Room acoustics

Almost everything about the sound field inside a room follows from two quantities: its impulse response, which can be measured, and its sound absorption, which can be designed. The four pages of this section cover the measurement chain built on the first, the prediction chain built on the second, and the rating of the background noise that occupies the room in between.

The measurement chain lives in Room Acoustics: acquiring the impulse response with the deterministic signals of ISO 18233, deriving the ISO 3382 parameters (reverberation time, EDT, clarity, centre time, and the open-plan speech metrics of ISO 3382-3), and, closing the loop, measuring a material’s absorption coefficient in a reverberation room per ISO 354. That absorption coefficient is precisely what the prediction chain needs.

Prediction gets two pages because two traditions coexist. Reverberation-time prediction (Sabine, Eyring, Arau) covers the classical statistical formulae (Sabine, Eyring, Millington-Sette, Fitzroy and Arau-Puchades), including the models that handle a non-uniform absorption distribution. Sound absorption in enclosed spaces (EN 12354-6) covers the normative European version of the same physics: the total equivalent absorption area assembled from surfaces, objects and air, and the reverberation time that follows from it, as a standard a design report can cite.

Room-noise criteria (NC / RC Mark II) answers a different question about the same room: whether its steady background noise (ventilation, distant traffic) is acceptable for its use, rated against the ANSI/ASA S12.2 criterion curves, with the RC Mark II rumble/hiss tag diagnosing why a spectrum fails.

Related pages elsewhere: measuring insulation between rooms continues in Sound insulation, and the speech intelligibility a room affords is quantified by the Speech Transmission Index.

Pages in this section

• Room Acoustics: impulse-response acquisition (ISO 18233), room parameters (ISO 3382-1/2), open-plan metrics (ISO 3382-3) and reverberation-room absorption (ISO 354).
• Image sources and the steady-state room field: the deterministic image-source room impulse response (Kuttruff/Vorländer) and the statistical steady-state level with the room constant, critical distance and Schroeder frequency (Bies).
• Room-noise criteria (NC / RC Mark II): the ANSI/ASA S12.2-2019 NC tangency and RC Mark II ratings.
• Reverberation-time prediction (Sabine, Eyring, Arau): the five statistical models with the air-absorption term.
• Sound absorption in enclosed spaces (EN 12354-6): the normative equivalent-absorption-area and reverberation-time prediction.