The "trick" to using the EQ is to use it very sparingly. Basically, if you find that there are bands that are pulled down by more than -6dB,you gotta problem. And there shouldn't be any boosts (for the time being). Roll off the very low end (below 120Hz) as much as possible, screw what I said about the -6dB in that region.
The compressors threshold settings should be fairly high, so that it acts more like a peak limiter. If the setting is too low, it will try to "suck up" all the gain and induce feedback.
Are the JBLs on poles? You definitely want them to be so ON A GIG, where the sound is being fired out front. Helps to maximize coverage.
BUT not so helpul in a cramped rehearsal room. Why? Because in that scenario, they are basically at the same height as your mics on stands!
when you turn them around to hear them firing at the band. they're also firing at the "hot spot" of those Shure mics, and that induces feedback, too. So, put the JBLs on the floor with the monitors, and aim them up at your heads. Use a cinderblock or an old spare tire to prop the speakers back on. Be sure to aim the speakers so that they fire at the "null" side of the mics. With the Shure PG58, that will be the rear of the mic, as opposed to the sides. BTW, the PG series from Shure is mediocre. A "real' SM58 will work and last much better.

Thanks for the advice!
Right now, the main speakers are essentially in the corners of the room, at ear height, facing the main vocalist. I tried not to box him in too much, so it didn't get too hat right where he is, although I do want him to hear it (obviously). The monitors are angled and on the floor, so I'm not too concerned about them.

I probably need to re-eq it, it's been messed with so much over time. I will definitely give the compressor a check as well.

I know it's not all the best quality, but I'd really rather not upgrade until something just doesn't work. I have a feedback destroyer that hunts down the hot frequencies, so I'm going to try that in the chain before the compressor.

I suppose I should invest in a new small format mixer, though, because I'm willing to bet it's giving me a pretty hot signal, and that wouldn't be helping the feedback issue.

All in all it's pretty good, but hopefully this will help me maximize what I have. Obviously it would be cool to have a killer PA down in my guitarist's basement... but there really isn't much of a purpose, seeing as we never take it out of there for anything.

Thanks again for the help, I'll reply if I have any breakthroughs! :lol:

My Experience

I hate to make this sound so simple but tell the band to turn down. If you do the PA vocals louder the band will just turn up.
On way to do it is to take, like the guitar players amp and position it so that the speaker points right at his $&@$(% head, do that for the rest of the band to, that usually let's them know how loud they are, not that it will knock any sense in their head and they'll turn down, but at least you get some satisfaction at shoving in their ear.
Funny this is on of my pet peeves..........why is it so hard for musicians to get it thru their thick heads that they have to play at the right volume to let the vocal or lead come out.............It just goes to show the caliber of brain power you're dealing with, I think a chimp would have enough sense to get a simple concept like that, but that's a chimp not a musician.
When no one is playing I'll bet your PA is plenty loud....all the band is doing is burying your vocal.
I can't tell you how many time I stop the song at rehersal and tell people (idiots) to turn down, I get sick of saying it, you'd think they'd freadin' get it.
If you can't get them to learn how to play in proportion and back up the vocal, you are in a losing battle, I feel your pain.
The second problem is probably that the band is just playing way to much as in just doing to much, to many notes, smashing cymbols, smashing guitar chords.
It just continues to amaze me that so many musician (so call musicians) never get it, just goes to show how good they really are if that can't catch on to a simple concept like that.
I'm going to see my friend's band tonite, haven't heard them before but I know exactly what it will sound like, like every other local chump band........just a big loud mush, simple amazing they never catch on, go figure, most bands would improve their sound 10 fold by doing one simple thing, PLAY CLEARLY and PLAY IN PROPROTION and DON"T BE AFRAID TO PLAY NOTHING SOMETIMES..............but we're not dealing with the smartest and brightest, we're dealing with musicians.

I suppose you didn't read my post entirely. Thanks for the rude assumptions anyway!
We're not all that loud, I have a Marshall DSL 50watt head and it's running through a 16ohm cab... that's not all that loud or offensive. My other guitarist is matched to that volume pretty well. None of us have the "loudness ego" anymore. It's really just the room and possibly some of the equipment (mostly my settings, probably), but thanks for the input!

A couple of quick reactions:
1. Moonbaby is right about the compressor. You really want at most a few dB of compression at any time. I don't really like using a vocal compressor on a "set and forget" basis. I feel it's better to have someone riding the threshold. It's the only way to smooth out soft passages without killing the loud ones. Idon't hook mine up in the practice room. Try it without and see what you think.
2. I've had some bad experiences with feedback destroyers. I've used some expensive ones that work pretty well, but I once had a Behringer that I renamed "gig destroyer." If you have one, give it a try; but be prepared to pull it.
3. The room may not be bad acoustically, but it could be better. Check out the acoustic forum. If you have a local source of Owens Corning rigid fiberglass (703 or 705) the easiest quick fix for your basement is to buy bales of the 2'x4'x2" sheets and put them in the corners unopened. It can make a huge difference with less than 15 minutes work.

All good ideas. As for a volume knob on the drummer - we've put items around the kit like a short bookcase, homemade baffle, blankets, sleeping bags, even a mattress on it's side. It is also possible to play drums quietly during practice without all that deading 'cause the bass drum get lost with all that padding. For vocals, we've been using Audix OM-6's. They call themselves a hypercradiod and don't get a mid eq proximity boost when the vocalists "eats" the mic. They have a pretty tight sweet spot, but once you're used to it you shouldn't need eq or compressors. We have our PA speakers along one wall (like you), with the drum kit to one side under a main. Your mains will probably sound better than your wedges. We also put our amps along that wall pointed at each player giving a "wall o' sound". This gives the PA, drums and amps room to "mature" as we stand on the opposite side of the room in an arc. This also allows for eye contact between the band and the drummer. Amp stands for the guitarists really improve the sound (we all use combo amps). A couple guitarists swear by Fender Blues JR. It's all tube, a lot lighter than a 4 x 12 cab, and some can plug their guitars in straight - getting great tone without pedals! Set the amp and guitar level at 5. Turn up for fuzz lead - turn down for clean! We eliminated the floor monitors (gaining a lot of floor space) except for the drummer 'cause even sitting amongst the amps, the sound is pointed at the rest of the band. A little reverb on a close miced snare can add a full texture - but use just little efx (no dry signal). Yeah, its a pain to mic the amps and send the drummer a full mix, but I know our drummers are grinning like monkeys when they can hear the whole band, and get ready to walk when they can't. The main thing, though, is to set each stage of each of your audio gain paths to "unity". Getting good mics, mic placement, vocal technique, each channel's trim set so it "breaths" naturally (not too low - not too high), go a long way to eliminating feedback and/or chasing levels before you ever turn up that power amp. Then, you can get to that "set it and forget it" place, have good sound throughout the room (not just in front of a monitor's sweet spot), and concentrate on having fun!