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    bigbang's Avatar
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    Need help tuning port low for a fixed volume box

    The only way I know how to lower a port tuning frequency is by enlarging a box, I don't know any other calculations. I want to place a pair of 10's in a port slotted box tuned to 25 Hz. The catch is the box must be a certain size for my trunk configuration. I want the response pretty linear between 25-60 Hz, with the roll-off occuring below 25 Hz because I personaly cant hear much below that point. I know that in a choice between high efficiency, small box size, and low end extension you cant have all three, so I am willing to lose alot of efficiency, my box is of fixed external dimensions, and my goal is reasonably flat output down to the mid 20's. I'm assuming that since the manufacturer frequency responce is rated down to 22 Hz my goal is realistic. Its a tough question but I'm totaly serious about it, and any help would be greatly appreciated. If its an unlikely idea or theres a better option out there please explain. I had them in a sealed box but I think this is a better option to keep the lows on par with the upper range. Thanks.

    Box: Face 13" x 35 1/4" (About 3.15 ft^3 internal, ports must be on face)
    Depth 15 1/2" (External dimensions, cannot be changed)

    Subs: 2x Audiobahn AW1006T
    Flame Q's (Don't laugh, I got a good deal a long while back)

    Fs: 35.2 Hz
    Qts: 0.72
    Vas: 12 liters or 0.42 ft^3

    Qes: 0.89
    Qms: 3.93
    EBP: 40
    Last edited by bigbang; 08-18-2007 at 07:30 AM.



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    jellyfish420 is offline i design boxes .......



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    Re: Need help tuning port low for a fixed volume box

    external port



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    Re: Need help tuning port low for a fixed volume box

    WinISD has a really tough time making a flat FR with that sub ported...has a crazy wave in it. The best is with a NET volume of 2.84 cu ft with a tuning freq of 19.5. It's within 1 decibel of reference all the way to about 19 hz, so should make you happy. I can't guarantee you won't run out of excursion at high power though, I'm not familiar with the limits of that sub.

    I don't have enough parameters to tell you if the port noise would be excessive. But the recommended circle port is 4 in in diameter with a length of 28 in, while the slot port would be about 16 square inches in area with 33 inches of length. Have someone double check that for you.

    Hope I helped a little, but please don't take anything I said as concrete truth, I'm an amateur at box designing. Good luck with the project.

    Oh yeah, and everything is with one sub. so make 2 identical enclosures side by side with the same specs.




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    Re: Need help tuning port low for a fixed volume box

    XanderMoser, thanks for the feedback. I got just about the same results when I tried this one 'ajvented' ported box calculator. Good to know I used it right. The sub is rated 900 watts RMS with an xmax of 19mm and displacement of .21 cubic feet. If only I had a larger trunk...I wish I could get the same results for the flatline even if it was a couple db lower across the board in a smaller box. Its also crasy how long the stupid ports end up being.



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    Re: Need help tuning port low for a fixed volume box

    how much port area are you using? can you trim it down some??



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    Re: Need help tuning port low for a fixed volume box

    Quote Originally Posted by bigbang View Post
    XanderMoser, thanks for the feedback. I got just about the same results when I tried this one 'ajvented' ported box calculator. Good to know I used it right. The sub is rated 900 watts RMS with an xmax of 19mm and displacement of .21 cubic feet. If only I had a larger trunk...I wish I could get the same results for the flatline even if it was a couple db lower across the board in a smaller box. Its also crasy how long the stupid ports end up being.
    If you make the port area smaller, the length of the ports will be shorter too. However, the smaller your port is, the more likely you will get port noise. There are a bunch of equations for calculating air velocity in the port, which equates to the amount of port noise you have. WinISD has a built in calculator thingy. I don't know the actual equations, so maybe someone else can help you there, or maybe a search would help.




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    Re: Need help tuning port low for a fixed volume box

    Hey, thanks for the help everyone. I ended up downloading WinISD beta, best thing I ever did. By draging on the frequency plot, I ended up with a 1.7 cubic foot box tuned to 25 Hz, which is very linear, within a decibel across 25-50 Hz. The port will be 11.5" x 1.75" and 45 1/4" long. This if for just a single sub, but I will be using two, so two symetric sides of these then. Check it out:

    http://i206.photobucket.com/albums/b...igbang/box.jpg

    Not to bad, I will probably cross the sub over at 63 Hz on my Pioneer deck. The box will be bigger than I wanted, guess I finally have to ditch the spare tire. Fix-a-flat ahoy. Oh well, guess it will give me the chance to do an amp rack on the trunk floor. Kind of sick of it looking like this anyway:

    http://i206.photobucket.com/albums/b...g/100_4553.jpg

    I guess my only questions now are at what point does a slot ported box become a transmission line/labyrinth design? And when designing the port, do I just use a center line between sides of the port as the length I measure? And is it necessary to put those triangular wedges in the corners when doing bends, if it is only air pressure in the port I wouldent think they matter, or are they reflecting waves around the bends? Do they cut down on port noise from inside the port or what? I've only done one ported box to date and it was a simple 8" long 3" PVC pipe sanded on both ends a little. It was very noisy.



    97' Toyota Camry, lol

    Pioneer Premier DEH-P980-BT & iPod interface
    160 Gig Ipod
    Optima Yellow Top
    Stinger 0 gauge wire, distribution, PDH5 cap, RCA's
    MTX 1501D monoblock
    2 Audiopulse 12" EPIC Subs - Sealed Box, 1.5 cubes per sub
    MTX 1004 four channel
    Infinity Kappa Perfect 6.1 components, front & back
    Dyanamat throughout

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