Above a critical frequency, room acoustics become statistically tractable as diffuse fields.

Evidence

A transition frequency between these regions is called the critical frequency fc (Schroeder, 1987) … Above the critical frequency the acoustic field is said to be diffuse. A diffuse field is composed of a large number of wavefronts travelling in all directions with equal probability, contributing to the high density of reflections and the high density of modes. Thus, a diffuse field can be modelled by statistical means, as the group behaviour of modes in the frequency domain and reflections in the time domain. — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 296

The magnitude response (see Section 3.2.5) describes how each frequency component is emphasized or attenuated (in dB) when transferred from the source to the receiver. The lowest modes are quite separate peaks, but at higher frequencies the modes start to overlap and fuse. A transition frequency between these regions is called the critical frequency fc (Schroeder, 1987), defined as … Above the critical frequency the acoustic field is said to be diffuse. A diffuse field is composed of a large number of wavefronts travelling in all directions with equal probability, contributing to the high density of reflections and the high density of modes. Thus, a diffuse field can be modelled by statistical means, as the group behaviour of modes in the frequency domain and reflections in the time domain. — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 295

Categorization

• DEFINE: Defines critical frequency and diffuse field, and explains why diffuse fields allow statistical rather than exact modelling.
• QUESTION: Critical frequency depends on room volume and reverberation time — worth chasing the exact K-range formula and its engineering limits for room acoustics simulation.
• corroborated: 2 independent passages support this claim — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 296; Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 295