An important standard for characterization of acoustics of inner spaces. A must for acoustic.

1. Characterization of closed spaces,
ISO 3382-3
R.Narasimha Swamy
Senior consultant
narasimhaswamy@yahoo.com

2. Introduction
• RT60 - just a single number and is a classical
measure of acoustics characteristics of the closed
spaces.
• However, RT60 is not sufficient to completely
characterize the enclosed spaces, as it does not
consider several important characteristics like
relative SPL, energy fraction of the early/late
reflections, lateral reflections, background noise
etc.
• These factors are very important measure for
spatial impression of auditoriums, speech
intelligibility in class rooms, offices, multi
purpose halls etc.

3. ISO-3382-3 (1997-E)
• ISO-3382 is a method suggested by ISO
organization for acoustic measurement of
the enclosed spaces.
• All the important characteristics like energy
fraction of the early/late reflections, lateral
reflections, background noise are derived
from the Sabin’s classical sound decay
characteristics.

4. ISO 3382 parameters
Description of
acoustic
parameter
Symbol Definition or expression
Proposed
by
Attributes
Reverberation
RT60
(sec)
Time taken for the sound in a room to
decay to 60 dB below the source level,
after the source is muted.
Sabine
1923
Characterizes the
enclosed space
Early decay
time
EDT
(S)
Early Decay Time is the reverberation
time, measured over the first 10 dB of
the decay.
Jordan,
1975
Provides subjective
evaluation of the
RT
Clarity
C50
Ratio
Early to late arriving sound energy ratio
Reichardt
1975
Acoustic clarity
with reference to
room size
perception
Definition
D50
(%)
The D50 parameter is the early to total
sound energy ratio. It is defined as
Thiele
1953
Speech
intelligibility and
sound definition
Signal to noise
ratio
SNR
(dB)
Lchner e
Burger,
1964
Speech
intelligibility
Rapid speech
transmission
index
RASTI
(ratio)
[S/N media +15]/30
Steeneken
e Houtgast
1980
Speech
intelligibility

5. 5
ISO 3382 Reverberation Time(s)
 Early Decay Time (EDT): extrapolated from 0 to -10 dB
 Reverberation Time T10: extrapolated from -5 to -15 dB
 Reverberation Time T20: extrapolated from -5 to -25 dB
 Reverberation Time T30: extrapolated from -5 to -35 dB

6. Reverberation time T20
Lp
(dB)
Time (s)
45 dB
-5 dB
-25 dB
T20

7. 7
Early – Late energy evaluation
Useful Energy Detrimental Energy

8. Early-Late parameters
 
  

















ms
ms
dττp
dττp
C
80
2
80
0
2
80 lg10
 Clarity Index C80 (symphonic music):
 Clarity Index C50 (speech):
Optimal Value = +/- 1 dB
Optimal Value = +/- 1 dB
 
  

















ms
ms
dττp
dττp
C
80
2
50
0
2
50 lg10

9. Early-Late parameters
 Center Time tS:
 
 






0
2
0
2


dp
dp
ts
 
 
100
dp
dp
D
0
2
ms50
0
2







 Definition Index D:

10. Other acoustical parameters
• Strength: dB31LSPLG w 
 
   
   










dthdh
dthh
t
2
s
2
d
sd
 IACC:
SPL at 10 m
IACC: Inter Aural Cross Correlation

11. Room impulse response and
Schroeder decay function
determined from an
experimentally
measured room impulse
response in two coupled scaled-
down model rooms.
(a) Room impulse response
octave band-pass filtered at
1kHz with peak-to-noise ratio
equal to 53 dB.
(b) Schroeder decay function.

12. Case studies of reverb and anechoic
chamber

13. Impulse response of reverberant room

14. Decay curve of reverberant room

15. Characteristics of reverberant room as per
ISO-4482

16. Impulse response of anechoic chamber

17. Decay curve of anechoic chamber

18. Characteristics of anechoic chamber as per ISO-4482

19. Importance of acoustics in learning

20. Thanks