Originally Posted by mob17
The problem with most BMW boots is that they are sealed. Putting a box in the boot is not a great idea, its like putting a box in a bigger box. Sound waves will just reflect and bounce back off the sides and cancel each other out (maybe explains your lack of perceived output). This will also cause a lot of rattle.
To minimise rattle and get an improved output the best 2 options are:
1) For a sub that requires a larger enclosure volume than what's available in the corner, an IB installl through the ski hatch will work well.
2) For a sub that requires an enclosure volume that is available in the corner, and if you can be bothered to make one/buy one, then a corner enclosure would work well. Apparently this method doubles the perceived output of the sub. Not sure why but that's what Kaigoss says.
Having said that I hope your issue is a configuration one and you manage to sort it out. If not try another sub!
Edit: No matter how much you Dynamat the boot, the rattle will still be there unfortunately with your set up
I can only agree with you, all coupe's, saloon's and especially convertibles have always been difficult to get bass into the cabin you only get a deformed wave which is completely different to the one in the boot, theres not a easy solution unfortunately, our best results was to always try to fire the base through the ski hatch if fitted or to remove a section of metal from the rear shelf, this is not to everyones taste as its a lot of work, whatever way you must also make sure there is a good seal so the pressure is on the cabin and not the boot.
I will try to did some photos out.
One thing I can say, the sub is not at fault and does require substantial running in, we used to leave them on for days at a low level in the showroom before installing in the car