Svantek SV 971A, User Manual

Page: 296 / 305

SV 971A User Manual
– Appendixes
296
The graphical illustration of data registering in this method is presented in Figure 7.
Fig 7. Data recording in the impulse method of the reverberation time evaluation
The measurement time in this method consists of:
•
The time before marker t
trig
in which the SVAN xxx analyser measures the actual sound pressure level
and waits for the very high impulse sound pressure level which will fulfil the trigger condition. The trigger
conditions will be fulfilled only when emitted impulse has maximal sound pressure level higher than L
t
level (cf. Fig. 6). The L
t
level in the SVAN xxx analyser is adjusted by parameter Level ( path: <Menu> /
Measurement / RT60 Settings ).
•
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 xxx instruments this time is equal to
the
Time Step ( path: <Menu> / Measurement / RT60 Settings ) 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 xxx instruments is adjusted by
Recording Time ( path: <Menu> / Measurement / RT60 Settings ) 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.
t [s]
L
[dB]
t
e
L
2
t
trig
10 dB
L
1
registration time
t
s
L
t