Since there have been several posts on shallow subs I figured this would be worthwhile on DIYMA. I am looking at offering a home theater inwall subwoofer and since I use Stereo Integrity drivers, I had to look at the new BM MK V as well as one of the JL shallow subs. In looking at the JL TW3 vs TW5, I liked the extra few mm of travel offered by the TW3 over the TW5. In terms of cost, the JL TW3 was also more comparable in cost, which made it even better. These measurements were measured under standard sub measuring conditions for ground plane testing; out in a field so nothing could interfere with the sound waves (besides the ground) and the microphone placed on the ground 6' in front of the enclosure. I used a Motu 1248 microphone preamp with an Earthworks M50 measurement microphone. All audio cables are Mogami Gold. Remember these measurements are in a field so don't have any room or cabin gain, which is why they start rolling off at 60 Hz. In a car, they wouldn't start rolling off until around 35 Hz with solid output down to at least 25 Hz, maybe a little lower.
The IW-QUAD with 4 SI BM MK V subwoofers provided each sub with about .63 cu.ft. and 600 watts each.
The IW-DUAL was tested with the JL 12TW3 drivers as well as the SI BM MK V drivers using the JL recommended enclosure volume of .8 cu.ft each, again with 600 watts each.
I also threw in the JBL S4S that a theater designer sent me to do some DSP work with, which is one of the better inwall subs on the market, especially if cost is brought in to play.
Just thought I'd share.