Key points are not available for this paper at this time.
In order to obtain a reasonably unbiased loudness function near the threshold of audibility by the method of magnitude estimation, several possible causes of bias were investigated. The investigation included a comparison between sound pressure level and sensation level as independent variables and a parametric variation of the reference SL and of the reference number. It is established that for certain pairs of reference SL's and reference numbers a reasonably unbiased loudness function can be determined down to a SL of 4 db.
Hellman et al. (1961) studied this question.