Sound Attenuation, H, M, L & SNR Values Frequency (Hz) Mean Standard Assumed Attenuation(dB) Deviation Protection Value 125 17.4 2.1 15.3 250 24.7 2.6 22.1 500 34.7 2.0 32.7 1000 41.4 2.1 39.3 2000 39.3 1.5 37.8 4000 47.5 4.5 43.0 8000 42.6 2.6 40.0 H = 40, M = 32, L = 23, SNR = 35