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Ohm/Wattage Question for PA

Discussion in 'Live Sound [BG]' started by bassburner, Nov 15, 2012.

  1. bassburner

    bassburner Supporting Member

    Dec 8, 2008
    This is related to another thread where I'm planning my PA, but this is a specific technical question that others in the future will find useful.

    For example let's say you have a couple of speakers rated at 1200W at 8 ohms

    and you're hooking up to a 2400W amp like the Crown XLS 2500
    Stereo, 2 ohms: 1200W
    Stereo, 4 ohms: 775W
    Stereo, 8 ohms: 440W
    Bridged mono, 4 ohms: 2400W
    Bridged mono, 8 ohms: 1550W

    When you put speakers in parallel that reduces the ohms. So if you have: amp -> speaker 1 -> speaker 2. Than both speakers are pulling 4 ohms instead.

    So if I'm understanding everything correctly if you take those two speakers and daisy chain them and plug only use one channel on the amp, you're pulling the full 2400W but if you plug one speaker into each channel (i.e. stereo mode), you're only pulling 440W?
  2. Zooberwerx

    Zooberwerx Gold Supporting Member

    Dec 21, 2002
    Virginia Beach, VA
    You're almost there. I have (2) 2500's coming in tomorrow so I'm familar with the specs. Appears that you have (2) 8 ohm enclosures; that's what I'm using as well. The DC 2500 is essentially two separate power amps, each of which is capable of pushing 440 watts into an 8 ohm load. Now, if you daisy-chain the enclosures, this will create a total 4 ohm load...so you're correct. If you plug this into one channel of a stereo / dual mono configured amp, they will see see 775 watts or ~380 watts per enclosure. Not that impressive, eh? Now, configure the amp in bridged mono which essentially ties the two power amps together creating a "push/pull" effect tripling the power (gross over-simplification). Connect the daisy-chained enclosures to channel 1 output and the pair will see 2400 watts or ~1200 watts per enclosure. Once in bridged mono, you can only connect one speaker load which has a total impedance of 4 ohms and above...which pretty much describes your gear situation.

  3. seanm

    seanm I'd kill for a Nobel Peace Prize! Supporting Member

    Feb 19, 2004
    Ottawa, Canada
    What speakers are you using that can take 1,200W?
  4. Zooberwerx

    Zooberwerx Gold Supporting Member

    Dec 21, 2002
    Virginia Beach, VA
    Gotta love posted specs! My Carvins are listed @ 400 cont / 800 program / 1600 peak...I can see why things get confusing.

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  6. Ive got this exact setup and same question and I would like to know what is more preferred.

    One Crown XLS 2500 http://www.crownaudio.com/xls-drivecore.html

    Two Carvin LS 1503 http://www.carvinguitars.com/products/LS1503

    Specs on the Carvin mains are 8 ohms 400w continuous /800w program /1600w peak

    Specs on the Crown for driving these speakers are 440w at 8 ohm each channel stereo or 2400w at 4 ohm bridge mono.

    Ive been running them stereo for a few months with no problems but I wouldn't say they put out a huge amount of volume and many times we've needed more vocal out front with everything cranked. Is it reasonable to run them in bridge mono at 1200w a speaker as long as I keep the amp power knob low and adjust as more volume is needed? Or will this be overkill for these speakers and cause them to smoke? I know they are budget speakers but i'm hoping they have been engineered to handle those kind of watts. Speakers will be Vocal only, need enough volume to get over a very loud drummer in a very small space with a couple of distorted guitars. Got a gig tonight that I want try this if anyone can help.
  7. Zooberwerx

    Zooberwerx Gold Supporting Member

    Dec 21, 2002
    Virginia Beach, VA
    Sidenote: I was able to snag two NIB 2500's for not much over & above the 1500, hence the purchase.

    Okay, I'll admit the 2500 is pretty much overkill for our shared situations but if you set the gain structure correctly, roll in any available limiters, and watch your volume, you should be okay. Speaking of volumes, your PA volume should meet the needs of the venue and the instrument levels should complement that of the PA / vocals. IOW, tell them to turn the %&*# down.

  8. seanm

    seanm I'd kill for a Nobel Peace Prize! Supporting Member

    Feb 19, 2004
    Ottawa, Canada
    +1 If you are playing small venues (< 200 or so) you shouldn't need more than 200W per side. 400W per side should be enough.

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