Cheap driver for ELF sub

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I am trying to build an ELF sub on a college budget. I have already built Rod Elliott's controller, now I'm building the sub. I am constructing my own cabinet, but could use some feedback selecting a 12" driver.

My main requirement is inexpensive, with a hard limit at $100 shipped. This in mind, along with the high Xmax requirements of the ELF design, I have opted for a car subwoofer, specifically the JBL GT5-12 (275w, Xmax 14.2mm, Fs 29Hz). Is this a decent selection? Any problem with going the car sub route?

I'll be powering it with a old pro amp (400w bridged).
I think the Infinity 1262 is similar and cheaper.
I still haven't decided between that one and the JBL. The JBL has slightly higher Xmax, but the Infinity has lower Fs, and they are both priced very similarly. My main question, however, is are these the right types of drivers to do what I am trying to achieve? Most people building these use much more expensive drivers. Will these cheap car subs work well with the ELF design (albeit much less loud)?
You want the sealed system resonance to be equal to the upper crossover point of the system.

For most of the Bag End designs that's about 80hz.

The original Velodyne subwoofers also had a sealed system around 80hz.

The ELF uses a two-pole low-pass filter at around 8hz, making the system flat up to the system resonance point, where it now rolls off at 12dB/oct (without any additional crossover components).

Of course you could always use a Linkwitz Transform if you have a low resonant frequency, high Q driver that ends up with a low system resonant frequency.
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I would advise that you're going to have a tough time getting really satisfying performance out of a 12" in a ELF/shelving filter arrangement. A 12x16 concrete college dorm is about the only place there would be enough room gain to compensate for the output level, but this would also give you a bit too much response in the low end due to the filter.

Personally, I would recommend a pair of 12's or a decent 15" in a moderate sized ported box with a low tune, this will give you a gradual rolloff that will mate with a room better, and much more output.

If you can stretch your budget a pair of these would be great, or the DVC version if you need it to get the correct impedance: Infinity Reference 1260w 12-Inch 1200-watt High-Performance Subwoofer (Single Voice Coil): Car Electronics

Also check out this thread for ideas:

Use plywood, cheapest decent stuff (not pine) you can find, not MDF.
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Also, keep in mind what your end use is. If you are using this for music at parties, the 12" ELF is going to run out of steam really quickly, the only thing it will be good at is movies at very moderate volumes. For party music, you really need something that hits hard from 40hz to 150hz, maybe 30hz extension for some genre's of music, that means a (large) front loaded horn or bass reflex cab.

I recently tried my pair of 15's as sealed with a huge amp and EQ flat to 20hz, they were pretty much maxed out at a reasonably loudish volume in a moderately sized living room, but were quite good overall. They are normally ported cabs tuned to 35hz. You could concevably build a convertable setup, where you run the sub sealed with the ELF filter for movies, and ported without the filter (would need a high pass/lowpass of course) for party music, etc.

I don't think the resonant frequency of the driver is a particular concern, F3 and Q in the box is more important, but there is more leeway there than you would think.

I would strongly recommend more than a single 12".
I have a double 18 for parties. I am experimenting with ELF because I think it is a cool idea. I know their is are better options for different applications.

Ah, I see....some threads here start with people wanting to build a design without any thought or stating of the application/goals, doesn't hurt to ask.

I still say the single 12" runs out of steam for practical use in a room larger than a 10x12 bedroom or concrete dorm room.
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