Leg length on down firing Shiva?

Discussion in 'Archived Threads 2001-2004' started by Stephen Hopkins, Jan 1, 2003.

  1. Stephen Hopkins

    Stephen Hopkins HW Reviewer
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    I've just finished construction of my EBS alignment Shiva. I've made a few modifications to the design, such as using 2 2" ports instead of a single 4" port and tuning it to 20hz instead of 18.1hz (to make the port length more manageable).

    Right now I have 2.5" legs on the bottom and i was wondering is enough clearance? If not, how long should the legs be?

    I hooked it up to the amp in my truck just to make sure everything sounded right and it sounded as good as could be expected firing down on a concrete basement floor. It will be in a room w/ minimally padded carpet after it's painted and trim pieces are stained and installed.

    Thanks
     
  2. Greg Monfort

    Greg Monfort Supporting Actor

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    I use a rule-of-thumb based on the driver's excursion capability and the circumference of the baffle that works well for me and others who've used it:

    18" dia. tube = 2.45" min.

    24" dia. tube = 1.84" min.

    FWIW I recommend you add a heavy base to attach your legs to, like the SVS, with spikes long enough to penetrate to the floor so that the base 'floats' on top of the carpet, and with some mass loading on top, such as a heavy plant.

    GM
     
  3. Ryan Schnacke

    Ryan Schnacke Supporting Actor

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    "I've just finished construction of my EBS alignment Shiva. I've made a few modifications to the design, such as using 2 2" ports instead of a single 4" port "

    Round ports, right? Do you realize that 2 2" ports will only have half the port area of a single 4" port? So they can only move half (or less if you count the added friction) the air as a single 4" port. And they need to be half as long as a single 4" port to get to the same tuning point.

    Anyway, the SVS subs get away with only 2" legs. At least the originals did. I don't have any others sitting around to measure. I used 3" on my DVC sonosub but I think 2.5" would be fine.
     
  4. Stephen Hopkins

    Stephen Hopkins HW Reviewer
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    I modeled everything in WinISD, and that was the proper length for twin 2" ports tuned to 20.5 Hz for my box volume (taking the loss of volume of the ports themselves into account).
    I'll look into adding a base, but that might be on down the road. I do plan on adding spikes to the legs themselves soon though.
    I'm glad 2.5" legs will suffice, because this thing is BIG and i can't imagine it getting any bigger.
    Thanks everyone [​IMG]
     
  5. Ryan Schnacke

    Ryan Schnacke Supporting Actor

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    You didn't mention the port length so I wasn't really meaning to suggest that you tuned it wrong. Probably right on the money. But I'd be concerned about air speeds with only 6.3 in^2 of port area instead of the 12.6 in^2 that's normally used. Hopefully they've at least got nice, big flares on each end. I suppose if you're planning on using limited power - say 120 watts or less - you'd be just fine.
     
  6. Stephen Hopkins

    Stephen Hopkins HW Reviewer
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    The vent match was in the green according to WinISD, but it was higher than a single 4" port or dual 3" ports. If i notice alot of port noise, i can always cut bigger holes and add dual 3" ports of the propper lengths.

    Thanks
     

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