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multiple cab impedence question

Discussion in 'Amps and Cabs [BG]' started by morebass!, Dec 23, 2004.


  1. morebass!

    morebass! I'm listening

    May 31, 2002
    Madison WI
    I'm thinking of running 3 cabs and want to see if anyone sees a problem with my setup. I have a Crest V900 that I'll run bridged. One cable (bare wire connection) will go to a 8 ohm Tubeworks 400 watt 4x10. The other cable (banana plugs out of same output connectors) will go first to one 4 ohm Avatar 700 watt 2x10, then out of that cab to a second 4 ohm Avatar 700 watt 2x10. I figure this will present a 4 ohm total load so I'll be okay. However, I wonder if I'll have volume balance problems because the Avatars won't be pushed as much as the 4x10. Any thoughts?
     
  2. IvanMike

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

    Nov 10, 2002
    Middletown CT, USA
    BAAAAAAAAAAAAAAAAAD idea. i didnt do the math on the fly but you'll be running tha amp below 2 ohms, or below one ohm per side!!!!

    run it in stereo . If the crest will handle 2 ohms per side you will be able to run the two avatar cabs off of one side as a 2 ohm load, and the 4x10 as an 8 ohm load off of the other side. If the amp will only safely drive a 4 ohm load per side you are stuck using two of the cabs.

    read this post
     
  3. morebass!

    morebass! I'm listening

    May 31, 2002
    Madison WI
    Please do the math. Two four ohm cabs in series equals an 8 ohm load. Take that and put it in parallel with the 8 ohm cab and you have a total of 4 ohms. The crest can handle 4 ohms bridged. That way I'll get 1100 watts out of it instead of the 700-800 if I put 8 ohms on one channel and 8 on the other.
     
  4. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    That amp can take 2 ohms per side when run in stereo, but 4 ohms when bridged.

    If you want to keep the amp bridged, try this. Wire up the 2 Avatar 4 ohm cabs in series. This creates a 8 ohm load so far. At this point pretend your two 2x10 cabs are now a single 4x10 cab rated at 8 ohms. Now connect the 8 ohm Tubeworks in parallel. The total load is 4 ohms and all 3 cabs are working.

    Whatever you do, make sure the Avatar's are connected in series, not parallel. Get that part wrong and there could be smoke.
     
  5. IvanMike

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

    Nov 10, 2002
    Middletown CT, USA
    problem is, you're running the cabinets in parallel Cabinets with multiple inputs have the wired in parallel, not series.
     
  6. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    It's possible to connect cabs in series, though it's not the standard way of doing it. It usually requires specially made cables, but given that we're talking bare wires and bananna plugs, it shouldn't be too hard.
     
  7. IvanMike

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

    Nov 10, 2002
    Middletown CT, USA
    just reversing the tip and ring (or positive and negative) on the connecting cables themselves will still wire the cabinets in parallel, just out of phase - so it'll sound weird AND blow the amp up. You'd need to modify the input jack wiring of the cabinets internally to convert the parallel input jacks to series input jacks.
     
  8. 7flat5

    7flat5

    Nov 28, 2003
    Upstate NY
    morebass, I know you're not a dope, but I hope you got the idea of where you went wrong in your thinking. In the above quote, you thought that since the cable is going from your amp to the first cab and from that cab to the second Avatar, that meant they were in series. They are not. Those two cabinets are still, when you do it that way, wired in parallel. That's why your math is not right. If they were in series your math would be right. Wiring them in series is a chore, involving mods either to the cabs or to the cables. It cannot be done with the usual cables available.
     
  9. Lyle Caldwell

    Lyle Caldwell

    Sep 7, 2004
    Memphis
    And while it can be done, that's a lot to ask of external cables that will be stepped on, stretched, etc. You could do it, preferably using 4 conductor cables and Speakon plugs/jacks, but it would be complicated and vulnerable to failure.

    Much better to trade for an 8 ohm Avatar 4x10.

    Hmm, or you could rewire your Avatar cabs inside so the speakers would be in series inside the cabs, giving you two 16 ohm 2x10s, which you could then run in parallel for an 8 ohm load.

    That would let you use all three cabs, but each 2x10 would be less useful on its own. Of course you could make each 2x10 switchable from 4 ohms to 16 ohms. Just label things carefully and triple check the switches before using them.
     
  10. Lyle Caldwell

    Lyle Caldwell

    Sep 7, 2004
    Memphis
    And never change the switch settings when the amp is on.
     
  11. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    Do the cabs have jacks? I'm under the impression they don't. The posts indicate the cabs have bare wire and bananna plugs.

    And I have actually wired up cabs in series before, using specially made cables that were in phase and required no modding of the jack itself. It's hard to explain but I'll give it a go..........

    The cable had a jack with both positive and negative on the jack that goes to the amp. Then I split it down the middle and put a jack on the positive wire with the negative terminal of that jack left empty, and another jack on the negative wire with nothing attached to the positive part of the jack. Label each jack as either + or - so you know which is which. One of these jack goes into the first cab, the other jack goes ito the other cab.

    Then you need another cable made from only one strand of speaker wire instead of the usual 2. Put a jack on each end, one connected to the positive terminal only, and the other end connected to the negative terminal only. Again label each jack + or -. Use this cable to go from the link on one cab to the link on the other. Provided each cab gets one + and one - jack, Whamo - series connection..........
     
  12. Dan Molina

    Dan Molina TalkBass Secular Progressive

    Jul 17, 2002
    Murr Town, California
  13. IvanMike

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

    Nov 10, 2002
    Middletown CT, USA
    I didn't read the initial post that way.
    I read it as he was going to use bare wire on the poweramp end of the connection to the 4x10, and a bannana jack on the power amp end of the connection to his 1st avatar 2x10. My guess was that he was intending to use a bare wire connection on the binding post output because he wasn't aware that bannana jacks could be stacked, or becasue he preferred the tighter connection of bare wire. He never stated that he was intending to use bare wire to hook up the cabinet end of things.

    My assumprion was that there was a jack of some kind on the 4x10, and that he would be using a bannana plug to connect to avatar #1, and use a 1/4" cable to connect Avatar #1 to Avatar #2. Or stack another bannana cable on the input jack of avatar #1, and run it to the bannana jack of avatar #2. Parallel connections in all cases.
     
  14. Lyle Caldwell

    Lyle Caldwell

    Sep 7, 2004
    Memphis
    It seems clear that the amp accepts bare wire, not the cabs. Avatars certainly do not.
     
  15. IvanMike

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

    Nov 10, 2002
    Middletown CT, USA
    If the avatar cabs accepr double male bannana plugs you have one other series wiring connection available. besides pete's great suggestion. To do it you would need Single wire cables and single bannana jacks. Take one cable and plug it into the positive terminal of the amp's bannana socket, and plug the other end into the positive bananna socket of avatar #1. Take a 2nd cable and plug it from the negative bannana socket of avatar #1 to the positive bannana socket of Avatar # 2. Take a 3rd cable and plug the negative bannana socket of avatar # 2 into the negative bannana socket of the amp. That should give you a series connection.

    IIRC, you can also make or buy series connection boxes that let you use the parallel 1/4" jacks on cabinets to make a series connection. You could also modify your cabinets to have both series and parallel output jacks.

    I wasn't rying to be rude in my earlier posts, just hate to see someone blow up an amp.
     
  16. morebass!

    morebass! I'm listening

    May 31, 2002
    Madison WI
    IvanMike,
    I stand (or sit) corrected. I was thinking that daisy-chaining the two 4-ohm 2x10s would be series and result in a 8 ohm load. You're also right about the connections - bare wire or banana on the amp and 1/4" on the cabs. Thanks for straightening me out on this. I'll have to rethink. I probably need to get another 8 ohm 4x10 and run the two 4x10s in parallel off the bridged amp.

    Confession: I really only have one 4 ohm 2x10 now and was going to try to save some $ by getting another 2x10 instead of a 4x10.

    Thanks to Petebass, 7flat5 and Lyle too. Probably won't try the series wiring so helpfully and creatively suggested by Petebass. Things are too complicated as-is :) I don't need more things to think about at the gig. The cabinet wiring option is more of an option for me.

    Anyone want to trade their 8 ohm 4x10 for a 4 ohm 2x10?
     
  17. IvanMike

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

    Nov 10, 2002
    Middletown CT, USA
    i seem to recall another guy calling avatar and they swapped cabinets or speakers with him. You might want to give them a call. As far as running an 8 ohm 210 and 8 ohm 410 together of of the same amp, it sounds fine. i've done it quite a bit.