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Reload Thread: Please Check My Math For Me

  1. #1
    LoneRanger's Avatar
    LoneRanger is offline Old Yamahas Give Me Wood



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    Please Check My Math For Me

    okay.....

    If I build a box that is (W=18" x L=35" x D=24") with a port that is (W=5" x L = 14" x D = 11") my calculations say that I will have a 5 cubic foot box (with a little left over for displacement of the sub basket) that is tuned to 52hz. If anyone knows how to check my work, I'd really appreciate a second or third opinion......I simply don't trust my math skills.



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  2. #2
    ramos's Avatar
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    Let's see I came up with a total volume of 8.75cuft . With your current port size the tuning would be around 35hz ( not exactly but closer to 35 than 34 ) But if you want to acheive a 52hz tuning the port would be 5" w x 14" L x 1.55" D for 70"^2 of port area and the port displacement would deduct another .06cuft. So a net volume before basket displacement of 8.69cuft . I could be wrong though



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  3. #3
    Trixter's Avatar
    Trixter is offline Keepin it Simple



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    I get the same for the total vol.: 8.75cu'. I don't know how to figure port size vs. freq.

    Ramos, what are the calcs. and how do you figure it?



    2006 Jeep Liberty
    Adire Audio, Cadence, Clarion, MB Quart

    Lv = [(14630000 x R^2) / (Fb^2 x Vb)] - 1.463R
    *Vb = vol. in cu"
    **R = sq.rt. A / Pi (for square/slot port)

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    ramos's Avatar
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    I use bassbox pro 6.0. But when I can't get to it I use the calcs at
    http://www.eatel.net/~amptech/elecdisc/caraudio.htm



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  5. #5
    wolfey's Avatar
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    lone ranger, are the internal or external dimensions? are you going to have lots of bracing inside or what? seems like you'll have larger than a 5 cf box even if you do, but weather those are internal or external dimensions is a big difference, cus then you'll have to subtract 1.5 inches off the hight, width, and depth, maybe more if you double baffled it.

    external dimensions i get:
    (18x35x24) /1728 =8.75 cf - (5x14x11/1728)=8.3 cf

    now lets say you gave us external dimensions, and you have a double baffle, and the baffle is on top, this gives you:

    15.75 x 33.5 x 22.5 /1728= 6.8 -(5x14x11/1728)=6.4 cf
    so it makes a big difference depending on what measurements you gave us, but theres no way you would get 5 cf with those dimensions unless you had the whole thing double baffled and tons of extra bracing, i don't know any subs that would need that much though. oh and you can subtract .1-.2 tops for your sub, i don tthink anything except 18's are bigger than .2, not sure on that though, i might be totally wrong, i thought someone said my brahma was lke .12 though and its pretty **** big. Also, why do you want to port so high, thats gunna sound like ***. and that long of a port should be lower than 52 like lone ranger said. i guess if its only for spl then tune it at 52 hz



    brahma 12 in 1.9 cf ported enclosure tuned to an ugly 38hz..

    REVO amp
    stock speakers in the front..

    looking to upgrade..

  6. #6
    LoneRanger's Avatar
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    okay.....how bout this

    W = 16", L = 30", H = 20"

    that gives me a little over 4 cubes to work with. what would be the optimal port size (Length, Width and Depth) to tune this bad boy to 52hz?

    I thank you guys for replying!



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  7. #7
    Trixter's Avatar
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    I get 5.57cu'.

    Do this: L x W x H x 0.00058. that will get you within a few hunderdths.



    2006 Jeep Liberty
    Adire Audio, Cadence, Clarion, MB Quart

    Lv = [(14630000 x R^2) / (Fb^2 x Vb)] - 1.463R
    *Vb = vol. in cu"
    **R = sq.rt. A / Pi (for square/slot port)

  8. #8
    Trixter's Avatar
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    What is your target volume???



    2006 Jeep Liberty
    Adire Audio, Cadence, Clarion, MB Quart

    Lv = [(14630000 x R^2) / (Fb^2 x Vb)] - 1.463R
    *Vb = vol. in cu"
    **R = sq.rt. A / Pi (for square/slot port)

  9. #9
    LoneRanger's Avatar
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    i meant five cubes, and that is my target after displacement of both the sub basket and the port. I need it tuned to 52hz for spl purposes. I don't think i'll need any internal bracing.....we'll see about that tho.

    The measurements i'm giving are exterior dimensions, and i think that's probably why your figures were coming up different than mine (well....except the first set, i don't know what the hell i was thinking. Also, I'm using 3/4" MDF as always and if need be 2x4's for bracing.



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  10. #10
    LoneRanger's Avatar
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    c'mon guys.....somebody's gotta know how to tune this *****....



    http://geocities.com/spawn571ko/speakerbox.jpg
    (if i click this link it doesn't work, but if i copy and paste it into my address bar, it works just fine.....god bless geoshitties!)

    This is what i've figured so far. I followed the link that ramos provided and used their calculators to come up with these numbers. hopefully, I'm right this time.....
    Last edited by LoneRanger; 10-19-2002 at 01:44 AM.



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  11. #11
    geonn's Avatar
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    ths is how i usually tune ported boxes go to this site and itll help ya figure out how to do it http://xsspl.tripod.com/Audio/VentCal1.htm




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