I've made some improvement to the sub. But first, here's some plans that "radman12" at AVS came up with*:
The box above is for an Anarchy Audio woofer. I like the woofer, but all of my car amps aren't really optimal for it. For instance, my mono sub amp maxes out at two ohms, so I'd be throwing away a lot of power if I used their woofer. Also, I could use my stereo amp with a pair of the Anarchy subs, but that would take up about five cubic feet of my car. That won't work.
So what's the solution?
The Alpine 823D or 843D. Take your pick. If you want to run a stereo amplifier, buy the 823D and hook up one voice coil to each channel. Want to run a mono sub amp? Get the 843D and run the voice coils in parallel. (The 843D has slightly different parameters, shouldn't make an audible difference in the bass.)
Here's the Alpine versus the Exodus. This is modeled with 250 watts into a 2ohm load. The Alpine is belting out a solid ten decibels(!) more. This isn't due to efficiency - in fact the Exodus is more efficient! It's simply because the Alpine's 2ohm coils are a better match for a car audio amp. (The Exodus has an Re of 6.4ohm.) If anyone's curious, the reason that the smaller woofer is more efficient than the larger one is that the Exodus has a higher efficiency bandwidth product, 96 versus 69.
Please note that the Alpine is basically maxed out at 250 watts. Their spec sheet says you can give it more power, but I'd be cautious - it's exceeding xmax by a little bit. BE SURE TO USE A SUBSONIC FILTER. Subsonic filters are absolutely necessary with designs like this. I'd set it at 30hz. You won't miss anything below 30hz - there's virtually nothing there in music. (Home theater is a different story, but this is a car sub, not a HT sub.)
For comparison's sake, here's the predicted and measured output of the sub with an Anarchy woofer. As you can see, it's nice and flat and deep.
Besides putting out more SPL with a car amp, the Alpine tapped horn has a bit more output because it has about fifty percent more displacement. This only makes a difference of about 2dB, but it should be slightly noticeable.Note that the dimensions of the Alpine tapped horn are IDENTICAL to radman12's design EXCEPT the width
The Alpine tapped horn has an internal width of 8.5"; the Exodus tapped horn has an internal width of 7.25". IF YOU DON'T ADDRESS THIS THE ALPINE WON'T FIT!! Just wanted to make that clear, in case anyone realizes their sub won't fit in the box!
* here's the link, and kudos to radman12 for taking the time to model this in Sketchup http://www.avsforum.com/avs-vb/showthre ... st18387271