enclosure recomendations for 12 jl w3 d4

I have a 2000 Chevy s-10 with a standard cab so... not a lot of room. To make things worse the previous owner installed  power leather bucket seats from some other vehicle , so the driver side seat is completely stationary, The passenger seat can come up  so I only have room to fit a small box behind it . I have one older model JL 12" w3 d4, which shouldn't  need much airspce , but I need to know how little airspace I can get by with without sacrificing sound quality or quantity. I hear this is the best place with the best people to help me with this. Any suggestions would be greatly appreciated. Also, feel free to share any knowledge you may have about these woofers. I'm 32 yrs old and my last system was about 10 yrs ago and I know A LOT has changed. Thanks !!!!

Welcome...
With a space constraint and a sub chosen, all that's left is making sure the box is proper and the power is strong. That sub can really rock in a sealed box built extremely well. Also throwing 300+/- watts of clean power at it and your looking about as good as can be. Are you building a box? Ya, uh JLw3's are single coil subs now... You also need a 1-1/4 ft3 of airspace, internally, ideally. +++ Prove me wrong, but I recall a 12" sub having a mounting depth issue back there.

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This is what I do for FUN!

yes you are correct...the 12 is 7" deep. I have 24"  in width accross the back behind my passenger seat. Oh, and yes... I am building my own box. I actually ues to build boxes for a Cadence dealer here in Baton Rouge, but he had a program that would break down the woofer with trunk space and print out the deminsions of the box and I would build it. So I've never had to figure out my airspace requirements and deminsions. Maybe this is asking too much but, do you know a website or somewhere that I could get deminsions for my box simply by giving the measurement behind the seat along with needing 1 1/4 cubic feet of airspace ? I know it sounds terribly lazy, but as much time, energy and money as I put into building a box, I'd hate to screw it up by having the wrong measurements. Thanks !

Well, JL is the best source to get your info.   However, I have built enclosures from their recommended dimensions which was 7 or so different enclosure designs. Back then, the dealers held the cards with these dimensions and I have never been able to obtain them elsewhere. If you can get real close to a 2.0ft3 net, port the box to the bottom right corner of your truck.(mind that port dimension it works!) If you can get the port to end firing down, four inches from the floor, it will fill the cab with a strong tone. Meaning, there will be a 3"X4"+\- wedge missing from the bottom left corner when your facing the baffle. If you cant get close to 2.0, the next most impressive sound will be from a SUPER SOLID sealed box. There cant be a lick of expansion. You will lose the in-cab experience the port offers, but you'll still be a bit smoother and louder than the 1-1/4 is going to offer in your cab. Most of this I imagine you already assume. Being it is, I do not have to abide by the authorized installer rules, I state my opinion. Please only consider the info given as a method to achieve a sound exceeding above the expectation of the listeners ....    Good Luck! Please post results regardless.

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This is what I do for FUN!