C) Separate Flown Arcs Array With Ground Stacked Subwoofers; Figure 21: Illustration Of Subwoofer Time Alignment - L-Acoustics ARCS Operator's Manual

c) Separate Flown ARCS Array with Ground Stacked Subwoofers

For a separate flown ARCS array with ground stacked subwoofers, time alignment of subwoofers is
required due to the geometric path difference between the two systems. This is illustrated in Figure
20, where the distance from the measurement microphone position to the subwoofers is d
the distance to the flown ARCS system: d
by the geometric path difference will time align the subwoofers at the reference position.
Note: Selection of the reference position for time alignment is always a compromise since the geometrical
path difference will vary with position.
STAGE
(SB218) (SB218)
TIME DELAY
PATH DIFFRENCE (meters)
T
=
343 (meters/second)
In most cases, 3W presets are used for flown ARCS and ground stacked subwoofer configurations in
(3-way mode or with separate aux drive for the subwoofers) since the subwoofers are always used
with positive polarity and this helps to simplify installation and system tuning. If more low frequency
energy is desired from the flown ARCS system, 3WX presets can be used with reference to Table 11
for guidelines concerning subwoofer polarity depending on how subwoofers are processed.
L-ACOUSTICS ARCS Manual V2.0
= d
ARCS
(ARCS)
PATH
DIFFERENCE

Figure 21: Illustration of subwoofer time alignment

+ PATH DIFFERENCE. Delaying the subwoofers
SUB
d d +
PATH DIFFERENCE
ARCS = SUB
d
sub (m)
2/13/2003
while
SUB
MEASUREMENT
MICROPHONE
FLOOR
36