for anyone with subs. i need some help

[C-10volvo]

i installed a new jbl 1200 watt amp not too long ago. it all works and sounds great for the most part. the real problem i have is the low range. its really weird!! when the doors are shut, and the windows up my spl reaches 132. but when the windows or down or the doors are open it reaches 139. the box is sealed well, and the subs can handle the power. could this be a drawback of having so much power in a small cab?
If you have subs in your truck, could you preform a little test for me? turn it all on, and crank it. open a door and listen for a change in low and mid bass. ive ran out on ideas on what this could be. a change of spl from 132 to 139 is a lot! thanks for your help, ken

[gldevall]

That has been the case in everyone of the systems I have had, see below. There is nothing wrong with you or your system. I think it is kind of like an echo. If you ever notice in outlaw spl they usually, if allowed, have a door open or a window down. I'm really not sure how to explain it.

1988 Nissan X-tra cab with (4) kicker 12's
1987 Camaro with (4) Kicker 10's
-then changed to (4) Pioneer 12's
1994 Nissan reg cab with (1) Kicker 12
1984 S-10 Blazer with (2) JL 10's
-then changed to (2) Kicker 12's
-then changed to (4) Kicker 15's

Man I miss this sometimes..

[69c10stepside]

Ok, here is the easy way to explain this i think..

When your car / cabin / etc is sealed off, the pressure is harder to bulid to create more db. When you have an area where the pressure can be released such as a window down or a door open, its able to create / move more volume of air so it inreases.. Its just how it works.. in my old system in my truck, It would seem like a night and day difference from when I burped the system with a door open or closed

[C&C Chevy]

spl?

[shavedchevy]

Exactly, It does this is my truck with 2 10's. Just think all a sub does, is move air, If the air has no where to go it will theoretically "hold" your sub back, thus not getting that huge "thud" that we love to hear.

[bagged74]

a ported enclosure will usually remedy this problem, or at least make a noticable difference.

[69c10stepside]

Originally posted by C&C Chevy
spl?

spl = sound pressure level which goes into what i said in my last message about stuff

If you have the air space requirements for your application (subs) go with the ported box for sure, i can give a web site link that gives detailed info on how ported boxes are greater then anything else.. and here it is http://www.ddaudio.com/caraudio/encl...o/portInfo.asp

[corn]

If you are shooting for max SPL you really should port the box you can almost always make a gain by porting. Another thing to look at is, is your box(s) big enough? When I did contests with my old s-10 blazer Id always try to crack the drivers window during SPL. Didnt always get away with it but sometimes I did. I havent entered a contest in YEARS so Im not sure how they run them now.

[1974StepSide]

I'm wondering how you measure SPL yourself?

[69c10stepside]

Unless you have spent several dollars on your own meter, you cant measure spl yourself.. Only at events or if your local stereo shop is good enough to let its customers try theirs if they have one.

[PHOENIX]

I notice my sterio sounds better with the windows down.