Stereophonic sound reproduction apparatus using a plurality of l

Electrical audio signal processing systems and devices – Binaural and stereophonic – Hearing aid

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381182, 381 28, H04R 500

Patent

active

057177660

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BRIEF SUMMARY
DESCRIPTION

The present invention relates to sound reproduction apparatus using multiple amplifiers.
The technical field of the invention is the field of manufacturing high fidelity equipment for reproducing any sound signal.
One of the main applications of the invention is generating three-dimensional sounds that reconstitute the notion of vertical low and high in the sound message.


BACKGROUND OF THE INVENTION

Numerous sound reproduction apparatuses are known and they always comprise a stage for amplifying a signal coming from some emission source such as a microphone, a magnetic tape, a disk, etc. . . . , together with one or more loudspeaker enclosures containing one or more loudspeakers transforming the amplifier output signals into membrane vibrations, thereby creating variations in sound pressure waves.
In order to enable such reproduction to be as true as possible compared with the quality of the original source, and in order to have a sound level that is sufficiently audible throughout an auditorium in which said reproduction is taking place, various different kinds of equipment have been developed:
to reproduce the three-dimensional effect, stereophonic methods are known both for recording and for playing back that serve to provide an impression of sound perspective in contrast to monophonic recording, by using at least two separate loudspeakers, each of which reproduces only a portion of the sound signal; for the same purpose, mention can be made of tetraphonic or quadraphonic techniques that made use of four channels; in all of those techniques, each channel is distinct and separate all the way from the playback emission source to each corresponding group of loudspeakers;
to reproduce the largest possible passband, a plurality of loudspeakers have been combined on each of said output channels within a common acoustic enclosure, each loudspeaker being adapted to an optimum and often-narrow waveband, and the set of speakers being complementary so as to cover the entire audible range, such that in general there can be found at least one low frequency loudspeaker for the base, a high frequency speaker for the treble, and a medium frequency speaker for mid-range. Each enclosure thus receives an overall signal which is reproduced with high efficiency by each of the speakers it contains within the optimum frequency range thereof: however, if it is desired to make modifications to playback at amplifier level by increasing or decreasing the emitted power, then each loudspeaker responds to such a correction in differing manner, so it is necessary simultaneously to correct their frequency ranges relative to one another; it is therefore the practice to act on filter systems which in fact modify the entire signal, thereby giving to rise to distortion and to phase shifts that spoil the original sound quality (Fletcher type equalization curves).
To avoid such phenomena, some manufacturers propose making adjustments at the input of each loudspeaker within a loudspeaker enclosure, but that does not avoid frequency separation filters that disturb reproduction.
Since the soundwaves are emitted from each loudspeaker which is a point source within the surrounding volume, they are subject to three-dimensional dilution within a sphere, i.e. they diminish with the square of distance, so to make it possible to achieve an adequate listening sound level, in addition to the need for a signal amplifier, loudspeakers are also provided with conical horns of regular or exponential shape for better directional effect, the horns surrounding the vibrating membrane so as to concentrate emission power towards the front of the loudspeaker; however there is always a lateral diffusion gradient and sound volume always increases very significantly with distance. Such directivity also limits the listening volume and can give rise to echo phenomena by reflection of the waves on room walls. In addition, when using a microphone, depending on the position of the microphone, there can occur an amplified feedback effect between the loudspe

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Electronic Components And Applications, vol. 5, No. 4, Sep. 1983, Eindhoven NL, pp. 200-206, W.J.W. Kitzen, "Multiple Loudspeaker Array Using Bessel Coefficients".
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