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Rookie Ohm question

Discussion in 'Amps and Cabs [BG]' started by gr8shot, Mar 21, 2014.

  1. gr8shot


    Mar 21, 2014
    Hi guys, first post here. Been playing through an ampeg svt350 for years now, with a ampeg SVT-410HLF cabinet. It's been a trusty setup that works great for me and only just recently had to put money into it for the first time ever.

    That all aside, I found a pawn shop locally that has another 410HLF cabinet for sale thats in great shape and I can probably get it for under $200. It's not the one like the SVT type that has the angled back and grab bar on the back. It's the shorter square cabinet but still ported (can't remember the exact model #, but it had a 3 position high freq attenuation knob on the back).

    My question is about using both of the cabinets. I can't find the exact cabinet on the web, but the similar newer models are 8ohm, and the SVT-410HLF I currently have is 4ohm. Here's where I'm confused. My amp has two power outputs on it. And I believe is rated for 350w at 4 ohm and 200w at 8ohm. Whats the right way to hook up two cabinets? Run one speaker wire to each cabinet and go? Is it safe/even possible to run different ohm loads out of each power output? I know I can't run them in series as that would wind up under at 2.6ohms and my amp won't handle that.

    So I guess the question is, can I run a 4ohm cabinet off one of the outputs and an 8ohm cabinet off the other? Will I gain much by doing so? I'd really only run the second cab for outdoor shows when at times I'm just a tad quiet compared with everyone else. 90%+ of the time I've got plenty of power for what we do.

  2. RickenBoogie


    Jul 22, 2007
    Dallas, TX
    The short answer is, you cannot run any other cab with the current 4 ohm cab you have. Your amp is 4 ohms minimum, and your cab is 4 ohms. Adding another 4 ohm cab drops you to 2 ohms, or another 8 ohm cab, to 2.6 ohms. The stickies explain how all this works, and is worth a read.
  3. With that amp (and most amps out there) the minimum TOTAL load you can run is a 4 ohm load. This would mean you could use either speaker output on the amp with either of those two cabinets, but not both. Combining a 4 ohm and an 8 ohm speaker would give you a total impedance of 2.6 ohms and though it may work for a while, eventually you'll overheat the amp and burn up the power section.

    Most amps out there run their speaker outputs in parallel, yours included. This means each time you add a cabinet, the ohms will be reduced. (There are exceptions if you get into special series boxes and other things but that's a whole other thing).

    With your current cab being 4ohm, the only practical way to add more speakers is to buy a bigger 4 ohm cab to use by itself (i.e. 6x10 or 8x10)

    IvanMike did a great write up on ohms, you should check it out:
  4. gr8shot


    Mar 21, 2014
    This is what I was looking for. Makes perfect sense. I just didn't know if the output jacks were in parallel, or how they were set up. As good of a deal as that cabinet is, guess I'll probably just pass and keep my eyes out for a 6x10 or 8x10.
  5. gr8shot


    Mar 21, 2014
    So basically it would be the same 2.6 ohm load on the amp if I hooked up each cabinet directly out of the outputs of the amp, or if I went from one output of the amp to one cabinet, then from the output of the cabinet to the next cabinet, correct?
  6. ezstep


    Nov 25, 2004
    north Louisiana
    Yes, the same. The amp sees "a load is a load is a load" regardless of how the speakers are connected - both to head, one to the other, etc. No difference whatsoever.

    If your amp would go to 2 ohm, you would be gold. But, like others have advised, don't use both these cabs at the same time with your current amp. All the smoke and magic will escape.
  7. gr8shot


    Mar 21, 2014
    Got it. Thanks!!