Audio Engineering

Acoustic Environment 109

sound underwent approximately 108 refl ections in this sample space before becoming
inaudible. The result is a lot different than hearing the sound just once.

3.13.2 Build-Up of the Reverberant Sound Field

Figure 3.13 shows the paths of direct sound and several refl ected sound waves in a
concert hall. Refl ections also occur from balcony faces, rear wall, niches, and any other
refl ecting surfaces. We can obtain a chart such as that shown in Figure 3.14 if we plot
the amplitude of a short-duration signal vertically and the time interval horizontally. This
diagram shows that at listener’s ears, the sound that travels directly from the performer
arrives fi rst, and after a gap, refl ections from the walls, ceiling, stage enclosure, and other
refl ecting surfaces arrive in rapid succession. The height of a bar suggests the loudness of

Wall

reflect

ionR^5

Ce

reflectiling

ion

D R^2

irect sound wave

Stage reflect

ion R 4

reflectWall

ion

R 3

Wall

reflect

ionR^1

Figure 3.13 : Sound paths in a concert hall.

Direct

sound Reflections

Initial-Time-Delay

Gapt 1

R 1

R 2

R 3

R 4

R 5

R 6

Time (ms)

Loudness

Figure 3.14 : Time relationship of direct and refl ected sounds.