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RE: Oh MeGodz...IT'S ALIVE!!

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In Reply to: RE: Oh MeGodz...IT'S ALIVE!! posted by Satie on August 27, 2010 at 07:32:09

Bipole? Moving weight doubled? C'mon. None of the configurations you've mentioned are even considerations. Except maybe removing the diaphragm from one of the drivers. But I'm not going to do that unless I already have a damaged one.....and I don't.

The preferred setup is mylar-to-mylar in a dipole configuration. As you mention this means one diaphragm will be moving toward its pole piece while the other is moving away. This is a well known concept for reducing even-order distortion when operating two identical drivers in concert with each other. Cavity resonance is not an issue since there is no pressure created in the space between the diaphragms.

By the way, I'm not speculating here. I already have a single prototype working and it's working well. :)

Cheers,

Dave.

Follow Ups:

RE: Oh MeGodz...IT'S ALIVE!! - Satie 10:42:49 08/28/10 (7)
OK

So you are essentially doing a push pull with the mylar surfaces aligned and contacting each other. Have you attached them to each other in some way? or are they free to move against each other? If so, have you taken any precautions to avoid shorting if friction scrapes off the insulation?

So would it be right to conclude that the drivers are perfectly mirror imaged and align well?

How did you wire the drivers? in reverse polarity for one speaker?
- RE: Oh MeGodz...IT'S ALIVE!! - Davey 19:15:18 08/28/10 (6)
  Are these serious questions or are you just messin' with me? :)
  
  Dave.
  - RE: Oh MeGodz...IT'S ALIVE!! - Satie 19:53:00 08/28/10 (5)
    I am just curious, and I had been thinking of getting more Tympani panels to make a push-pull set of bass driver(s). The questions are some of what was bugging me in deciding whether to try this or not.
    
    I don't kid around and elbow folks on the forum, if I am joking you will know it. I am here to learn and help. It is up to you whether you want to share your thoughts and experiences on this.
    
    If you find my questions or comments lacking in some way please point out where things should have been obvious, the question nonsensical, etc.. I have not taken this concept far in my mind and have not done any experiments.
    - RE: Oh MeGodz...IT'S ALIVE!! - pictureguy 20:19:49 08/28/10 (4)
      Are you going to enclose the air space BETWEEN drivers? Isobaric is the name, at least when designing a sub.
      
      Several logical orientations. Both face same way. So, you'd still have choice of mylar or pole pieces facing the listener.
      Both mylar out.
      Both pole pieces out.
      
      With the 2nd 2 choices, at least with a panel which is divided into high and low frequency sections, you may NOT want the hi from panel #1 facing the lo from panel #2. vice versa, too.
      
      There is a way to line up the HF and LF sections of panels mounted like that......panel #1 is mounted normally. Panel #2 is inverted....the connection tabs are now on the TOP of the panel, so now the HF / LF sections will line up......???
      
      I don't know how strong.....or the distance.....the magnetic field extends. Be careful of interaction here......
      
      Too much is never enough
      - RE: Oh MeGodz...IT'S ALIVE!! - Satie 21:46:46 08/28/10 (3)
        
        In Reply to: RE: Oh MeGodz...IT'S ALIVE!! posted by pictureguy on August 28, 2010 at 20:19:49
        
        I am hoping to get Davey to tell us how he did his experiment and what it actually performed. Then we would know which way to go.
        
        I have seen posts about an Isobaric conversion that was bipolar. The guy liked it but I am skeptical because the panel tuning just shouldn't make it work so easily.
        
        RE: Oh MeGodz...IT'S ALIVE!! - pictureguy 23:20:52 08/28/10 (2)
        
        In Reply to: RE: Oh MeGodz...IT'S ALIVE!! posted by Satie on August 28, 2010 at 21:46:46
        
        I have NO idea whatsoever how to make this work....or IF it would work. That the panels can go together any of 4 ways, is simple geometry.
        How much space between 'em? Good question! And, for THAT matter, I don't even know what difference the amount of air trapped between drivers would make! Also, could you get the panels close enough together for the Magnets to interact......badly?
        
        But the good news, for me, is that since I can ONLY afford the panels I already OWN, I'm not IN the market for Isobaric Magnepans! (Huge sigh of relief)
        
        My first take would be to go whatever the 'easy' way was. Build a 2x6 frame, route the panel depth on both sides, and mount 'em both pole piece out. Wire 'em in SERIES out of phase. That'll get you to about 8 ohms, fairly flat and needing a couple hundred watts MINIMUM. These would also be a 'natural' for bi-amping. Since I think........(memory....memory?) that you gain about 3db sensitivity in such a situation, you might be OK with only 2x your current amp......Still a bunch.
        
        You'll be a candidate for a tight fitting sleeveless jacket before you're done. And, living in your car with a couple cats. or a Rat Terrier named 'Moe'.
        Too much is never enough
        
        RE: Oh MeGodz...IT'S ALIVE!! - Davey 08:07:34 08/29/10 (1)
        
        In Reply to: RE: Oh MeGodz...IT'S ALIVE!! posted by pictureguy on August 28, 2010 at 23:20:52
        
        Well, they could actually go more than four ways..... :)
        
        Isobaric Magnepans? This isn't an Isobaric configuration fellas....nor is it intended to be. There are no sealed air cavities and there's no attempt to lower bass response or reduce box size by one-half or any other principles associated with a true Isobaric configuration.
        
        All I've done so far is cut a piece of plywood the same size as an MMG frame, routered a "hole" in it the same size as the MMG transducer membrane and then rebated both sides so the transducer frames are flush. The two transducers are mounted mylar-to-mylar and temporarily held in place by spring clamps. There's a gap in between sufficient that possible magnet north/south conflicts are not a concern and the cutouts for the (stock) terminal strips (which are face-to-face) preclude any air sealing of the internal "cavity."
        
        Both elements of the two transducers are wired with opposite polarity for a dipole configuration. (I never even considered wiring them in a bipole configuration....that seemed pretty silly.)
        
        As you know, one MMG transducer (left) has a single button and the other (right) three buttons that create six different panel tuning "zones" so the L/R system won't drone in a narrow range in the bass region. Since I've coupled a left and right transducer together both speakers.....assuming I build another one.....would be identical in this regard. I don't believe this difference in "tunings" between two different transducer panels in the same speaker will be detrimental.
        
        It's just proof-of-concept at this point. I don't think it will be practical ultimately considering the simpler alternatives and the necessity of two pairs of drivers and more complicated construction scheme. Just something to play around with since I have a "spare" pair of MMG transducers.
        
        I am convinced the sandwich scheme is the way to go however. My existing speakers (the ones you've seen the photos of) can also be improved further by removing/reducing some of the variables in that configuration. That's on my plate also.
        
        Cheers,
        
        Dave.
        
        RE: Oh MeGodz...IT'S ALIVE!! - Satie 23:12:29 08/31/10 (0)
        
        In Reply to: RE: Oh MeGodz...IT'S ALIVE!! posted by Davey on August 29, 2010 at 08:07:34
        
        I understand now what you did and what you were after, this is interesting and different from what I came across before.
        
        Any preliminary observations on the resulting sound vs. plain ole' MMG?

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