Is it possible to simply drop in a new sub in the IS350? like I meant why do people get enclosures in the trunk does it play a vital role in the acoustics or is it just b/c those people get like 12 inch + subs?

 

Yes. Will it sound better (louder, play lower or both) than the stock sub? It depends on the Theile/Small parameters of the current sub compared to the T/S parameters of the new sub. To almost guarantee a better sound, you should get an aftermarket about to power the new sub.

Some people want the tight sound of a sealed sub. Others may go for more SPL and use a ported sub. You can still use a 12" sub in an infinite baffle configuration (that's the alignment of the stock sub) but it requires either enlarging the opening or creating an adapter for the larger sub.

-Robert