JimJ

You don't need it. Adding polyfill, to a point, will make the driver behave like it's in a slightly larger enclosure, so a heavy use of polyfill can help if you're under the recommended volume. 2.1 is right on, so I don't think you need it unless you're unhappy with the low end extension...the "rule" is something like 1 pound per cubic foot, but that's not set in stone.

You can add some if you want, I'm not sure if the 2.1 cF box is the .707 Qtc alignment for that driver or not, but a little polyfill won't hurt things. Add to taste.

$500ish could get you a workable pair of used speakers, the trick is whether or not you'll be upgrading to 5.1 any time soon in the future, because you'll want at least the front three to be matching.

I'm not. And I need to tape the van up this summer, but it's going to be when I repaint the rain gutters It's a little late to care about bugs or chips on the front... Quality paint, whats that? Actually, it hasn't started to peel or crack anywhere, I'm a bit surprised. Faded, sure, but it's never been waxed regularly, and it's a commercial vehicle anyway so I couldn't give a shit.

I'm going with neither. Instead of the SSD and AQ amp, put that money into front speakers and you'll get much more of a return on investment for SQ

I'm not. And I need to tape the van up this summer, but it's going to be when I repaint the rain gutters It's a little late to care about bugs or chips on the front...

If SQ is anywhere near a priority, I'd go with $150 worth of drivers bi-amped actively over $150 of passives any time.

Is that depth including any mounting rings? Speakers really should be mounted on a solid baffle made out of MDF or similar material, never directly to the metal...

Since you already have a four-channel amp available, I'd skip the passives and just go active...$300 is a very workable budget, while the Hybrid stuff sounds great with a little careful mixing and matching you can get amazing results for your budget as well Go on places like zaphaudio.com, read the reviews, then lurk on Madisound, Parts Express and other stores. Measure your doors to see what fits. Since you'll be mounting in the doors, good off-axis response might be something you may want to keep in mind. Also, don't forget to prep the door, for whatever speakers you end up with. Multiple layers of deadening, and sealing up any large holes in the inner door skin with rigid materials are two keys for improving midbass response in a door

I'll be conservative and say Celts in 7...

EE folk...can never trust 'em...

OK, you can figure out the complex impedance of a series circuit using a right triangle and calculating the net effect of the capacitive and inductive reactance, but what's this shit about admittance? Sounds like a job for a Uni-bit, although there's probably some specific marine tool just for that purpose

Unless you're mounting them inverted or have a Plexiglas enclosure, you'll never notice any cosmetic change. And yes, they perform better than the previous generation, IMO

Just wow...

Are you limited to door placement only?

Downloading the whole Adobe CS2 suite while I'm at it...this is quite a big torrent.

I'm doing some logo work, I wish I could freehand better in Photoshop because that would be the easy way to do what I'm thinking.

Mo magnets mo betta, you know that Just curious...does anyone know what a good source for free images that can be used commercially?

Your idea has already been thought of and put into production It's called the DD Z and it retails for a couple grand. Oh, and neodymium is a rare-eath magnet

Just an FYI for your friend, he'd need a heck of a lot more cone area for it to work as a passive radiator. One 12" out of 5 isn't going to do it.

When you start talking sense, I'll be here

If I read your post right, you're talking about high efficiency, PA-style woofers in the 96-100dB/W range?

Super-efficient woofers = very large enclosures required.

Saturn is a GM product...

http://www.knukonceptz.com/productDetail.cfm?prodID=KRY1.4M Those. Unless you already have all the parts on hand, it's hard to beat that price by DIY