Effective Implementation of Microperforated Panel Absorbers
Transcript of Effective Implementation of Microperforated Panel Absorbers
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David HerrinUniversity of Kentucky
Effective Implementation ofMicroperforated Panel Absorbers
September 18, 2020
Vibro-Acoustics Consortium
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Microperforated Panel Absorbers
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Advantages
β’ High temperature resistant
β’ Chemically stable
β’ Non-combustible
β’ Wear resistant / Rugged
β’ Fiber free
β’ Washable
β’ Aesthetic appearance
β’ Acoustically tunable
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Hindrances to Use
β’ More expensive than traditional absorbers
β’ Properties must be measured
β’ Requires thoughtful integration into the product
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Suggested Design Process
β’ Select a MPP and measure transfer impedance.
β’ Consider the environment the MPP is placed in.
β’ Partition the backing cavity so it behaves in a locally reactive sense.
β’ Vary the depth of the backing cavity to improve low and broadband frequency attenuation.
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MPP and MSP Absorbers
0.89 mm
3.75 mm
Thickness
Thickness
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Thin layer with flow resistance π π‘ where π is the flow resistivity and π‘ is the thickness.
π π‘ 2ππ for each case
Long, 2014 based on Ingard, 1994
Porous Absorbers Basics for Designers
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π
π·
Plane wave
Air Cavity
π§
Sound Absorption of MPP
π§ π§ π cot ππ·
π ,π’ π ,π’π§
1πππ ππ’
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MPP Transfer Impedance
Grazing Flow
High SPL
Allam and Γ bom, 2013
π Reπππ‘ππ 1
2π π
π½ π ππ½ π π
2π½π πππ
π’ππ
πΎππ
π₯ Imπππ‘ππ 1
2π π
π½ π ππ½ π π
0.85πππΉ 1 π’ππ
ππ
π ππ4π
π 2
2 πππ
πΉ1
1 12.6π
π§ π ππ₯
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π· cavity depth
π hole diameter
π porosity
π‘ thickness
π½0 zeroth order Bessel function
π½1 first order Bessel function
π½ 2 for rounded and 4 for sharp edged holes
πΎ 0.15Β±0.0125
π kinematic viscosity
π dynamic viscosity
π grazing flow Mach number
π’ peak particle velocity
Symbols
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Maaβs EquationMaa, 1975
π§32ππ‘ππππ 1
π½32
232 π½
ππ‘ π
ππ‘ππ 1 3
π½2 0.85
ππ‘
π½ πππ4π
π· 0.1 mπ‘ 1.0 mm
Given
0.0
0.2
0.4
0.6
0.8
1.0
0 200 400 600 800 1000 1200 1400 1600
Soun
d Ab
sorptio
n Co
efficient (Ξ±
)
Frequency (Hz)
0.20 mm
0.25 mm
0.40 mm
0.45 mm
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π πππ§ π π
π
Sample
Loudspeaker
Microphones
Measure Transfer ImpedanceWu, Cheng, and Tao, 2003
π
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Assumptions:1. A MPP can be simulated using Maaβs equation with an effective holediameter and porosity.2. Measured absorption coefficient πΌ is accurate.
Measure πΌ
Assume porosity and diameter
Calculate πΌ using Maaβs Equation
Compare in aLeast Squares Sense
Minimize the error to find effective porosity and holed diameter.
Procedure (Liu et al., 2014)
Determine Equivalent ParametersLiu et al., 2014
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0
0.2
0.4
0.6
0.8
1
0 1000 2000 3000 4000
Abso
rptio
n C
oeffi
cien
t
Frequency (Hz)
Measured
NLLSF
0
1
2
3
4
0 1000 2000 3000 4000
Nor
mal
ized
Tra
nsfe
r Im
peda
nce
Frequency (Hz)
Real (Measured)Real (NLLSF)Imag (Measured)Imag (NLLSF)
Fitted Hole Diameter: 0.242 mmFitted Porosity: 4.11%
Determine Effective Parameters
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0
2
4
6
8
10
12
0 0.1 0.2 0.3 0.4 0.5
Poro
sity
(%)
Hole Diameter (mm)
0.0
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0.6
0.8
1.0
0 1000 2000 3000 4000 5000
Abso
rptio
n C
oeffi
cien
tFrequency (Hz)
2% Porosity8% Porosity
Manufacturing Variability
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Suggested Design Process
β’ Select a MPP and measure transfer impedance.
β’ Consider the environment the MPP is placed in.
β’ Partition the backing cavity so it behaves in a locally reactive sense.
β’ Vary the depth of the backing cavity to improve low and broadband frequency attenuation.
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Air Compressor
Airbrush
Powder container
Spray booth
MPP
Filter
Air Flow
Spray Booth
Impedance Tube
Effect of Contamination
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0
0.2
0.4
0.6
0.8
1
0 1000 2000 3000 4000
Abso
rptio
n C
oeffi
cine
t
Frequency (Hz)
1.4% Porosity, 0.3 mm Diameter
1.7% Porosity, 0.3 mm Diameter
2.0% Porosity, 0.4 mm Diameter
2.8% Porosity, 0.4 mm Diameter
0
0.2
0.4
0.6
0.8
1
0 1000 2000 3000 4000
Abso
rptio
n C
oeffi
cine
t
Frequency (Hz)
0.9% Porosity, 0.2 mm Diameter2.0% Porosity, 0.2 mm Diameter2.3% Porosity, 0.2 mm Diameter2.0% Porosity, 0.2 mm Diameter4.2% Porosity, 0.2 mm Diameter
Effect of Contamination
1.0 mm thick MPP with slit perforations 0.6 mm thick MPP with circular perforations
Liu et al., 2014
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Suggested Design Process
β’ Select a MPP and measure transfer impedance.
β’ Consider the environment the MPP is placed in.
β’ Partition the backing cavity so it behaves in a locally reactive sense.
β’ Vary the depth of the backing cavity to improve low and broadband frequency attenuation.
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Test Case
1. Without MPP (Reference)2. With MPP3. With MPP + Partitioning
3 Cases
πΌπΏ πΏno mpp πΏmpp
54 Measurements on Plane in front of MPPx
y
z
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Measurement Setup
Cardboard Partitioning
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Partition the Backing Cavity
-10
0
10
20
30
0 200 400 600 800 1000
Frequency (Hz)
IL (d
B)
MPP with PartitioningMPP
(1,0,0) (0,1,0)(2,0,0)
(0,0,1)
(2,1,0)
(1,0,1)(3,0,0)
(3,1,0)
(4,0,0)
(0,0,2)(0,3,0)
-10
0
10
20
30
0 200 400 600 800 1000
Frequency (Hz)
IL (d
B)
MPP with PartitioningMPP
(1,0,0) (0,1,0)(2,0,0)
(0,0,1)
(2,1,0)
(1,0,1)(3,0,0)
(3,1,0)
(4,0,0)
(0,0,2)(0,3,0)
Liu and Herrin, 2010
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Vibro-Acoustics Consortium
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Suggested Design Process
β’ Select a MPP and measure transfer impedance.
β’ Consider the environment the MPP is placed in.
β’ Partition the backing cavity so it behaves in a locally reactive sense.
β’ Vary the depth of the backing cavity to improve low and broadband frequency attenuation.
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100 mm
Baseline
Vary the Cavity Depth
100 mm
10 mm
40 mm
33.33 mm
Three-Channel
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0
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1
0 400 800 1200 1600
Abso
rptio
n C
oeffi
cien
t
Frequency (Hz)
MeasurementPlane Wave
Empty Airspace
0
0.2
0.4
0.6
0.8
1
0 400 800 1200 1600Ab
sorp
tion
Coe
ffici
ent
Frequency (Hz)
Measurement
Plane Wave
Three Channel
Impedance Tube Measurements
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β’ AAP Reverberation room: 10.87 m3 with no parallel walls, and the noise source was a distributed loudspeaker
β’ Humidity: 56%~ 60%, temperature: 21ΒΊC
β’ Box: 60 cm X 40 cm
β’ 24 cells (10 cm X 10 cm)
Reverberation Room Test
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Design ConfigurationsPartitioned Three channel
Half Three channel
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0.00
0.20
0.40
0.60
0.80
1.00
100 1000 10000
Abso
rptio
n C
oeffi
cien
t
Frequency( Hz)
MPP only
Partition0.00
0.20
0.40
0.60
0.80
1.00
100 1000 10000Ab
sorp
tion
Coe
ffici
ent
Frequency( Hz)
MPP only3-channel (full)3-channel (half)
Partition and Three-Channel
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100 mm
MPP
12 mm
Double Leaf Configuration
0
0.2
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0.8
1
0 400 800 1200 1600
Abso
rptio
n C
oeffi
cien
t
Frequency (Hz)
MeasurementPlane Wave
Normal Incident Sound Absorption
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0.00
0.20
0.40
0.60
0.80
1.00
100 1000 10000
Abso
rptio
n C
oeffi
cien
t
Frequency( Hz)
MPP only
Double leaf
Double Leaf Configuration
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Vibro-Acoustics Consortium
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Suggested Design Process
β’ Select a MPP and measure transfer impedance.
β’ Consider the environment the MPP is placed in.
β’ Partition the backing cavity so it behaves in a locally reactive sense.
β’ Vary the depth of the backing cavity to improve low and broadband frequency attenuation.
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Ultra Thin MPP
β’ Much thinner than a traditional MPPβ’ Ideal for use as a fiber cover
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Curve Fit to Determine Parameters
Effective ParametersThickness: 0.65 mm;Hole diameter: 0.23 mm;Porosity: 8.0%
0
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0.8
1
0 1000 2000 3000 4000
Abso
rptio
n C
oeffi
cien
t
Frequency (Hz)
Measured
Fitted
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Silencer with MPP
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0102030405060708090100110120
100 1000
Transm
ission Loss (d
B)
Frequency (Hz)
56β48β
Absorptive(Perforated, Fibrous Material)
Transmission Loss Measurement
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References
1. Maa, D. Y., Theory and Design of Microperforated-Panel Sound-Absorbing Construction, Scientia Sinica XVIII, pp. 55-71, 1975.
2. Allam, S., Guo, Y., and Γ bom, M. Acoustical Study of Micro-Perforated Plates for Vehicle Applications, SAE Noise and Vibration Conference, Paper No. 2009-01-2037, St. Charles, IL, 2009.
3. Allam, S. and Γ bom, M. A New Type of Muffler Based on Microperforated Tubes, ASME Journal of Vibration and Acoustics, Vol. 133, 2013.
4. Herrin, D. W., Liu, W., Hua, X., and Liu, J., βA Guide to the Application of Microperforated Panel Absorbers,β Sound and Vibration, Vol. 51, No. 12, pp. 12-20 (December, 2017).
5. Herrin, D. W., Liu, J., and Seybert, A. F., βProperties and Applications of Microperforated Panels,β Sound and Vibration, Vol. 45, No. 7, pp. 6-9 (July, 2011).
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