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amp bridge questions...

Discussion in 'Amps and Cabs [BG]' started by dadodetres, Jul 17, 2005.

  1. dadodetres


    Dec 19, 2004
    i have a yamaha P3200, and i was looking for using the bridge function.

    it says that when in bridge i should be using 8-16 ohms.

    my cabs are SWR goliath jr and a yamaha 1x18m both 8 ohms.

    so connecting both cabs resultas 4 ohms, right? is this to low for the P3200?? what alternative do i have?

    also, if it could be done, what should i look after? having a good electrical instalation in were i play? leaving a 1 space rack above the power amp?

    also, since i wont be using my crossover, cant i damage the 2x10 with extreem low freqs? or do the net inside the cabs will prevent this? if so: will i get more power and headroom using mthe bridge mode or running the it in stereo with the crossover?

  2. KJung

    KJung Supporting Member

    A bridged amp sees 1/2 of the total ohms of your combined cabs... so when you run an 8ohm total load, the bridged amp is really only seeing 4ohms... which is the typical minimum for bridged amps (some new models, like the new Eden800B can now run into a 4ohm load bridged... effectively running at 2ohms).

    So, unfortunately, you can't really use both of your cabs efficiently. One of your 8ohm cabs will get the full power from your bridged amp. Two in parallel would result in too low of a load, thereby damaging your amp. Also, running in stereo would only present 8ohms per side... thereby resulting in relatively low power.

    So, you need to do one of four things:

    1) Get an 8ohm cab that is loud enough to use as your only cab (or use one of the cabs you have)... running the gridged amp at full power.

    2) Buy two 4ohm cabs and run the amp in stereo, each side running at full power.

    3) Buy a mono head for use with your current cabs.... most mono heads put out their full power into 4ohms, and those that go down to 2ohms can still run safely at 4.

    4) Use the cabs and amp you have in stereo.... you won't be getting the maximum power out of your amp... but usually adding speakers results in more sound than having more power... so your two cabs running at reduced wattage in stereo would probably be louder than a single cab running full wattage bridged.

    PS You won't hurt the 210 without a crossover... modern 210s are designed to take a full range signal.
  3. dadodetres


    Dec 19, 2004
    hey thancks! ill stick with the stereo function using both of my cabs.

    even if i send the heavy low end that i want to send to my 1x18 to the 2x10?
  4. If you run it stereo, it wouldn't hurt to block some of the really low's from the 2x10, its not adding much useful output there anyway compared to the 18's, and that frees it up to just reproduce the crucial mids/highs to give you that modern sound.

    But you definitely will have to run stereo, as others have pointed out, the bridge into a 4 ohm load will not survive, or at the least will overheat the amp, leading to thermal shutdowns.

  5. KJung

    KJung Supporting Member

    I'm sure some other TBer's will kick in here with their comments also. While that 210 cab is designed as full range, if you really put a massive amount of low end and watts into it, it won't sound very good and I guess you could do some harm. I would just try it out and listen very closely for clipping and distortion. That SWR 210 is not the loudest or lowest of 210's, so it probably won't have enough volume and bottom for you as a stand alone cab for moderately loud gigs.

    However, again, there's nothing wrong putting a full range signal into a 210.

    Good luck, and again, you will shortly get some other options/opinions from other TBers.


    Mar 12, 2003
    USA, PNW
    Dadotres, what are you driving your SWR with. Sometimes I run a line out from my TNT output into a 100 watt tube amp that feeds the 210. Another line out from the TNT combo(low output) is used to feed an 18inch sub powered by a bridgeed Mackie. So the total available power might seem like a lot, but, rarely do I have to turn the volume adjustment up very high, which is a benifit of having so much headroom. Basically, I think you are on the right track if you bridge your amp to a dedicated 8 ohm sub and used and independent amp with a low frequency blocker\crossover on the SWRjr. The SWR has plenty of midrange and uppermidrange punch and lacks bottom end.
  7. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    A bridged amp doesn't really see an 8-ohm load as a 4-ohm load; that would be electrically impossible. Actually what happens is that each channel (bridged mono is just two amp channels connected in series, each a mirror image of the other) "sees" half the load impedance. So an 8-ohm load in bridged mono would be electrically equivalent to two 4-ohm loads, one on each channel.
  8. KJung

    KJung Supporting Member

    Thanks for the technical clarification... I never really understood how that worked.