency of the sound transmitter. In addition to determining the shape and size of the sound-absorbing room, the amount of the sound-absorbing material is adjusted so that the sensitivity at the lowest sound resonance frequency of the sound-absorbing room after filling with the sound absorbing material is not more than twice the sensitivity at 1 KHz. A remote installation type microphone that is characterized in that: 3. The remote-installed transmitter according to claim 1, wherein a frequency at which the audio frequency characteristic of the transmitter starts a monotonous attenuation characteristic in a high-frequency region is equal to or more than ／ times the upper limit frequency of the used audio. A remote-located transmitter. 4. The remote-installed transmitter according to claim 1, wherein a length from a tip end face of the pipe to a center position of the microphone is equal to or less than 波長 of a wavelength of an upper limit frequency of a voice used by the transmitter.
Alternatively, a remote-installed transmitter characterized in that the distance is 1/8 or more and 1/4 or less. 5. An ambient noise suppressor circuit according to claim 1, wherein an output terminal of the microphone has an amplification characteristic whose amplification gain increases with an increase in the output level of the microphone. Distant installation type microphone which was connected to. 6. The remote transmitter according to claim 5 , wherein the ambient noise suppressing circuit amplifies and outputs an output signal of the microphone, and a specific one of output signals of the microphone. A band amplifier that passes only a signal in a frequency band, a peak detector that detects a peak value of a signal that has passed through the band amplifier, a peak value output from the peak detector is held for a predetermined time, and the held peak value is held. And a hold circuit that controls an amplification gain of the gain controller according to the following. 7. A hands-free type two-way voice terminal device provided with one transmitter and one receiver that can be used without using hands, wherein the transmitter is used as a transmitter. Using a remote-installed transmitter, the receiver is attached to a first fixed portion facing the caller's ear, and the transmitter is attached to a second fixed portion separated from the talker's mouth by a predetermined distance. A hands-free type two-way audio terminal device, wherein the end of the pipe is mounted so as to face the caller. 8. The hands-free two-way voice terminal device according to claim 7 , wherein said receiver and said transmitter are arranged in a vehicle. 9. The hands-free two-way audio terminal device according to claim 7 , wherein said receiver is mounted on a center pillar, and said transmitter is mounted on a sun visor. Audio terminal device. 10. The hands-free two-way audio terminal device according to claim 7 , wherein the receiver is mounted on one side of a headrest of a seat, and the transmitter is mounted on the other side of the headrest. A hands-free two-way voice terminal device characterized by the above-mentioned. 11. The hands-free type two-way audio terminal device according to claim 7 , wherein the receiver and the transmitter are attached to a belt-like member detachably mounted on a headrest of a seat, and the receiver and the transmitter are provided. Is a hands-free type two-way audio terminal device, which is arranged so as to be located separately on the left and right sides of the headrest.