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Why Stereo vs. Bridged Mono?

Discussion in 'Amps and Cabs [BG]' started by Greatcrimson, Jan 24, 2003.


  1. Greatcrimson

    Greatcrimson Supporting Member

    Nov 17, 2002
    Central NJ, USA
    I’m considering a new rig and have already decided on a Stewart 1.2 as the power amp (thanks partially to the advice of my friends here). Now comes the decision on whether to run stereo or bridged mono.

    I’m using a SansAmp RBI for the preamp and considering (2) 2X10 Eden or EA cabs. As an alternate I may consider a 4x10 since it’s a little cheaper that 2X10s. I understand the fact that in stereo you have control over each cabs volume separately but so what? Is that really that important? Also, in bridged mono you get much more power. Isn’t that what it’s really all about? I obviously need to decide before I pick cabs since I’ll need to get the impedance right.

    All comments are welcome. :)
     
  2. ZuluFunk

    ZuluFunk

    Apr 14, 2001
    Pennsylvania
    They 210s may be more expensive, but often a single 210 is sufficient. So you can cut your load nearly by half.

    When running two different cabs, a 4ohm 400-800w 210 and an 8ohm 200-400w 115 like I do, stereo is nice so I can accentuate one cab or the other to get the balance I want. Also, my rig in stereo provides far more headroom than I'll ever need. I can only make use of so much. Going mono in my current set up would be insane.

    If I had just a 4ohm 410, I might consider running it bridged seeing as I wouldn't really need to consider the power per channel. Same thing if I were running two identical 210s.
     
  3. Chasarms

    Chasarms Casual Observer

    May 24, 2001
    Bettendorf, IA USA
    IF you are going to run only one model of cabinet, there is no real advantage to running stereo.

    Although as mentioned, if you are running two sizes of drivers or even just two different models of cabinets, stereo allows you to get a better balanced sound.

    Chas
     
  4. monkfill

    monkfill

    Jan 1, 2003
    Kansas City
    Some amps aren't as stable running bridged mono. If you're pushing an amp hard, and its running bridged mono, you're asking *some* amps to work at or near their design limit. This will make the amp run hotter, potentially causing it to shut down, and that excess heat can wear its circuitry over time.

    On the other hand, most amps are running more comfortably in stereo mode (unless you're running something like 2 ohms per side).
     
  5. lo-freq

    lo-freq aka UFO

    Jan 19, 2003
    The Republic of Texas
    I would advise checking with the manufacturer regarding running any specific model in bridged mode for bass amp usage.

    Some models are more resilient than others when bridged and pushed to near their design limits.

    In general, if you have a good brand amp and its power rating is 2x that of your speakers, the amp should not be getting enough stress to be concerned with (the speakers will be distressed before the amp--which you can usually hear).
    But that said, if you're doing really loud and/or distorted music or your speakers are not very efficient or have relatively low power handling capacity, it is much better to be safe than sorry (contact the manufacturer).

    P.S. If an amp is designed well, when you bridge it, it acts as a differential (balanced) amp and should sound cleaner and quicker (slew rate usually doubles=better transient response).

    From what I have heard, I would recommend a QSC PLX1202. They are extremely reliable. It would be more than plenty for a cab such as an Eden 4x10 (here again, check out some other brands: Bag End, EA, Aguilar, Epifani, Bergantino--mainly depends on what kind of sound you are after; don't jump on any bandwagons, cause in the end you have to mainly please yourself).
     
  6. chucko58

    chucko58

    Jan 17, 2002
    Silicon Valley, CA, USA
    I paid for all my gear myself. Well, me and MasterCard.
    4 ohm bridged operation really pushes an amp to its limit. The Stewart World 1.2 already has a reputation for overheating if the airflow around it is less than ideal. IMHO driving a bridged 4 ohm load with one is asking for trouble.

    If you insist on bridging into 4 ohms, get a beefier amp. A better choice would be any amp that has a built-in cooling fan and is rated for 4 ohm bridged work, like the Stewart World 1.6, QSC PLX series, etc.
     
  7. Greatcrimson

    Greatcrimson Supporting Member

    Nov 17, 2002
    Central NJ, USA
    Thanks for the help!

    Well now I think I'm leaning toward a Stewart 1.6 and an Eden 410XLT. I think with the RBI I already have that should be a killer rig.

    Anyone have experience with this combination of gear?
     
  8. N*Joy

    N*Joy

    Nov 30, 2002
    Birmingham, UK
    Unless you are feeding two different signals - it's mono (same signal in each side), not stereo. i.e. stereo fx
     
  9. Cantstandsya

    Cantstandsya

    Jul 27, 2001
    Fontana, CA
    SWR anybody?
     
  10. ChenNuts44

    ChenNuts44

    Nov 18, 2001
    Davenport, IA
    While you could, technically, say that feeding the same signal to two power amps would be dual-mono operation, we have come to accept having two independently amplified channels, regardless of the input, as stereo operation.
     
  11. lo-freq

    lo-freq aka UFO

    Jan 19, 2003
    The Republic of Texas
    -------------------------------------------------
    While you could, technically, say that feeding the same signal to two power amps would be dual-mono operation, we have come to accept having two independently amplified channels, regardless of the input, as stereo operation.
    -------------------------------------------------

    Sorry to split hairs, stereo is not just having two output amp channels, it is also having two different input signals (otherwise there is no perrceived "stereo" separation and the resultant output is indistinguishable from a one channel mono setup). If you take one signal and either split it or as with some modern amps run it into one two-channel amp input and set the amp for what is called a parallel mode (which means the one signal it fed internally to both channels) then you have a dual mono setup.

    If I am wrong, one of the more technical guys can correct me, but I'm pretty sure that's the gist of it.
     
  12. The World 1.2 at 4 ohms in bridge mono will definitely overheat and shut down when pushed or on a hot day (outdoor stage) or if the line voltage drops. Then you will have to wait the longest 2 minutes of your life for it to reset so you can try to baby it through the gig.

    Some guys get by with a fan in the rack, but why face that stress ?

    The 1.6 and 2.1, as well as the QSC PLXs, are bulletproof. My 1.2 stays home for practice.

    Aloha,

    Jonathan
     
  13. ChenNuts44

    ChenNuts44

    Nov 18, 2001
    Davenport, IA
    My point still stands. It's like having words take on meanings outside of their original definitions due to misuse over time, eventually becoming accepted as correct meaning, etc. etc. I never said it was correct. I actually agreed with you. I'm saying that people and manufacturers really don't look at it like that anymore. If they did, we wouldn't be seeing "stereo" amps with a single input that feeds both channels. I hope that clarifies what I was trying to say. And you're not splitting hairs... ;)
     
  14. N*Joy

    N*Joy

    Nov 30, 2002
    Birmingham, UK
    Don't worry about it - I was just being a finicky twit.



    EDIT: moderator. You meant "twit", right?
     
  15. lo-freq

    lo-freq aka UFO

    Jan 19, 2003
    The Republic of Texas
    I believe he was addressing that to me.

    I'm the obsessive-compulsive around here (at least one of 'em).

    Maybe engineers shouldn't be musicians (no, I think I got that backwards).
     
  16. Greatcrimson

    Greatcrimson Supporting Member

    Nov 17, 2002
    Central NJ, USA
    Okay everyone settle down. I said “stereo” but I think what I really meant was “dual mono”. I agree that unless the input signals are discreet, the output can’t be true stereo. As it turns out I’m going to end up with a single Eden 410XLT and a Stewart World 1.6. So bridged mono is the way I’m going for now unless I find a pile of money somewhere to pickup an additional 2x10 or something.

    Thanks for all the feedback. If anyone has this setup (with a SansAmp RBI), I’d still be interested in real world experiences, issues, pluses.
     
  17. ChenNuts44

    ChenNuts44

    Nov 18, 2001
    Davenport, IA
    I'm in school to become EE right now... hehehe
     
  18. SCT1422

    SCT1422 Supporting Member

    You can run bridged mono with no problem as long as you do not go below the allowable load... I was running two 8 ohm cabs, which ran in parallel equals a 4 ohm load with a QSC PLX-2402 bridged mono with no problem and plenty of headroom... I now went with a 4 ohm cab and run that with the QSC bridged mono and have no problem.. I've checked everything out with the manufactures of the cabs and thats what they recommend.. I do plan on adding another cab for bigger gigs, but I will have to use stereo because the amp should not be run below a 4 ohm load in bridged mono...
     
  19. 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
    True, an amp's slew rate doubles in bridged mono, but its voltage swing also doubles, so it's a wash.

    Nevertheless, slew rate is rarely a problem with a modern amp. I've yet to hear of any power amp designed in the past decade or so that doesn't have sufficient slew rate to handle the full audio spectrum at full power.

    There are a few amps that have too much slew rate, and as a result they do a pretty good job of amplifying RF noise--which is not a desirable thing.
     
  20. chucko58

    chucko58

    Jan 17, 2002
    Silicon Valley, CA, USA
    I paid for all my gear myself. Well, me and MasterCard.
    At which point you effectively have an unlicensed AM radio transmitter... and you might find your performance curtailed by an agent of the FCC!