Doing a small amount of research we learn that there are two ratings of interest
when considering a material for sound control, NRC Noise Reduction Coefficient
= sound absorption Cork said to be 0.7 NRC means 70% absorbed 30% reflected
at specific frequencies 250, 500, 1000, 2000 HZ
STC Sound Transmission Class = ability to block noise, Cork said to be 89 that
makes Cork rather unique it both blocks and absorbs noise, perhaps this is why
it passed the lab testing at Airbus so successfully.
I came across a article from 16 years ago on airliners.net saying the next step
for airbus was a two year test in the fuselage of one of their jets with Cork
insulation.
Then one must decide the best locations to place it, top cowl & firewall to
start
I suppose.
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http://forums.matronics.com/viewtopic.php?p=511391#511391
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