Sound Attenuation, H, M, L & SNR Values Frequency (Hz) Mean Standard Assumed Attenuation(dB) Deviation Protection Value 125 11.6 4.3 7.3 250 18.7 3.6 15.1 500 27.5 2.5 25.0 1000 32.9 2.7 30.1 2000 33.6 3.4 30.2 4000 36.1 3.0 33.2 8000 35.8 3.8 32.0 H = 32, M = 25, L = 15, SNR = 27