JPS5856563A - Transmission and reception unit for loudspeaker telephone set - Google Patents

Abstract

PURPOSE:To perform a conference communication of a small scale without the effect of reflected wave and with less sound coupling, by providing a pair or a plurality of pairs of microphones on the upper surface of a speaker box and lowering the position of a speaker. CONSTITUTION:A bottom surface 2 of a speaker box 1 is floated from an installing surface 4, a speaker 5 is provided at the center of the surface 2 of the box 1 and the position is lowered and a pair or a plurality of pairs of microphones 6a and 6b are located at the upper surface of the box 1 so that the directivity is provided at a symmetrical position by taking the directivity to the inside, allowing to almost avoid the interference phenomenon of the reflection waves from the surface 4 and the direct waves and to prevent the disturbance in the transmitted sound of the microphones 6a and 6b and the reception sound, and the directivity can be controlled to either bidirectional or a omnidirectional performance. Through the combination of the microphones 6a and 6b facing the directivity to the inside mutually with a differential amplifier, the sound coupling between the speaker 5 and the microphones 6a and 6b can be decreased.

Description

[Detailed description of the invention] A loudspeaker ML communication system that is bidirectional or omnidirectional to 1%, has excellent acoustic frequency characteristics, and reduces acoustic coupling between the speaker and the microphone to enable small-scale uniform calls. Regarding the receiving unit.

Conventional transmitting/receiving units of this type include, for example, a speaker box provided with a speaker at the top end and one omnidirectional microphone at the bottom end facing away from each other on the same axis line. . However, in this case, so-called acoustic coupling occurs between the speaker installed at the top end and the microphone installed at the bottom end, which serves as a return path for the transmitter/receiver system, resulting in howling or f-phenomenon. Sometimes. To deal with this, a voice switch is sometimes installed to switch between transmitting and receiving, but this can sometimes result in the end or beginning of a sentence being cut off when the state is switched. In order to eliminate problems caused by such acoustic coupling, it is necessary to increase the acoustic distance between the speaker and the microphone, resulting in the disadvantage that the transmitter/receiver unit itself becomes larger.

In addition, in the above conventional example, the sound waves that directly reach the listener's ears from the speaker installed at the top of the speaker box and the sound waves that reach the listener's ears after being reflected from a table or other installation interfere with each other at a certain frequency. They may cancel each other out, creating deep valleys in the speaker's acoustic frequency response.

To explain this with reference to diagram IK1, the path of the direct wave from the speaker 8 directly reaching the listener's ear is defined as SL, and the path length is frl. On the other hand, let SOL be the path of the reflected wave that is reflected at the zero point on the installation surface T and reach the listener's ear, and the length of this path is trz. The above direct wave and reflected wave are emitted from the same sound source 8, and these Ik! Iw! Difference D1 r
When 21 is a frequency corresponding to an odd multiple of 7 of the wavelength λ of the sound wave, the two mosquito waves interfere with each other. That is, =)λ
An interference phenomenon occurs when . r21 21rl-r2+ ' 2
At a frequency of 1r1-r21'', the direct wave and the reflected wave interfere and cancel each other out, creating periodic deep valleys on the acoustic frequency characteristics of the speaker S.
Since the values of height h and distance As the height Z increases, the valley of the first acoustic frequency characteristic, fl--1-1-121 rl r2 l, falls within the voice band of the telephone (300Hz to 34001(z
) may fall. In such a case, there is a drawback that the reception 'ii from the speaker S becomes very difficult to receive. In addition, in the sg1 diagram, the receiver L
1r The mouth of the Ministry of Transmission [k1! The same thing can be said reversibly even if speaker S is replaced with a microphone for transmitting speech.
In such a case, a deep valley will be formed in the acoustic frequency characteristics of the stray speech to the microphone. Such disturbances in acoustic frequency characteristics are caused by the interference phenomenon between the exposed waves and reflected waves, so if the microphone or speaker is positioned low to eliminate the effects of Lyc waves or reflected waves. good.

The present invention was made in response to the above-mentioned circumstances, and it is possible to lower the position of the speaker and attach one or more pairs of microphones to the top surface of the speaker box to eliminate the influence of reflected waves, thereby achieving excellent acoustic frequency characteristics and a speaker box. An object of the present invention is to provide a transmitting/receiving unit for a loudspeaker telephone, which can reduce acoustic coupling between a microphone and a microphone, and can conduct conference calls in a bi-directional or non-directional manner.

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

In FIG. 2, a speaker box 1 is a box-shaped container such as a rectangular prism, hexagonal prism, or cylinder, and serves as a housing for a transmitting/receiving unit according to the present invention, and has legs 3. 3, . . . are attached so that the bottom surface 2 is held floating above the installation surface 4 such as a table.

Inside the speaker box 1, the lower surface 2 is used as a baffle surface, and a speaker 5 is provided at the center of the bottom surface 2, with the lower surface 2 facing downward and facing the installation surface 4. This speaker 5 amplifies and transmits the received sound from the transmitting side. Since the speaker 5 is located at a low position facing the installation plane 4, the received sound reaching the receiver from the speaker 5 is reflected from the installation FIIRKJ4 as a king, as shown by the arrow in FIG. It is. In this case, there is also a circular wave that penetrates the bottom surface 2 of the speaker box 1 and reaches the receiver side, but this is slight and because the speaker 5 is installed at a low position, the above-mentioned interference The phenomenon is rare, and there is little disturbance in the acoustic frequency characteristics of the received sound from the speaker 5.

On the dove edge of the upper surface of the speaker box 1, unidirectional microphones 5a and fib are provided in pairs. The microphones $a and 5b are provided at line-symmetrical positions in FIG. 2 and point-symmetrical positions in FIG. 3 with respect to the central axis 7 of the speaker 5, and as shown in FIG. , respective directivity directions (arrows 8a and 8
b) are attached with the two facing inward towards each other. The microphones 6a and 6b pick up the voice from the speaker and send it to the public address telephone system, but because of their unidirectionality, they only pick up the voice in that directional direction. For example, in FIG. 3, the microphone 6a picks up only the voice of the speaker P in front of it, and picks up the voice of only the speaker P behind it. It does not pick up audio from. Similarly, what about microphone 8b? The voice from P is picked up, but the voice from P is not picked up. In this way, the microphone @
As a pair of a and @b, bidirectionality can be exhibited. In addition, as mentioned above, each microphone 6 Todoroki,
6b are arranged at the periphery of the upper surface of the speaker box 1 with their directivity directed inwardly. ! As shown in FIG. 2, the direct wave PB from the speaker P passes above the speaker box 1 and reaches one of the microphones 6a without any obstruction, where it is picked up with sufficient sensitivity. At this time, the direct wave P is transmitted to the other microphone 6b.
Since M comes from the opposite direction, it is hardly picked up by the wrinkle microphone 6b. On the other hand, the reflected wave of the voice from the speaker P that is once reflected by the skin 0 on the installation surface 4 and goes towards the microphone 6a of the speaker box 1 is the @ of the speaker box 1.
The reflected wave POC is reflected again at the point C on the surface and moves in the direction D, and in the end the reflected wave POC does not reach the microphone 6aKFi.

Note that some waves reach the microphone 6a due to diffraction of the reflected waves, but this is very small and can be ignored. As a result, only the direct wave PB of the voice from the speaker P reaches one microphone 6m. For this reason, the aforementioned interference phenomenon hardly occurs in the sound waves reaching the microphone 6a, and disturbances in the acoustic frequency characteristics of the input to the microphone 6a can be reduced. The same can be said about the other microphone 6b.

The output equipment of the above pair of micro-holes/@a, 6b has a fourth
As shown in the figure, a differential amplifier 9 that takes the difference between the electrical outputs
is connected. This differential amplifier 9 is configured such that the sound from the speaker 5 is reflected by the installed [104], and after 7'C, the surroundings of the speaker box 1 are included in 31 ICs, and each of them is installed at the same distance from the speaker 5, and the nine microphones 5a and fib are connected to each other. By taking the differential output of the microphones 5m and 5b due to the sound waves toa and tab input from the directional direction and canceling the electrical output of both, the systembee force 5 and the microphone @a,
5b. The output e of the differential amplifier 9 is input to a loudspeaker telephone device. Additionally, the microphones 5a and ib have their directivity directed inwardly toward each other.As shown in FIG. input from the counter-directional direction, and the acoustic distance for input from the directional direction to microphones @a and @btlc is large. Compared to the case, according to the present invention, the acoustic coupling between the speaker 5 and the microphone 6b can be reduced.

Note that, as is clear from FIG.
Since the sensitivity in directions intersecting the P P' direction becomes dull,
If necessary, as shown in FIG. 5, another pair of microphones 6C, 6d and their differential amplifiers may be additionally provided in a direction perpendicular to the PP direction. In this way, almost no directivity can be achieved around the four circumferences. In addition, in FIGS. 3 and 5, 1 microphone is shown as being installed in the center of each side of the speaker box 1, but the present invention has an 11M glass installed on the diagonal of the speaker box 1. It's okay. Note that, as described above, the speaker box 1#i may have a hexagonal columnar shape, a cylindrical shape, or the like.

As described above, in the present invention, the speaker 5 is provided on the bottom surface of the speaker box 1 to lower its position, and one or more pairs of microphones 6a, 6b, . . . are provided on the top surface of the speaker box 1. Since the directivity directions are placed in symmetrical positions with each other facing inward, there is no interference between the direct waves and the reflected waves from the installation surface 4! l! It is possible to almost eliminate the disturbance hf on the acoustic frequency column in the transmitted sound of the micro-hoy 5a, fib, . . . and the received sound of the speaker 5. Also, the directivity directions are within 1111
By combining the microphones 5a, 5b, . . . for 1K and the differential amplifier 9, it is possible to reduce the acoustic coupling between the speaker 5 and the microphones lia, 5b, . Furthermore, by providing one or more pairs of unidirectional microphones 5a, fib, . Due to these effects, the receiving sound is not difficult to hear even during the transmission volume, and there is no feedback, echo, or blocking.
Furthermore, it is possible to make small-scale conference calls between several members without creating a voice blind spot.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the interference phenomenon between direct waves and reflected waves of sound waves, FIG. 2 is a front view showing a transmitting/receiving unit for a loudspeaker telephone according to the present invention, FIG. 3 is a plan view thereof, and FIG. FIG. 5 is an explanatory diagram showing the connection of the differential amplifier, and FIG. 5 is a plan view showing another embodiment. 1...Speaker box 2...Bottom surface 3...Legs 4...Installation side 5...Speaker 6 a, 6 b, 6 C, 6d ------
Microphone T...Central axis Ba, Bb...Directivity direction 9...Differential amplifier Applicant: Fujitsu Co., Ltd. Agent: Patent attorney Hiroshi Matsutoshi, 4th Department... . Transfer to E-115 Figure 1 Figure 2 Figure 3 Figure 51 Figure 4

Claims (1)

[Claims] a speaker box that is held with its bottom surface floating above the installation surface; a speaker that uses the bottom surface of the speaker box as a baffle surface and is provided with a central ISK on the bottom surface facing the installation surface; and one speaker that is mounted on the top surface of the speaker box. a pair or multiple pairs of unidirectional microphones installed at symmetrical positions with respect to the central axis of A transmitting/receiving unit for a public address telephone, comprising a dynamic amplifier.