external roundover size for floor-standing mtm

Discussion in 'Home Theater Projects' started by MikeCTM, Nov 11, 2003.

  1. MikeCTM

    MikeCTM Auditioning

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    what is the best size roundover to do on some ported floor-standing mtm cabinets? this is for the outside. in addition to the front baffle's four edges, is it beneficial to round over the eight other sharp external edges? thanks in advance
     
  2. KyleGS

    KyleGS Second Unit

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    I doubt you would have to go any larger than ~3/4". I've used that for my floorstanders- very pleased. I do not think there would be any audible difference for you to round any other corners but the front four.
     
  3. Dave Poehlman

    Dave Poehlman Producer

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    I used to have a link to a cool animated graphic that demonstrated edge diffraction... I'll keep looking, but perhaps someone else has a link to it.

    Actually, any frequency with a wavelength longer than the roundover radius isn't going to "see" the roundover anyway. Since a 3/4" wavelength is around 18000 Hz, there really isn't an audible difference with or without the 3/4" on the edges. You have to start getting into the 2-3" range before you'd hear any significant change in edge diffraction.


    It's mostly for asthetics IMHO.
     
  4. Allen Ross

    Allen Ross Supporting Actor

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    i am happy with my 1/2 incher, i was kinda hard up for cash and 40 bucks for a whiteside round over was a little much
     
  5. Greg Monfort

    Greg Monfort Supporting Actor

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    A 3/4" radius means a circumference of ~4.7124" or ~2877Hz. That said, it's acoustically a moot point since the baffle's far wider than this.

    GM
     
  6. KyleGS

    KyleGS Second Unit

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    Allen is that a Henckel Knife!? love 'em [​IMG]
     
  7. CarlDais

    CarlDais Stunt Coordinator

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    I think Parts Express magazine did an aritcle about round overs.....can't recall hte exact conclusions, but 1-2 "
    was needed to audibly hear the benefits.
    That said I think Dennis Murphy has a note about round overs on his site....he felt there was a benefit to even
    smaller 3/4 or 1" round overs
     
  8. MikeCTM

    MikeCTM Auditioning

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    i think i will do roundovers and i'm thinking 3/4", which is the largest option i have. doesn't internal bracing bring up the freq's and then they dissapate through rounded-over edges and acoustic foam and poly fil? am i assuming correctly the more extensive the bracing the greater results in bringing up resonanting freq's
     
  9. Hank Frankenberg

    Hank Frankenberg Cinematographer

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    I do 3/4" radius roundovers as IMO, they're the best-looking aesthetically. I've always read about the acoustical uselessness of roundovers under ~2", but I do recall mention of smaller being a bit helpful. I have a new 1 1/4" monster bit that I'd like to try some day.[​IMG]
     
  10. Allen Ross

    Allen Ross Supporting Actor

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    Wow KyleGS, i never noticed it was in the pics, nice of you to notice it, its a great knife unfortunately the only work out it gets is when i open packages and cutting apples, in my dorm, but i put it to good use when i am back home.
     
  11. Dave Poehlman

    Dave Poehlman Producer

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  12. Greg Monfort

    Greg Monfort Supporting Actor

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    >That said I think Dennis Murphy has a note about round overs on his site....he felt there was a benefit to even smaller 3/4 or 1" round overs.
    -----
    >The theory behind roundovers has to do with when a wave moves across the surface of the baffle and encounters a corner, it reflects off creating a second wave. A rounded corner will sort of "fan-out" that reflection... the more rounded, the more dissipated that reflection is.
    ====
    Yes, strong standing waves develop when a driver is centered between two boundaries (edges in this case), and is intensified if more are added, such as a tweeter that's ~equally spaced between L-R-top of the cab, and why at least tweeters should be offset on the baffle in a golden or acoustic ratio or have some baffle damping. Since I do both as a matter of course when using cone/dome drivers, I completely forgot about this phenomenon.

    When either of these are done, the small roundover has no audible effect. Really, for best imaging the baffle area around the tweeter needs to be damped, or at least have the vertical foam strip tweak that NHT and some others do.

    GM
     

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