% Amplitude attenuation of air at 20 C and 50% humidity
125                       5.063204894065097E-5
250                       1.5078859842549607E-4
500                       3.1408405882321486E-4
1000                      5.370402802004922E-4
2000                      0.001138270272702961
4000                      0.003415326781762908
8000                      0.012121911780290923