Acoustic foam at first-reflection points reduces high-frequency comb filtering at the mix position

First reflections are sound waves from the speakers that bounce off side walls, ceiling, and desk before reaching the listener. These delayed copies arrive within ~5–30 ms of the direct sound and create comb-filtering at the listening position, coloring the perceived frequency response at the mix sweet spot. Placing absorptive panels at the reflection points (located by a mirror on the wall) reduces this coloration, giving a more accurate picture of the mix tone. Foam is effective here because the reflected high-frequency content is what primarily causes comb-filtering audible to humans.

Examples

Mirror test: sit at the mix position and have an assistant slide a mirror along the side wall until you see a speaker in it—that is a first-reflection point requiring treatment.

Assessment

Describe how first reflections cause comb-filtering at the monitoring position, and explain why targeting first-reflection points is more effective than lining an entire room with foam.