Perfect diffusion is an unattainable ideal in real rooms

Evidence

A perfectly diffuse sound field is isotropic: at any point within the sound field sounds may be expected to arrive from all directions with equal probability. It is also homogeneous: it is the same everywhere in the space. True diffusion exists only as an academic ideal. Reverberation chambers used to measure the absorption of acoustical materials are designed to be diffuse and can come close, but as soon as a test sample of absorbing material is introduced into the space, it ceases to be—contributing to variations in sound absorption coefficients measured in different labs. The assumed “random incidence” sound field is corrupted. — Toole, Floyd E, Sound reproduction- the acoustics and…, 1254

Categorization

• DEFINE: Defines diffusion precisely as isotropic plus homogeneous, and notes the practical limit in reverberation chambers.
• XREF: Connects to the measurement-laboratory variation problem in absorption coefficient testing, parallels the reproducibility issues in lab measurement discussed elsewhere in acoustics literature.