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between two loudspeakers positioned 60° apart in the horizontal plane. When loudspeakers were placed 90° apart the error in the perceived direction increased significantly (Long, 1993). In most recording studios and mixdown rooms, loudspeakers spacing has standardized to a 60° spacing. Here the stereo image can be maintained and comfortably manipulated with panning.

In the vertical plane the ability of the brain to interpret time delays is much weaker, since our ears are on the sides of our heads. Results of localization tests in the vertical plane

Figure 3.32 Perception of Source Direction with Delay (Madsen, 1970)

Rangs of time delay and intensity over which time/intensity trading takes place, and also the limits of applicability of the precedence

Figure 3.32 Perception of Source Direction with Delay (Madsen, 1970)

Rangs of time delay and intensity over which time/intensity trading takes place, and also the limits of applicability of the precedence

show a greater error and greater tolerance of wide loudspeaker placement. Our inability to precisely locate a vertical source makes realistic sound reinforcement systems possible. A properly designed loudspeaker cluster located above a stage can be used to augment the natural sound of the performers while maintaining the illusion that all the sound is coming from the stage.

The level-delay tradeoff has been carefully studied (Meyer and Schodder, 1952) by asking subjects to indicate the level difference at which the sound seemed to come from midway between a pair of stereo loudspeakers for various delays (Fig. 3.34). Study of this experiment is most helpful in the design of sound systems for it shows how far one can go in raising the loudspeaker level to augment the natural sound. It also shows how the apparent

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