1. IO dB greater ambient noise level can be present for the same amount of masking: further, it can be seen American Standards Association,(195 i).
2. Statement on the difficulty of calibration of circumaural earphones;American Standards Association Committee on Couplers;J. acoust. Soc. Amer. Letter,1966
3. Atherley, G. R. C., Lord, P., and Walker, J. G. (1965).
4. se Congres International d'Acoustique, Lilge, I965. Rapports, Ib, Paper J52
5. The normal threshold of hearing for pure tones by earphone listening. B. S;British Standards Institution,1954