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Tempest enclosure measurements?

Discussion in 'Archived Threads 2001-2004' started by Dave George, Jan 24, 2001.

  1. Dave George

    Dave George Well-Known Member

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    I'm deciding upon the final plans for my dual tempest sub, and came across this post by Dan Wiggins on HTT from a while ago:
    "OK, here's yet another design to kick around... You know, I just come up with these, like I'm a speaker designer or something...
    For good "tight" sound, a Q of 0.577 is often used. It's maximally flat in terms of phase rotation (group delay). But, for home theater, you want a pretty low Fc (down around 20 Hz or so). So, how about this:
    175L per Tempest
    64 ounces of stuffing
    Tune to 17.5 Hz (4"ID by 13"L vent; note that our 4" flared vent kit would work well here - yes, that's a shameless plug... )
    You'll have a response that:
    Has an F3 anechoic of 22 Hz with the typical LFE crossover.
    Is power limited to 500W above 15 Hz (for linear operation).
    Mimics a 3rd order Q=0.577 Fc=20 Hz filter to +/- 0.25 dB down to 13 Hz.
    Should provide a typical in-room F3 around 17 Hz.
    Is capable of more than 110 dB SPL from 16 Hz and up, anechoic.
    Is capable of more than 118 dB SPL from 17 Hz and up, in a typical room.
    How does that design sound? Yeah, it's different again, but should be a good combination between tight articulate bass for music, and smack-you-upside-the-head SPL capability...
    Dan Wiggins
    Adire Audio"
    The sub will be for 50% music, 50% HT. Any comments on this design?
    Dave
     
  2. Dave George

    Dave George Well-Known Member

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    Anyone?
     
  3. Patrick Sun

    Patrick Sun Moderator
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    Dave, you heard it from the horse's mouth. Dan designed the Tempest, so you'd think he'd know how best to utilize it with the goals in mind. Go for it!
    ------------------
    PatCave ; HT Pix ; Gear ; Sunosub I + III ; DVDs ; LDs
     
  4. Hank Frankenberg

    Hank Frankenberg Well-Known Member

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    Dave, this is EXACTLY the sonosub that I just finished building! I took that post by Dan and designed my sonosub around it. 6.2 Liters, 17.5 Hz tune. I just fired it up and it is utterly amazing! I wasn't going to post until I developed my pictures and scanned them to post with my words (may take several days), but since you referred to Dan's design post, I just had to comment. In a word (or 2), IT WORKS [​IMG]. No measurements, I'm breaking it in. No critical music test yet, but I will. BTW, I attached an enclosure to the side and mounted the Adire 250-watt amp to it so it's one structure. Go for it...
     
  5. Hank Frankenberg

    Hank Frankenberg Well-Known Member

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    OOPS! Make that 6.2 ft^3 [​IMG].
     
  6. John LaB

    John LaB Active Member

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    Yes! After reading just about all of the 195 posts that match 'Tempest', I think this is the design I am going with.
    Seems to be perfect for my application. I know this post is about 9 months old, but I wanted to bump it up and see if anyone else has gone with it?
    I'm off to order my tempest.
    -jpl
     
  7. Dan M~

    Dan M~ Well-Known Member

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    Is'nt a 4" port small for this driver?
    -Dan
    ------------------
    -Dan M~
    My Small Collection
     
  8. Isaac C

    Isaac C Well-Known Member

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    Dan M~, you're right that a 4" port is rather small for the Tempest, but not so in this case because a flared port was specified, which as you might already know reduces port noise [​IMG]
    ------------------
    Subwoofer Simulator
    Factor Conversion Tool
     
  9. Hank Frankenberg

    Hank Frankenberg Well-Known Member

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    Dave and John, there's a picture (sorry for the low resolution) on my Geocities page: http://www.geocities.com/hankbond1/My_page.html
    Dan - no, the 4" port is fine. Dan Wiggins has posted many times about 4" being sufficient, despite some die-hard opinions out there. The quilifier is of course that the port tube be DUAL-flared (flare on each end of the tube). Wiggins pointed out that the "effective" diameter is that of the flare ends, which is 6". I hear no port noise on my sub.
    [Edited last by Hank Frankenberg on October 22, 2001 at 11:29 AM]
     
  10. Jack Gilvey

    Jack Gilvey Well-Known Member

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    Also, when considering port size, you've also got to consider power. If "only" 250 watts is used, folks have done fine with one 4" dual-flared. Also, while port noise will likely be alleviated or reduced by the flares, high-level port compression which might occur wouldn't really be "noticed" as such unless compared to a similar design with more porting.
    ------------------
    [​IMG]
     
  11. DanWiggins

    DanWiggins Well-Known Member

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    Another issue with the use of smaller vents at low frequencies is the power sepctrum of the signal. It's very rare to find levels above -10 dBFS down below 18 Hz or so. As such, the delivered power down low is considerably less than the 25-50 Hz range. Less power down low means less swept volume down low, meaning less issue with port compression down low.
    Dan Wiggins
    Adire Audio
     
  12. CarlDais

    CarlDais Well-Known Member

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    Dan....many months ago you posted a design and a link for John Morris....(John Morris Sonobox file)...Do you still have that? Remember what thread it was under? At the time I was unable to open it. Can you recall the key features or deminsions?
    Back to the subject of Vents.
    Why to we use Straight vents?
    I read once in an old article that perhaps a 6 degree taper (which isn't much) was a good compromise. The article went into much more depth of the principles of fluid dynamics. The salient point made was that a very slight taper and a very smooth internal surface worked best. Another point was a more precise ratio of straight:taper vents. From a commmercial Mfg. point of view this is costly however, form a DYI it might be doable. Any thoughts? I am having a guy at a sheet metal shop (heating and air duct fabrication) make a vent with such a taper.
    thanks
     
  13. DanWiggins

    DanWiggins Well-Known Member

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    Carl,
    The small tube design? It's still downloadable at http://www.adireaudio.com/Files/JohnMorris-sono.box , but here's the details:
    Two Tempests, isobaric clamshell
    115L enclosure volume
    20 Hz tuning
    Twin 4"ID by 31"L effective vents
    Wire each Tempest in series, then parallel the drivers. You'll have a net 8 ohm load. Drive with ~800W into 8 ohms, and corner loaded in a standard IEC room, and with a 2nd order 80 Hz low pass crossover, you should have +/- 3 dB from ~16 Hz to 60 Hz. And at a typical listening distance, you should be in the ~108-112 dB SPL range.
    Using a 50" length of 16" tube, you should be able to offset the bottom plate 7" up into the tube, to hide the clamshelled drivers on the bottom. Mount the vents out the top, use 1.5" thick endcaps, and you should be set.
    Dan Wiggins
    Adire Audio
    [Edited last by DanWiggins on October 25, 2001 at 09:59 AM]
     
  14. CarlDais

    CarlDais Well-Known Member

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    Thanks Dan for your help and assistance.
    Any thoughts about the notion of Vents i.e., tapered, straight, flared, exotic flares.....the math in the article and text was 'Greek' & it's been 30+ years since diff-eq. Is this in the realm of gilding lillies and insignificant minutia (that's sorta redundant wasn't it?)...in the big scheme of things?
    Thanks once again.
     

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