Dipole subwoofers / Push - Pull configurations

Discussion in 'Home Theater Projects' started by Javier_Huerta, Mar 4, 2004.

  1. Javier_Huerta

    Javier_Huerta Supporting Actor

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    Hi,

    I was wondering... for my next project, I'd love to do something unusual.

    I saw the MartinLogan Descent sub and some hybrid electrostats with a weird woofer. It has two drivers, one on each face of a cube. One "pushes" air into the enclosure, while another "pulls" it out.

    For all I know, this should be a dipole subwoofer, which would need to be heavily eq'ed in order to work.

    But maybe there's a bit more about this design... box parameters, something else.

    I was wondering if someone ever built something like it.

    TIA!

    Javier.
     
  2. ThomasW

    ThomasW Cinematographer

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    THIS link and THIS link should get you started.

    Just do a google search for dipole subwoofers, you'll find a ton of info.

    They are some of the best sounding subs around. And yes they need a little extra help with EQ.

    Also there's a Topica email list for dipoles
    http://lists.topica.com/lists/dipoles/
     
  3. Frank Carter

    Frank Carter Screenwriter

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    The ML Descent is not a dipole sub, it uses 3 10" woofers spaced 60 degrees apart to cancel out mechanical forces on the enclosure, it's very effective.
     
  4. ThomasW

    ThomasW Cinematographer

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    If your talking about this,

    [​IMG]

    Then yes it's a dipole sub from the Martin Logan Statement loudspeaker system
     
  5. Justin Ward

    Justin Ward Supporting Actor

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    I've been considering doing a DPl12 based dipole sub. Are dipoles appropiate for use in a small room?
     
  6. ThomasW

    ThomasW Cinematographer

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    Dipole subs should be no less than 4'-6' from the rear wall. If that works in your room, then you're good to go.

    Linkwitz talks about this but I don't remember where...
     
  7. Justin Ward

    Justin Ward Supporting Actor

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    Well looks like I'll have to scratch the dipole sub off the list. This would be unreasonable for a university room. Heck, even in the middle of the room it may be pushing it in terms of closeness to the wall.[​IMG] What would be my next best bet for a music only sub? I guess a sealed DPL12 would be pretty nice?
     
  8. Javier_Huerta

    Javier_Huerta Supporting Actor

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    Hey, I do have that kind of space. Thomas, thanks a lot for the links! I'll definitely be checking them out, and will probably build the sub...
     
  9. Chris Tsutsui

    Chris Tsutsui Screenwriter

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    I'd never give up on dipoles. I've heard some of the stuff out there and it's just crazy wonderful.

    Hang the dipoles from the ceiling in floating clusters if you have to save space. [​IMG]
     
  10. Bryan Michael

    Bryan Michael Supporting Actor

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    is the svs pb4 one too?
     
  11. Justin Ward

    Justin Ward Supporting Actor

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    lol, I'll keep that in mind.[​IMG] I was browsing the Linkwitz web site and there is just so much information that it is really overwhelming. I'm no expert but I'd like to think my acoustic knowledge is proficient and most of the information on that site is beyond me.

    However, about the distance from the wall statement, I was sure I read on their somewhere that dipole subs could be placed near a wall but not in a corner. Maybe I misinterpreted though.

    I would like to build a pre-designed dipole that I know would sound good for music in a small room. Also I would like it to be small and aesthetically pleasing(though I could live with it being a little weird looking if the size was smallish).

    I think one like this would be good [​IMG] (the middle one) but they do not have specific numbers for something like that. Having the drivers visible would be awesome, front or back(the DPL12 has an awesome looking backside[​IMG] )
     
  12. ThomasW

    ThomasW Cinematographer

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    If you want small then build a "W" baffle

    Adjust the measurements to fit the dimensions of your driver. Pay attention to the April 2002 notice in the Linkwitz design
     
  13. Justin Ward

    Justin Ward Supporting Actor

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    That looks do-able. One of the potential designs is dual Shivas. Would it be better to substitude DPL12s? Or should I just go with the given design?

    I just notiec you said "rear wall", why can it not be close to a rear wall but a side wall is acceptable?
     
  14. ThomasW

    ThomasW Cinematographer

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    DLP12's will work better than Shivas

    Dipoles create a null at the sides of the baffle. I'm not sure how that will effect placement
     
  15. RichardHOS

    RichardHOS Second Unit

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    Dipole subs are directional... kind of like a spotlight instead of a bare lightbulb. There's not much sound eminating from the sides, so placement near a side wall isn't that bad.

    Bass wavelengths are long. In dipole subs, the rear wave is out of phase with the front phase. The rear wave will be reflected from a wall back towards the listener at some attenuated volume. If placed too close to the wall, the ratio of speaker/wall/speaker length may be small compared to the length of the wave being played, and thus will not have much phase shift relative to its phase when leaving the sub. Since that phase was opposite that of the forward wave, there is the potential to have a large degree of cancellation.

    The same thing happens with omni subs when placed too far from a wall. In general, an omni sub (sealed or ported) should be placed close to a wall to avoid this possibility. I've seen arguments rage on for pages about whether this SBIR effect or modal effects are the most imporant low frequency acoustic consideration.

    As it pertains to this thread, all you need to know is that dipole subs are their best in a really long room.
     
  16. Justin Ward

    Justin Ward Supporting Actor

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    This is getting to be a tough decision. The dipole placement and equalizing sounds pretty tricky but I'm intriqued by the potential sound quality. Would a W-baffle DPL12 dipole be much better than two separate 75 liter sealed DPL12s?
     
  17. Jason Bosch

    Jason Bosch Agent

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    Since it was mentioned, I was wondering if anyone has attempted a DIY version of the Martin Logan Descent sub. With the triangular cabinet and the 3 10's firing away from each other. I saw that at my local Hi Fi Buys and that thing was awesome. They put a quarter standing up on it and then turned up LOTR. It never moved. It's a truly dead enclosure. Although I admit I never tried doing that on another sub. So it may not be too impressive a feat. But the thing does sound fantastic.
     
  18. Bryan Michael

    Bryan Michael Supporting Actor

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    i can do that with my sub but it is 400 lbs and olny has dual 15
     

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