The Transparency Approach
b = 0.054"
d = 0.023"
t = 0.0184"
Example 1.
A perforated sheet of 26 gauge steel with O.O23-in. holes on 0.054-in. staggered centers leads to the following parameters:
b = 0.054"
d = 0.023"
t = 0.0184"
A = Sheet area per hole
= b2cos 30�
= (0.054)2 X 0.87
= 2.525 x 10-3 sq in;
Then n = 1/A = 396 holes/sq in;
a = b - d
= 0.054 - 0.023
= 0.03";
P = [(11d2/4)/A] X 100
= [(11 X (0.023)2/ (4 x 2.525 x 10-3)] x 100
= 16.45%.
We calculate the Transparency Index by two methods; first by:
TI = nd2/ta2
= [396 x (0.023)2/0.0184 x (0.03)2
= 12,650;
or alternatively by:
TI = 0.04P/11ta2
= [0.04 x 16.45/11 x 0.0184 x (0.03)2
= 12,648.
The two values of TI agree very well. The sound attenuation at 10 kHz is only 0.9 dB.
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