building folded horn box?

http://www.decware.com/newsite/mainmenu.htm

i'm guessing that you want to get an insane amount of output correct?

a horn is not the way to do it. a horn is designed to be a long throw device( sound 100% better from far away) that is why you typicaly see them in big venues such as concerts,raves,etc. these do not sound good in a car or a home  period.

if you want extreme output look into other box designs. here are a few suggestions

Transmission line: extremely hard to design and build but gets good output and awsome sound quality.

voight pipe: similar to the t-line but easier to design and build and has increased output with decreased SQ (kickers solobaric slot ported box is very close to what a voight pipe looks like)

servo driven: EXPENSIVE!!!! basicaly a speaker that is driven by a servo motor extremely efficient i had one that i used in my DJ rig. its specs said it was 102 db at  1 watt/1 meter. with max input of only 200 watts i was shacking glasses off the bar and flexing double pane windows about 5 inches.

ELF (extended low frequency: this is very space efficient but requires a special type of dsp that isnt available very cheap but can be built for about $65. the dsp basically evens out response below resonence. so instead of your sub dropping at 12 db per octive below resonence it will actually play flat below resonence. the cool thing about it is that propper design actually calls for a pretty small box. i first saw this box at the national association of music merchants show made by a company called Bag End . the rep was fanning paper in front of a mic and the speaker was responding to it by moving in and out at the same pace. thats extremely low output.