Need help to figure out port size and legth for a dd 3512 please
 

hey all you gurus out there.. I have a new 2011 ranger with the back seats out... I can build a box fine I am pretty good at it... but it is the damn port that is stumping me.. here it goes..

I want a wedge shape box... botom wider the the top....
3/4 inch MDF
1.5 inch baffle with sub recessed in 3/4"
bottom depth 16 inches,
top depth 12 inches
height 16 inches
I have up to 35 inches of width to play with... all dimensions are EXTERNAL....
I have the idea of putting my amps on each side of the top of the box with a round port in middle (so port firing up) the sub, I'm gonna put it in the middle too (it would be just behind the arm rest but I think the length of the port might hit the magnet on the DD so I could put the sub on either side...
now building this box is a piece of cake... but calculating the port size and length is what friggs me up..... I say 6" dia but how long? I want 39hz

I read that dd subs dont like box making software... and that the say that 16 spuare in per cu ft is the norm...


thanks for everyone's help....

dd3512 running off a macrom 1500watt rms amp...at 2 ohms..

I'm not going to make things worse by trying to help with your box, but will reccomend you should go with the 6" port. I went with dual 4's instead, and am am now going to change to a single 6".
As for box software, meh. Figure out what you need liike you did, and avoid a cube shape. Also, go with DD's reccommended 2.5ft^3 (net) or more; they love big boxes. (you know that DD has box plans on their site, right?)

Yes good box plans on there site.

can anyone lend a hand?

For a 2.5 cuft net, tuned to 39 Hz using a straight 6" dia. port, the length you would need is 15 5/8 ", however the port area will be on the smaller side, if you can only use round ports I would recommend using a 6'' flaired Aero port (length = 16 5/8").

A slot port would be better, if your application can allow it.

you think you can explain how you got to this length? If I would have known I would never asked...a Slot port would be best, I know, But would have NO IDEA how to incorporate it into the box....I could use 2 ports... how do you get thhis "port area" that I need, and how do u know how long...

There is alot that goes into designing an enclosure accurately for a specific driver and what you desire. here is a link that can help http://www.carstereo.com/help/Articles.cfm?id=31

Hey - there's that link again. Anyone who reads this should bookmark that page. Truly, using a box design program like WinISD is the best way but this page is great if you just want port lengths.

thats a nice page... but will that program work for a dd3512 sub.. these subs dont work well with box software... I calculated I think I need around 42-47 square inches of port area, but how to I get that with round ports... Im fubard in my port length though as I only have 16-maybe 17 inches of hiegth for a port... I dont want to put the ports on the sides... and I read that one 6 inch port is better than two 4s or three 3s.. Im lost.... ... Ill paypal some one cash if they just give me the port size and length for the box that I posted above.this is for a DD sub box programs wont work or will i even notice the difference... I play this LOUD and dont wantto blow it.....

1) A 6" port has about 29in^2
2) To tune a 2.5 cubic foot to 39Hz, just get yourself a 6" port and make sure its 15 5/8" long. You can use an aero port which helps avoid port noise (chuffing) then be sure to read & follow the instructions as they have to be a little longer due to the flares.
The problem with adding port area, if your port length increases(with 2 6" ports, each would have to be over 35"!!). You'll have to choose between port area and length.
You can have the port extend out of the box; that doesn't matter. It also helps not "waste" internal volume you would have to account for(when you see 2.5 cubic feet, that's after taking the sub and port volumes into account, aka 2.5 is NET internal volume)