free to air subs are virtually unheard of in the ICE scene. i just had a look around and it seems like they really arent "free to air" but in reality are designed for use in applications like you decscibr. mounted in a boot. performance wise they dont give as good response as sealed or ported designs. you also need to seal between 'below' and above the shelf as good as possible. plus having 6x9s in there too may affect things.
a sealed box is the simplest, easiest and safest way to go.
sealed boxes take up less space than ported ones. the reason i said 'safest' is that there is the possibility of blowing a sub thats in a ported box if you overdo it, whereas you're safe with a sealed enclosure. plus you dont need to get the tuning freq right (distance of port from sub, diameter and length are crucial) the trade off is that you will get better bass response from a ported box. (i.e. lower bass).
i've got 2 small 8" rockford fosgate subs in a custom sealed enclosure. (well two enclosures with a frame holding the amp in the middle... its on rails so heat can escape on all sides)
it looks like this if you flip the rear seats fwd -> | SUB | AMP | SUB |
The enclosure isnt that big.. in depth anyways, but combined its the full width of the car.. each enclosure is 2/3rds of a cu ft each (i think) maybe less. think the depth is around 7 inches at the widest point (bottom), and they're def only 12" high (and 15 wide i think). i have them mounted behind the seats. i still have most of the boot space so there is still a lot of storage room and the spare comes out easily, but the seats cant be flipped forwards. i designed it this way, and spent ages picking the right subs for my purpose.
oh and along with the usual parameters most subs come with simple plans for sealed and ported boxes. most things available from the manufacturers site too.
there are some good online box design things these days.
btw... wouldnt a sub in a shelf vibrate the shelf quite a lot too?
