Frequency (Hz)			63    125   250   500   1000   2000   4000   8000
mean attenuation (dB)   	20.5  19.4  16.0  16.5 	20.9   31.4   35.3   36.0 
standard deviation (dB)   	4.2   5.4   4.1   4.2	2.5    4.3    3.6    4.0 
assumed protection (dB)   	16.3  14.0  11.9  12.3	18.4   27.1   31.7   32.0