Total sound absorption depends on material area, not just absorptivity.

Evidence

In real rooms, we must also allow for the presence of a variety of different materials, as well as accounting for their variation of absorption as a function of frequency. This is complicated by the fact that there will be different areas of material with different absorption coefficients, and these will have to be combined in a way that accurately reflects their relative contribution. For example, a large area of a material with a low value of absorption coefficient may well have more influence than a small area of material with more absorption. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1889

Categorization

• DEFINE: Clarifies absorption coefficient as an area-weighted quantity rather than a per-material constant.
• XREF: Connects to any practical acoustic treatment decision — why carpets and drapes matter in rooms with hard reflective surfaces.