Binaural Summation of Loudness

The common assumption that a given stimulus sounds twice as loud in two ears as in one turns out to be both true and false It is true for a particular level (roughly 90 db) but false for all other levels. The power functions governing the two loudness scales have different exponents: binaural is approximately 0.6 (the sone scale), monaural is approximately 0.53. These relations were determined in five kinds of experiments: (1) monaural-binaural loudness matching, (2) magnitude estimation, (3) magnitude production, (4) cross-modality matching between loudness and apparent strength of a vibration on the finger tip, and (5) halving and doubling of loudness, monaural vs binaural. Binaural loudness ranges from about 1.4 times as great as monaural loudness at about 40 db to 2.3 times as great at about 100 db.