The measurement time in this method consists of:
• The time between markers t
on
and t
off
in which the omnidirectional sound source emits acoustic power and
the SVAN 958A instrument measures the actual sound pressure level.
• The time between markers t
off
and t
trig
in which the omnidirectional sound source is switched off and the
SVAN 958A instrument waits for trigger condition fulfilment.
• The time between markers t
s
and t
trig
registered since the trigger condition fulfilment back till point t
s
to allow
recognising the beginning of the decay region. In the SVAN 958A instruments this time is equal to
Time Step (path: <Menu> / Input / RT60 Results) parameter value multiplied by 50.
• The time between markers t
trig
and t
e
registered since t
trig
forward to record whole decay curve together with
significantly long period of the noise level. This time in SVAN 958A instruments is adjusted by
Recording Time (path: <Menu> / Input / RT60 Results) parameter.
The above graph shows that the proper setting of the Recording Time value is very important. The registration
time has to be long enough to acquire sufficient number of background noise level values. In other case the
decay curve region could not be properly analysed or decay region could not fulfil the dynamic condition
mentioned above. It is recommended to set the Recording Time parameter two times longer than expected
reverberation time.
➢ IMPULSE method
In the Impulse method, Reverberation Time is computed by using the reverse-time integrated impulse
response. This way of measuring sound decay was introduced firstly by M. R. Schroeder in two historical
articles:
o New Method of Measuring Reverberation Time, Journal of Acoust. Soc. Am.1965
o Integrated-Impulse Method Measuring Sound Decay without Using Impulses, Journal of Acoust. Soc. Am.
Vol. 66(2) 1979
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