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Sizing questions

Discussion in 'Amps and Cabs [BG]' started by Steamtronic, Apr 6, 2015.

  1. Hi folks,

    Hoping someone can point me to an appropriate resource!

    As I previously only used combos Ive never had to worry about sizing head to cabs. Now I have a head!

    I need to build an understanding of how to work out what I can run off my head. I've currently got a 750W Peavey Tour head and a Peavey Headliner cab 410 800W, 1600W peak. I also have access to some 2x12 and 1x15 cabs but Im not sure on their power rating.

    Can anyone point me to a resource or thread (or even tell me outright) to help me understand:
    1. The difference between the 800W and 1600Wp peak stats,
    2, What happens when I plug additional cabs into the head - ie would plugging a 15" driver in as well as my 4x10 reduce the output to each cab?
    3. Is there a difference if I plug in speaker cabs in series (ie running successive cabs off the same output) vs parallell (ie using the 2x outputs in the back) ?
    4. Will I blow out a 200W 15" driver with this a,p if I crank it up to 11 or is that a myth?
    5. Does 4 x 200W speakers take as much power as 1x15" driver?

    I keep finding contradictory information when I google this - different sites say different things and claim the other rxplanation is a "myth" that they are busting. PLease help!!!

  2. Read the stickies at the top of this forum.
    cfsporn likes this.
  3. RickenBoogie


    Jul 22, 2007
    Dallas, TX
    Yes, stickies, faq's. Lottsa info in there. Bottom line, most important "numbers" are the impedance of the cabs, and what the amp wants in that regard.
    cfsporn likes this.
  4. Brilliant, thanks. Missed the sticky on sizing when I looked earlier for some reason, its explained nearly everything. :)
  5. In case this one was unanswered:
    "3. Is there a difference if I plug in speaker cabs in series (ie running successive cabs off the same output) vs parallell (ie using the 2x outputs in the back) ?"

    Both of the ways you described are parallel and are the same. Series wiring cabs requires a special made series cable that has one connector at the amp end and two at the cab ends (all three must be used or no connection and no sound).
    CL400Peavey likes this.
  6. iualum


    Apr 9, 2004
    Joined in February of 2012?
  7. So? I started playing then, and am now getting to the point where I'm about to play live. I haven't had to size cabs till now.

    The great thing about this site is noobs can ask questions without attracting trolls and I hope it stays that way. Thanks everyone for your support.
    yakmastermax, B-string and JimmyM like this.
  8. JimmyM

    JimmyM Supporting Member

    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    Never saw this thread before so since you're still here, I'll try to answer the more specific questions you asked:

    1. If an amp says 800w RMS, that is basically what it produces clean. Anything past that, and the sound gets distorted. And it's a little different for micro amps, but traditional solid state and tube amps are capable of putting twice their rated RMS power in peaks for very short durations. You can get really in-depth about how it all works but that's the short and simple version.

    2. This is where speaker impedance and how your amp is designed plays a big role. With solid state amps, the wattage increases if you have two bass cabs, and the cabs will each split the wattage provided they're the same impedance and in spec for the amp. Tube amps rarely have wattage changes dependent on how many cabs you use, but they'll also split whatever wattage is available. You get into all sorts of other implications if cab impedances are different, so it's best to stick with the same impedances whenever possible, and always make sure your total impedance doesn't go below what your amp can take...i.e., running two 4 ohm cabs into a head with a 4 ohm minimum creates a 2 ohm load that can harm the amp or cause it to shut down if you're lucky enough that the protection circuit kicks in. Again, this is the short version.

    3. No. And with rare exceptions, no speaker jacks are wired in series...almost always parallel.

    4. Yes, with an amp like the Tour 700, you can easily blow pretty much any cab you throw at it if you're not careful. But you can also keep from blowing any of your cabs through common sense and judicious use of the amp's volume knob.

    5. If you are asking if your 115 will limit how loud you can crank the 410, the answer is yes. With that line of Peavey bass cabs and most commercially made bass cabs, a 115 will have approx. the same output as a 210. On the bright side, there aren't many gigs you can't handle with a single 8 ohm 410 and as much power as the 700 puts out at 8 ohms, so a second cab is expendable. You'll probably get asked to turn down a lot more than you'll get asked to turn up unless you're playing doom, for which I'd ditch the 115 and get another 410 ;)

    Also, don't go strictly by numbers when trying to crank as loud as you can without blowing your stuff. If it sounds like the cabs are going to explode, they will, regardless of what they tell you they can take.
  9. Thanks Jimmy! Super helpful as always, you the man :).

    Id hate to get up on stage for the first time and blow my rig up in the first number. Not a good look. We're going to hire out a good sized rehearsal room and crank up to what we think will be performance levels, bringing along a few friends to assess the sound before we go live. I understand the venue acoustics will all be very different but at least getting to know our gear will give us a reference point. With luck well have some helpful in-house sound guys.
    JimmyM likes this.
  10. JimmyM

    JimmyM Supporting Member

    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    Ha! I just noticed that you were the one in a different thread that asked about this rig + a guitar amp for stoner music. Yeah, definitely consider the second 410 in place of the 115 in the future.
    Steamtronic likes this.

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