The Direct to Reverberant ratio (D/R) - the ratio of the energy in the first wave front to the reflected sound energy - is absent from most discussions of room acoustics. Yet only the direct sound (DS) provides information about the localization and distance of a sound source. This paper discusses how the perception of DS in a reverberant field depends on the D/R and the time delay between the DS and the reverberant energy. Threshold data for DS perception will be presented, and the implications for listening rooms, hall design, and electronic enhancement will be discussed. We find that both clarity and envelopment depend on DS detection. In listening rooms the direct sound must be at least equal to the total reflected energy for accurate imaging. As the room becomes larger (and the time delay increases) the threshold goes down. Some conclusions: typical listening rooms benefit from directional loudspeakers, small concert halls should not have a shoe-box shape, early reflections need not be lateral, and electroacoustic enhancement of late reverberation may be vital in small halls.
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