Audio Engineering

Acoustic Environment 99

0 50 100

Distance (ft)

16 8

Noise

Noise

Arbitrary loudness units

Figure 3.9 : Sound from an orchestra enclosure in an open fi eld with no wind.

an open fi eld with no wind. The sound at 100 ft is one-half as loud as that at 30 ft, although
the amplitude of the vibration of the air particles is roughly one-third. Similarly, the sound
at 30 ft is one-half as loud as the sound at 10 ft. Because the sound is outdoors, atmospheric
effects, ambient noise, and so on cause diffi culty for the talker and listener. The ancients
learned to place a back wall behind the talker, and many Native American council sites
were at the foot of a stone cliff so that the talker could address more of the tribe at one
time. Figure 3.9 illustrates how a refl ecting structure can double the loudness as compared
to totally open space. The weather and some noise still interfere with listening.

Figure 3.10 illustrates the absorptive effect of an audience on the sound traveling to the
farthest listener. Figure 3.11 shows the right way and the wrong way to arrange a sound
source on a hill. In Figure 3.11 (a), the loudness of the sound at the rear of the audience
is enhanced by sloping the seating upward. In addition, the noise from sources on the
ground is reduced. Figure 3.11 (b) is a poor way to listen outdoors.

While the Bible doesn’t say which way Jesus addressed the multitudes, we can deduce
from the acoustical clues present in the Bible text that the multitude arranged themselves
above him because:

1. He addressed groups as large as 5000. This required a very favorable position
   relative to the audience and a very low ambient noise level.