Head shading creates interaural level differences used for sound localization

Evidence

Acoustically, the entire head (and shoulders) makes part of the external ear. The distance between the two ears, located at opposite sides of the head, causes an arrival time difference of the sound wavefront that depends on the angle of incidence. A difference in sound level appears at high frequencies due to shadowing by the head to the side that is opposite to the sound source. — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 726

The other cue that is used to detect the direction of the sound is the differing levels of intensity that result at each ear due to the shading effect of the head. This effect is shown in Figure 2.26 which shows that the levels at each ear are equal when the sound source is on the median plane but that the level at one ear progressively reduces, and increases at the other, as the source moves away from the median plane. The level reduces in the ear that is furthest away from the source. — David Howard, Jamie Angus, coustics and Psychoacoustics, 721

Categorization

• DEFINE: Establishes the physical basis of interaural time delay and head-shadow level differences, the two classic binaural cues.
• corroborated: 4 independent passages support this claim — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 726; David Howard, Jamie Angus, coustics and Psychoacoustics, 721
• XREF: connects to: Interaural level differences and time shifts trade off to control lateralization — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 1431; Head symmetry creates a cone of directions where sound localization is ambiguous; Head shadowing gives roughly 6 dB interaural amplitude difference near 1.85 kHz (+12 more)

Broader Connections

• A 5-dB hearing asymmetry doubles the perceived interaural level difference #expands (0.72) — Jennifer Lentz, Psychoacoustics- Perception of Normal…, 1582
• Direct sound determines localization, loudness, and perceived spectrum quality #qualifies (0.70) — , Toole, Floyd E - Sound reproduction-…, 1546