Svantek SV 973, User Manual

Page: 209 / 212

SVAN 973 User Manual
– Appendixes
209
In case of the impulse method , the sound pressure level values between points t
2
and t
3
are approximated
with the straight line (y = a
· x + b) by the linear regression. The RT 20 value is calculated using the slope
coefficient ‘a’ according to the formula:
RT 20 =
– 60.0 / a
In case of the decay method , the RT 20 value is calculated according to the formula:
RT 20 = 3
· (t
3
– t
2
)
Fig 3. The RT 20 evaluation
➢
RT 30 (reverberation time calculated with 30 dB dynamics):
The RT 30 decay curve region is pointed out by markers t
1
and t
4
(cf. Fig. 4). It is checked whether the selected
decay curve region has proper dynamics to the RT 30 calculation:
L
1
– L
4
> 5 + 30 dB + noise margin
It is recommended by the ISO-3382 standard to set 10 dB value for noise margin.
In case of the impulse method , the sound pressure level values between points t
2
and t
3
are approximated
with the straight line (y = a
· x + b) by the linear regression. The RT 30 value is calculated using the slope
coefficient ‘a’ according to the formula:
RT 30 =
– 60.0 / a
In case of the decay method , the RT 30 value is calculated according the formula
RT
30 = 2·
(t
3
– t
2
)
t [s]
L
[dB]
t
4
t
1
L
1
L
4
5 dB
noise
margin
linear approximation
t
2
t
3
20 dB
L
2
L
3