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Loss with less ohms?

Discussion in 'Amps and Cabs [BG]' started by bassicrunner, Sep 2, 2002.


  1. bassicrunner

    bassicrunner

    Sep 23, 2001
    By having 2 cabinets at 8ohms, will my rig be significantly quieter than a rig with 2 4ohms cabinets? (Assuming the cabinets are all the same size.)

    ps - i couldn't find this on the search
     
  2. Jazz Ad

    Jazz Ad Mi la ré sol Gold Supporting Member Supporting Member

    It doesn't mean a thing.
    It all depends on your power amp.

    two 8 ohm cabs will make a total 4 ohm load. It's usally the best an amp can deliver.

    two 4 ohm cabs will bring a 2 ohm impedance. Not so many amps can stand this. Actually, most will fry. It all depends on your amp's species.
     
  3. FretNoMore

    FretNoMore * Cooking with GAS *

    Jan 25, 2002
    The frozen north
    Everything else being equal - yes.

    It also depends on your amp though, is it mono or stereo?

    If it's mono, the result could be the opposite of what you would first think:

    Not all amps can drive a load of 2 ohms (which is what you would get with two 4 ohm cabinets in parallell) and so you would have to connect them in series (with a resulting 8 ohm load).

    Two parallell 8's on the other hand would result in a 4 ohm load and a louder result than the example above.

    So, first check what your amp can handle, and if you state what amp you have perhaps we can be more specific.
     
  4. FretNoMore

    FretNoMore * Cooking with GAS *

    Jan 25, 2002
    The frozen north
    Jazz, you beat me to it, while I was editing my reply! Seems we agree though. :)
     
  5. bassicrunner

    bassicrunner

    Sep 23, 2001
    hopefully will be an SWR SM-900 :D , and thanks for the help.
     
  6. Matthias

    Matthias

    May 30, 2000
    Vienna, Austria
    With the SM-900 you have the following options:
    - run one 4Ohm cab from each side in stereo mode: total power output: max. 800W (400W@4Ohm per side)
    - run one 8Ohm cab from each side in stereo mode: total power output: max. 480W (240W@8Ohm per side)
    - run both 8Ohm cabs (=4Ohm load) in bridged mode: total power output: max. 900W (900W@4Ohm mono)

    I don't recommend connecting two cabs in series (this can cause trouble if the cabs are not identical)
    BTW if you connect one cab to the amp and the second cab to the first cab using normal speaker cables this is still parallel connection!!

    Matthias
     
  7. bassicrunner

    bassicrunner

    Sep 23, 2001
    Thanks, but to make sure, you're telling me the first two above are ok to do, but the third is not? That sucks since that is twice as powerful as the other option I have (second choice). Thanks.
     
  8. BenF

    BenF

    Mar 29, 2001
    Boston area
    bassicrunner - Matthias' third option is fine. I run my sm-900 bridged into a 4 ohm load all the time. The only caution is that with a bridged 4 ohm load the amp gets pretty hot even with the internal fan going full blast - I keep a little desk fan blowing on the amp if I've got a long gig with the amp set up this way.

    Alot also depends on how sensitive and efficient your cabs are.
     
  9. Johnny BoomBoom

    Johnny BoomBoom Supporting Member

    Jun 8, 2001
    Glasgow, Scotland

    No - what he is saying is that if you daisy chain the cabs, they will actually be in parallel. So option 3 is the optimum for you!
     
  10. bassicrunner

    bassicrunner

    Sep 23, 2001
    Well that's super duper. Thanks alot.
     
  11. Matthias

    Matthias

    May 30, 2000
    Vienna, Austria
    That's what I've been trying to say. Thank you for clarifying.
    Matthias