I recently made a box made of MDF for my JBL W15 GTI MKII, and it still makes a rattling noise and slides around in the trunk from the bass. i realize that every rattle takes away some bass, and id like to have as much as possible as it is a big car and its an expensive sub. i made the box by cutting the pieces, using liquid nails and screws to keep it together, and let it dry for about 45 minutes. I put it in my trunk and it is very obvious that there is alot of power, but it seems like alot of it is concentrated on shaking the box. the box has two circular ports about 3 or four inches diameter and was thinking i may need more as there is alot of air coming from those two holes. i was also considering fiberglass? id like to keep the same box because it took a while to make. also, i didnt use the provided screws that came with the sub, could that make a difference? its just really frustrating that a 5000 watt sub isnt as loud in a caprice as two 1000 watt subs were in a sunfire..

 

you said its still rattling...to me this box won't rattle, if its definately a rattle coming from the box then its probobly that your dustcap is a bit loose...try tapping on the dust cap if it makes a clack noise it will need to be reglued down

 

well the sub is brand new...could that be a problem already? i got the sub two days ago..

 

Just because it is brand new does not mean it is perfect - it could be loose due to not being glued right or something could have happened during shipping - i had a 2000 watt 15" sub just last week that came strait from the manufacturer with the coil not connected to the cone properly and the coil came through the dust cap at about 300watts (it sounded like golf ***** bouncing around in there until it blew)

 

 

you never mentioned if the box is built to JBL specs??
the box should be fastened down so it doesnt move around back there, it's working against itself and gravity....

the rattle could be a million different things (give or take)

 

how thick is the wood you used on the box? also make sure your screws for the subs are real tight, maybe try mounting your box as well.

 

From the sounds of it the box is not built to spec. "Should I add more ports because there's a lot of air coming out of the two that are already in there?" What's that all about? Doesn't sound like it's built properly. Secondly, I would suggest no less than 3/4 inch MDF for the box and even a double baffle for the front. As well, mounting that box into your trunk would help a lot.

 

Jbl GTI 15... 4cu.ft slot port 2inX14.25in tuned to 30 hz. and put a couple braces inside the center, from top to bottom and front to back. And that icludes the port and driver displacement in there. also the front baffle should be at least 1.5 inches thick.

 

It is possible that the box is badly made. I've heard Bassworx and other cheap enclosures before, and they do not take power well. If you give them over 750 watts, that start to "cave" under pressure.