frequency for x volume

Discussion in 'Archived Threads 2001-2004' started by Matt Weyen, Mar 10, 2002.

  1. Matt Weyen

    Matt Weyen Stunt Coordinator

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    I'm going to have a 3.434ft^3 volume tube and I want to know what frequency I should tune it to. Patrick Sun :

    "The tune might be asking a little too much for a 6 ft^3 enclosure for the 15" Tempest driver, and I might pick up more port noise than optimal, but I'll get to see how adversely port noise will affect the overall sound quality of this subwoofer in normal operating conditions. The reason I choose 16Hz as the tuning frequency is to provide as much driver protection with such a low tune. This is because the driver is "unprotected" at frequencies underneath the tuned frequency of the box/enclosure, so by going with 16Hz, it's protected for most low end frequencies while sacrificing a bit of output near the 20-25Hz range. But for a subwoofer this small, I can live with a few less dBs of SPL (Sound Pressure Level) down in that low end region."

    So... any suggestions?

    thanx-

    MW
     
  2. Matt Weyen

    Matt Weyen Stunt Coordinator

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    oh... this is considering I use the same drive Patrick Sun is (Adire Tempest 15")

    sorry for leaving that out...

    MW
     
  3. Dustin B

    Dustin B Producer

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    3.5ft^3 is too small for a Tempest. It would be good for a Shiva or Dayton DVC12" though. The smallest I've seen a Tempest put in was 160L or 5.5ft^3 with a 4" flared port and that was considered pushing it. Remember the smaller the enclosure the longer a port has to be to maintain the same tuning freqeuncy. Compound this with the higher the Vd of the driver the wider your port should be and the wider your port gets the longer it has to be to tune low.

    Result, you rapidly run out of room for adequate porting in small boxes with high Vd drivers.
     
  4. Greg Monfort

    Greg Monfort Supporting Actor

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    I agree with Pat, but it doesn't apply to your design. You're using a much too small a Vb for even PRs, much less vent tubes. For a sonotube application, this can only be sealed for decent performance transient response wise, and there won't be much output below 30Hz due to a steep rolloff.

    GM
     
  5. Rudy H

    Rudy H Stunt Coordinator

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    I have my 15inch Dayton DVC in a 5.3cf sealed box, and it sounds AWESOME. 3.5cf stuffed would be fine though.

    No way I'd ever do anything less than 6cf vented.
     
  6. Patrick Sun

    Patrick Sun Moderator
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    Vip! Welcome to the HTF! (Vip/Rudy usually hangs out over on the PE tech board).
     
  7. Matt Weyen

    Matt Weyen Stunt Coordinator

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    I think I'm finding volume incorrectly... I am using

    V=wpi(R2-r2)... I don't think I'm finding the correct volume.

    My tube is going to be 3ft tall, 18" in diameter and half inch thick (I'm guessing its going to be .5").

    thanx-

    MW
     
  8. Matt Weyen

    Matt Weyen Stunt Coordinator

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    I found a conversion page that took care of business...

    actual volume: 150liters, 5.3ft^3
     
  9. Matt Weyen

    Matt Weyen Stunt Coordinator

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    I can go larger,,, my dad is the head civil engineer for the city and can get my pvc for free. I can get any length I want at 18" diameter. Considering that I am on a tight budget and know less about this stuff than you guys, would a smaller, closed design with a shiva be a better bet or should I go all out and try to get a longer piece of tube and do the ported tempest? Also, will winISD get me close enough or am I likely to screw up?

    thanx all who respond,,, I'm very new to DIY but am very interested...

    MW
     
  10. Greg Monfort

    Greg Monfort Supporting Actor

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    Cardboard tube diameter is usually inside, so [(1.5^2*pi)/4]*3 = ~5.3ft^3. Subtract ~0.5ft^3 for the driver/vent/end caps and you're left with ~4.8ft^3. Still too small for getting the most out of a Tempest, but at least it can be tuned to ~16Hz with a flared 4" vent.

    GM
     
  11. Greg Monfort

    Greg Monfort Supporting Actor

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    I see you posted while I was off-line, but in for a penny, in for a pound I say, so get a longer piece to get a bit more of your money's worth out of the Tempest. 7ft is about the practical limit with the driver at one end and the vent at the other, and will have dramatically more output below ~30Hz.

    Unless winISD has been corrected, it gives errors on some calcs, and if it still doesn't show excursion limited plots it's pretty much worthless IMO. That said, many folks here have used it to design subs they've been pleased with.

    As long as you stick with Adire drivers, their freebie version of Lspcad is the best around IMO, though the learning curve is steeper due to its power/flexibility.

    GM
     
  12. Jack Gilvey

    Jack Gilvey Producer

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  13. Rudy H

    Rudy H Stunt Coordinator

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    Thanks Pat and Jack [​IMG]
    I like UniBox a lot better because it has excursion, impedance and step response graphs. What can I say, I wanna see excursion [​IMG]
    Rudy
     
  14. Rudy H

    Rudy H Stunt Coordinator

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    I'll stick with UniBox for now [​IMG]
    But I am getting a bit tired of long loading times....
    But I do have a fair bit of drivers in UniBox already.....
     
  15. Rudy H

    Rudy H Stunt Coordinator

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    Hmmm....If it's got the XLS's, BPD's and Adire's....hmmm...I wouldn't have that much tossing over to do [​IMG]
    I'll take a good look into it, but I gotta clean up my HD's a bit first; running out of space with my pair of 4.55gig Cheetah's [​IMG]
    Rudy
     
  16. Greg Monfort

    Greg Monfort Supporting Actor

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    >Greg,

    the alpha version of WinISD Pro has been out for a while. I've played with it a bit, and it's much more useful than the original (excursion plots, etc.) and seems really nice overall. Still has the user-friendliness the basic program is known for (I love the on-the-fly unit conversions) but I haven't tried to compare results with other programs to check results. I'd love to know what you think of it.

    ====

    Thanks for the update. I'll download it later on tonight, but realistically won't get to evaluate it till next weekend at the earliest.

    GM
     

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