Page 88 - Master Handbook of Acoustics

inner ear and finally to the brain for interpretation.
This directional encoding process of the sound signal is shown in Fig. 4-14. The sound wavefront
can be considered as a multiplicity of sound rays coming from a specific source at a specific

horizontal and vertical angle. As these rays strike the pinna, they are reflected from the surfaces, some
of the reflections going toward the entrance to the auditory canal. At that point these reflected
components combine with the unreflected component.

FIGURE 4-14 A wavefront of a sound can be considered as numerous rays perpendicular to that
wavefront. Such rays, striking a pinna, are reflected from the various ridges and convolutions. Those
reflections directed to the opening of the ear canal combine vectorially (according to relative
amplitudes and phases). In this way the pinna encodes all sound falling on the ear with directional

information, which the brain decodes as a directional perception.

For a sound coming directly from the front of the listener (azimuth and vertical angle = 0°), the
“frequency response” of the combination sound at the opening of the ear canal is shown in Fig. 4-15.
A curve of this type is called a transfer function; it represents a vector combination involving phase
angles.