How binaural loudness summation is measured changes the measured effect by several dB

Evidence

Binaural loudness summation can also be studied with loudspeakers in a standard stereo arrangement. The loudness summation depends both on the frequency separation and time separation of the sounds from the two loudspeakers. For zero frequency separation and zero temporal separation, two loudspeakers produce a larger loudness than one loudspeaker, corresponding to a level difference of about 4 dB. For frequency separations as large as 4 kHz, the loudness increase for presentation over two loudspeakers corresponds to 12 dB at low loudness levels (45 phon) and to about 8 dB at high loudness levels (85 phon). — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 1739

Categorization

• XREF: Relevant to stereo/multichannel audio engineering and loudness of reproduced music.
• corroborated: 2 independent passages support this claim — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 1739