User Guide

Sound System Design Reference Manual
Step Two:
We now have to determine what the nominal
operating level of the system should be for the
farthest listeners, which we will assume are some 20
meters away from the loudspeaker. Let us further
assume that the reverberation time in the room is no
greater than 1.5 seconds in the range from 250 Hz to
2 kHz and that the average noise level room is in the
range of 25 dB(A). Referring to Figure 7-2, we can
see that for an ambient noise level in the 25 dB(A)
range, the EAD for a lowered voice would be about
2 meters, or a speech level of about 60 dB SPL.
For a direct field level of 60 dB at a distance of
20 meters, the LF section of the loudspeaker will
require a signal input of 0.1 watts (into 8 ohms). In
the biamplification mode the HF section will require
considerably less than 0.1 watt input in order to
reach the desired level at a distance of 20 meters.
7-4
Figure 7-2. EAD versus A-weighted noise levels