Quick Stereo vs. Bridged Question

Discussion in 'Amps and Cabs [BG]' started by E.O.M., Sep 30, 2004.

  1. E.O.M.


    Dec 7, 2001
    Grand Rapids, MI
    Is there a difference between running 400 watts per side @ 8 ohms with each side going into an 8 ohm cab, and running 800 watts bridged @ 4 ohms with those 2 same cabs daisy chained into the bridged channel?

    Sorry if I didn't explain that correctly...
  2. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    Well, the amp will technically see 2 ohms per channel with a 4 ohm bridged load. But producing "only" 800 watts there might not really be a heating difference.

    Usually the ratings would be 400 per channel into 4 ohms, 800 bridged into 8... I realize that that isn't the question that you're asking though...
  3. E.O.M.


    Dec 7, 2001
    Grand Rapids, MI
    See that is what confuses me. If an amp is rated at 800 watts bridged into 8 ohms, should the amp be hooked up with an 8 or 4 ohm total speaker load? And what is louder, 800 watts bridged into 8 ohms or 400 watts/side into 4 ohms (assuming same cab availability)?
  4. IvanMike

    IvanMike Player Characters fear me... Staff Member Supporting Member

    Nov 10, 2002
    Middletown CT, USA
    it sounds like the amp you're talking about can handle a minimum cabinet impedance of 4 ohms pers side. When running such an amp bridged into an 8 ohm cabinet each side "Sees" 1/2 the load, which is 4 ohms. Thats why bridging it into 8 ohms produces double the wattage as it produces in stereo at 4 ohms pers side. The amp probably cannot run at 2 ohms per side, which also means it can't run bridged into 2 ohms.
    if you run it into say, an 8 ohm 410 bridged, it will not be as loud as running it into 2 8 ohm 410s stereo just because the 2 cabinets will move more air. But it's gonna be loud anyhow

    check out this post for ohms info that i think you'll find helpful

    ohms info
  5. HomeBuild


    Sep 28, 2004
    Whether you should use bridged mode or sterio mode will depend partly on your speaker combination. Normally, when you daisy chain speakers they are actually connected in parallel and not, as you might expect, in series. This has the effect of lowering the impedence.

    The available output power decreases as load impedance increases. The following assumes that the available power is inversely proportional to the impedance. This is an over simplification and does not take into account losses within the amp. The general rule, however, shows the principle. Also the resultant volume will depend on the efficiency of the speakers, which tend to become less efficient if driven hard.

    If you have 2 x 16 Ohm speakers, these would result in a 8 Ohm load when connected in parallel. For an amp giving 400W per side at 4 Ohm and 800W bridged into 8 Ohm, these speakers would give you a full 800W bridged into 8 Ohms but would give you only 100W per side into 16 Ohms, i.e. 200W in total.

    2 x 4 Ohm Cabs with the same amp would give you 400W per side, i.e. 800W in total, but the speakers when connected in Parallel would give you only a 2 Ohm load; which is way below the minimum load, 8 Ohm, for Bridged mode.

    With 8 Ohm Speakers the combined impedance, 4 Ohm, is below the minimum for bridged mode, but would give you 200W per side, i.e 400W in total. If you were able to connect these cabinets in series, your total impedence would be 16 Ohm and you would be able to get only 400W bridged.

    Therefore you could configure your setup to give 800W with either 2 x 16 Ohm or 2 x 4 Ohm cabs but only 400W with 2 x 8 Ohm cabs.