Central Line Array With Electronic Delay Processing; Figure 72: Centre Subwoofer Line Array (A) Without And (B) With Electronic Delay Processing - L-Acoustics dV-DOSC Operator's Manual

3.5.2 CENTRAL LINE ARRAY WITH ELECTRONIC DELAY PROCESSING

A central ground stacked line array optimizes low frequency SPL output since all subwoofers couple
acoustically and the mirror image ground plane effect doubles the number of subs. Given the same
number of subwoofers, the overall SPL obtained by ground stacking in this manner is higher than any
other configuration. An additional advantage of the centre line array is that the vertical directivity is
omnidirectional (into half space) - this is useful for venues where there is an audience tribune. Since
subwoofers are physically separate from the flown dV-DOSC arrays they are normally driven via aux
send (although the system can also be operated in 4-way mode).
Limitations of the central ground stacked line array configuration are as follows:
Tonal balance has an exaggerated low frequency contour for the closest members of the audience
(integrating distributed front fill loudspeakers or a stereo infill system with the central line array of
subwoofers can help offset this).
Increased amount of low frequency energy behind the central line array which can cause feedback
problems on stage
Unless electronic delay processing is applied, the horizontal directivity will narrow (the extent of
narrowing depends on the length of the central line array)
Potential for reduced throw due to audience absorption (this problem is likely to occur with any
ground stacked configuration).
A good technique for controlling the directivity of a central ground-stacked horizontal line array is to
use delay processing to electronically arc the array. Electronic delay processing in this manner will
decouple sections of the array so that tonal balance is improved up close while at the same time low
frequency coverage is smoother throughout the audience in the horizontal plane. The optimum arc
radius is typically equal to half the length of the central line array - delay taps are calculated
geometrically based on this arc radius and the physical distance to the centre of a given subwoofer
group off the center line reference.
Note: Experiments into the use of additional rear channel subwoofers (located at the focal point of the
delay processed central line array) to provide energy cancellation behind the array and enhanced control
flexibility are ongoing.
(a) Horizontal line array

Figure 72: Centre subwoofer line array (a) without and (b) with electronic delay processing

To implement electronic delay processing, a 4- or 6-channel DSP is dedicated to subwoofer drive and
the SB218 DELAY ARC 80 Hz preset (subs with negative polarity) used in conjunction with X preset
processing or 3W stereo presets for the flown dV-DOSC/dV-SUB arrays. Alternatively, the SB218
DELAY ARC 60 Hz preset (subs with positive polarity) can be used in conjunction with INFRA preset
processing for the flown dV-DOSC/dV-SUB arrays (60 Hz crossover point).
For field implementation, SB218s are circuited in blocks of four symmetrically about the centre axis
and powered by half of an RK124 amplifier rack. The appropriate delay tap for each half of an amp
rack is then selected using the DSUBTK comb connector kit (set of 6 COMB connectors for T1-T6).
dV-DOSC dV-SUB Manual V3.0
(b) Delay processed horizontal line array
June 2005
93