Quote:
Originally posted by lessthanpunk
I'm looking to buy a decent Pa system for use djing, for my band, and for shows that I hope to be putting together. Right now, we have a 300 watt powered peavey mixer and 2 avatar 15 inch pa speakers. Sometimes we DJ dances for the local schools and other events, but the bass is very minimal. So I'm looking at a pair of speakers like we have now, 1 or 2 18 inch passive subs, a 8-16 channel mixer, a cd player, and one or two qsc? power amps. All rack mounted. Since I've never used power amps or subwoofers, what would i need to do to make that work? And how would i separate the lows to the subs and the highs to the mains? Would i need two separate power amps? And what kind of mixer would I need to do that? All help is greatly appreciated, I'll probably have more questions I may post later. Thanks! |
I came to this thread late, so you may have worked all this out. But just in case...
The missing piece here is an active crossover. That will take the output from your mixer's mains and separate the frequencies that should go to the subwoofer(s) from those that should go to your main Front Of House (FOH) cabinets. The signal chain for that is as follows:
mixer mains output => active crossover
high frequency crossover output => PA Mains power amp => PA Mains cabs
low frequency crossover output => Subwoofer power amp => Subwoofer cab(s)
If you're running PA for your band, try to avoid running in stereo and panning to establish a "soundstage image". It usually creates more problems than it solves, and sometimes doesn't permit you to position the cabs to cover oddly-shaped rooms properly. Remember, the primary function of the PA is to allow every person there to hear the band. If they can't hear the lead guitar because he or she is panned to the other side of the room, they won't hear your band the way they would from right in front of the stage -- and they will think the guitar (in this example) can't be heard. Same with singers, etc. -- run a mono mix, and that will eliminate that problem, as well as make your mixing life easier.
For a DJ gig, you may get away with panning a little -- but, on balance, a mono mix generally works better for the same reasons I just outlined.
These requirements mean that two channels of power amp are a bare minimum -- but four will be a lot better. Why? Well, since subwoofers and their low bass frequencies require a lot more power to reproduce at a given volume level, it's likely that you'll have to bridge two channels of a power amp for the subwoofers alone. If you're running a DJ mono mix, you can run the second power amp in bridged mode for the mid/high frequency Mains (for example, your Avatar cabinets), or just run a single channel and keep the other channel in reserve as a backup. If you're running a band PA, you'll need a power amp channel for monitors as a minimum -- and, if you want to have different mixes for different musicians, you'll need a power amp channel for each separate mix you provide. In addition, the mixing board you select must be able to support at least as many
pre-fader sends as you have monitor mix channels -- otherwise, different mixes with varying levels wouldn't be possible.
Don't forget backup, either. If I can stress something to you, it would be this:
never gig without backup. You don't necessarily have to duplicate all the equipment, nor even just the major pieces. But you MUST have a plan of action in case something fails. If a piece is critical (like the mixer, for example), it must be backed up. Maybe a less-capable, cheap mixer could cover it if the new mixer you plan on buying goes down for some reason. You may need to run only one monitor mix, or the subs may not be as powerful as you'd like if their power amp blows.
But you MUST be able to complete the gig, somehow. It might take running all the vocals through the guitarist's amp, but it's better to do that than to have to halt the gig altogether. Her's another suggestion: write the backup plan down. Have you and your bandmates run down all you think could go wrong, and how you would cover it if you had to.
Sorry for the long-winded post. I've just been there. done that, and bought the t-shirt.
