Hi, im about to order a fi btl in the next few weeks. Im deciding between a btl 15 and a btl 18. I have a hyundai elantra with a 220 amp alternator, 2 batteries and a soundstream rubicon 2500d. I listen to almost all rap and im looking for the loudest system i can build for the lows. I can only fit a 6.7 cube internal volume ported box which is 5 cubes net. I dont know which sub would be louder in this size box. But i really want the 18.

Go with the 15'' since you only have enough room it

Don't skimp on it, it won't help you any at all. Last I checked 5cuft was less than Fi's lowest recommendation for the 18 so I think I'd go with the 15, or at least that's what I would do.

NVM.... just checked the website... says 4.5 to 8 cuft.... which is news to me.... I'd wait for Nick or Scott to chime in here, but apparently 5cuft will work for the 18...

Okay thanks guys for replying rite away

Make absolutely sure you're accounting for the volume of internal bracing (budget up to 0.5cf), port wall, double baffle, and a properly-sized port (which means you need to decide on your desired tuning and port area now to do your calculations). If that pushes net below 5cf, go with the 15 for sure.

Our trunk is rather huge, but you won't get 5+ cubes in there without building it in the trunk, can you do that?

Also, where is your alternator from? I've been looking and had little luck.

alternator is from powerbastards.com and i got all these box specs from klausaudio.com i was going to have them build it to 32 hz.

The Fitzall alternator? How do you like it?

The Fitzall alternator? How do you like it?

I'd run away from that alternator seen a few guys who they said it would fit and it didn't fit.

go with the 18"

15 in a proper box > 18 in an inadequate box.

as long as he can fit a 4.5 ft3 or bigger box in the car....id say go with the 18

but i agree if you cant fit the proper box for the 18 then go with the 15..

Edited October 5, 201113 yr by 10000wrms

15 in a proper box > 18 in an inadequate box.

This.

HUGE difference between Net and Gross box size. Considering the wording of the question, I'd guess that is 5cuft gross in which there is no way in hell to make the 18 work.

15 in a proper box > 18 in an inadequate box.

This.

nDeed.