Interaural level differences grow with frequency and reach up to 20 dB.

Evidence

As a result, the level difference (in dB) between the two ears, the interaural level difference (ILD) varies as a function of frequency and location of the sound source. Feddersen, Sandel, Teas, and Jeffress (1957) measured ILDs as a function of the azimuthal angle and frequency using human listeners. They placed a small microphone in their ears and measured the sound levels for a variety of sounds. Their measurements are shown in Figure 7–2, which plots the ILD in dB as a function of the angle between the center of the head and the sound. A sound directly in front is presented at 0°, whereas a sound directly to the side is presented at 90°. … For all frequencies tested, the ILD was 0 dB when the sound source was directly in front or in back of the listener. • The ILD was greatest when the sound source was 90° to the side of the listener. • The size of the ILD increased as frequency increased. The ILD can be as large as 20 dB for high frequencies (>4000 Hz), particularly for sounds located to one side of the body. — Jennifer Lentz, Psychoacoustics- Perception of Normal…, 1456