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Bridged mono - would this work to get more headroom?

Discussion in 'Amps and Cabs [BG]' started by mrpackerguy, Dec 26, 2005.

  1. mrpackerguy

    mrpackerguy Supporting Member

    Jul 3, 2004
    Madison, Wisconsin
    I don't want to fry anything so I'm looking for advice from the learned gurus here.

    To try and get a little more headroom from my present set-up running out of my Yamaha p5000s in parallel to my two 4 ohm Acme Low B2 cabs, wanting to know if this would work/is even possible.

    Run bridged mono into one Acme cab via speakon conncection. Then, daisy chain the other Acme cab via 1/4"?

    Not only: can I do it without frying anything? But can you daisy chain the 1/4" inputs on the Acme cabs or do you need a dedicated output from one Acme cab, which obviously it doesn't have?

    I realize this would put a 2 ohm load on the Yamaha which in itself may not be smart. Maybe I just need to upgrade my power amp....again.
  2. IvanMike

    IvanMike Player Characters fear me... Supporting Member

    Nov 10, 2002
    Middletown CT, USA
    well, 1st off a bit about bridging.

    I'm not sure about the specs of your yamaha, but no matter what you should not do what you are proposing.

    when you run an amp in bridge mono, each side "sees" 1/2 of the total load. running those two 4 ohm cabs together will result in a 2 ohm load. Bridging your amp into that 2 ohm load wil lresult in each side "seeing" a 1 ohm load.

    some amps are rated for a min of 4 ohms per side stereo, or 8 ohms min bridge mono, some are rated for 2 per side stereo and 4 bridge mono. No bass amps, and only very, very, very, big and expensive poweramps are rated for 1 ohm per side/2 ohms bridge.

    after that -

    yes, daisy chaining your cabs will always result in a parallel circuit. cabs with multiple input jacks have them wired in parallel and jacks liek that are meant to be daisy chained if so desired.

    last but not least, to get a 3 dB increase in volume (which is just noticeable), you need to double your wattage. Acmes are great sounding, but are notorious for being inefficient and power hungry. To get a substantial volume increase you need to look at a lot more wattage or more efficient cabs.
  3. mrpackerguy

    mrpackerguy Supporting Member

    Jul 3, 2004
    Madison, Wisconsin
    The Yammy specs say it'll run at 4 ohm bridged. I think what you're telling me is that I'd really be running it at 2 ohms because I'd be running bridged into one 4 ohm cab, then daisy chained into the 2nd 4 ohm cab = 2 ohm load?

    Sorry, not quite understanding the 1 ohm thing.

    Yammy bridged mode - -> 4 ohm cab---daisy chain--> 4 ohm cab
  4. mrpackerguy

    mrpackerguy Supporting Member

    Jul 3, 2004
    Madison, Wisconsin
    Just answered my own question and thanks to IvanMike.

    I browsed the Yammy manual. Can only bridge a minimum 8ohm speaker.

    Looks like from QSC's PLX series manuals that they talk aout bridging a single speaker. No where do I see a daisy chained config acceptable.
  5. "Daisy chaining" by itself really isn't the issue. What's important is the impedance load that is created when two or more cabs are connected together (usually in parallel).

    You've got a 4 ohm cab. Add another 4 ohm cab in parallel, and the impedance is cut in half--to 2 ohms. (See the FAQ section and look for a thread on OHMS). As Ivan Mike said, ain't too many amps that can run a 2 ohm bridged load.

    You could have a situation where you have an 8 ohm cab, and then "daisy chain" a second 8 ohm cab. The resulting load is now 4 ohms, which some--but not all--amps can handle (it sounds like your Yamaha cannot handle a load as low as 4 ohms in bridged mode).

    There is good news!! And now, for once I'm not talking auto insurance...You could make a special cable and run your two 4 ohm cabs in SERIES...making the total load 8 ohms..and if I read your post correctly, it can handle an 8 ohm load in bridged mode. Running two cabs in series isn't normally done, so it has the drawback of being risky in that it is so unusual (somebody could mistakenly plug in the wrong cable and suddenly you're running in parallel instead of series, disaster!!)
  6. IvanMike

    IvanMike Player Characters fear me... Supporting Member

    Nov 10, 2002
    Middletown CT, USA

    that's very true and i forgot to mention it.

    however, thinking about it for a minute screws you over.

    you're already getting 4 ohms per side into each cab (the yammies max wattage) making a series cable and bridging the Yamaha into the resulting 8 ohm load will once again give you the same max wattage into each cab.

    but the series cable is always a good trick to know. i need to make one.
  7. Lowtonejoe

    Lowtonejoe Supporting Member

    Jul 3, 2004
    Richland, WA
    A series cable or a series box like this one:


    Just throw the box in your gig bag and use it when needed with regular cables.


  8. bigbajo60


    Nov 7, 2003
    Laredo, Texas
    There's always the option of calling Andy Lewis (Mr. Acme), and talking to him about what it takes to reconfigure your cabs into 8 ohm boxes.

    THEN you could use that P5000 bridged to power 'em.

    1300 watts per box should get a pretty good rumble going. :smug:
  9. According to the specifications for the P5000S, you get 750W into 4 ohms per channel stereo, or 1500W into 8 ohms bridged.

    You cannot run the cabinets in parallel and run the amp bridged, as that would be 2 ohms, which is far below the bridged load rating. And if you wired the cabinets together in series, you would still get exactly the same 1500W as you get by running the two cabinets stereo.

    IMO, you need more efficient cabinets for the volume you are playing at.
  10. bigbajo60


    Nov 7, 2003
    Laredo, Texas
    Just quoting Yamaha's posted Specs my friend:

    Technical Description


    Output Power
    1kHz, THD+N=1% 8 Ohms Stereo: 525W + 525W
    1kHz, THD+N=1% 4 Ohms Stereo: 750W + 750W
    1kHz, THD+N=1% 8 Ohms Bridge: 1500W
    20Hz-20kHz, THD+N=1% 8 Ohms Stereo: 500W + 500W
    20Hz-20kHz, THD+N=1% 4 Ohms Stereo: 700W + 700W
    20Hz-20kHz, THD+N=1% 8 Ohms Bridge: 1400W
    1kHz, 20mS nonclip 2 Ohms Stereo: 1300W + 1300W
    1kHz, 20mS nonclip 4 Ohms Bridge: 2600W

    The way the specs read though, it may well be that going to 4 ohms in bridged mode isn't a "Yamaha Approved" config.
  12. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    There are two types of bridging, parallel and series. Series, where you double the voltage output for 6dB additional gain, but don't get any more current capability. Parallel bridging, where you double the current without additional gain, allows you to go into lower impedance loads. That's how you'd want to do it, with the cabs paralleled also. However, if your current rig is capable of producing at least the rated power capacity into each of your cabs as you have it set up now it's unlikely that you'd gain any audible difference.
  13. mrpackerguy

    mrpackerguy Supporting Member

    Jul 3, 2004
    Madison, Wisconsin
    Thank you gentlemen for all the pro-audio responses.
  14. 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
    Bridging does not have to be into a single loudspeaker--it can be any number of loudspeakers, as long as the resulting load impedance is equal to or exceeds the amp's minimum--but it is inherently into a single load.