On the Lack of Agreement between Earphone Pressures and Loudspeaker Pressures for Loudness Balances at Low Frequencies
Wayne Rudmose · The Journal of the Acoustical Society of America · 1963
The “missing 6 dB” has remained a problem for many years. The author has previously shown [W. Rudmose, in Proceedings of the Fourth International Congress on Acoustics, Copenhagen. 1962 (to be published)] that pressure thresholds and freefield thresholds, at 100 Hz, can be made to agree if the masking effect of physiological noise is minimized. In this paper, data and experimental techniques are presented to show that “pressure” and freefield” loudness balances, for 100 Hz, can also be made to agree. Three procedures, (1) monaural, (2) monaural using transfer earphone, and (3) binaural, are discussed, showing how the missing 6 dB can be attributed to certain experimental techniques. No single explanation fits all experiments. Some factors affecting judgments are (a) failure to occlude the nonused or transfer ear in monaural balancing, (b) the loudspeaker location (some subjects require different pressures for loudspeaker balancing if only the loudspeaker changes), (c) mechanical vibrations from the loudspeaker reaching the subject, (d) unexpected results, with some subjects from small amounts of distortion. What affects one subject may have no effect on another. [This work was done at Southern Methodist University and supported in part by the Callier Trust.]