# Please Check My Math For Me

• 10-18-2002
LoneRanger
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.
• 10-18-2002
ramos
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 :)
• 10-18-2002
Trixter
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?
• 10-18-2002
ramos
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 :)
• 10-18-2002
wolfey
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
• 10-18-2002
LoneRanger
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!
• 10-18-2002
Trixter
I get 5.57cu'.

Do this: L x W x H x 0.00058. that will get you within a few hunderdths.;)
• 10-18-2002
Trixter
• 10-18-2002
LoneRanger
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.
• 10-19-2002
LoneRanger
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.....
• 10-19-2002
geonn
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