I picked up my truck yesterday and have had to change my plan already. The truck, a 1991 regular cab D250, came with an empty bass cabinet and I made some assumptions based on that cabinet, but . . . the cabinet doesn't quite fit behind my bench seat. First, though, some basics on speakers:
It was determined back in the 50's that to accurately reproduce bass in a pair of sealed acoustic suspension speakers you needed eight 12" woofers and a LOT of cabinet space. There were other possibilities. I saw a picture once of a house that was actually built around a pair of 15" Altec speakers and their eighteen foot concrete horns. So the first thing to realize is that you are not going to get stereophonic quality bass in your truck. Before I go on I must comment that none of the "subwoofers" you see for sale are actually subwoofer. Any self respecting woofer will get you down to about 30 hertz. A real subwoofer takes care of the bass below 35 hertz, reinforcing the weaker bottom frequencies and extending lower. The Paradigm subwoofer I have in my home has decent volume down to 16 cycles, below human hearing, but you can feel it.
So when upgrading speakers in our trucks the best we can hope for is decent bass down to about 50 hertz. If you'd rather have thumping instead of musical bass it's much easier, but that's not what I'm addressing here.
The biggest problem is space. With older cars one could mount the speakers on the deck above the huge trunk. My truck being a regular cab, has very little space. I thought about building a console that is actually a woofer cabinet but I like my bench seat and don't want to give up that space. I thought about the extra space in the ceiling but wasn't keen on drilling holes in the roof to support it. There's not enough space beneath the seats, so we're left with the space behind the seat. The only thing that really fits is a shallow 10" woofer in a 5.5" deep box that is at least 13.5" tall and 20" wide. So I ordered this:
http://www.amazon.com/Clarion-WF2510D-Voice-Shallow-Subwoofer/dp/B0032FOJKM/ref=sr_1_1?s=electronics&ie=UTF8&qid=1298837245&sr=1-1There are many cheaper ones available, but it's not worth it to me to go cheaper.
I didn't mean to dis the back speakers, but in a regular cab they are firing into a mostly closed space and can't contribute much. Bass however doesn't need a big opening to fill the cab.