NTi Audio XL2 Sound Level Meter - Manual (Page 74)

74
Reverberation Time RT60
Reverberation Time RT60
The XL2 measures the energy decay from 63 Hz to
8 kHz using the Schroeder method in 1/1 octave resolution.
The optional Extended Acoustic Pack enables 1/3 octave band
resolution from 50 Hz to 10 kHz. Use either an impulse source
(e.g., a starter pistol) or a gated pink noise as the test signal.
What is Reverberation Time RT60?
Reverberation time RT60 is the time required for the sound
pressure level to decrease by 60 dB after the sound stimulus
signal is stopped. Since ambient noise often defeats the mea-
surement of a 60 dB level decrease in practice, it is difficult or
even impossible to measure a 60 dB decay in many real life
rooms. Thus the applicable standard ISO3382 specifies
The measurement of a 20 dB level decrease multiplied by 3. •
The final 60 dB decay result shall be labeled T20. •
RT60 (T20) = 3 x decay time of 20 dB
In detail the reverberation time RT60 is based on a linear least-
squares regression of the measured decay curve from -5 dB
down to -25 dB according. It is sufficient to create a test level
at least 35 dB above the background noise within each fre-
quency band. Please see the next drawing for details.
If the overall RT60 is short (e.g. < 0.3 seconds) the room
acoustic is referred to as being “dead”; for example, a heavily
furnished room with thick carpets, curtains and upholstered
furniture may have such an acoustic character.
If the overall RT60 is long (say more than 2 seconds) the room
acoustic is referred to as being “live” and echoic; for example,
a large empty room with painted plaster walls and a tiled floor
may have such an acoustic character.
Level [dB]
0 dB
-5 dB
-25 dB
-35 dB
Time
distance to
noise floor
20 dB level range to
obtain the reverbera-
tion time