User Manual

8
In order to better understand the conditions affecting the sound energy picked up by a microphone located near a
speaker, let’s take a look at both a line-array speaker and a point-source speaker, assuming that the distances to the
listening point and the sound-pressure level at that point are identical for each.
In the case of the line array speaker, the coupling mechanism described above ensures that the microphone picks up the
combined output only from those speaker units for which the distance difference is within a quarter wavelength, whereas
all of the sound output by the point-source speaker will be picked up by the microphone. In other words, the sound
energy picked up by the microphone will be smaller in the case of the line array, so feedback is less likely to occur.
Another reason given for line-array speakers being less prone to feedback is the fact that the per-unit output is smaller
than with point-array speakers, meaning that a microphone positioned nearby picks up less sound energy. Furthermore,
whereas sound pressure decreases by 6 dB for each doubling of distance in the case of point-source speakers, this is
only 3 dB for line arrays. The amount of radiant sound energy that needs to be output is also lower by the same amount,
so the sound-pressure level close to the speakers is lower and volume is affected less by location.
(a) Line-array speaker
(b) Point-source speaker
Microphone
Output is combined for only some of the speaker units,
so the microphone picks up less sound energy.
Microphone
The microphone picks up all of the sound output by the single speaker unit.