Page 134 - Master Handbook of Acoustics

CHAPTER 6

Reflection

I magine a sound source in a free field, or an approximation of one, such as an open meadow.

Sound emanates from the source radially in all directions. Direct sound from the source moves

past you and never returns. Now consider the same source in a room. Direct sound moves past, but
when it strikes room boundaries, it reflects from the boundaries. Thus a sound moves past you once in
a direct path, and many additional times as many reflected paths, until it dies out. Sound comprising
many reflections sounds dramatically different than sound in a free field. The reflections convey
significant information about the room’s size, shape, and boundary composition. Reflections help
define the sonic characteristics of a room. Not insignificantly, reflections can add pleasing qualities
to a sound. Conversely, reflections can also degrade sound quality.

Specular Reflections

The essential mechanism of reflection from a flat surface is simple. Figure 6-1 shows the reflection of

point-source sound waves from a rigid, plane wall surface. The spherical wavefronts (solid lines)
strike the wall and the reflected wavefronts (broken lines) are returned toward the source. This is
called a specular reflection and behaves the same as light reflections from a mirror, described by
Snell’s law.