I am getting ready to start running a audio system that consist of two Harbinger HX151 two way speakers with a JBL JRX118 sub. I have two amps (RMX1450 by QSC) one for the mains and one for the sub. I will run one amp in stereo and use a bridge mono setup for the sub. Here is my question, do I need to use an active crossover to seperate out the low end prior to to send the signal to the sub amp?
If your receiver or processor has a LFE output, then that will handle the sub signal. If the sub has a cutoff filter, then the mains can be signalled fom there.
Yes, it's what you have in front of the amps that determine whether you'll need an active crossover. My guess would be that since you asked, you do not have any sub or "LFE" outputs. If that's the case, yep, you'll need a crossover to get the best performance.