References
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- Davis H., et al. Harvard University Press. 1947, Hearing Aids: An Experimental Study of Design Objectives.
- Knight J. J., Littler T. S. J. Laryng. 1953; 67: 248
- Medical Research Council. 1947, Special Report Series No. 261. H.M.S.O., London.
- Richards D. L. J. Brit. Sound Rec. Assn. 1962; 7: 1