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2. Allen, C. H., Frings, H., and Rudnick, I. (1948). J. acoust. Soc. Amer., 20, 62.
3. Atherley, G. R. C. (1964). Brit. J. industr. Med., 2I, I50.
4. -and Fordyce, I. D. (1963). Ibid., 20, 231.
5. The normal threshold of learning for pure tones by earphone listening;2497, British Standard,1954