iso 3382 standards for acoustic measurements
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Characterization of closed spaces, ISO 3382-3
R.Narasimha SwamySenior consultant
narasimhaswamy@yahoo.com
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.
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.
ISO 3382 parametersDescription 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 C50Ratio Early to late arriving sound energy
ratio
Reichardt1975
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
1953Speech intelligibility and sound definition
Signal to noise ratio
SNR (dB)
Lchner e Burger, 1964
Speech intelligibility
Rapid speech transmission
indexRASTI (ratio) [S/N media +15]/30
Steeneken e
Houtgast 1980
Speech intelligibility
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
Reverberation time T20
Lp (dB)
Time (s)
45 dB
-5 dB
-25 dB
T20
7
Early – Late energy evaluationUseful Energy Detrimental Energy
Early-Late parameters
ms
ms
dττp
dττpC
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
dττpC
80
2
50
0
2
50 lg10
Early-Late parameters
Center Time tS:
0
2
0
2
dp
dpts
100
dp
dp
D
0
2
ms50
0
2
Definition Index D:
Other acoustical parameters
• Strength: dB31LSPLG w
dthdh
dthh
t2s
2d
sd
IACC:
SPL at 10 m
IACC: Inter Aural Cross Correlation
Room impulse response and Schroeder decay function determined from an experimentallymeasured room impulse response in two coupled scaled-down model rooms.
(a) Room impulse responseoctave band-pass filtered at 1kHz with peak-to-noise ratio equal to 53 dB.
(b) Schroeder decay function.
Case studies of reverb and anechoic chamber
Impulse response of reverberant room
Decay curve of reverberant room
Characteristics of reverberant room as per ISO-4482
Impulse response of anechoic chamber
Decay curve of anechoic chamber
Characteristics of anechoic chamber as per ISO-4482
Importance of acoustics in learning
Thanks
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