Help - adding active subs to our PA

[Walker]

We are an acoustic band (3 x vox, acoustic guitars, uke, banjo, keys, un-mic’d drums and me on bass and EUB). We don’t play loud. After sounding a bit thin during our last gig, I’m looking to add some cheap active subs to our PA system. The subs I’m looking at have an adjustable cut off frequency.

Could I just run them from a aux from the desk, turn the volumes up on the subs and control their volume from the desk using the aux slider until the right level of bass is achieved?

Also, the sub cut off frequency range is 40 - 150Hz, and my tops have a frequency range of 55 Hz-20 kHz.
How should I set the sub cut off or is it a ‘try it and see’ thing?

Thanks
Chris

[JTUK]

What tops you using...?

They may well have a sub connect

We run ours from a controller.

[Walker]

Good thinking, but no, they don't I'm afraid.

We are using a little Yammy Stagepas 500 system as an amp and tops. Enough volume for the gigs we play, We feed that from our desk.

[flyfisher]

[quote name='JTUK' timestamp='1362414938' post='1999298']
What tops you using...?

They may well have a sub connect

[/quote]

Alternatively, the subs may have a filtered output for the tops anyway (or tops&separate amp in this case).

We use a single Mackie SWA1501 sub with two Mackie 450 tops. The main stereo mix from the desk connects to the sub and there are outputs from the sub to each top.

[JTUK]

If you run subs from the aux channel, you'll waste an out signal...but if that isn't an issue, you have a degree of control.
You could see if the subs you buy have an out to the tops which will x-over the signal to the tops..


If you aren't loud you may just get away with one Sub...

[mike257]

One benefit of running subs from an Aux send is that you can control which individual signals are sent to the sub and only send the channels that will benefit from that level of low frequency reinforcement. Can achieve a clearer and more focussed bottom end that way.

[Walker]

[quote name='mike257' timestamp='1362438969' post='1999941']
One benefit of running subs from an Aux send is that you can control which individual signals are sent to the sub and only send the channels that will benefit from that level of low frequency reinforcement. Can achieve a clearer and more focussed bottom end that way.
[/quote]

Very good point, little point sending the mandolin signal to the subs! That makes a lot of sense.

Thanks for the input everyone - I'll try one sub first too.

[Dad3353]

[quote name='Walker' timestamp='1362555302' post='2001111']Very good point, little point sending the mandolin signal to the subs!...[/quote]

Hmmm... Dunno about that. Depends on the instrument, perhaps..?

[attachment=129156:Bass_mand.jpg]

[Walker]

[Monckyman]

This is perhaps the fourth post about subs today, something in the air?
You need a crossover to properly set up your system.
Running from an aux is fine, and if the sub has a passive crossover in it to limit what it does thats fine, but you also need to tell your tops not to reproduce anything below the frequency the subs top out at,(150Hz) otherwise youll get both sets of speakers trying to do the same frequency range and it all gets a little confused and muddy.
Your tops may have a filter on them, or a passive crossover in them, and it would be useful to know if they do, and at what frequency they are fixed at.
if not you need a separate crossover.
A cheap crossover can be had for app £50, will let you set the range of frequencies you want for your cabs, and then individually balance the volume of all four outputs.
Saves on that aux out as well.