Lateral early reflections arriving within 20 ms create perceived spaciousness

Evidence

The presence of high-level diffuse early reflections, which come to the listener predominantly from the side, that is, lateral early reflections. This adds spaciousness and is easier to achieve over the whole audience in a shoebox hall rather than a fan-shaped one. The first early reflections should ideally arrive at the listener within 20 ms of the direct sound. The frequency response of these early reflections should ideally be flat, and this, in conjunction with the need for a high level of lateral reflections, implies that the side walls of a hall should be diffuse reflecting surfaces with minimal absorption. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 2275

Categorization

• XREF: Explains why shoebox concert halls (like Symphony Hall Boston) are prized over fan-shaped ones.