music distorting when trunkspace sealed

would anyone happen to know why my music sounds so much cleaner when i fold my back seat down-(making the trunk and the cab one big airspace)... when i have my seat up-(separating the trunk from the cab), the music particularly from my rear 6X9's sounds scratchy so to speak... somewhat distorted..   

i have gotten one response from mentioning it in a different thread-

"Maybe the pressure in the trunk when it is closed, pressure from the woofers, is moving the 6x9s more than they want to be moved."

and that is exactly what i thought it was... so what i did was i went and bought a pair of what i want to call "speaker buckets" or the things that would ideally make an in-door sealed enclosure for the speakers.. i'm sure you guys have a name for them but they're like a 6X9 fitted bucket that you sit the speaker in and then screw that into your door or in the rear deck above the trunk. well they wouldn't fit just right so i had to cut them and it basically defeated the whole purpose of the enclosure..

does anyone have a solution in mind?

Air pressure from your trunk is making in-door speakers distort?  What?

I understanding what you are talking about - but the idea that your trunk is sealed up like some sort of hermetic vessel is totally wrong.  You probably have more than a hundred seperate points of air transfer between the trunk and outside, and the trunk and the cabin - whether or not it appears to be closed. . . what kinda vehicle is this?

Either way - you aren't going to be getting some sort of catastrophic blowback from the woofers that causes this sound you describe -

it sounds to me like run of the mill vibration you haven't nailed down completely. . . . but of course - I can't hear the problem.

it's just a little 95' protege... i mean i completely believe that the trunk isn't completely air tight but i just thought that possibly the air movement from the subs would be pushing against the cone of the 6X9's and causing distortion... but i obviously don't know the problem and that's where the assumption comes in.

run of the mill vibration? what exactly is that? i'm guessing it's just a term i don't understand.. but anyways, the problem is ONLY when i have the seat closed.. when it's down, it's sounds so much better... and of course that's how i've been driving but it's a pain if i want passengers in my car..

and i'm not talking about the door speakers, i'm talking about the 2 rear 6X9's that are facing up and the magnets suspended in the freespace of the trunk... those are the ones that i notice the distortion.. and that's why i related the distortion to the air movement in the trunk... because the backside of the cones of the 6X9's are freely exposed to any air movement  caused by the trunk.. and once again i believe you when you say it's slim for that to be the cause.. it was only my assumption..

when the actual trunk lid is closed it's fine.. it's the rear floding seat wall that causes the difference in sound

-seth

Best remedy for a car without a rear parcel shelf baffle is to 1) remove the rear parcel shelf speakers and relocate them (or do away with them altogether..), and / or 2) cut or otherwise vent through the parcel shelf from trunk to cabin, permanently.

If you were to remove the offensive deck speakers, you can modify the cutouts with grilles etc.and those can be used for the trunk-to-cabin venting.

If you want to continue using the rear deck speakers, the "hats" are, as you found, a lousy way to separate them from the sub's pressure.  If they DO fit right, they confine the airspace for those speakers into too small of a volume.   The best solution, then, is to replicate the baffle found in most sedans.  It is a simple carpeted piece of fiberboard that is molded to form the part of the trunk that fits under the rear parcel shelf.  In your car, you would have to fashion one yourself.  It would separate the speakers from the pressure but allow the greater airspace that those speakers really need.

Along with that, make a cutout in the center of the shelf for venting the sub pressure throughout the cabin.  That will reduce the excessive pressure that you have found troublesome and will make the subs sound louder and cleaner.  The cutout itself has to be separated from the air volume within the new baffle, so that adds a bit more complication to the project.

Old pic of my car but it's still in use:

I didn't have to make a baffle because this sedan was provided with one.  What you see in that pic are the "hats" that you already cut the backs out of.  I used a couple of those along with a length of air duct to separate this vent from the airspace within the baffle.  The sub gets vented through to the cabin and the rear speakers don't suffer from the pressure.

This car was provided with a center 6 X 9 speaker cutout for factory "sub".  I used that for the vent hole and covered it with a generic grille.  (The rear speakers hide underneath factory cloth):

Try the venting first.  You may find that by venting the sub throughout the car the pressure is reduced enough that the rear speakers stop complaining.  That would be a relatively easy and painless solution.