Adding an active subwoofer to passive foh speakers

[jeffhill]

Hi, Ive just bought a powered class d sub for my band pa system to run with 2 existing passive front of house speakers. I haven't run them together with the live band yet, but I can get a good balance with music from my ipod. My question is, do I need to use the high pass from the subwoofer to the top speakers or do you think it will mix ok live as a stand alone?
Thanks

[Feanor]

Hi, Ive just bought a powered class d sub for my band pa system to run with 2 existing passive front of house speakers. I haven't run them together with the live band yet, but I can get a good balance with music from my ipod. My question is, do I need to use the high pass from the subwoofer to the top speakers or do you think it will mix ok live as a stand alone?
Thanks

It often works out well to run the mains speaker full-range and the sub with an appropriate setting of its built-in low-pass filter. However typically the sub's low-pass setting must complement the mains inherent low frequency roll-off.

That is, if you main speakers (by design) roll off at, say, 50 Hz, then your sub's low-pass should probably be set at 50 Hz to match it. Phase should also be considered: most subs have a phase switch, 0 or 180 degrees or variable. Typically you set the phase to the position that yields the most over-all bass at a given sub volume setting, then set the sub volume for the right total sound spectrum balance.

On the other hand if your main speakers' power handling is limited, you might benefit from using a high-pass filter to limit the bass going to them to something above their inherent roll-off. So the mains roll-off might be 50 Hz, but you would use a low-pass to limit input to them to 80 Hz or even 100 Hz, and let the sub carry the lower frequencies.

[harley .guy07]

I agree with Feanor in that I always will try to let the main speakers run full range when adding a sub when the speakers can handle it. This allows there to be no interaction between amp and main speaker and they always will remain their most natural sounding. Only if the main speakers have a low end weakness(can't handle bass well) or you are simply going to run the pa speakers at volumes that will hurt the mains if you ran them full range would I ever suggest putting any kind of high pass crossover circuits on the main speakers.

[jeffhill]

Thanks for the advice, it sounds pretty simple really!