16 november 2012acoustical parameters (iso 3382) 1 acoustical parameters iso 3382
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16 November 2012 Acoustical Parameters (ISO 3382) 1
Acoustical parameters Acoustical parameters ISO 3382ISO 3382
16 November 2012 Acoustical Parameters (ISO 3382) 2
ISO 3382 acoustical parameters
16 November 2012 Acoustical Parameters (ISO 3382) 3
From Impulse Response to Sound Decay
• Schroeder’s backward integral
• Makes it possible to reconstruct the decay of a stationary source by backward integration of the measured impulse response
0
A
B
t
g t d t2
0' '
g t d tt
2 ' '
g t d tt
2
0' '
16 November 2012 Acoustical Parameters (ISO 3382) 4
Schroeder’s BW IntegrationPressure Impulse Response
Energetic Impulse Response (in dB)
Stationary Sound Decay (in dB)
Reverberation time T20
Lp (dB)
Time (s)
45 dB
-5 dB
-25 dB
T20
16 November 2012 Acoustical Parameters (ISO 3382) 5
16 November 2012 Acoustical Parameters (ISO 3382) 6
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
16 November 2012 Acoustical Parameters (ISO 3382) 7
Early – Late energy evaluationUseful Energy Detrimental Energy
16 November 2012 Acoustical Parameters (ISO 3382) 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
16 November 2012 Acoustical Parameters (ISO 3382) 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:
Other acoustical parameters
• Strenght: dB31LSPLG w
dthdh
dthh
t
2s
2d
sd
IACC:
SPL at 10 m
16 November 2012 Acoustical Parameters (ISO 3382) 10
16 November 2012 Acoustical Parameters (ISO 3382) 11
Other acoustical parameters
ms
ms
W
ms
ms
WY
LFC
dh
dhh
J 80
0
2
80
5
LFC:
ms
ms
W
ms
ms
Y
LF
dh
dh
J 80
0
2
80
5
2
Lateral Fraction:
16 November 2012 Acoustical Parameters (ISO 3382) 12
Spatial analysis by directive impulse responses• The initial approach was to use directive microphones for gathering some information
about the spatial properties of the sound field “as perceived by the listener”• Two apparently different approaches emerged: binaural dummy heads and pressure-
velocity microphones:
Binaural Binaural microphone (left)microphone (left)
and and
Pressure-velocity Pressure-velocity microphone (right)microphone (right)
16 November 2012 Acoustical Parameters (ISO 3382) 13
IACC “objective” spatial parameter• It was attempted to “quantify” the “spatiality” of a room by means of
“objective” parameters, based on 2-channels impulse responses measured with directive microphones
• The most famous “spatial” parameter is IACC (Inter Aural Cross Correlation), based on binaural IR measurements
LeftLeft
RightRight
80 ms80 ms
ppLL(())
ppRR(())
ms1...ms1ttMaxIACC
dtpdp
dtpp
t Ems80
0
2R
ms80
0
2L
ms80
0RL
16 November 2012 Acoustical Parameters (ISO 3382) 14
Lateral Fraction (LF) spatial parameter• Another “spatial” parameter is the Lateral Fraction JLF
• This is defined from a 2-channels impulse response, the first channel is a standard omni microphone, the second channel is a “figure-of-eight” microphone:
Figure Figure of 8of 8
OmniOmni
ms
ms
o
ms
msLF
dh
dh
J 80
0
2
80
5
28
hhoo(())
hh88(())
16 November 2012 Acoustical Parameters (ISO 3382) 15
Are binaural measurents reproducible?• Experiment performed in anechoic room - same loudspeaker, same
source and receiver positions, 5 binaural dummy heads
Are IACC measurements reproducible?• 90° incidence - at low frequency IACC is almost 1, at high
frequency the difference between the heads becomes evidentIACCe - 90° incidence
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
31.5 63 125 250 500 1000 2000 4000 8000 16000
Frequency (Hz)
IAC
Ce
B&K4100
Cortex
Head
Neumann
16 November 2012 Acoustical Parameters (ISO 3382) 16
16 November 2012 Acoustical Parameters (ISO 3382) 17
Are IACC measurements reproducible?
• Diffuse field - huge difference among the 4 dummy heads
IACCe - random incidence
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
31.5 63 125 250 500 1000 2000 4000 8000 16000
Frequency (Hz)
IAC
Ce
B&K4100
Cortex
Head
Neumann
16 November 2012 Acoustical Parameters (ISO 3382) 18
Are LF measurents reproducible?• Experiment performed in the Auditorium of Parma - same loudspeaker,
same source and receiver positions, 4 pressure-velocity microphones
• At 7.5 m distance, the results already exhibit significant scatter
Comparison LF - measure 1 - 7.5m distance
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
31.5 63 125 250 500 1000 2000 4000 8000 16000
Frequency (Hz)
LF
Schoeps
Neumann
Soundfield
B&K
Are LF measurents reproducible?
16 November 2012 Acoustical Parameters (ISO 3382) 19
16 November 2012 Acoustical Parameters (ISO 3382) 20
Are LF measurents reproducible?• At 25 m distance, the scatter is even larger
Comparison LF - measure 2 - 25m distance
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
31.5 63 125 250 500 1000 2000 4000 8000 16000
Frequency (Hz)
LF
Schoeps
Neumann
Soundfield
B&K
16 November 2012 Acoustical Parameters (ISO 3382) 21
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