check my math please

[dru 10+ year member]

Well this is for a SI MAG D2 12"

2.86 cuft net @ 35 hz

2 flared precision ports 4 inches in diameter and about 17 inches each

thanks to whoever

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[PSturmer 10+ year member]

i am getting 16.41 inches in length but it doesnt consider flares.

 

[dru 10+ year member]

precision port's site says you add an inch to "compensate" for the flares

its not like im tryin got get EXACTLY 35 hz you know? 33 to 37 hz is fine I believe. not like i can hear the diff

 

[PSturmer 10+ year member]

precision port's site says you add an inch to "compensate" for the flares
its not like im tryin got get EXACTLY 35 hz you know? 33 to 37 hz is fine I believe. not like i can hear the diff

yeah i know what you mean

 

[dru 10+ year member]

well other than that, does it look good?

 

[PSturmer 10+ year member]

the only thing i would be worried about is port area. but since there aero looks fine

 

[dru 10+ year member]

ttt

 

[PV Audio 5,000+ posts]

But you can hear the difference between 33 and 37 //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif

Good luck in figuring this out.

 

[Trixter 10+ year member]

well, according to the precision port formula....

Lv = [(8466.4 x R^2 / Vb x Fb^2) - 1.463] - 5

you'll need to cut your Vb in half (since you have 2 ports) so Vb = 1.43

Lv = [(33865.6 / 1751.75) - 1.463] - 5

Lv = (19.33 - 1.463) - 5

Lv = 17.87 - 5

the subtraction of the 5 is because each flare is 2.5" long. you'll cut your center section to the Lv figure.

but now that we have the length, we need to subtract the port displacement from the Vb and refigure....

2 X (Pi R^2) = 12.56

12.56 x 17.87 = 224.44

224.44 / 1728 = .13

1.43 - .13 = 1.3

our new Vb is 1.3...now redo the math to get....

Lv = [(33865.6 / 1592.5) - 1.463] - 5

Lv = (21.27 - 1.463) - 5

Lv = 19.81 - 5

Lv = 14.81

so cut your center section to 14.81 (i'd do 14.75 to make it easy) and add your flares.

i hope you already accounted for sub displacement, or your Vb will change again. if you accounted for port displacement in the original 2.86 you gave, let me know and i do it agin for you...or you can, now that you have the formula. only use net volume with the sub displacement and then recalculate like i did when you know that port displacement.

enjoy