Early reflections must stay below roughly 15 dB to avoid blurring a stereo image

Evidence

In order to achieve a reflection-free zone, it is necessary to suppress early reflections, but by how much? Figure 7.24 shows a graph of the average level that an early reflection has to be at in order to disturb the direction of a stereo image. From this, we can see that the level of the reflections must be less than about 15 dB to be subjectively inaudible. Allowing for some reduction due to the inverse square law, this implies that there must be about 10 dB, or α = 0.9, of absorption on the surfaces contributing to the first reflections. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 2294

Categorization

• SHARE: A specific reference-room number (≈15 dB, α=0.9) worth sending to anyone setting up a listening room or doing acoustic treatment.