Typical sound systems for supplying relatively large surroundings, such as, for example, a conference room on the one hand or a concert stage in a hall or even in the open air on the other hand, suffer from the problem that, due to the conventionally small number of loudspeaker channels used, a location-true reproduction of sound sources is ruled out anyway. However, even if a left channel and a right channel are used in addition to a mono-channel, the level problem will always remain. Thus, the rear seats, i.e. the seats far away from the stage, have to be provided with sound to the same extent as the seats close to the stage. If, for example, loudspeakers are only arranged in the front of the audience space or at the sides of the audience space, it will be inherently problematic that persons close to the loudspeaker will perceive the loudspeaker as exaggeratingly loud, so that the persons at the very back will still be able to hear something. Put differently, due to the fact that individual supply loudspeakers are perceived in such a sound scenario as point sources, there will always be persons saying it is too loud, whereas other persons will say it is too soft. The persons for which it is normally always too loud are the persons very close to the point source-type loudspeakers, whereas the persons for whom it is too soft are seated at a great distance from the loudspeakers.
In order to try and avoid these problems at least to a certain degree, one tries to arrange the loudspeakers at a higher position, i.e. above the persons who are seated close to the loudspeakers, so that they at least do not perceive the complete sound, but a considerable amount of the loudspeaker sound spreads above the heads of the audience and thus is not perceived by the audience in the front on the one hand and nevertheless provides the audience further back with a sufficient level on the other hand.
Other ways, in order not to overstrain the persons in the front rows, i.e. close to the loudspeakers, are providing a low level so that, of course, further back in the room there is a danger of everything being too soft again.
Directional perception is even more problematic. A single mono-loudspeaker in a conference room, for example, does not allow directional perception. It will only allow directional perception if the position of the loudspeaker corresponds to the direction. This is inherently due to the fact that there is only one single loudspeaker channel. However, even if there are two stereo channels, one can at most switch between the left and right channels, i.e. perform panning. This may be of advantage when there is only one single source. However, when there are several sources, localization, which is only possible very roughly with two stereo channels anyway, is completely impossible. Even with stereo, there is a directional perception, however, only in the sweet spot. With several sources, this directional experience will become more and more blurred with an increasing number of sources.
In other scenarios, the loudspeakers in medium-size to large auditories of this kind which are supplied with stereo or mono mixtures are arranged above the audience so that they cannot reproduce any directional information about the source anyway.
Although the sound source, i.e. a speaker or a theater actor, is on the stage, it will be perceived as coming from the lateral or centrally arranged loudspeakers. A natural perceptional direction, however, is still dispensed with. People are already satisfied when there is sufficient loudness for the audience at the back and when it is not unbearably loud for the audience at the front.
Certain scenarios operate with so-called “support loudspeakers” which are positioned close to a sound source. Here, one tries to restore natural audio localization. These support loudspeakers are normally driven without delay, whereas the stereo sound is delayed via the supply loudspeakers, so that the support loudspeaker will be perceived first and thus a localization becomes possible according to the law of the first wave front. Support loudspeakers, too, are problematic in that they are perceived as point sources. On the one hand, this has the result that a difference to the actual position of the sound emitter forms and that, additionally, there is the danger that this may again be too loud for the audience at the front, whereas it is too soft for the audience at the back.
On the other hand, support loudspeakers will only allow a real directional perception if the sound source, exemplarily a speaker, is in direct proximity to the support loudspeaker. This would work if a support loudspeaker was installed in the lectern and a speaker was always standing at the lectern, wherein it is impossible in this reproduction space for somebody to stand next to the lectern and speak to the audience.
With a local difference between the support loudspeaker and the sound source, the result for the listener will be an angular error in the directional perception which, in particular for listeners who may not be accustomed to support loudspeakers, but stereo reproduction, results in further uneasiness. One has found out that in particular when the law of the first wave front is used for operation and when a support loudspeaker is used, it is better to deactivate the support loudspeaker when the real sound source, i.e., for example, the speaker, has withdrawn too much from the support loudspeaker. Put differently, this point is related to the problem that the support loudspeaker cannot be moved so that, in order not to produce the uneasiness mentioned above among the audience, the support loudspeaker is deactivated completely when the speaker has withdrawn too much from the support loudspeaker.
As has already been mentioned, in support loudspeakers, conventional loudspeakers are usually used which in turn have the acoustic characteristics of a point source—as do the supply loudspeakers—the result in close proximity to the systems being too high a level which is perceived as being unpleasant.
USPTO Backgrounds
USPTO Backgrounds