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.