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Thread: Push-Pull benefits

  1. #1
    Senior Member cvjoint's Avatar
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    Push-Pull benefits

    How far do they extend? If it's true that they offset any asymmetry this can be huge. Would it completely offset any inductance variation? That would be huge in terms of driver choice. Might even go as far as selecting woofers without shorting rings in order to achieve closer gap placement of the voice coil and therefore higher sensitivity.

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    Senior Member minbari's Avatar
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    I think that is the idea behind it. are you talking about isobaric or just one woofer inverted?

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    I assumed he was talking about the push-pull as suggested elsewhere with teh 830987 from peerless... "push-pull 830987" brings up a link to DIYMA.

    - Bret

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    I couldn't find it, but I though the linkwitz pluto claimed a reduction in 2nd order or even order distortion.

    Here are some push pull measurements and comments in the links on this page including shorting rings vs push pull.
    Pi Speakers - Push/Pull Basshorn Subs

    Taking what Eminence said about shorting rings below 150Hz and most distortion in Klippel reports is due to mechanics and not motor inductance, it makes sense.
    Last edited by durwood; 06-11-2012 at 03:14 PM.

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    Senior Member cvjoint's Avatar
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    Push-pull as in mounting one driver in opposite direction and flipping phase or push-pull as in the Tympany LAT where the drivers are in phase but still push-pull. Not isobaric.

    Great links guys, I will have to read that DiYMA thread top to bottom. So far I can tell you that I have bassfromspace's LAT 250s, all of them and another two for a total of 8. I just want to understand them well enough before I throw them in the door.

    Reading Durwood's link from PI it seems that they believe inductance asymmetries are offset by the push-pull as well. I guess my question was if the push-pull reduces assymetries of every kind, BL, CMS and LE. My impression from that article and in general is a resounding yes, but all people talk about is 2nd order reduction which is the final output, I don't get to see the levers if that makes sense. Now, if it is true that all assymetries and therefore 2nd order distortion is reduced through all three mechanisms BL, CMS, and LE then I misjudged Tympany's design. It's much better. I criticized it for having what looks like a simple overhung motor with no shorting rings. In fact, it may be that's the best way to go for push-pull. Their choices translate to the most heatsinking and sensitivity one could get at no cost. In my application with the dual LAT700s in IB, power dissipation is the weak point anyway. Even that beefy coil and dozens of pounds of aluminum (endcaps and armature are aluminum) cannot dissipate heat fast enough to bottom the thing out in 5 cubes of trunk space.

    So if Tympany could replace the LAT motors in the 700 model with NE12 motors the performance might actually suffer. The copper caps would do little, and the motor would overheat faster.

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    Correct me if I am wrong, but isn't the tymphany reversed polarity? They are mechanically connected, so if one wasn't flipped they would do nothing.

    The problem I had with the PI link is it appears to compare push pull to non-push pull, but where is his exact design measured with push pull and without? Instead it compares other brands of subs...too many variables unless I missed it. I only linked it as a possible lead on further information.
    Last edited by durwood; 06-11-2012 at 08:42 PM.

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    Quote Originally Posted by linkwitz
    Two drivers are used for increased output volume and to
    reduce distortion. The two pistons move in tandem in
    the same direction relative to the H-frame. Push-pull
    mounting of the drivers reduces even order distortion by
    more than 10 dB.
    http://www.linkwitzlab.com/AES-Munic...%20live-18.pdf

  8. #8
    Senior Member cvjoint's Avatar
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    Quote Originally Posted by durwood View Post
    Correct me if I am wrong, but isn't the tymphany reversed polarity? They are mechanically connected, so if one wasn't flipped they would do nothing.

    The problem I had with the PI link is it appears to compare push pull to non-push pull, but where is his exact design measured with push pull and without? Instead it compares other brands of subs...too many variables unless I missed it. I only linked it as a possible lead on further information.
    I think they are in phase mechanically, that's the only way to cancel the vibration. The woofers "squeeze" air through the cavities. I can pull on some rods just to verify this and get back to you. It could be that Typmany reversed the colors on the motors so that + is actually - but otherwise they should be connected in parallel or series just like any other speakers which indicates to me that if the polarity is represented truly they are in phase.

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    Senior Member cvjoint's Avatar
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    No talk about inductance in Linkwitz's paper but maybe inductance assymetries are not a big deal for the intended purpose. I can see how CMS and BL are effectively leveled off. But yeah, we don't have the right experiment to see the inner workings here. Someone needs to grab a centered perfectly optimized driver and relocate the coil on on the former or something.

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    I am pretty sure tymphany labeled the terminals in such a way that people would hook it up so that it worked.

    I have to agree with you, it should be pretty easy to measure with a pair of drivers, any drivers. Take a few different drivers and see if the change is roughly the same. It would be cool to take a really asymmetric woofer and compare to a symmetric woofer. Also compare non-push pull with push pull at different levels. If you had some that Erin did klippel measurements on, then you could compare and maybe link the two tests.

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