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Reverberation time, also known as the decay time or RT60, is the amount of time it takes for the sound energy in a space to decay by 60 decibels after the source of the sound has stopped. It is an important acoustic characteristic of a space that determines how long a sound will last after it has been produced, and it can have significant effects on the clarity and intelligibility of speech and music in a space.
The RT60 equation is an empirically found formula that establishes the relation between the reverberation time and the absorptive properties of the room. It can be written as:
RT60 - Reverberation time
V – Total volume of the room (in m3)
A – Effective absorbing area of the room (in m2)
Reverberation time is typically measured in seconds and is dependent on the size, shape, and absorbency of a space, as well as the frequency of the sound being produced.The reverberation time measurement is defined in the ISO 3382-1 standard for performance spaces[ISO1], the ISO 3382-2 standard for ordinary rooms[ISO2], and the ASTM E2235 standard[ASTM]. The reverberation time of a space can be measured using a sound level meter or an impulse response measurement system. The measurement is typically taken in the middle of the space, and the sound source is typically a broadband noise or a pulse of pink noise. The sound may be generated through a loudspeaker, and then turned off, which is known as the interrupted method. The reverberation time is defined as the time it takes to decrease the sound pressure level by 60 dB[NTI].
The reverberation time of a space can be adjusted through the use of sound-absorbing materials, such as wall and ceiling panels, curtains, and carpets. This can be useful in spaces where the reverberation time is too long or too short, as it can improve the clarity and intelligibility of speech and music. In addition to its practical applications, reverberation time is also of interest to researchers studying the acoustics of historical buildings and spaces, as it can provide insight into the materials and construction techniques used in the past. It is also used in the design and evaluation of modern performance spaces, such as concert halls and theaters, to ensure that the acoustics are suitable for the intended use.
Typical reverberation times
Large, reverberant spaces such as churches or concert halls tend to have longer reverberation times, while smaller, more absorbent spaces such as offices or classrooms tend to have shorter reverberation times[comaudio].
[ISO1] ISO 3382-1:2009 Acoustics — Measurement of room acoustic parameters — Part 1: Performance spaces
[ISO2] ISO 3382-2:2008 Acoustics — Measurement of room acoustic parameters — Part 2: Reverberation time in ordinary rooms
[ASTM] ASTM E2235-04(2020) Standard Test Method for Determination of Decay Rates for Use in Sound Insulation Test Methods
[NTI] NTi Audio: https://www.nti-audio.com/en/applications/room-building-acoustics/reverberation-time