User Manual

7
Appendix
Why is feedback less likely to occur with line-array speakers?
Line-array speakers are commonly said to be less prone to audio feedback than point-source speakers, and the reason
can be attributed to the coupling mechanism used with the individual speaker units, and the way in which volume
attenuates over distance.
Line-array speakers capitalize on the increase in sound pressure achieved as a result of coupling together scattered
sound from multiple speaker units so that they operate as a line source. Generally speaking, a boost in sound
pressure is produced by those speaker units for which the difference between corresponding straight-line distances
for each speaker to the listening point is within a quarter wavelength. However, units for which the difference in
corresponding distances is greater have the opposite effect, and phase cancellation occurs when the difference
approaches half a wavelength.
At listening points separated from the array by at least a certain distance and where the distance differences are within
a quarter wavelength, all of the speaker units contribute to higher sound pressure. In contrast, the relative difference in
distances from the central and end units becomes greater when the listening point is relatively close to the array, thereby
limiting the number of units that can contribute to higher sound pressure and reducing the combined sound energy.
(a) Listener is relatively far away from the array
(b) Listener is relatively close to the array
Speakers in red region: Contribute to higher sound pressure
The difference in the distances from speaker units
1
and
2
is within a
quarter wavelength; therefore, sound pressure is boosted by all of the units.
Speakers in red region: Contribute to higher sound pressure
Speakers in blue region: Sound pressure drops and phase
cancellation occurs
The difference in the distances from speaker units
1
and
2
is within a quarter wavelength; therefore, sound pressure is
boosted by the speakers in the red region.
The difference in the distances from speaker units
1
and
3
is greater than a quarter wavelength; therefore, sound
pressure is reduced by the speakers in the blue region, and
phase cancelation occurs.