Nexo GEO T - Manual (Page 46)

Page 46/67 NEXO NX242 D IGITAL C ONTROLLER FOR GEO T
Stacked CD18s
If the CD18s are stacked on the ground, delay will have to be adjusted on the CD18 NX242
TDcontrollers according to the distance difference
r
1
–
r
2
(see figure below).
5.6 Driving the CD18s from the AUX send
It is quite common to use the AUX send of a mixing desk to drive the Sub section of a PA system. This
gives the mixing engineer more flexibility to set the level of the subbass relative to the main PA, apply
special effects, or to use a different EQ on the Sub. However, it also raises some serious issues for the
performance & safety of the system (mostly time alignment).
5.6.1 What is the phase relation between the AUX and MAIN output of your mixing desk?
At NEXO, when we align systems, we take great care to have an optimum phase alignment from one
octave above to one octave below the crossover frequency point. By doing so, we ensure that both
drivers are working perfectly together and providing the best efficiency possible. It is then up to the user
to adjust the delay on the NX242 to match the physical path difference of the different systems. It is thus
possible to get a well adjusted system, even without measuring instruments.
If you choose to drive the Sub from the AUX, you feed the NX242 with two signals coming from different
sources. If those two sources (MAIN output & AUX send) are not exactly in phase, you are introducing a
delay – without knowing it – into the crossover between your GEO T array and your CD18 subs. Without
the proper measurement tools, you will never be able to tune the system as it should be.
5.6.2 Why it is unlikely the AUX and MAIN have the same phase?
• Signal paths are likely to be different; any filter modifying the bandwidth and EQ of the
signal is also affecting the phase.
Example: a 24dB/oct high pass filter set at 15Hz is affecting amplitude of the signal by only
0.6dB at 30Hz, but the phase shift is 90°!! At 100Hz we can still measure 25° of phase shift.
1200 mm [47.24"]
750 mm
[29.53"]
750 mm
[29.53"]
1200 mm [47.24"]
750 mm
[29.53"]
750 mm
[29.53"]
1200 mm [47.24"]
750 mm
[29.53"]
750 mm
[29.53"]
r
1
r
2
1200 mm [47.24"]
750 mm
[29.53"]
750 mm
[29.53"]
1200 mm [47.24"]
750 mm
[29.53"]
750 mm
[29.53"]
1200 mm [47.24"]
750 mm
[29.53"]
750 mm
[29.53"]
r
1
r
2