---
title: "Room acoustics"
description: "The sound field inside a single room: impulse-response measurement and the ISO 3382 parameters, the ANSI S12.2 room-noise ratings, and reverberation-time prediction by the classical formulae and the EN 12354-6 normative model."
---

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](/phonometry/guides/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)](/phonometry/guides/reverberation-prediction/)
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)](/phonometry/guides/enclosed-space-absorption/)
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)](/phonometry/guides/room-noise/)
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](/phonometry/guides/sections/sound-insulation/), and the
speech intelligibility a room affords is quantified by the
[Speech Transmission Index](/phonometry/guides/speech-transmission/).

## Pages in this section

- [Room Acoustics](/phonometry/guides/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](/phonometry/guides/room-image-sources/):
  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)](/phonometry/guides/room-noise/):
  the ANSI/ASA S12.2-2019 NC tangency and RC Mark II ratings.
- [Reverberation-time prediction (Sabine, Eyring, Arau)](/phonometry/guides/reverberation-prediction/):
  the five statistical models with the air-absorption term.
- [Sound absorption in enclosed spaces (EN 12354-6)](/phonometry/guides/enclosed-space-absorption/):
  the normative equivalent-absorption-area and reverberation-time prediction.
