Am going to try a sealed DIY sub-HELP!

Discussion in 'Home Theater Projects' started by Eric Ha, Mar 22, 2005.

  1. Eric Ha

    Eric Ha Stunt Coordinator

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    After enjoying my SVS PB12Plus/2 for almost a year now, I want to try my hand at a DIY sub, and have bought a used Tempest driver. I have really wanted to try a sealed sub and have been reading today about Linkwitz Transform additions to the Rythmik amps. I'm wanting to come "reasonably" close to the SVS's output and extension. I have some questions:

    Should I use the Tempest with a Rythmik amp? Which one?

    Should I sell the Tempest and get an Avalanche or Atlas 15?

    Are the servo amps preferrable to the LT amps?

    What size enclosure should I go with a Tempest or Ascendant driver? Will one size work with both so I can upgrade to an Ascendant down the line?

    Any and all help very much appreciated.
     
  2. Ryan Schnacke

    Ryan Schnacke Supporting Actor

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    In order to match the low frequency (~20Hz) output of a ported sub you'll need to have 2X to 3X the driver displacement in a sealed sub. I don't know if anyone outside of SVS knows the displacement capabilities of the dB-12 woofer but I'd guess its somewhere around 2L to 2.4L. And of course there's 2 of them in the PB12Plus/2.

    A Tempest displaces 2.56L.
    An Avalanche 15 displaces 4.04L.
    An Avalanche 18 displaces 6.53L.

    So to match the output in a sealed box I'd really want to have a pair of Avalanche 18's. I honestly don't think a single sealed Tempest would get you anywhere close. More like 4 sealed Tempests. At this point its more feasible to build an infinite baffle sub.

    I don't mean to be negative here, its just that the math doesn't work out well in this case. Ports can really do a lot for the bottom end, especially with the right combination of subsonic filtering to protect the driver from unloading.
     
  3. GrahamT

    GrahamT Supporting Actor

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    Hi Eric,

    I dont think it is worth it to upgrade to an Atlas since you already have the Tempest. Try looking at some of the designs on the Adire Website. I have tried a few and recommend the EBS Tempest. Definitely go ported, IMO. And if you do, there is no need for an LT amp obviously. 250-350W would be plenty. It is a great budget sub.

    http://www.adireaudio.com/Files/Vent...plications.PDF

    If you can swing the Avanlanche then that is another story. Chad could recommend the appropriate enclosure.

    Later,
    Graham
     
  4. Rudi B

    Rudi B Stunt Coordinator

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    You can try using more-or-less-the-same as SVS's Plus units TC Sounds TC2+ units from SoundSplinter, Oaudio,...

    Just yesterday I whipped up a little 40l sealed test box for a TC2+ ... Heck, plays quite nicely with 100 watts in room. It's meant for a car, but it really surprised me! It sure doesn't go as deep as a PB/12 Plus/2, but has nice "fast, tight" bass (probably because of the very absence of deep bass).

    Fun stuff.
     
  5. Eric Ha

    Eric Ha Stunt Coordinator

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    Thanks for the suggestions. I already have a very nice, very large, ported sub in the SVS. I want to try my hand at a sealed sub. Does anyone have suggestions on the Linkwitz Transform setups from Rythmik, and what box size I should go with on a Tempest or Avalanche 15 with the LT setup? If I have to lose SPL for SQ and extension, so be it.
     
  6. Eric Ha

    Eric Ha Stunt Coordinator

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    So is this why they call it the "do it yourself" forum? [​IMG] Someone must have built a sealed Tempest with a LT circuit in it.
     
  7. Brian Fellmeth

    Brian Fellmeth Supporting Actor

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    I've built a sealed tempest and approached the roll off problem differently- using a BFD to flatten the response to 20 Hz. The BFD can provide that ultra deep lift that a LT does plus completely flatten the response.
     
  8. Michael R Price

    Michael R Price Screenwriter

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    Bigger is better because the box size corresponds to efficiency at low frequencies; even though you can theoretically obtain the same response from any box size using the LT circuit, the larger box will demand less power for a given output.
     
  9. Geoff L

    Geoff L Screenwriter

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    If your just looking to do a DIY sub and hopefully enjoy building it, I'd just use the Tempest that you have in hand and talk with Brian at Rythmik about LT'ing it.

    Forget about "coming close" in output to the U/2, NO contest the SVS wins easy. Large vented encloser along with more diver displacment going aginst a single 15" with what now is considered about average xmax and also small sealed, nope ain't gona happen.

    Extension tho, yah you can get down their aways for sure with the LT-circuit and proper power, but at the cost of some spl.. Only so much x-max and thermal handling to work with.

    You might also call and or email Dan/Adire about what your trying to do, for his personal take on LT-ing the Tempest.

    ===>
    I don't know of anyone that has LT'ed a Tempests, anyone know of one..????
    ===>

    Can't beat the price from Brian/Rythmik when buying the Amp and LT ~{all in one shot from him}~. Think it's like 30.00-35.00 for him to design one up, if I remember correctly.. Don't have to get your hands dirty except for building the box.
    You could build our own LT-circuit, but for what he charges, I'd just let him do it. Thats just me tho, not much schematic, tronics, & soldering experience on this end...[​IMG]

    Brian is a super nice guy to deal with and very helpfull even when "pestered with questions", like from me..:b

    Good luck with (what ever driver & or alignment) you might decide to do. I'd make sure the used Tempest driver is "fine" before you do anything with it!!!

    Cheers
    Geoff ¥
     
  10. Eric Ha

    Eric Ha Stunt Coordinator

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    Thanks Geoff, that's very helpful. I'll have to call Rythmik to get the optimum box size I think. Might try to get a hold of Adire also. Thanks again.
     
  11. Jack Gilvey

    Jack Gilvey Producer

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    Howdy,

    I'd definitely go with the suggestion to have Brain do the LT for you...very nice guy and price is extremely reasonable. His 350 watt amp has enough power to push a Tempest to full excursion below ~30Hz in a 3.5 ft^3 sealed box, so that's what I'd go with. Starting from that box, with an Fc of 37Hz and a Qtc of ~.7, you can choose whatever Fc/Qtc you'd like (almost), realizing that you'll max out at about 103dB @ 20Hz...with the rest of your chosen curve falling in around that.

    http://home.comcast.net/~jgilvey/CB_...re_Tempest.gif
     
  12. Eric Ha

    Eric Ha Stunt Coordinator

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    That's great Jack, thanks a lot. Any idea what dimensions that would be on a 3.5 cu.ft. box, factoring in driver and bracing displacement?[​IMG]
     
  13. Eric Ha

    Eric Ha Stunt Coordinator

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    Fantastic! I was wanting something other than a cube. Thanks for all your help.
     
  14. Dan Wesnor

    Dan Wesnor Second Unit

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    A Tempest will do 102dB @ 20Hz, which is enough. Throw in room gain and you're up around 100dB, which is well more than enough. It only takes about 200W to do this.

    You might want to try it in about 110L without an LT first. You might find that you like it that way. Going flat to 20Hz can sound lumpy and unnatural. I roll off at 30Hz in the big room, about 40Hz in the small room, and I can actually shake the chairs in the small room with a 12" sub. If you don't like it you can always change it.

    Glad to know somebody's building pre-built LT's. I'm bookmarking that page!!
     
  15. Eric Ha

    Eric Ha Stunt Coordinator

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    Thanks Dan. I suppose I could always have Rythmik make me an LT later. Cheap is good, as I'm just starting my DIY sub experience, and know that there will be a 2nd incarnation.........or 3rd ........ [​IMG]
     
  16. Eric Ha

    Eric Ha Stunt Coordinator

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    Yeah, my SVS curve is rising to a peak at 20hz, then starts gradually trailing off to 16hz. Great sound.

    I think I do want to keep the costs down since this is my first DIY sub. I scored a 250w amp from Brian at Rythmik on Ebay, and picked up a used Tempest driver, so total cost will be below $250. I've got a spare Rane 31 band eq laying around for some cheap and dirty eq'ing. If I like the mid q sealed sound, I'll move to the next level. Maybe an AA driver and more power with LT circuit.
     

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