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Building a PA With What We Have

Discussion in 'Live Sound [BG]' started by tonybassman, Jan 2, 2014.

  1. tonybassman


    Jul 27, 2011
    I am trying to build a decent PA for a cover band that I am in. We are ready to gig in few weeks. I am trying to use the passive speakers and gear that we have collectively. Later down the road I am looking into powered JBL cabs and a Mackie passive mixer, but to get us started I am trying to use what we have.

    • Yamaha EMX512SC powered mixer
    • Yamaha BR12M (4 each)
    • JBL JRX118 (2 each)

    We can do a small gig with two BR12M’s for mains and two for monitors using the internal amps in the mixer. That would mean that we only put vocals, guitars, and maybe the kick in the front mix. Not the best but it will work.

    I want to get a full sound and use the subs. I believe the only way to do so is to use a pair of power amps with built in crossovers as I have shown in this cheesy diagram.

    So here are my questions:

    Will this design work ok?

    If so, what amps would you suggest?

    Is there a single beefy enough amp that could pull this off instead of two?

    Should I place the tops on stands and place the subs together in the center of the stage (or either side)?

    I am looking at these amps. The Behringers look attractive due to their weight!
    • Behringer NU3000. $299 each, 4 Ohm per side at 880 Watts. 8.75 lbs
    • QSC GX3. $299 each, 4 Ohm per side at 425 Watts. 27 lbs
    • QSC GX5. $399 each, 4 Ohm per side at 700Watts. 28 lbs

    Thanks in advance!
  2. You usually see it set up that way and it's all wrong. Get to that later.

    I would avoid Behringer digi amps myself. They aren't well built. I'm not completely anti Behringer as they make a few standout value items, but I don't think these will make that short list.

    Generally split subs like you indicate are bad for business. If they can't go together in the middle in front of the stage you want to wall load them to one side.

    Best bang for buck is used, but I am envious of new QSC gx5 for $400 all the same.

    If I was you I would get a proper 3way rack crossover and run mono mix. Use the mid and high outputs The low out is discarded as your highpass to protect your subs, while getting the most out of them. Then you can use any old amps. Your tops need less than half the amp than what your subs need.

    Stereo is for the birds. In a bar nobody hears the stereo unless they are close to equidistant.

    You'll make quite a racket with that little lot! Enough that you'll want to get in on it with the bass. If your rig is a 4x10 or bigger you will create a lot of mud unless you dial it right back on stage. Otherwise forgo the PA.
  3. 4Mal

    4Mal Supporting Member

    Jun 2, 2002
    Columbia River Gorge
    Group the subs as you can. Tops on stands. I would prefer a decent active crossover. Not a lot of dough, more precise control... I would look at a used qsc plx2402 as a single amp solution. I used to run 1 as my amp for tops and bottons using a Yamaha EMX5000 powered board. On board power went to monitors and things were just fine. I would also add a more surgical EQ. Stereo 15 band like the Peavey FLS that shows you where feedback is occuring through their led light systems.

    One band I'm in uses the same powered head as yours into a pair of passive 15 and horn PA cabs that I built up years ago and a pair of Carvin wedge monitors. We put the kick into the PA but not bass. Small clubs it works fine... And I don't have to carry it...
  4. Does plx2402 do 2 ohms?
  5. 4Mal

    4Mal Supporting Member

    Jun 2, 2002
    Columbia River Gorge
    IIRC... Yes. Gotta go webby and remind myself... Yep. 1200 watts at 2 ohms and 1% thd.

    Here's a link to the old specs at Zounds

    I used to think of the old beast as an 'audio welder'. Just get a couple of subs and a couple of welding rods and fix the low end as we know it... It is a ridiculously strong amp...
  6. tonybassman


    Jul 27, 2011
    Downunderwonder – Thanks for the tips. I understand that keeping the subs together is best. I agree that the QSC would probably be a better choice than the Behringer, just heavier for this old man!

    And although I was using the left and right outs, everything is really just mono. I am not left-right signaling anything.

    This is what we are going to start with, but with 12's since that is what we have. I have done this before and it works ok for small clubs.

    Perhaps we could go with this version using a single sub and a single QSC GX5. That would be one purchase and give us 700 watts to the tops and 700 watts to the sub. That should be plenty of power.

    I understand that better EQs’ and crossovers would be best, but I am trying to do this cheap for now.

  7. 4Mal

    4Mal Supporting Member

    Jun 2, 2002
    Columbia River Gorge
    I personally would spend for the used 2402... It is a way more industrial amp... Lighter too! A decent eq and crossover is maybe a $250 buy used. Yeah, I know. It all adds up.... Trust me as I know that well... Still. You really want to present as best you can and the outboard gear will really help. I would also add a decent compressor to the mix...
  8. Zooberwerx

    Zooberwerx Gold Supporting Member

    Dec 21, 2002
    Virginia Beach, VA
    Sounds like you're off to a good start with what you have on hand. Probably be just fine for a small / medium venue. I would be concerned about your EQ capability, though, if to control feedback if nothing else.

  9. Barisaxman

    Barisaxman Gold Supporting Member

    Aug 17, 2005
    Omaha, NE
    Disagree here...unless you are actually trying to fix something specific with the comp, don't bother. You'll likely create more problems than you'll fix. There's a million web posts about putting a comp in, generally "just because" when most bar-level operators/musicians don't even know what they really do or why they would use it, especially across the whole main bus.
  10. tbirdsp

    tbirdsp Supporting Member

    Sep 18, 2012
    Omaha, NE
    I have a Behringer powered mixer similar to your Yamaha. I assume you have 2 power amps in the head that can be used either left/right or main/monitor? What I did - took one side off the powered mixer for two 8 ohm Carvin PM-12 top speakers. Other side for two 8 ohm 12" Behringer floor wedge monitors. Ran left main out to a Crown XLS 2000 bridged into a 8 ohm Carvin LS-1801 sub. Amp's low pass set to 105 hz. I had the sub cab on one side with a PM12 on a pole over it, other PM 12 on a stand. This doesn't keep the lows out of your 12's, but with the sub carrying the bottom you don't need to turn up loud enough that it will be a problem. Worked well for a blues band. For more grunt I would just add my second sub cab so the XLS 2000 would be running at 4 ohms. In your case you could just run the amp dual mono then with a 4 ohm sub on each side.

    There are several ways you can hook it up, and it sounds like you have a pretty good handle on things. You'll be fine.
  11. tonybassman


    Jul 27, 2011
    Thanks for all the feedback. I think we will try the single amp-sub setup. Will report back on that later!
  12. will33


    May 22, 2006
    I've been running my system just like you describe for quite sime time noww, works great, and really, until you get to larger dancehalls, crowds over a couple hundred, or loud music like metal, you really won't need any more system.

    Can find crossover and poweramp, $300-$400 used for both. I run out from frontend of powered mixer and through that, sub on one side, mono mains on the other, then use mixers built in amps to run monitors.

    Also lets you scale back to just the mixer for rehearsals, really small bar gigs, etc.

    Setup is fairly easy. With good positioning and gain structure, you shouldn't much trouble with feedback out front. May want to pickup one additional eq if you're having trouble with monitors ringing.

    The better your group is at mix-slotting your own tones, the less knob twisting you'll have to do. We got ours down to where there's only about 3 channels that require much for "real mixing" and can get a fairly professional sound out of such a simple setup. Plenty good to impress in the smaller places we play. I don't have to drag out the "big system" much anymore.

    The more streamlined, less complicated you can make this thing, the easier it will be to get a good sound faster when running it all yourself.
  13. I would never run those 12's full range with sub. The sound you eq for the sub will play merry hell with them.
  14. tbirdsp

    tbirdsp Supporting Member

    Sep 18, 2012
    Omaha, NE
    Not ideal I agree - but it worked. I was able to EQ everything by using the graphic on the mixer and the level control on the sub amp.
  15. That looks like it would work fine, but your diagram appears to be using a single line from mixer to amp. This would give you no mixer control over the Mains/Sub balance. I would feed the amp with L and R lines so you can use your L R controls to control Mains/Sub balance (or, on that mixer, perhaps just a "balance" control." Your way you could set that balance with the amp channel attenuators or on an adjustable crossover and run in "set and forget" mode, but I prefer having that immediate control available.

    700 watts to the sub will probably be more than adequate, and 700 to those two mains definitely will be.

    Edit: WAIT I just looked at a closeup of that mixer, and I see that mixer has no control over balance on the inputs OR the outputs (sorry, I'm used to mixers with a lot more features), which means that you would still have all your inputs feeding into the Sub and no balance control. I would use the "Effect Out" as my Sub send, which would allow me to prevent sending anything to the Sub from inputs I didn't want in the Sub, as well as putting control of the Sub/Main balance on the mixer.
  16. Two 250w channels in the mixer should be plenty for monitors and tops. The trick is the routing. As nifty as aux fed subs can be it can be dispensed with if too tricky. I'm inclined to insist on the crossover inserted on your main mix to get the sub amp in play and two subs running.

    And Eq! Old Rane 31band EQ have a shelving, great for your monitors to keep sub frequencies out of them.
  17. tonybassman


    Jul 27, 2011
    I did not draw up the second diagram correctly. The left and right main line out would go to the amp, one each side. The amp has a crossover in it. So the volume would be controlled from the mixer's main volume control.

    I would have to tweak the left (low pass) and right (high pass) volumes on the amp itself a little to get that balanced but I think this will work fine.

    edit: and although I am using left and right outs, nothing is stereo. All mono.
  18. That requires you to use the amp's crossover frequency, also has no highpass on the subs, and you need two big amps.

    Used crossovers and EQ units are cheap as everyone goes digital and you need only one big amp doing it as recommended.
  19. tonybassman


    Jul 27, 2011
    I might not be explaining myself clearly, sorry.

    All of the amps I am looking at have a built in crossover. High pass and low pass. So I believe this will work fine.

    Just need to set it to use the crossover instead of full range. Tops off of channel 2 and the single sub off of channel 1 of the power amp. I would just need to dial in the channel 1 and channel 2 levels on the amp and drive the overall volume with the master volume on the mixer.

    I would be using left and right main outs, but everything is mono so it would be the same signal. I think this makes sense...?

  20. 100 Hz is getting up into the directionally perceptible frequencies. I think 80 Hz or below is preferred for Subs. It would still work though, and you could upgrade to a fancier crossover later.

    I would still recommend using your Effects Send for the Subs, as it's the only way I see on that mixer to have control over which channels are sent to the Subs. The fewer available feedback loops, the better,.