Tumult Sealed w/LT or Tumult with 2 18" PR

Discussion in 'Home Theater Projects' started by Tom Rosback, Sep 13, 2003.

  1. Tom Rosback

    Tom Rosback Stunt Coordinator

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    I have a smallish theater room, 11' x 17' x 8', or 1500 cf.

    Back of the napkin shows I should be able to get 105 dB in room to 15 Hz, without exceeding the driver Xmax. Correct? This is not accounting for room gain.

    So, should I go with the extra cost and complexity of a PR setup? Or will I be happy with a sealed/LT setup?

    I'm currently running DIY full range mains with 12" ACI SV-12 woofs in 2 cf boxes, and an LFE sub with an ACI DV-12 driver in a 2.5 cf sealed box. This is a dedicated HT setup. Sounds great but doesn't go looooooow.
     
  2. Tom Rosback

    Tom Rosback Stunt Coordinator

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    Thanks, Jack. I'm running some PR alignments with LEAP and so far I haven't gotten flatness and GD to come into line with a reasonable box size. I like what I see in 2.5 cf sealed alignment, though.
     
  3. Greg Peniston

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    Tom, I have a Tumult with a PR set up(pictures and construction at wmeckle.com) and a Crown K2 and I am very satisfied with the results. This is coming from a guy with an on going membership to the sub of the month club. After using the Stryke test CD and an Art 351 EQ to flatten response, it sounds great for both music and movies. What seals the deal is that I have a heavy hand at times with the gains and regardless of what movie I put on or how deep the bass, the sub is never stressed. The peace of mind not having to run for the volume say for an oncoming T-Rex is priceless. Now that only leaves a larger box size and increased GD (although the XBL2 technology yields a very clean sound) compared to the LT which also isn't a free lunch. Like Jack said you will need a large amp to compensate for the equalization. I'm not saying the PR set up has increased fidelity over the LT but you did say it was a dedicated HT set up and when the going gets tough the PR set up is going to be cruising along when it comes time to go loooooooow.
     
  4. Tom Rosback

    Tom Rosback Stunt Coordinator

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    Hey Greg,
    Looking at your website, you've got a charter membership to sub-of-the-month club! Awesome.

    I see your Vb is 5.2 cf. This size box would be no problem for me to fit in the theater.

    Where are the PR's tuned: Vas, Mms, fs?
     
  5. Greg Peniston

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    Hi Tom, actually the website belongs to my friend Bill. The PRs are 2500 grams so the performance numbers will be very similar to the Denali from Acoustic Visions. The Tumult is great in this set up it just seems undaunted by anything I send its way. On a side note if you're interested in increased impact/feel you might want to try some tactile transducers/shakers. I use 4 Aura Pro Shakers (soon to be a Clark Synthesis Platinum) and in conjuction with the Tumult movies just come alive. The trees in LOTR 2 and the scene with the wraith or whatever it is flapping its wings is awesome, I can't watch most films without them anymore!
     
  6. Tom Rosback

    Tom Rosback Stunt Coordinator

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    Thanks Jack, thanks Greg.

    I'm converging on a 5.6 cf enclosure with two of the Stryke 18" PR's. I've modeled both 1600g and 2500g versions, and both go scary low. With 2500g, the PR/box is tuned to 14.0 Hz, With 1600g the tuning is around 17.5 Hz.

    14 Hz seems really low to tune the box. The response almost looks like and EBS alignment.

    With the 1600g PR's, the response looks like a Chebychev with about a dB of peaking.

    Both alignments are only 6 dB down at 15 Hz, ignoring room gain. Ouch! [​IMG]

    In any case, the driver will be unloaded at very low freq's - looks like a rumble filter is mandatory.

    Making the box bigger than 5.6 cf doesn't seem to be an advantage. Dropping it to 4.0 cf, I get a lot more peaking.

    For the PR's, I can't get the Vas spec of 2045 liters to agree with what I'm calculating for Cm given fs and Ms for both versions. I get a Cm=900um/N.

    Any thoughts on what I might be doing wrong?

    PS: Greg, my Aura Pro's just arrived from Parts Express, they're on closeout for $25 clams a copy. I've pulled 'em apart and am modifying the spider to lower the resonant frequency. Should be fun!
     
  7. Brian Bunge

    Brian Bunge Producer

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    Tom,

    For your situation I'd go with the sealed enclosure and employ an LT if you deem it necessary. It that "small" room you should get plenty of low end response I'd think. After all, my whole house (roughly 1700-1800ft^2) is my room due to the wonderful open floor plan homes they like to build around here. [​IMG]

    One thing that may make your decision easier is that last I spoke to John he was completely out of 18" PR's and I believe the new baskets he got in were the wrong ones. So I wouldn't expect them to be available anytime soon.

    Of course, like Jack said you could always build the sealed enclosure large enough to accomodate the PR's once they are available.

    P.S. Sorry I didn't respond to your email. I think it rolled off the page before I got to it. Send me another if you still have any specific questions and I'll make sure to respond.
     
  8. Jack Gilvey

    Jack Gilvey Producer

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    When I get home tomorrow I'll run the sims to get the PR specs. I use Unibox, so I only plugged in the Mms,Fs, and Vd from the Stryke site...the Vas changes as I change Mms.

    I agree on the use of an infrasonic filter. With the big amps used on subs like this, not using one is asking for trouble. I'm using the SVS/Marchand box, which has lots of gain for pro amps that need it and a selectable 24dB/Oct rumble filter @ 15/20/25Hz.

    Like Brian says, try a simple sealed box first...room gain may well get you what you want.
     
  9. Tom Rosback

    Tom Rosback Stunt Coordinator

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    Jack, Brian,
    I like the sound of sealed subs, and like I mentiond in my first post, a single 15" Tumult should hit 105 dB at 15 Hz in my room, without busting Xmax. If I can't get the PR's, that will help drive my decision.

    But I'm curious, why the recommendation away from a PR setup? Again, just curious.

    So far, I see the following sealed advantages:
    1,) Easier to build.
    2.) Lower sensitivity to driver parameter shifts. In a driver this big, with a Vas this low, I always am thinking..what's the unit-to-unit variation in the compliance spec?
    3.) 2nd order highpass rolloff makes equalization and compensation easier.
    4,) Air loading makes the driver harder to bottom out at very low frequencies.

    I see the following PR advantages:
    1.) More output at very low frequencies
    2,) Less main driver excursion at very low frequencies (to a point)

    Anything else I'm missing? I've got to admit I'm smitten by the simulated performance of the PR setup, but simulation and real world don't always match.

    Brian, didn't miss anything in the e-mail, just a quick hello and the same question I'm asking here.
     
  10. Jack Gilvey

    Jack Gilvey Producer

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    I love PR subs, and the sub I'm using at the moment (as another card-carrying member of the sub-of-the-month club) is a Stryke AV12 with two Lambda 15PR1400's. So, I don't mean to come across as dissuading you. My point is that, since the Tumult can move so much air, you might not need a reflex to achieve your SPL goals.
    I'd agree with your assessment above, and there's no doubt that a PR sub will have more output/headroom/sensitivity down really low.
    Tough to say what you'd get in-room, hence my recommendation to start with a simple sealed box, add EQ if necessary (if the box is big enough, say below a Qtc of 0.7,you won't need an LT...just a simple shelving boost), then add PR's if it's not enough.
    Later on I'll see what box I'd go with that would allow this sort of progression. You'd have to build assuming the reflex, so you'd wind up with a fairly low-Q sealed box.
     
  11. Tom Rosback

    Tom Rosback Stunt Coordinator

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    Jack,
    Thanks for the info. I like your idea of building to accommodate the PR's initially, but not adding them until I test the sub in-room. Since I've got to get a big amp and eq anyway, this makes good practical sense. It will make the internal cabinet bracing a little more complicated, but so be it.

    BTW, LEAP sez sealed box alignments for the Tumult are:
    Butterworth - 1.74 cf
    Bessel - 3 cf

    For the PR, a 5 cf box looks really good on paper. I'll model some smaller boxes today.
     
  12. Craig Treusdell

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    Tom,

    Until recently, I had never heard a ported system I thought sounded good, so I always stuck with sealed enclosures.
    Then I took a chance and built a ported enclosure with a Tempest using the Adire alignment. WOW! A ported box that sounded great. Tuned to ~16 Hz and I don't think much music is affected by the group delay. It sounded just as good in my Tahoe.

    Then came the Tumult. And the PRs. So I built a box, 5ft^3, added two 18" Stryke PRs loaded with 1600g, listened to it and measured it with LMS, and liked it. I added 900g to each of the PRs, although I should have bought them that way, and liked it even better. I haven't measured that setup yet. Final result: 5 ft^3 with 2-18" PRs 2500g.

    I seem to recall that the LT adds about the same amount of group delay as a ported enclosure. Anyone modeled this in SPICE?
     
  13. Tom Rosback

    Tom Rosback Stunt Coordinator

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    Craig,
    I've modeled a 5.6 cf 2 2500g 18" Stryke PR setup, and a 2.5 cf sealed/LT combo using LEAP. The group delay at 15 Hz in both cases is about 45 mSec. No advantage to the LT there. This is as I would expect, as with any given driver diameter, there is no free lunch.

    The real difference is in excursion, the sealed LT combo runs about 20 mm Xmax at 20 Hz with 100 watts, the PR is running 10mm.

    At 15 Hz the LT combo is running 38mm and the PR driver is running at 5 mm, and the drones are running 7.5mm each.

    This is fun!
     

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