JPH0562518B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a public address system used in places with large reverberations and high background noise, such as tunnels, underground malls, and station premises.

Configuration of conventional example and its problems A conventional loudspeaker system will be explained using FIGS. 1 to 5. FIG. 1 is a block diagram of a conventional loudspeaker, in which 1 is a microphone, 2 is a microphone amplifier, 3 is a main amplifier, and 4a to 4d are loudspeakers. In such a conventional system, the loudspeakers 4a to 4d are arranged at speaker intervals so that their axial directions coincide. Since the axes are aligned, the radiation of sound in the direction perpendicular to the axes is relatively small, but when they are played back at the same time, there is a propagation time difference between each loudspeaker, so as shown in Figure 2, At point A in Figure 1, there was a problem in that echoes appeared and the clarity deteriorated.

FIG. 3 shows a second conventional example, 3a to 3
d is a main amplifier with a gain α, and 5a to 5d are delay circuits. The delay circuits 5a to 5d have delay times τa, τb, τc, and τd corresponding to the propagation time difference corresponding to the distance from the loudspeaker 4a to each of the loudspeakers 4b to 4d.
[However, τa<τb<τc<τd] is set. The gains α of the main amplifiers 3a to 3d are all the same. As shown in Figure 4, when this public address system is used, each loudspeaker 4 is placed at position A in Figure 3.
The echo due to the propagation time difference from a to 4d disappears,
Clarity is improved. However, as shown by the polar patterns of the loudspeakers in FIGS. 5A and 5B, the sound radiated backward is -13 dB [500 Hz] compared to on-axis. Therefore, as shown in FIG. 4B, at the position B in FIG. 3, echoes b, c, and d due to the rear radiated sound from the loudspeakers 4b to 4d appeared, which caused the intelligibility to deteriorate. .

OBJECT OF THE INVENTION The present invention solves the above-mentioned conventional drawbacks, and is a public address system that reduces the influence of echoes due to propagation time differences between loudspeakers at the listening position and the rear radiated sound of front loudspeakers, and provides good clarity. The purpose is to provide

Structure of the Invention In order to achieve the above object, the loudspeaker of the present invention includes a plurality of loudspeakers arranged at appropriate intervals, and a loudspeaker from the base loudspeaker to each loudspeaker, starting from the end loudspeaker. A delay circuit arranged for each loudspeaker has a delay time corresponding to the sound propagation time difference, and the output level of each loudspeaker is determined according to the distance attenuation of the sound from the base loudspeaker to each loudspeaker. This configuration includes attenuation means for attenuating the.

According to this configuration, the influence of the sound emitted from the rear surface of the loudspeaker is reduced, and good clarity can be obtained at the listening position.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 6 is a block diagram of a loudspeaker according to an embodiment of the present invention, in which the same components as those shown in FIGS. 1 and 3 are given the same reference numerals. In FIG. 6, 1 is a microphone, 2 is a microphone amplifier, 4a to 4d are loudspeakers, and 5a to 4d are loudspeakers.
5d is a delay circuit with propagation time differences τa to τd, 6a to 6
d is a main amplifier with a gain of αa to αd,
The loudspeakers 4a to 4d are arranged in a straight line at appropriate intervals within the tunnel.

The audio signal received by microphone 1 is amplified by microphone amplifier 2, and the delay time is τa ~ τd (τa
Delay circuits 5a to 5d set to <τb<τc<τd)
The outputs of the respective delay circuits 5a-5d are amplified by main amplifiers 6a-6d and applied to the respective loudspeakers 4a-4d. Here, the gains αa to αd of the main amplifiers 6a to 6d are set so as to correct distance attenuation due to the loudspeaker spacing l. For example, if l=100m, the gain αa
The difference between and αb is about 2 dB, and the gains αa to αd are
It is set to decrease by 2 dB in the order of αa → αb → αc → αd. In this way, between the loudspeakers 4b and 4a in FIG. 6, the person who is located near the loudspeaker 4b will be able to receive more information from αa to αd than if the gains α of the main amplifiers 6a to 6d were all the same. By changing the gain of each loudspeaker 4a, 4
The sounds coming from b, 4c, and 4d are 0dB, -2dB, -
The indirect sound level is reduced to 4 dB and -6 dB, as shown in FIG. 7B, and the clarity is improved. Furthermore, at point A in front of the loudspeaker 4d in FIG. 6, the reproduced sound from the loudspeakers 4a to 4d is as shown in FIG. are reached at the same time, resulting in good clarity. Note that the gain difference between the main amplifiers 6a to 6d is set to be larger as the loudspeaker interval l becomes longer.

In the above embodiments, an example was explained in which the loudspeaker was installed in a tunnel, but the same effect can be obtained even if the loudspeaker is installed in a long and narrow place such as a station platform or an underground mall where the reverberation time is long.

Further, in the above embodiment, the gain of the main amplifier is changed, but the same effect can be obtained by changing the amplification sound level by using loudspeakers with different efficiencies.

Effects of the Invention As explained above, according to the present invention, the delay circuit is used to correct the sound propagation time difference due to the distance between the loudspeakers, and the attenuation means sequentially adjusts the reproduced sound level from the loudspeakers with the shortest delay time τ. Since it is made small, it is possible to reduce the influence of indirect sound caused by rear radiated sound from the front loudspeaker, and to obtain good clarity.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram of a conventional loudspeaker system, Figure 2 is an explanatory diagram of the echo time pattern at point A of the same loudspeaker system, Figure 3 is an explanatory diagram of another conventional loudspeaker system, and Figures 4A, B is an explanatory diagram of the echo time pattern at points A and B of the same loudspeaker, FIGS. 5A and B are explanatory diagrams of the polar pattern of the loudspeaker, and FIG. 6 is a configuration of the loudspeaker according to an embodiment of the present invention. 7A and 7B are explanatory diagrams of echo time patterns at points A and B of the same loudspeaker. 4a to 4d... public address speakers, 5a to 5d...
Delay circuit, 6a to 6d...main amplifier.

Claims (1)

[Claims] 1. A plurality of loudspeakers arranged at appropriate intervals, and a delay time corresponding to the difference in sound propagation time from the base point loudspeaker to each loudspeaker, starting from the endmost loudspeaker. a delay circuit arranged for each loudspeaker; and attenuation means for attenuating the output level of each loudspeaker according to the distance attenuation of sound from the base loudspeaker to each loudspeaker. Device. 2. A patent claim in which the attenuation means consists of a main amplifier arranged for each loudspeaker, and the gain of these main amplifiers is made to vary depending on the attenuation of the sound from the base loudspeaker to each loudspeaker. A public address system according to item 1 within the scope of . 3. The attenuation means consists of each loudspeaker itself;
2. The loudspeaker system according to claim 1, wherein the efficiency of each loudspeaker is varied according to the distance attenuation of sound from the base loudspeaker to each loudspeaker.