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Help me understand 'bridge' & 'bi-amp'

Discussion in 'Amps and Cabs [BG]' started by Brock385, May 7, 2001.

  1. Brock385


    Nov 5, 2000
    I see these terms all over, what do they mean?
    Thank you
  2. mikezimmerman

    mikezimmerman Supporting Member

    Apr 29, 2001
    Omaha, Nebraska
    A lot of power amplifiers are stereo, with two separate channels.

    If you "bridge" the power amp, you are combining the two separate channels together to get (roughly) twice as much power output, usually to power a single speaker cabinet.

    If you "biamp", you're splitting the signal from the bass (and preamp) into two separate halves, with the low frequencies going through one channel of the power amp into one speaker cabinet, and the high frequencies going through the other channel of the power amp into another speaker cabinet.

  3. embellisher

    embellisher Holy Ghost filled Bass Player Supporting Member

    Here's a simple but a little more detailed explanation. I'll leave the big details to the gurus like throbbinut, Joris, MikeyD, etc.

    Running bridged(or, in bridge mode) or biamped are 2 things you can do with an amp head that has 2 separate power amps in it. There are other ways to run biamp, but like I said, this is the simple explanation.

    • Bridge mode is a way to put all of your 2 channel amp's power into one speaker, of course, there are other reasons to bridge, but this is the simplest reason to.

      Imagine a head with 2x200 watt power amps inside(won't get into ohms and stuff in this post).

      Say you have one 4x10 speaker cabinet, and you want to put all of your power into that one cabinet, because you need as much volume as possible, and don't have another cabinet. You could bridge the 2 power amps together and run them into your single cab, getting the most volume and bang for your buck.
    • Biamping is a little more difficult to explain, but here goes. This was very popular a few years ago, and while a lot of people still do it, I think that more guys are running full range nowadays than biamp.

      Imagine the same 2x200 watt head, with an active crossover built in, and say you have a 1x15 and a 4x10 cabinet.

      If you wanted to biamp, you could set the crossover at say 150 - 200 hz, and run the lows into your 1x15, and then run the highs into your 4x10.

      The theory behind biamping is that you let your big speaker handle the ultra low bass, which it is(in theory, anyway;)) better at, and let your smaller driver(10's and the horn, if your 4x10 has one) handle the lower midrange, mids, and highs.

      This also divides the power, giving half of it to the lowest 1 or 2 octaves(the lower the hz, the more clean power you need to hear it) and then the other half to the bulk of the audio spectrum.

    Biamping and triamping is still very popular for PA use, and it is not unusual to see 4x the power for the lows that the highs get in a triamp PA system. For example, 4000 watts to your subs, 2000 to the midbass drivers, and 1000 watts to the high frequency horns.

    Sorry this is so long, it was meant to be easy to understand, and I hope that it helps.
  4. Brock385


    Nov 5, 2000
    Thanks for clearing all that up! So if you had a choice to either bi-amp or bridge, which would be the smarter (better?) choice?

    I'm looking to get a stereo head so that's why i'm asking all these questions.
  5. mikezimmerman

    mikezimmerman Supporting Member

    Apr 29, 2001
    Omaha, Nebraska
    1) People usually bridge their stereo amps because they have one cabinet and want to put more power into it than they can get with one channel of the amp. They're essentially turning their stereo amp into a mono amp.

    2) People biamp their stereo heads because they have two cabinets--usually one is better at reproducing lows and the other at reproducing highs, like a 1x18" and a 2x10"--and they want to have more control over the amount of power and the frequencies that go to each of the two cabs. Some people prefer the way a biamped rig sounds, and some don't.

    Which of these situations describes what you want to do best?

    Personally, I run a stereo Mackie power amp in bridged mode into a single Acme cab, because I like the way the Acme sounds. I didn't choose to buy a stereo power amp specifically because it was stereo and I could bridge it--I bought it because it was reasonably affordable and produced the amount of power I wanted when bridged, if you see the differerence. A mono power amp which put out the same amount of power would have suited me just as well.

    On the other hand, there are people who really like the sound of a biamped rig. No way around it, though--you need two cabinets, or one great big cabinet with separate inputs like the old Peavey 1820--to biamp. Neither is better or worse, though, and there's nothing preventing you from bridging when you only want one cab, and biamping when you're using two, if that's what you want.

  6. CrawlingEye

    CrawlingEye Member

    Mar 20, 2001
    Easton, Pennsylvania
    Anyone care to explain how you bridge a stereo head?

    I mean, you have 2 outputs in the back of your head, and 1 input on your cab. Is there some sort of Y cable for the job?
  7. mikezimmerman

    mikezimmerman Supporting Member

    Apr 29, 2001
    Omaha, Nebraska
    What amp are you talking about, specifically?

    First, two outputs doesn't necessarily mean it's a stereo head. Lots of mono amps have multiple output jacks. You really don't want to try and combine them!

    Second, not all stereo amps can be biamped. The ones that can usually have a switch to put them in biamp mode, so you're sending the same input signal to both channels. On the output side, they have either banana plugs placed so you can put one banana plug between the + side of both channels, or they have a separate 1/4" or Neutrik jack specifically for bridged output. If you just have two 1/4" or Neutriks jacks, with neither one marked as being for bridged output, it's likely that the amp is not intended for it. When in doubt, consult your manual or the manufacturer!

  8. MikeyD


    Sep 9, 2000
    Mike Z. speaketh the truth. Not every stereo amp is designed to be bridged. You must consult the manual or mfr., unless you are an electronics expert and know how to design amplifiers yourself. If an amp is capable of being bridged, the manual will tell you. You must also adhere to the impedance guidelines very carefully or you may overload it.
    - Mike

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