seat. These subs are 15-inchers and free-air ones for that matter. I haven't really looked into what's behind the seat as it's been sub-zero temps here and I just don't feel like going out into my garage :-)
I think it's metal back there??? If it is, does it provide any purpose as far as support?

I would rather not have a box in the trunk and would like to nstall it behind the rear seat.

Thanks all,
SM
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90 BMW 325is, 98 BMW 528i, 90 Volvo 240DL

I've put subs in both our 240's. As others have said, cutting sheet metal behind the back seat is a bad idea. There are more elegant ways to get good bass, but I don't know about 2-15's...they'll be hard to fit without carving. Before you do any chopping or serious spending, think about what you want and the consequences to everyday use of the car. Look at the problem long enough, surf the net for info, and an answer will appear.

My better installation is in the 83 and is a Rockford-Fosgate single 10-inch in a bandpass box. The port tube communicates with the car interior through an opening in the center of the rear deck with a small grille over it. Very unobtrusive. This will make the rearview mirror jump at even modest volume with the 100W (RMS) sub amp. Drawbacks are the box in the trunk (but it's up near the seat and leaves the main trunk well clear) and loss of the ski pass-through.

My son's 81 has another RF 10-incher, but in a sealed trapezoidal enclosure (also sometimes called an "infinite baffle") which I built to fit snugly against the seatback metal/cardboard. This is sealed to the ski pass-through opening by a high-density foam rubber ring I cut from a sample from an upholstery shop. Lower the rear seat armrest and thar she blows. Neither makes the air rumble like a Vandenburg AFB missile launch, but both kids report their friends are at least moderately impressed.
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Bob (81-244GL B21F, 83-244DL B23F)

I am pretty sure the metal behind the rear seat is part of the cars structure. Not being an engineer I would assume it stiffens the body to reduce flex. If it was not important I'm sure Volvo would have put a folding back seat in the sedans. So I would not cut very big holes in that sheet metal. Some people even freak out about cutting holes for 6 by 9s in the rear deck.

This is just free air subwoofer advice...The name "free air" seems to imply something that isn't true, that all you have to do is mout them inthe trunk and go. You still need to isolate the 2 sides of the woofer cone. This means you have to perfectly seal the cabin of the vehicle from the trunk. I've listened to most free air systems and they sound bad. I've also listened to the ones that people have isolated the cabon from the trunk and they sound great. So, free air simply means that driver will work in an enclosure with a much larger range of volumes. Sounds like a fun project.
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Portland, OR 1987 240 dl wagon (not so rusty anymore) 'rustbucket'

Another way to say the same thing is that "free air" speakers do not need the back pressure of an enclosed space to keep the cone from deforming. The other extreme FYI is "acoustic suspension" where the cone feels loose when uninstalled and distorts across the band and can even self destruct if played that way. This design uses more power (to overcome the back pressure) but the controlled cone movement and complete isolation of the +waves in front from the -waves behind yield a much cleaner sound. Also saves space and is kinder to neighbors.

Jim Weiss
83 245T, 90 760TI, 93 940TI wagon, want more . . .