Sencore SP395 - Reverb Decay Time

SP395 SoundPro Audio Integrator Form7492 Operation Manual
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Reverb Decay Time
The Reverb Decay Time function computes the reverb decay time for a room, referenced to the
standard RT60 time. RT60 is defined as the time that it takes sound to decay by 60dB. The RT60
time may be computed full spectrum (20-20kHz), with no filtering (Flat), with A or C weighting
filters, with any of ten standard octave band filters, or with any of 30 standard 1/3 octave band
filters. An “octave band” is defined as one octave of sound, centered around one of the ISO
standard octave frequency values, such as 1000Hz. Ear protection is recommended when using
this function.
When a steady sound is applied to a room, the sound energy builds until it reaches a constant
level. When the sound source is removed, the sound energy doesn't immediately cease, but
decays over a short period of time. The length of time the sound energy reflects off multiple
surfaces inside a room before it is absorbed by the room's contents is called decay time. The time
needed for the sound level to decay by 60 dB after the sound source is removed is called
reverberation time, or RT60.
Optimum decay time depends largely on the room's size, whether you are listening to speech or
music, and listener preferences. As heard by a listener, decay time, or reverberation, creates
room ambiance - the sense that the performance is taking place in either a large or small space. A
decay time that is too long causes echoes, while a decay time that is too short makes the room
sound "dead" and unnatural. Music requires longer RT60 times for best sound, while speech
requires shorter RT60 time to be intelligible. An average-sized home theater should typically
have an RT60 time between 0.3 and 0.6 seconds.
A room's volume (physical dimensions) and the sound absorption qualities of objects inside the
room (i.e.: carpet, drapery, wall treatment, people etc.) determine its decay time. Make RT60
decay time measurements with all of the furnishings in place and, if possible, with someone
seated in each listening position. If the final acoustical panels aren't available, place temporary
panels at the speaker mirror points to eliminate early reflections.
The SP395 Reverb Decay Time function works by first measuring the room's ambient noise
level, then the sound level with the test pink noise is applied. The difference in levels is the
decay range (at least 26 dB is required for the test to continue). After the decay range dB is
determined, the function outputs an interval of pink noise, followed by silence. As soon as the
pink noise is stopped, the test measures the time needed for the room’s sound level to drop by the
decay range dB amount. This time is displayed as the Decay time reading. The RT60 time is
determined by extrapolating the decay time to 60 dB.