How about this sub

[maxserg]

First time I see it. It seems to look like the Aura NRT18's cousin.

Don't know if it could be a good sub for IB but it has a good XMax despite the accordian style suspension:

www.worxaudio.com/product_desc_true.php?id=56

Too bad they don't provide the Thiel parameters

[moonfly]

It looks more like a PA driver to me. All of the enclosures they are using it in are the typical horn loaded ones. Without the TSP's though, its all guess work anyway.

[maxserg]

The Aura NRT-18 is a pa sub mostly used in ported enclosures: www.aurasound.com/professional-audio.html

The 18' other aurasound is the NS18-992 used in car audio or home hi-fi: www.aurasound.com/hi-fi-home-theater.html

The Worxaudio is a PA driver and the shape of the magnet looks like the NRT-18.