Upgrading EBS Shiva

Discussion in 'Archived Threads 2001-2004' started by Stephen Dodds, Oct 14, 2002.

  1. Stephen Dodds

    Stephen Dodds Second Unit

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    While I am generally very happy with my EBS Shiva, I do have some tracks that fall below its tuning with rather sonically unpleasant results.

    I could, of course, get some kind of rumble filter.

    However, I saw in one of the threads that the Stryke AV12 is a drop in (or close to it) replacement for the Shiva. So the thought came to mind that replacing the Shiva with the AV12, plugging the port and using a Linkwitz transform might be a possibility.

    Anyone tried anything like this or am I going madder?

    Steve
     
  2. Patrick Sun

    Patrick Sun Moderator
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    Do you have a high wattage amp to power the AV12 if you do use a LT?
     
  3. Stephen Dodds

    Stephen Dodds Second Unit

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    I can throw up 650 watts per channel in four ohms.

    However, it isn't really so much volume as depth.

    Steve
     
  4. Jeff Meininger

    Jeff Meininger Second Unit

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    The "suggested enclosure alignments" graphics on stryke.com and acoustic-visions.com indicate that an EBS box for the AV12 is 5 cubic feet tuned to 18 Hz. In other words, almost exactly the same as the EBS shiva. If you're going to get the AV12, the "sonically unpleasant results" will most likely dissapear without needing to go sealed/LT.

    The AV12 has 23mm Xmax to the shiva's 15.8mm.
    The AV12 has 30mm Xsus to the shiva's 22(?)mm.

    Whether your unpleasantries are due to exceeding Xmax or actually bottoming out, it looks like you'll have more protection against both with the AV12.

    BTW, I just finished my EBS shiva and I _LOVE_ it. Fellowship of the Ring bottomed it, but none of my other DVDs can. I was running the sub WAAAAAY hot when I bottomed it. I should try it again now that I've dialed it back to "just a tiny bit hot". I have a PE 250W amp with rumble filter but no bass boost.
     
  5. Stephen Dodds

    Stephen Dodds Second Unit

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    It's not a volume related thing, the driver simply unloads below the 18Hz tuning frequency. If you happen to have the Telarc DTS sampler, play the opening track and you will see what I mean.

    In other words, I'm not sure what a more powerful driver tuned to the same frequency will do to improve on this, but I'm all ears.

    Apart from this, the EBS Shiva is pretty cool, don't you think. LOTR was no problem with mine.

    Steve
     
  6. Greg Monfort

    Greg Monfort Supporting Actor

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    Ideally you want the sub to be tuned to the lowest frequency it's expected to reproduce. This may cause over-excursion in the octave or two above Fb where there's probably more signal. Swapping to a higher displacement driver with the same Fb increases available distortion below Fb. Not a good plan IMO.

    Reproducing infrasonic signals at a meaningful SPL is all about displacement and the power required to make it, so you'll need to either increase the number of drivers to gain efficiency, or swap to a much higher displacement driver, such as the Tumult, and a more powerful amp to benefit from it.

    With only 250W, the amp is probably clipping on LOTR since I've yet to measure any movie's soundtrack that had significant infrasonic output WRT their harmonics, including the 'sub references', U-571, The Haunting, etc..

    GM
     
  7. Baldemar Garcia

    Baldemar Garcia Stunt Coordinator

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    *
    With only 250W, the amp is probably clipping on LOTR since I've yet to measure any movie's soundtrack that had significant infrasonic output WRT their harmonics, including the 'sub references', U-571, The Haunting, etc..
    *

    Greg,
    Can you clarify this statement, or simplify what you mean?
    Specifically, the part about the 'infrasonic output WRT their harmonics'.

    Thanks.
     
  8. Greg Monfort

    Greg Monfort Supporting Actor

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    Infrasonic (>20Hz).

    Normally, the fundamental has the most acoustic energy, with its upper harmonics progressively less. On the movie soundtracks I've monitored, the first two or three harmonics of a very low fundamental have much greater energy (SPL) WRT the fundamental, i.e. a 20Hz fundamental will have 40, 60, 80Hz harmonics that are much higher in SPL, as much as +12dB IIRC. Even without an amp bass boost, this much 'punch' with the gain cranked up can clip a modest power amp.

    GM
     
  9. Griff

    Griff Stunt Coordinator

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    EBS Tempest time.
     
  10. Stephen Dodds

    Stephen Dodds Second Unit

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    You've started me on a horrible DIY path Chris. Not only am I thinking about this but I am also building a set of Linkwitz Orions.
    [​IMG]
     
  11. John E Janowitz

    John E Janowitz Second Unit

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    Stephen,

    There are a few things you can do to get better response down below the 18hz tuning. First, and most importantly is lower your tuning frequency. As Greg said, your tuning frequency should be about equal to the lowest frequencies you are asking the subwoofer to play. The drawback is that you also lower the frequency of the excursion peak above Fb. This peak is located 1/2 octave above Fb. So if your tuning is 18Hz, your excursion peak should be at 27Hz. The more you lower tuning, the lower in frequency you push the excursion peak, and the more you increase it's magnitude.

    So by tuning lower, you'll get more output, and your woofer won't unload at those lower frequencies. Then you need to have more excursion available at that peak to keep from bottoming at that frequency. Greg mentioned a higher displacement driver. The AV12 does have a good deal more available displacement than the Shiva. Almost as much as a Tempest, but will work in the same enclosure size. As you said, pretty much a drop in replacement. You may need to slightly enlarge your hole though. I think the Shiva has a slightly smaller cutout than the cast baskets.

    The other issue is that around tuning, you may be experiencing high vent noise problems. The plans show for a single 4" vent. You mentioned you had 650W or so available. At that level, your vent velocity at Fb will reach up around 60m/s. That is well above the level you'd want to keep distortion and compression down. The flares will help with keeping noise down, but velocity inside the vent is still the same level. You may want to try larger vents if you can fit them in the enclosure.

    The other option is to go with PR's. No problems fitting them in, or getting a lower tuning. They also have a mechanical suspension, so they do not unload quite the same below tuning as a vent would.

    John
     
  12. John E Janowitz

    John E Janowitz Second Unit

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    Hi Jack,

    Below the tuning in a port, the driver fully unloads. There is no coupling left. With the PR, there is still that mechanical suspension there to offer some resistance. I guess i really can't explain it better than that.

    As far as the vent noise/compression goes, majority of the noise is from turbulence at the end. I'd say the majority of compression is also attributed to this. You can have audible vent noise problems way down around 20m/s. Using a flared port will eliminate these issues. By the time you get up to 50 m/s though, you're going to have some compression through out the vent no matter how you flare the ends.

    John
     

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