Nexo NXAMP - Manuel (Page 36)

ENGLISH
PAGE
36
APPLICATION NOTE : DRIVING THE SUB FROM THE AUX SEND
NX242 USER MANUAL LOAD2_22
DATE : 12/3/2004
The two overlapping phases are those of the CD12 and S805 as they should be. The green curve is the
same as the blue one with a 2ms delay.
0
-90°
-180°
0
90°
180°
50 100 100 20 200
0
-10
-20
0
Hz
Sound Pressure
(dB)
2ms delay on Sub
System in Phase
50 100 100 200 Hz
System Phase
Sub Phase
Sub Phase delayed 2ms
On the magnitude graph display the difference between the well aligned system and the one with the
CD12 2ms delayed. The difference is 2dB at 100Hz. This example is displaying the consequences of a
slightly incorrect alignment. If we add to this the delay introduced by a slightly different electric path plus
the “small” delay introduced by some processing, plus a EQ filter done by the user near the cut off
frequency…The graph above could shows differences in excess of 6dB. (Up to the point where the
system might work better if you reverse the polarity of the sub !)
Precautions & check
Before using the AUX send of your desk ensure that the output are in phase (you can feed a 100Hz
signal at the input and monitor the MAIN and AUX on a dual trace scope)
Always apply EQ or processing to both signals feeding the NX242. So the phase relation is not affected.
Never add additional low pass filtering on the SUB. (or high pass to the main system)
Inverting polarity on one channel should always result in a massive difference near the crossover point. If
the sound is more or less the same the system is no longer aligned.