Design of a spherical array of microphones for room acoustics … · 2014. 6. 2. · Laboratory of...
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Design of a spherical array of microphones for room acoustics applications.
ABAV AG 28 may 2014 1
Intelsig Research group Laboratory of Acoustics
H. Feron (*) and J.J. Embrechts (Intelsig group, Laboratory of Acoustics, University of Liege, Belgium)
(*) Now at Deltatec s.a. (Ans-Liège)
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ABAV AG 28 may 2014 2
Intelsig Research group Laboratory of Acoustics
The room impulse response RIR
(between an omnidirectional source and an omnidirectional receptor)
time
sou
nd
pre
ssu
re
P S
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P S
ABAV AG 28 may 2014 3
Intelsig Research group Laboratory of Acoustics
The directional (or spatial) room impulse response DRIR
(between an omnidirectional source and a directional receptor)
time
sou
nd
pre
ssu
re
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ABAV AG 28 may 2014 4
Intelsig Research group Laboratory of Acoustics
Directional room impulse responses DRIR can help to:
- Evaluate « spatial » room acoustics parameters, such as the lateral energy fraction LEF, the left/right ratio LRR or the reverberation time in a particular direction,
- Detect possible (flutter) echoes in a particular direction,
- Create 3D auralization of acoustic spaces.
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ABAV AG 28 may 2014 5
Intelsig Research group Laboratory of Acoustics
How to measure Directional room impulse responses DRIR ?
- With a microphone antenna (microphone array), which can provide beamforming and beamsteering.
Beam pattern of array output
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ABAV AG 28 may 2014 6
Intelsig Research group Laboratory of Acoustics
Which kind of antenna for that application ?
(form, size, number of microphones,…)
- Master project of Hermine Feron (2013),
- Spherical array, 10cm radius,
- Rigid sphere,
- 16 microphones,
- Nearly uniform distribution
on the sphere,
- Two souncards (8 inputs each),
- Recordings in *wav format,
- DSP in Matlab.
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ABAV AG 28 may 2014 7
Intelsig Research group Laboratory of Acoustics
How does it work ?
(some hopefully few mathematics)
- The sound field P(k,r,W) existing around the antenna can be described by a series of spherical harmonics functions.
W = (f,d).
- k=2pf/c (the wave number).
Spherical coordinates
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ABAV AG 28 may 2014 8
Intelsig Research group Laboratory of Acoustics
How does it work ? (some hopefully few mathematics)
- If you know the spherical coefficients Pnm(k,r), then you obtain the sound field in any direction W.
- « n » is limited to the order « N » of the array => the directional lobe of sensitivity has a non-zero extent.
N=1 N=2 N=3
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How does it work ? (some hopefully few mathematics)
- The spherical coefficients Pnm(k,r) are determined by combining the 16 pressure signals measured in the directions Wj (j=1,16).
ABAV AG 28 may 2014 9
Intelsig Research group Laboratory of Acoustics
Array output:
= =
W=WN
n
nml
n
nm
nmlPWY
0
* )(),(),( P(,Wj)
16 microphones signals
Pnm()
(N+1)² Spherical coefficients Several algorithms…
Weights: they depend on the steering (look-up) direction Wl.
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ABAV AG 28 may 2014 10
Intelsig Research group Laboratory of Acoustics
Measurement of Directional room impulse responses DRIR.
Sound source: log sine sweep signal
(250-4000 Hz).
Deconvolution of the 16 recorded sweeps leads to 16 RIRs (not yet DRIRs !)
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ABAV AG 28 may 2014 11
Intelsig Research group Laboratory of Acoustics
Example 1: One reflecting panel in the anechoic room.
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ABAV AG 28 may 2014 12
Intelsig Research group Laboratory of Acoustics
Example 1: One reflecting panel in the anechoic room.
Time evolution of array output in the horizontal plane: Algorithm ‘Delay and Sum’ (DAS)
Spherical coordinates
ᵠ [°]
Tim
e [m
s]
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Intelsig Research group Laboratory of Acoustics
Example 1: One reflecting panel in the anechoic room.
Space distribution of array output in a specified time window (direct contribution):
Algorithm ‘Minimum-variance distortionless response’ (mvdr) Spherical coordinates
ᵟ [°
]
ᵠ [°]
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ABAV AG 28 may 2014 14
Intelsig Research group Laboratory of Acoustics
Example 2: DRIRs in a shoebox reverberant room.
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ABAV AG 28 may 2014 15
Intelsig Research group Laboratory of Acoustics
Example 2: DRIRs in a shoebox reverberant room.
Direct
Floor
Ceiling
f [°]
ᵟ [°]
Tim
e [m
s]
Tim
e [m
s]
14 to 16 ms
10,7 to 12,7 ms
17 to 18,2 ms
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ABAV AG 28 may 2014 16
Intelsig Research group Laboratory of Acoustics
Example 3: DRIRs in a long corridor, closed by reflecting doors.
0 200 400 600 800-200
-150
-100
-50
0
X: 529
Y: -46.95
temps [ms]
Réponse impulsionnelle omnidirectionnelle
Flutter echoes
Omnidirectional RIR
Time [ms]
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ABAV AG 28 may 2014 17
Intelsig Research group Laboratory of Acoustics
Example 3: DRIRs in a long corridor, closed by reflecting doors.
0 50 100 150 200 250 300 350 400 450 5000
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
X: 417.6
Y: 0.02576
temps [ms]
Réponse impulsionnelle directionnelle dans la direction dl = 0° et f
l =180°
1
2
3
1
180° 0°
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ABAV AG 28 may 2014 18
Intelsig Research group Laboratory of Acoustics
Example 3: DRIRs in a long corridor, closed by reflecting doors.
0 50 100 150 200 250 300 350 400 450 5000
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
X: 417.6
Y: 0.02576
temps [ms]
Réponse impulsionnelle directionnelle dans la direction dl = 0° et f
l =180°
1
2
3
2
180° 0°
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180° 0°
ABAV AG 28 may 2014 19
Intelsig Research group Laboratory of Acoustics
Example 3: DRIRs in a long corridor, closed by reflecting doors.
0 50 100 150 200 250 300 350 400 450 5000
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
X: 417.6
Y: 0.02576
temps [ms]
Réponse impulsionnelle directionnelle dans la direction dl = 0° et f
l =180°
1
2
3
3
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ABAV AG 28 may 2014 20
Intelsig Research group Laboratory of Acoustics
Example 4: DRIRs in an auditorium.
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ABAV AG 28 may 2014 21
Intelsig Research group Laboratory of Acoustics
Example 4: DRIRs in an auditorium.
Direct sound
Floor and tables
Ceiling
Blackboard wall
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ABAV AG 28 may 2014 22
Intelsig Research group Laboratory of Acoustics
Example 4: DRIRs in an auditorium.
Effect of absorbing material on the blackboard wall.
DRIR between 15 and 25ms
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ABAV AG 28 may 2014 23
Intelsig Research group Laboratory of Acoustics
Future works … - Improving the selectivity of the antenna:
- Illustration of the dynamic evolution of the
reflections (at least the first-order ones).
- Automatic computation of the room acoustics’ spatial parameters.
- Tests in great volumes (theatres, industrial halls).
ᵠ [°]
Tim
e [m
s]