efterklangstid

Efterklangstid, or reverberation time (RT60) in acoustics, is the time required for sound in a closed room to decay by 60 decibels after the source stops. The value, usually denoted T60, is frequency dependent and varies with room size, materials, geometry, temperature, humidity and occupancy. It is a central parameter in the design and evaluation of room acoustics.

Measurement and estimation: RT60 can be measured from the room impulse response generated by an impulse, a sine-sweep or noise. Analysis across octave bands (for example 125 Hz to 4 kHz) reveals the frequency dependence. When direct measurement is difficult, Sabine’s formula T60 = 0.161 V / A provides an estimate from room volume V and total absorption A (in sabins). For highly absorbing or nonuniform spaces, Eyring’s model may be used for refinement.

Applications and norms: Efterklangstid informs speech intelligibility and musical clarity, guiding treatment in classrooms, concert venues, studios and public areas. Standards such as ISO 3382-1 and ISO 3382-2 describe measurement procedures and reporting of RT60, including frequency-specific values. Typical target ranges vary by use: speech-focused rooms often aim for about 0.6–1.0 s, while concert halls and large spaces may target 1.8–2.2 s.