Loudness Summation under Masking

Loudness summation has been shown to be greatest at SPL's between 40 and 70 db. The present experiments show that a decrease in loudness summation occurs also when a complex is heard in a uniform masking noise. The loudness of a 4‐tone complex centered at 2000 cps was matched to that of a 2000‐cycle tone. Both the complex and the tone were presented with the masking noise through a single PDR‐8 earphone. Three independent variables were studied: (1) the frequency separation ΔF between the highest and the lowest components of the complex, (2) the SPL of the standard signal (which was sometimes the complex, sometimes the tone), and (3) the over‐all sound pressure of the masking noise. Results for six subjects show that when the standard was at either 40 or 60 db and ΔF was greater than 300 cps (the value of the critical band at a center frequency of 2000 cps), loudness summation decreased as the level of the background noise was increased. When the level of the standard was 20 or 80 db or when ΔF was less than a critical band, the background noise had, for the most part, little or no effect upon loudness summation. (This research was supported by a grant from the National Institute of Health, U. S. Public Health Services.)