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Help a P/A moron with some technical advice

Discussion in 'Recording/Live Sound' started by justonwo, Feb 2, 2008.

  1. justonwo

    justonwo Member

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    Guitars? I have that completely covered.

    P/As? - All I know is that ours sounds terrible.

    Here's the setup: I play with my band in our 20' x 12' rehearsal space every week. We gig maybe a couple of times a year. Mostly, we just play for ourselves. The singer is consistently lost in the mix, the P/A just plain sounds bad, and our mics feedback like crazy if the volume gets too high.

    Our current signal chain for the vocals:

    Shure SM58 --> Mackie CR1604-VLZ mixer --> QSC USA900 amp --> Shure Model 702 floor monitors

    One thing I noticed right away. The amp is 450 Watts per channel and those pathetic floor monitors are 50 Watts. I don't know what you need to do to get 450 Watts out of that amp, but I'm pretty sure those monitors are being overwhelmed. I'm also fairly certain that the floor monitors are low quality to begin with (not to mention old and probably terribly inefficient).

    What I would like:

    1) More volume out of the P/A
    2) More clarity
    3) No feedback

    My questions:

    1) I assume I need new floor monitors or P/A speakers. Which one is preferred for my application? If new floor monitors are required, I have a budget of $600 for two new ones. I have an opportunity to get two SM12Vs for $250 each, but I'm not sure if that's a recommended model. Any other suggestions on models would be appreciated.

    2) How do you regulate the power out of the amp? Since you are driving it externally, how would you even get 450 Watts out of it (i.e., max power)? (I noticed there are pots on the amp input that look like they attenuate the input signal).

    3) Do I need a better mic? The salesperson at the local music store said that an AKG D-5 would be better overall, especially the anti-feedback technology.
     
  2. loudboy

    loudboy Member

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    If you're talking about Yamaha Club Series wedges, they're pretty decent. Probably #1 in their price range.

    However, to really get them cranking, you'll need a 31-band graphic EQ. dBX makes some good ones that are reasonably priced. Avoid Behringer, as it will make it sound worse...

    It goes between the mixer and the power amp.

    Loudboy
     
  3. epluribus

    epluribus Member

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    Process of elimination...

    The mics are fine unless they're busted. Shure SM58s are just about the most road-proven vocal mic in existence. :) BTW, feedback doesn't equal busted.

    The power amp is also an excellent road warrior. Great S/N, transparent, very reliable.

    The knobs on the back are gain knobs. Two schools of thought on power amps with gain knobs. (Many, btw, don't have them at all and run full blast all the time.) Some folks run 'em wide open, (per the above parentheses) and turn the rig down with the master faders. Others run the faders at Unity gain (the zero index near the top) and set the house volume with the gain knobs on the power amps. I prefer the latter, gain structure, S/N and all.

    As for the speakers, I'm not big expert on those. That said, I suspect they may be too small for anything other than your rehearsal room. Though I'm sure they're "full-range" monitors, they probably simply don't have the oomph to do justice to the low end. I'd also bet that absent global EQ, they're coloring your sound quite a bit. As for whether to keep or sell, I bet there's lots of other folks around here who can answer that much better than I. (See Loudboy above. I trust his speaker opinions more than mine. :))

    Feedback...you likely have two or three problems, none of which mean you have a "bad" system, but may also be something you can do nothing about.

    I note you don't use a 31-band graphic EQ between the mixer and the power amp. Sometimes you can alleviate feedback by dialing the offending freq down. But that may not be enough in your case.

    Mic orientation is really important. My second suggestion would be to take a look at that. Ideally, you want the speakers directly behind the mic in the dead spot, and that will go a very long way in killing feedback...except in a small room.

    In your case, you have sound bouncing off the walls like crazy, and getting the speaker output into the mics may be all but inevitable. You could try adding mic baffles just for fun, but I'd bet it still feeds back. You could also try covering the walls with acoustically dead material to reduce reflection, but 20 x 12 is gonna be a bouncy space no matter what you do. (Short of anechoic foam I suppose.) It may just be the room. Annoying, but spending dough won't fix it, so you may as well save the cash for something more fun. To see if this is indeed the issue, try the rig in a bigger space and see if the feedback doesn't go away. If it does, it's the room.

    So personally, I'd keep the mics and the amp, good stuff there. I'd try the rig in a bigger space, and I'd also borrow or demo a graphic EQ and see if that doesn't solve both your feedback and tonal issues. Finally, I'd borrow or demo a new set of speakers, but definitely try before buy. You may just discover that new gear isn't the answer, or at least not the gear you thought. Some nice machinery you got there.

    jm2c.

    --Ray

    BTW, the Yahoo group RigTips is very PA and FOH oriented, you might peruse the archives there. Their Files collection is must-read stuff, very useful as well. And of course you could always ask this question in an actual post. :)
     
  4. justonwo

    justonwo Member

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    Thanks so much for the in-depth answers, guys. I appreciate your time. One question about the speakers. If the power amp is rated at 450 Watts, then I'm assuming a big enough input off the Mackie will actually give you 450 Watts. If we are anywhere near that output, I'm surprised we haven't blown those speakers (50 Watts each) to bits. What gives?
     
  5. dk123123dk

    dk123123dk Member

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    I'm assuming you are running the amp in stereo mode? Ie both outputs are being used to drive one speaker?

    Also assuming the monitors are 8ohms. With the amp on full blast you will be running 270 watts according the the manufacturer. That is enough to blow your current speakers if you haven't already!

    So you're looking at
    1- 31 band eq
    2- 15" Monitors

    http://www.musiciansfriend.com/product/dbx-131-Single-31Band-Graphic-EQ?sku=183525
    +
    http://www.musiciansfriend.com/product/Peavey-PV-15M-15-Floor-Monitor?sku=601421

    = $650

    Like others said you gotta watch the placement of the speakers in relationship to the mics. That shure mic you have has is strong point in the front or sides, so make sure you point that end AWAY from the speakers.

    It might require you to setup the practice space around the PA system, not the damn drummer! Ha!

    dk
     
  6. bigroy

    bigroy Member

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    PM me for more details, but first things first, you need an EQ for both mains and monitors . A dual 15 band should work. Start there. You can snag a decent quality unit for around $100.

    I'll be happy to walk you through the process....
     
  7. justonwo

    justonwo Member

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    Ray, great tip on the Yahoo Group. The information in the "files" is definitely helpful.
     
  8. loudboy

    loudboy Member

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    I would strongly recommend against 15" drivers in monitors. 12's will handle all the frequencies you need to hear much better and be both smaller and cheaper.

    The Yamaha Club Series is a proven performer, and will give him just what he needs, especially since he has enough power to drive them with.

    Loudboy
     
  9. justonwo

    justonwo Member

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    loudboy, if the power amp is rated at 450 watts per channel, and the monitors are only 350, how do I ensure that I don't blow them up?
     
  10. loudboy

    loudboy Member

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    You won't - there's actually LESS chance of blowing them up if the amp is slightly more powerful. Pushing a lower powered amp into clipping is what will kill a speaker. Yours will be matched up just about perfectly.

    Loudboy
     
  11. drfrankencopter

    drfrankencopter Member

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    How are the acoustics of your rehearsal room...? If it's pretty lively, then your best bet is to deaden it up with absorbtion prior to spending dough on different monitor cabs/amps.

    How about an in-ear monitor approach? Is it within budget?

    Cheers

    Kris
     
  12. dave s

    dave s Member

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    What you have:

    Good board
    Good power
    Good mic(s)

    Gotta be your speakers. As most have indicated, a 31-band EQ between the power and board would be a good idea.

    Look for a couple of USED 15/horn cabs that are inside 5 years old and say Yamaha, JBL, Yorkville, EV or even Peavey on them. Wedges or boxes--either will work.

    To get the most horsepower out of your power amp, you run the amp in bridged-mono mode, run a single line to one speaker, and a second line from speaker 1 to speaker 2 creating a 4-ohm load on the amp. This should get you about 600w of power from the amp.

    Use the board to set gain levels (run them up to "0") on the led strip, or until the loudest 'screams' turn the channel peak light on. Back down channel gain just a bit.

    Turn up mains on board, you should have loud AND clear vocals.

    dave
     
  13. epluribus

    epluribus Member

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    Glad you liked it. Quite the Rosetta Stone they have there, even useful for understanding what your guitar rig is trying to do. Great group of regulars too, very enthusiastic about helping n00bs. :BEER

    --Ray
     
  14. justonwo

    justonwo Member

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    Ok, so now I have my dual 15-band EQ and a new pair of Yamaha SM12V monitors (8 ohms each, 350 Watts each).

    How on earth do I connect these things to the power amp to match up the power ratings correctly? I understand that I don't want to under- or over-power the speakers.

    The power amp manual is here.

    http://media.qscaudio.com/pdfs/usausr.pdf
     
  15. 6789

    6789 Member

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    First, replace the shure sm58 mics. yeah, they are the industry standard but so is Britney Spears. Get an Electrovoice N/D967 it is much louder, fuller, richer, deeper, and has more clarity than the sm58. in side by side comparisons, the 58 sounds like a sock is covering it. the N/D967 will give you much more volume before feedback.

    then get a feedback destroyer. about $40 on ebay.
     

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