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mixing powered mains with passive subs?

Discussion in 'Live Sound [BG]' started by stinger12345, May 2, 2010.


  1. stinger12345

    stinger12345

    Jan 24, 2009
    Hayward, CA
    My local 'list has some db Arena 18's for a good price of $275. Does anybody have any experience with these? I tried searching, but it's hard to get good results with such a short search subject. They're passive, but have an internal crossover, which I think is a plus. Also on the specs page, it says, "Frequency Response [+/- 3dB] 35 - 150 Hz", can anybody tell me what that means in lehman's?

    I'm also curious what the logistics are behind combining powered mains (older JBL Eon 15s) with passive subs like these. I don't imagine there should be any problems, but I want to confirm it with you guys before I do anything I shouldn't. And lastly, considering they're 600W rms and 1200W peak, what's the power amp wattage range I should look at?

    Thanks!
     
  2. Kael

    Kael

    Dec 26, 2004
    Oklahoma City
    I play with an act that does this. We use a couple powered mains and then use a passive 18" Peavey sub. We fake a crossover to the mains by using the global EQ on the board to kill all low end going to the mains then we run the passive sub full range using an aux send. For the record, this is NOT an optimal way to run sound, but it sounds better than I had anticipated it would. The low end would be tightened up if I could filter some high freq's out of that sub, but most of the high end can be avoided by just not sending any aux send from channels that don't need subs (ex: why turn the vocals or guitar aux sends to the subs up at all?). We really ought to just get a crossover and stick it in the case with the power amp we use to power the sub, but it is working for the moment.
     
  3. TimmyP

    TimmyP

    Nov 4, 2003
    Indianapolis, IN
    If they are 1200 peak, they are 600 program and 300 RMS - not a lot of poop unless they are very efficient (at least 103 below 80Hz).

    The internal passive crossover is not a plus.

    Using EQ as a fake crossover - whether as the subs low pass or the tops high pass - is far from ideal.

    You want a proper electronic crossover. And since you need EQ for the system anyway, I'd get a used DriveRack 260 or a DriveRack PA.
     

  4. +1 to what Timmy said. Passive crossovers soak up power. Bypassing it will get you the equivalent of doubling or even tripling amplifier power.

    Regards,
    Wayne A. Pflughaupt



    Pedulla Club #45

     
  5. uhdinator

    uhdinator

    Apr 20, 2010
    Maine
    Nominal Power Rating 600 W
    Peak Power Rating 1200 W
    Impedance 8 Ohms
    Frequency Response [+/- 3dB] 35 - 150 Hz
    Max SPL 132 dB
    LF 18 "
    Voice Coil LF 4 "
    Internal Crossover Yes
    Crossover Frequency (passive) 150 Hz

    You need and amp that is 500-600w per channel @ 8 ohms to run 2 cabs/ one each channel stereo.......OR

    one amp bridged at 1000-1200W @ 4 ohms and run them daisey chained (mono) = Less cost for amp if running bridged

    You need a Crossover and I would use a Xover setting at like 100Hz.
    Mixer into Xover Left/right if stereo
    Xover Hi output goes to JBL Eons (prob 150w gray version I'm guessing)
    Xover LOW output goes to amp for subs.

    Without a crossover (not optimum)
    Run main out of mixer to EQ then JBL's left/right (turn some bass down on back of JBL's and or EQ
    Run a post fader aux send to Amp for subs (most mixers have balanced outs 1/4 TRS-XLR cable) and only send bass and kick drum out that Aux. Crossover in subs
    will only send 150hz and lower to speaker. (the passive Xover will suck up the freq's above 150hz which as mentioned why passive Xovers are less efficient

    If you run stereo for subs and tops you want and amp that has a parallel switch or ability to send Aux into both sides of amp (either a switch or dual input jacks so you can jumper input 1 of amp to input 2. If amp is run bridged you only need one input to channel 1 of amp.

    See your local pro audio dealer where you get the amp and they should be able to explain if you have questions (getting a crossover highly recommended so mixer is going to EQ then Xover so you have more control of tuning in the system. IMO most Subs can sound better if crossed over at around 100hz, higher than that they can sound a bit honky depending on brand/design.
     
  6. 4Mal

    4Mal Supporting Member

    Jun 2, 2002
    Columbia River Gorge
    I do this now...

    Yamaha board (EMX 5000/12), Stereo L&R out to DBX crossover (knob based not driverack style), then to a compressor set to limit the L&R hi's as speaker protection, then onto the JBLS. I take the sub out signal back to the Yamaha as it has on board power and from there to the sub. In bigger places, I use a QSC RMX amp bridged for the sub. As the RMX is an additional amp, I'm happy to leave it home when I can ;~)

    The sub is a fEarful 12. Small, light and more than powerful enough to hang with the eon's.
     
  7. stinger12345

    stinger12345

    Jan 24, 2009
    Hayward, CA
    Wait, so you use a powered board with the JBL Eons? Aren't the JBL's powered? Because I thought you weren't supposed to use a powered mixer with powered speakers? Can someone clarify this for me
     
  8. uhdinator

    uhdinator

    Apr 20, 2010
    Maine
    some powered mixers have line outs as well as speaker (power amp outputs)
     
  9. AndyLES

    AndyLES

    Aug 25, 2008
    New York
    why is it not optimal? all a crossover is is a filter system (ie. EQ).

    Also, major touring acts feed their subs from an aux ALL the time.
     
  10. 4Mal

    4Mal Supporting Member

    Jun 2, 2002
    Columbia River Gorge
    Yep. My EON's are powered.

    My board has pretty flexible i/o and power amp configuration. I generally put the power amps on Aux 1 & 2 which are assigned as 1 of ...

    - 2 monitor mixes (passive floor wedge style)
    - monitor mix & sub
    - monitor mix & bass or keys

    Stereo L&R out I take at line level to my ouboard rack where the crossover & compressor live, along with power conditioning and monitor EQ.

    The EMX5000 series are nice and clear, have 2 effects processors, 2 Auxes, sweepable mids. 500 watts per side into 4 ohms. It's a heck of a board for low dough ... one just sold on the local CL for $375 ... Killer deal for what it is. Sound quality wise it will hang with some much more expensive boards. It's good enough that we upgraded our mic's from beta 58's to Senn 421's ... not that many mic's happily.

    My one gripe is that the 9 band EQ is dedicated to the main outs. If it had another EQ I could dedicate to an Aux - I would lose 1 device from my outboard rack. I know - 9 bands isn't supposed to be real precise but it seems to be pretty effecive for my uses.
     

  11. Not so. A crossover filter continually rolls out response beyond its frequency setting, according to its slope. For instance, consider an 80 Hz low pass (passes only low frequencies, attenuating frequencies above it) with a 24 dB/octave slope (pretty common these days). Response will be down 3 dB at 80 Hz, and down 24 dB at 160 Hz, which is one octave above 80 Hz. At 310 Hz, two octaves above, response will be down 48 dB, and so on.


    n160fig5.
    Response of Various Crossover Slopes


    By comparison, an equalizer filter is a bandpass filter, meaning its action is “hay-stacked.” I.e. its gain change (boost or cut) peaks at the center frequency, with its action (gain change) diminishing on either side of the center. When you try to force an equalizer to be a makeshift crossover by using a multitude of filters, the most gain reduction you’re going to get is a mere 12 dB (or perhaps more in the case of a digital EQ). That’s it, period. Beyond your “crossover frequency,” response will level off to flat, not continually fall like it will with a real crossover. And not even flat, really; the adjacent filters will actually cause a saw-tooth effect, as you see with the picture below. It shows the response of a 2/3-octave graphic EQ when all filters are boosted or cut to max. Note the red lines – that’s the frequency response you end up with when an equalizer is used in such a fashion.


    attachment.
    Response Characteristics, 2/3-Octave Analog Equalizer


    In addition, EQ filters basically work by altering phase. In layman’s term, the perceived change in tone is accomplished by delaying the frequency slightly, then mixing it back with the original signal (see this article for a more detailed explanation). So, when you whack a multitude of filters to accomplish your “crossover,” and each one adds phase alterations. Do you really want to pollute your signal with all that?

    Regards,
    Wayne A. Pflughaupt




    Pedulla Club #45

     

    Attached Files:

  12. AndyLES

    AndyLES

    Aug 25, 2008
    New York
    Wayne - I'm happy to say I stand corrected re. crossovers vs. conventional EQ.

    I will, however, still stand by the claim that many pro soundmen do often feed their subs via auxs (or even busses).
     
  13. mcapote

    mcapote

    Sep 9, 2009
    Miami Florida
    hmm seems to me you are going to have to buy alot of stuff to run them unpowered subs, kinda takes the $275 price and puts in in a new perspective huh? I would suggest a dSP amp like a crown XTI but the crossover feature wont help with the mains to cut below 100hz
     
  14. Kael

    Kael

    Dec 26, 2004
    Oklahoma City
    Said better (or at least more thoroughly :bag:) than I would have.
     
  15. You still need a LPF ahead of the aux fed subs. Decent subwoofer boxes tend to be built for a very specific purpose, any midrange or upper bass that makes it's way in to the subs is going to give you a lot of honking ugliness. It's also going to create interference with the tops in an unpredictable and almost certainly destructive manner.
     
  16. stinger12345

    stinger12345

    Jan 24, 2009
    Hayward, CA
    Well it sounds like a good thing I decided to pass on the subs. Crazy the things your brain says to you when you see something you can afford!

    It's no surprise I'm new to PA systems......but does anybody have some sort of audio clip or youtube sample of what the "honking" sounds like? I hear a lot about it on these forums, but I kinda wanna know what it sounds like before I'm put in a place where I might experience it, just so I'm prepared.
     

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