Reverberationstider

Reverberationstider, or reverberation times, is a term used in architectural acoustics to describe how long sound persists in a closed space after the source stops. The most common reference value is RT60, the time required for the sound pressure level to decay by 60 decibels. Reverberationstider depend on room volume, surface absorption, and the distribution of materials, as well as room geometry and diffusion.

Measurement and calculation are based on the decay of the impulse response. An impulse or swept signal is produced, and the resulting decay curve is analyzed to estimate how long it takes for the level to drop by 60 dB (RT60). Sabine’s formula T60 = 0.161 V / A provides a simple estimate, where V is the room volume and A is the total absorption in sabins (A = sum α_i S_i, with α_i the absorption coefficient and S_i the surface area). More complex models (such as Eyring) and measurements using impulse responses or MLS methods are used for spaces with high absorption or non-diffuse fields.

Typical values vary by function: large concert halls often aim for RT60 around 1.8 to 2.2 seconds, classrooms and lecture halls around 0.6 to 1.0 seconds, and recording studios for controlled acoustics often 0.3 to 0.6 seconds. Excessively long reverberationstider can reduce speech intelligibility, while very short times can make a space sound dry and lifeless.

Control of reverberationstider is achieved through materials and geometry. Absorptive surfaces (carpet, porous panels, drapery), diffusers, and, in some spaces, movable or adjustable acoustics help tailor the RT60 to the intended use. Standards such as ISO 3382 describe methods for measuring RT60 and related acoustical quantities.