JPS6053936B2 - Loudspeaker simultaneous call intercom - Google Patents

Description

[Detailed description of the invention] The present invention relates to a loudspeaker type simultaneous call intercom.

In general, most of the speakers used in intercoms are small diameter speakers, and many have a diameter of about 5 to 9.2 mm. Further, the diameter of most microphones is about 1 to 5C7I. And the intercom casing is also 30CTf.
In many cases, it is less than the L angle. The ideal form of intercom can be said to be of the loudspeaker simultaneous call type. Therefore, under the above conditions,
When using a simultaneous call intercom as an amplification type, the acoustic coupling between the speaker and microphone installed in the same housing became more convenient, and the band of the intercom (500Hz~
5 KHz), howling occurs particularly in the range of 1 to 3 KHz, making it impossible to emit sound from a speaker at a volume that is acceptable for practical use and to conduct simultaneous phone calls.

Therefore, it is necessary to reduce the degree of acoustic coupling in this howling band. Therefore, when making a call using loudspeaker,
Usually, an alternate conversation system is adopted, but the alternate conversation system has the disadvantage that operations for transmitting and receiving calls are complicated.

In order to reduce the complexity of such an alternate calling system as much as possible, the use of an automatic alternate calling system using a voice switch is being considered (Takahashi, Mafune, Acoustic Design of Simultaneous Calling Intercom, Acoustic Review, 10, (1976 and Takahashi, Mafune, A Study on the Voice Switch System, Onko Ronshuu, 1011977), this system is also an alternate call system,
And also with audio. Since this method performs alternating switching, it inherently has the following drawbacks.

In other words, in this method, the transmitting and receiving levels are compared, and when the transmitting state is reached, the receiving function is stopped, and when the receiving state is set, the transmitting function is stopped. When switching states, truncation of the endings and beginnings of words can be seen.

Additionally, if this device is installed in a place where there is noise or noise in the surrounding area, the voice switch may operate against the caller's will due to the noise and noise, and the quality of the call may deteriorate significantly. Put it away.

Furthermore, since it is an alternating call system, the simultaneity of calls is inevitably impaired, and the atmosphere of having a face-to-face conversation with the other party cannot be created, and only the content of the conversation between the one person who is speaking loudly is always heard. communication and insufficient communication of will.

On the other hand, there have been reports regarding the diffraction effect of sound waves on disc-shaped diffraction surfaces.

(G.G. Muller, R, BIack & T.E.D.
avisTheDiffractiOnprOduce
dbycyllndricaIandcubicalO
bstaClesandbycircuIarandS
squarePIates, J. A. S. A. ■01.1
0, JuIy1938; FM. ．． WieIler: Di
ffractiOnbyDisksandSquare
Plates, J. A. S. JA. 2O. 1949; Tomita, Nakajima: Diffraction effect on sound receiving surface on obstacle surface - Part 1. “゜On the diffraction coefficient of discs, NHK Technical Research, 2.
1950). The inventors of the present invention conducted intensive research based on general knowledge regarding these diffraction effects in order to resolve the difficulties of the conventional technology using such voice switches.
We have found that howling can be effectively prevented by appropriately utilizing the directivity and diffraction effect of sound waves in amplified intercoms that have a speaker and microphone installed in the same housing.

Therefore, one object of the present invention is to provide a loudspeaker simultaneous call intercom that effectively prevents howling in a high frequency region by utilizing the directivity and diffraction effect of sound waves. One object of the present invention is to prevent acoustic coupling in the low and medium frequency ranges by performing anti-phase addition using multiple microphones in addition to the above-mentioned high frequency range, thereby suppressing howling in a wide band as a whole. It is an object of the present invention to provide a loudspeaker type simultaneous call intercom which substantially prevents communication.

Further, according to the present invention, a loudspeaker simultaneous call intercom employing such howling prevention method can be obtained.

The invention will now be described in detail with reference to preferred embodiments shown in the drawings.

In FIG. 1, a loudspeaker simultaneous call intercom is shown in which a microphone 12 and a speaker 14 are mounted in the same housing 10.

According to a feature of the present invention, the microphone 12 and the speaker 14 are arranged in the same housing with a specific mutual relationship by appropriately utilizing the directivity of sound waves and the diffraction effect.

Specifically, the sound receiving surface 20 of the housing 10 for the sound waves entering the microphone is placed on the housing 10 in the radial direction (indicated by the arrow) of the radiation surface 16 of the housing 10 for the sound waves emitted from the speaker 14. On the other hand, it is arranged at the rear, that is, at a position retracted from the radiation surface 16 in the opposite direction to the radiation direction. Here, as the microphone 12, an electret condenser microphone having a vibrating surface 22 or other acoustic-electrical transducer can be used.

Further, as the speaker 14, a dynamic speaker having a vibrating surface 23 or other electro-acoustic transducer can be employed. These microphones 12 and speakers 14 have slits 24 and 26 in the housing 10, respectively.
It is attached to the sound receiving surface 20 and the sound emitting surface 16, which are constructed by drilling holes in the sound receiving surface 20 and the sound emitting surface 16, respectively. In the embodiment shown in the drawings, the mounting surfaces of the microphone and speaker are substantially at the same positions as the sound receiving surface 20 and the radiation surface 16 of the housing, but in some cases they may be located at the same position as each other. They may be angularly offset or spaced apart and may be attached via tight fittings if necessary. When a plurality of microphones 12 are used, not only speaker A but also speaker B can produce sound, which is suitable for conference calls. The casing was created under the following conditions.

Dimensions of the housing... Effective radius of the baffle surface 18 A dynamic speaker with approximately the same diameter as the effective radius of the radiation surface 16 is attached to the radiation surface 16, and the center and radius of the radiation surface 16 are By mainly changing the angle 01 formed by the line connecting the center of the sound receiving surface 20 of the casing and the normal L2 erected on the radiation surface, the sound waves entering the microphone of 0.5 CrfL reach the microphone at that time. The value 1D1 of the diffraction effect of the sound wave was measured.

The results are shown in Figure 2. Generally, the emission and reception of sound waves are reversible, and the radius R is on the baffle surface with radius ■.

Considering the sound receiving surface, taking the center of the baffle surface as the coordinate origin, and placing the baffle surface within the X, y plane, the sound wave will be z
The average diffraction coefficient 1D1 when considering the sound receiving surface when the sound is incident at an angle α with the axis, the integral value Φ of the velocity potential of each part of the sound receiving surface, and the sum of the velocity potential at the same location when the baffle surface is removed. The value of the diffraction effect, that is, the average diffraction coefficient 1δl is expressed by the following equation. Here V.

=Sin-1? Bow, (Ksinα●SinvO) is a first-order Bessel function of the first kind.

Pe? ．． Is (COsα) the first type spheroid? It is a wave function, and generally Pe pattern (Z)=,Ffn. A■,,P'(z
)=]A:,n+2r'Pnm! It is expanded to 2r(z) and becomes 7.

PeJ(0) represents Waka・Pe÷(z) when z=o.

Re2(0) is a radius function and generally ReW(z)=Pn,m-Pe■(z)-1 (-1)
5Dn,. ．．・? ■Represented by (z).

Is Qe piece (z) the th here? It is a kind of spheroidal wave function, where PP'(z), QI''(z) are Legendre (
Lugiandre).

Also, , where ηo=COsvO.

Note that the above also holds true when the radiation surface is considered. In the same figure, the three curves are KR
Measured values for =1, 3 and 5 are shown.

Here, K is W/C, (W=2πF, C=sonic speed)
R is of course the effective radius of the baffle surface.

As is clear from Figure 2, 01 is 120A~1502
It can be observed that when this happens, the diffraction effect becomes significant and is suitable for preventing howling in a simultaneous call intercom. That is, when 01 is in this angle range, it becomes difficult for the sound waves from the speaker to reach the microphone.

Using this result, if the angle θ2 between the line L1 and the normal L set on the sound receiving surface 20 is set to the same 1001800, preferably 1200 to 1501, it will be difficult for the microphone to receive sound waves from the speaker. It will become.

Furthermore, as is clear from FIG. 2, it can be observed that as K becomes larger, that is, as the frequency becomes higher, the diffraction effect becomes more significant. Therefore, by using the diffraction effect in this way, it is possible to reduce the acoustic coupling between the microphone and the speaker in a high frequency/wavenumber region (for example, 1500 Hz or higher) and to prevent howling.

Furthermore, the effective radius r of the radiation surface 16 and its baffle surface 1
The ratio r/R to the effective radius R of 8 is 0.3≦r/R≦1
It turned out that it had to be.

However, if r/R is larger than 1, it will be difficult or impossible to attach the speaker to the housing, and if it is smaller than 0.3, the volume of the housing will be too large and diffraction effects will occur. This is because it has been proven that the The reason for this is r
This is thought to be because when /R becomes less than 0.3 and becomes 5, it is considered as point-received sound, and therefore, the sound waves no longer go around to the back of the speaker. If the usage condition is relatively fixed, such as in an intercom, and if the microphone and speaker are placed in the same housing, both converters are not far apart from the housing surface and will not be affected by the change in θ1 mentioned above. The influence of the diffraction effect can be obtained almost unchanged.

As a result, the degree of acoustic coupling between the speaker and the microphone, especially in the high range, becomes, for example, a firefly = 15 cm.
=9an speaker? When a microphone with =1α was attached and an experiment was conducted at 01 = 120-, the degree of coupling was reduced by about 10 [B] at frequencies above 1500 Hz.

If the degree of coupling is reduced to this extent, it is possible to sufficiently realize a loudspeaker type simultaneous call intercom. Furthermore, if it is intended to reduce the degree of coupling by about 10 [DB] in a band of 1,500 Hz or more using other methods, quite complex and large-scale technical means will be required. In this regard, the present invention has shown that by appropriately selecting and arranging the diameter ratio of both converters and their baffles, and the angle formed by both, it is possible to achieve this degree of coupling reduction very easily. In the configuration using the diffraction effect described above,
Combining the following technical measures can help prevent howling, especially in the low frequency band. That is, FIG. 3 shows an example in which two microphones are used for the intercom on one side, and a speaker 14 is arranged inside the housing 10, and the sound waves emitted from the speaker are transmitted to the housing 10. A first microphone 12 and a second microphone 12'' are installed on any same phase plane.

The output end of the first microphone 12 is connected to one input end of the summing circuit Σ via a phase shift circuit 7 that shifts the phase of the output voltage by π [Rad]. In addition, the output end of the second microphone 12'' is directly connected to the other input end of the summing circuit Σ.In the intercom configured in this way, if the speaker C now speaks, the voice is received by the first microphone 12 and the second microphone 12''.

Here, the sound waves received by the first microphone 12 and the second microphone 12'' are different in distance from the speaker C and have different directivity. Even if the phases and sound pressure levels are different, and therefore the output voltage of the first microphone 12 is made out of phase in the phase shift circuit τ and added to the output voltage of the second microphone 12'' in the summing circuit Σ, An output voltage S is obtained.On the other hand, the output S from the summing circuit Σ causes the speaker of the intercom (not shown) of the same configuration at the other end to sound, and the sound wave is immediately transmitted to the other end located in the same manner as shown in FIG. The sound is received by the two microphones on the side, but since the two microphones are placed in the same phase plane in the housing of the sound wave emitted from the speaker, the output voltage of one microphone 12 is phase shifted. The phase of the voltage is reversed in the circuit, the levels of both are equalized, and the voltage is added to the output voltage of the other microphone 12'' in the adding circuit, so that they cancel each other out and no output is produced. Therefore, the utterance of the speaker C is not emitted from the speaker 14 of the speaker 14 via the intercom of the other party, and howling is effectively prevented. Next, we will apply the above principle to the fourth
A detailed explanation will be given using formulas with reference to the figures.

In Fig. 4, 12, 12': Microphone PM: Sound pressure emitted by the speaker at the reference position Ps: The radiation surface 16 of the sound wave emitted from the speaker installed at a predetermined position.
Sound pressure Ls: Distance from the radiation surface 16 to the receiving surface 20, 2'' of the sound wave entering the microphone (on the equiphase plane) LM: Distance from the reference position to the intermediate position between the two microphones 12, 12'' Then, from the same figure, we can obtain.

First, the speaker speaks at the reference position, and the sound pressure is 2.
The component Pl vertically incident on the microphones 12, 12''
, P2, add P2 in opposite phase and divide it by (d+LMcOsθ)PM, and let X be the value. Here, A=MaV, B=length 5, and x
If we find the effective value of , we get the r earth PLj morphism IllO/. ;Ya”
Get λku.

From equation (8), unless the speaker speaks at a position of 0=90λ, the difference output Y between the two microphones will appear less than μ.

LM=60cm. ．． d=20C7! FIG. 5 shows the frequency characteristics of the difference output obtained by changing the angle 0.

In addition, in FIG. 5, 20 (Hz) in the case of O=0th
Let the difference output Y be 0 (Db). Therefore, the sound pressure emitted from the speaker 4 is transmitted through the two microphones 12, 12''
Since they are incident with the same phase, by making one of them in opposite phase and adding them together, the difference output becomes 0.

Note that if there is a sensitivity difference between the two microphones 12 and 12'', an adjustment circuit that amplifies or attenuates the output voltage of either one to equalize the output level is placed before the summing circuit. This allows the output difference to be O.

As shown in Fig. 3, sound waves in the low and middle range, for example, 1.5 KHz or less, have longer wavelengths than the dimensions of the microphones 12 and 12'' and are well aligned in phase, so as shown in Figure 3, A plurality of microphones are arranged on the same phase plane in the housing 10 of the sound waves emitted from the speaker (generally at geometrically symmetrical positions with respect to the speaker), and are placed at the same level,
By receiving sounds with the same phase, shifting the phase of one microphone output by 1800 (πRad) compared to the other, and then adding both outputs together, the effect of the feedback sound pressure from the speaker is substantially reduced. are canceled and acoustic coupling is prevented. As is clear from the above examples,
According to the present invention, by utilizing the directivity and diffraction effect of sound waves, it is possible to prevent acoustic coupling particularly in high frequencies.

Furthermore, by performing anti-phase addition using a plurality of microphones, it is possible to prevent acoustic coupling, particularly in the low and mid ranges. Therefore, by using both of these means in combination, it is possible to prevent howling in a wide band as a whole, and a loudspeaker type simultaneous call intercom can be constructed. Furthermore, howling removal in the present invention does not require a special electronic circuit or high-precision adjustment for howling removal, and can be achieved by simply setting the relative positional relationship between the speaker and the microphone, resulting in stable and inexpensive sound amplification. It is possible to provide a simultaneous call intercom.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing one embodiment of the present invention, and FIG. 2 is an explanatory diagram showing an embodiment of the present invention.
A graph showing a curve of diffraction effect and diffraction angle, FIG. 3 is an explanatory diagram showing a configuration for improving low frequency applied to the embodiment shown in FIG. 1 of the present invention, and FIG. FIG. 5 is an explanatory diagram showing the principle of the configuration shown in FIG. 3 is a graph showing the frequency characteristics of the difference output obtained. 10... Same housing, 12, 125... Microphone, 14... Speaker, 16... Radiation surface, 18... Baffle surface, 20, 2'. ... Sound receiving surface, 22, 23 ... Vibration surface, 24, 26 ...
...Slit, L...Line connecting the center of the radiation surface and the center of the sound receiving surface of the housing of the sound wave entering the microphone,...Normal line erected to the radiation surface, L3・・・・・・
・Normal to the sound receiving surface, 1D1... Diffraction effect of sound wave, T... Phase shift circuit, Σ... Addition circuit, A, B, C. ...Speaker~01? θ2・
00 angle.

Claims (1)

[Scope of Claims] 1. In a loudspeaker simultaneous call intercom in which a microphone and a speaker are installed in the same housing, the center of the radiation surface of the housing for the sound waves emitted from the speaker and the housing for the sound waves entering the microphone. The angle θ_1 formed by the line L_1 connecting the center of the sound receiving surface of the sound wave emitted from the speaker and the normal line L_2 made to the radiation surface of the housing of the sound wave emitted from the speaker is 120° to 150°, and the sound wave emitted from the speaker is A line L_1 connecting the center of the radiation surface of the casing for the sound waves entering the microphone and the center of the sound receiving surface of the casing for the sound waves entering the microphone, and A loudspeaker simultaneous call intercom characterized in that the angle θ_2 with respect to the normal L_3 is 120° to 150°. 2. The radius ratio r/R of the effective radius r of the radiation surface in the housing of the sound waves emitted from the speaker and the effective radius R of the baffle surface thereof is 0.3≦r/R≦1.0. A loudspeaker simultaneous call intercom according to claim 1, characterized in that: 3. In a loudspeaker simultaneous call intercom in which a microphone and a speaker are installed in the same housing, the center of the radiation surface of the housing for the sound waves emitted from the speaker and the center of the sound receiving surface of the housing for the sound waves entering the microphone. The angle θ_1 formed by the line L_1 connecting the two and the normal line L_2 made to the radiation surface of the casing of the sound waves emitted from the speaker is 120° to 150°, and the radiation of the sound emitted from the speaker in the casing is 120° to 150°. An angle θ_2 formed by a line L_1 connecting the center of the surface and the center of the sound receiving surface of the casing for the sound waves entering the microphone and a normal L_3 erected to the sound receiving surface of the casing for the sound waves entering the microphone. is set to 120° to 150°, and the microphones include a microphone belonging to a first group and a microphone belonging to a second group installed on the same phase plane in the housing of the sound waves emitted from the speaker. and a phase circuit that reverses the phase of the output voltage of the microphones belonging to the first group; 1. A loudspeaker simultaneous call intercom characterized by comprising a circuit group including an addition circuit in addition to an addition circuit. 4. A patent characterized in that the circuit group includes, in the preceding stage of the summing circuit, an adjustment circuit that equalizes the output levels of the output voltages of the microphones belonging to the first group and the output voltages of the microphones belonging to the second group. Claim 3
Loudspeaker type simultaneous call intercom as described in section.