tunning box

[Brad]

i have posted this same question in one other forum a while back now i just want a second opnion....i have 4 MA audio 12's in a 6cu/ft sealed enclouser..i want to port the box..but according to MA audio specs each sub requires 2cu/ft of air for porteded enclouser...so i thought maybe if i could cut down the port size that it might work...this is what i came up with...a 100sq/in port 13.5in long..that would tune it at 45hz (i think)..i would like to tune it lower maybe to 35hz to do that dont u make the port longer?..so anyway..tell me if im doing right or if im gonna mess my box totally up..its a wedge box where my back seat usedo be and i have them firing towards the celing dont know if all that makes a difference or not..all and any ideas welcome..thanks

inner dem.of box..
H.29 1/2
W.49 1/2
D.17 1/2

[William from NOLA]

What do you drive?
What is the thickness of the wood you are using?
and finally,
Are you going for SPL or a mix of SQ and SPL?

[GlassWolf]

2cu ft is about right for a ported 12" sub.
tuned frequency for a port is based on enclosure volume (net) after subtracting port and driver displacement (or volume) as well as the port cross-sectional area.
if you just shorten the ports, you'll raise the tuned frequency.

you just need a larger enclosure to properly dampen the sub when you use a vented box.
if you don't have the space, either stay sealed, go to two ported subs instead, or go with four isobaric or iso-vented subs which will require less space, and increase efficiency, but you'll lose a bit in overall SPL.
those are your best options.

[Dustin from Huntsville]

Or build a new box altogether :)

[Brad]

i drive a civic..my box is 3/4' MDF..and im going for a mix of SQ and SPL...but it sounds like im just stuck with what i got unless i just want to build a whole new box..which is out of the question cause my box is now finished and complete and would be hell trying to rip out :)...what if i just went ahead ported the box according to MA's specks..which are.....2Cu/Ft box 25sq/in port 15.5in long (per sub)...or am i just better off keeping what i got

[Ryan from Ohio]

If it is a wedge style box you didnt leave complete dimensions.

I punched in the dimensions you left and came up with a 14 cube box... :banghead

[Brad]

ok this is where im lost..yes its a wedgs box...how do i come up with the right dimensions..do i need to subtract some from the H-W-L of the box :confused:

[Ryan from Ohio]

MTX Formula's (http://www.mtx.com/caraudio/education/enclosureConstruction.cfm)

That should help ya out...

[GlassWolf]

highschool geometry anyone?