Spaciousness and envelopment in musical acoustics

Conventional wisdom holds that spaciousness and envelopment are caused by lateral sound energy in rooms, and that it is the early arriving lateral energy which is most responsible. However small rooms often have many early lateral reflections, but by common definition small rooms are not spacious. This paper (briefly) describes a series of experiments into the perception of spaciousness and envelopment. The perceptions are found to be related most commonly to the lateral (diffuse) energy in halls at least 50ms after the ends of notes (the background reverberation) and less often but importantly to the properties of the sound field as the notes are held. Experiments with orchestral music at high reverberant level indicate that it is the very late >300ms reflected energy which is most responsible for spaciousness. A measure for spaciousness Lateral Early Decay Time (LEDT) is suggested, and results of this measure in several halls are given. A good match between the new measure and subjective impressions of the halls is found.