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FOH amp combo

Discussion in 'Sound, Music, and Intercom' started by llewop, Apr 28, 2009.

  1. llewop

    llewop Member

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    I am considering the purchase of two Peavey sp2's. I have a Crown XLS602 amp to run them. Is their any benefit in running in bridge mode. That would be a 4 ohm load for 1648 watts. Or should I just run in stereo mode for 380 watts per 8 ohm speaker / channel? Would the sound be louder for either mode? I'm just getting into these things out of necessity. I want to build a first quality sound system for my musical endeavors. I do have some miked drums playing with me at times. I play acoustic guitar and when I get the opportunity to get a strong rythm player I break out the Strat.
    These sp2's are rated 500/1000/2000watts. Two way speakers.
     
  2. avkid

    avkid Not a New User Fight Leukemia

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    You definitely do not want to run stereo, there's not enough power for the speakers.
    In an ideal situation you would supply them with around 850 watts.

    An XLS 5000 would be the perfect amp for these cabinets.
     
  3. Derrick

    Derrick Member

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    I agree. I have six of the SP2 that I power with 3 QSC PLX3402 in dual channel. They soak up all the 3402 can put in to 'em.
     
  4. museav

    museav CBMod CB Mods Departed Member

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    I am disappointed as the correct answer is "it depends", especially since the question was about using an existing amplifier and not what amplifier to buy. There is a difference between "how loud can I get" and "how loud do I need to get", between "what is the most power I can practically put into a speaker" and "what is an appropriate amplifier and speaker combination to use for an application" or "Will this work?". Are you playing living room concerts or outdoor festivals? Folk or thrash metal? Lots of dynamics or heavily compressed? When you mic the drums, do you mic the kick? What are the relative importance of absolute loudness, sound quality and reliability?

    One benefit to running the XLS602 in bridge mode powering both speakers might be if you want a new amp. I'm not sure where you got the 1,648W, 4 Ohm bridge mono rating as all the current information Crown shows for the XLS602 indicates that the XLS602 is not rated for a 4 Ohm load in bridge mode operation.

    FWIW, going from 380W per speaker to 1,648W for two speakers would be a 3.4dB increase, a discernible but hardly dramatic difference if the goal is simply more output level.
     
  5. llewop

    llewop Member

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    Thanks for the response. I will be using these for an outdoor gig w/ 300 to 500 folks and possibly more.
    I talked with Crown Tech support about the 602 and bridge mode at 4 ohms. The comment was that though not advertised, the amp would do the work. He did say this was the most difficult load for the amp.
    I should wire my two speakers in parallel for 8 ohms in bridge mode for the most power with available amp and least risk of equipment failure. Right?
     
  6. museav

    museav CBMod CB Mods Departed Member

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    The SP2 is a nominal 8 Ohm box when run full range, however the specified minimum impedance is 6 Ohms, so while two in parallel would be a nominal 4 Ohms, the load would be as low as 3 Ohms at some frequencies. When running near the extremes of a device's operating parameters factors such as the difference between the nominal and minimum impedance ratings can matter. I won't contradict Crown but I personally would not try running two SP2s off a bridge mono XLS602 unless I was taking it easy on the amp, which sort of defeats the purpose.

    Maybe we look at this another way. Ideally you would define the levels desired and back into the output required from the speaker and from that then determine the power required to the speaker. But we can run it the other direction to look at what you might get out in the audience based on the amplifier you already have. When run full range the SP2 has a rated sensitivity of 98dB/1W/1m. Your amp is rated at 380W/channel into 8 Ohms, but that is a 1kHz rating so assume a little lower for full range operation, maybe 350-360W/channel. Based on this data the speaker would generate 123-124dB at 1m. Not knowing the actual audience area let's assume that the furthest person is maybe 75' away. Distance loss outdoors at 75' compared to 1m would be 27dB. That gives a level of 96-97dB at 75'. But that is on axis and the audience off axis might see a lower level, so let's assume 90-91dB there. However, that is also the peak level, so assuming 10dB for dynamics/headroom that would then be an average level of 80-81dB. Is 80-81dBSPL loud enough? If so, then you're probably fine to run the XLS602 in stereo. And unless the difference between an average level of 80-81dB and one of maybe 84dB really makes an important difference, it would seem difficult to justify running the amp in mono bridge mode to power both speakers.
     
  7. llewop

    llewop Member

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    Thank you, I can tell that for the optimum perfomance range, I need to power these speakers with, for instance, a QSCRMS4050 or equal.
    I think for this application, at an outdoor motorcycle rally in a covered pavillion, I should be ok, so I have some time to get the proper equipment.
    Thank you for your excellent explanation and answer.
     
  8. Derrick

    Derrick Member

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    I would go to a Peavey dealer and ask to hear the SP2's at different power levels. The SP2 seems to sound muddy when driven softly. They seem to like 500 watts and up.

    Hey don't call me crazy, the Peavey dealer in Tuscaloosa put me on to this. I kinda looked at him like "yeah!?!" but it is so.

    Also have older and newest XLS602 for monitors. Never considered powering SP2 with'em, though now I'll hafta try it!:p
     
  9. llewop

    llewop Member

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    You know I have decided to buy another 602 and run one amp bridged for each SP2. 1200 Watts per SP2 should be just what I'm looking for. I have another europower 2500 amp that I can use for my stage monitors. Should be nice an neat. Down the road I will probably be asking questions about: external crossovers and bi-amping, do I need to look into a compressor/limiter/gate, graphic equalizer, how to place subs into my system. It just takes time for me.

    I had heard some JBL JRX215's and thought they sounded pretty good, then I heard these SP2's. To me they sound fantastic, much more clarity and punch.
     
  10. avkid

    avkid Not a New User Fight Leukemia

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    Very good decision, you'll be much happier when you have headroom to spare.
     
  11. llewop

    llewop Member

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    I hope so. I talked with Crown that let me know that 1240 watts was the top of the recommended 125% of the program rating. I am kind of nervous about running at the top instead of somewhere in the mid range.
    Do I consider the wattage of the amp to be constant no matter how the main mix slider is set? So if I am using 1240 watts even if no signal is coming through the amp, the amp is still seizing the coil of the speakers at that 0 db level. I am just worried about someone dropping a mic or unplugging without thinking and then the speaker cone coming out of the cage. Would I be better served to buy two Crown XLS402 AMPS one for each speaker instead of the two 602's? That would be 900watts per side. Just under the 1000w program rating.
    This stuff is expensive. I've got to get it right with what I've got.
     
  12. Derrick

    Derrick Member

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    PM me or email me at [email protected]

    I'll give you my phone number and I'll help you out. Just too much to discuss and I don't type that well or fast..

    D
     
  13. museav

    museav CBMod CB Mods Departed Member

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    Personal perspective, but such requests are probably better made via PM rather than posted to the entire group. And keeping discussions that are relevant to a thread in the forum can potentially benefit more people.
     
  14. llewop

    llewop Member

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    I have sent you my email addresss and contact info.
     
  15. llewop

    llewop Member

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    I know think the best thing is to obtain a peavey CS4000. It must be designed specifically for these speakers. 800 watts per channel at 8 ohms for $1000.00.
     
  16. Derrick

    Derrick Member

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    Check your PM

    D
     
  17. llewop

    llewop Member

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    Derrick, I'm not sure how to use PM.
    llewop
     
  18. Derrick

    Derrick Member

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    After you have logged in, look to the top right area of the page. Under your login name you dhoule see "private messages" highlighted and underscored. Click that, a new page opens. Find the message from me and click it.

    D
     
  19. museav

    museav CBMod CB Mods Departed Member

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    Amplifiers are capable of providing their full output if provided sufficient input signal, with power amps the level controls are adjusting the attenuation or gain for the input or driving signal rather than adjusting the amplifier output. That is why limiting is often applied to control the maximum input signal the amplifier would see in situations such as those you defined.

    Another option would be to just use the existing XLS602 in stereo mode and incorporate some system processing instead of buying another amp. That may provide some additional flexibility and set the stage for future upgrades such as adding subwoofers.
     

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