This is really strange and I've had it happen to me too many times to ignore now. But has anyone else noticed the bass hits cleaner with stuff in the trunk and/or back seat? I didn't have chance to experiment too much but it feels similar to the improvements I felt right after I put the "dynamat" around front door speakers and rear deck (and the rest of the door and deck).

Not sure what I'm on but hoping someone would agree, or have scientific explanation (either about the sound or my brain .-.)

 

I usually don't stuff up the trunk with too much stuff but it makes complete sense that it would change the low end sound. The trunk does work as an enclosure, sort of. Not in the sense where it's painstakingly sized, damped, and designed around the TS parameters of the drivers in use but still an enclosure. So by packing it up you are changing both its effective volume and damping. That said, the trunk is so leaky who knows how much the sound would really would change. In a very generalized sense you would probably get a slightly "boomier" low end with faster decline at lower frequencies. If the "boom" or "hump" in the response happens to be at a frequency that "works" with what you are listening to you might like it!

 

crack open the sunroof and the bass will be improved as well