Many moons ago I had a car audio subwoofer, but I'm not sure exactly what kind it was. The box was fairly large, probably about 4' x 2' x 2'. It contained two 15" woofers in the center that faced eachother. You could see these two speakers through a plexiglass window. Then on the backside of each speaker there were two ~3" ports.

This was about 15 years ago and I just bought it based on the referral of one of my other 15 year old friends, but I had the box for several years and was always pleased with the sound it put out with two 15" Orion woofers. I remember that the bass it produced felt very good inside the car, but it wasn't rediculously obnoxious outside the car. I believe the box was referred to as an "isobaric" design, but I'm not sure if that's correct.

Is there any applications for this type of subwoofer in a home theatre environment?

http://prosites-allmanmusic.homestead.com/files/bpencl.jpg

That is what the box looked like, but I don't remember my speakers being mounted on an angle.

Any HT applications for a design like this?

That looks like a bandpass enclosure as opposed to isobaric IIRC.

Apologies for resurrecting an old thread, I'm doing some searching for another thread and this one came up as well.

Agreed, that looks like a bandpass, not a true isobaric (http://en.wikipedia.org/wiki/Isobaric_speakers) enclosure. Bandpass enclosures, in general, have a strong resonance in the mid-bass (hence the name which implies the frequency band which gets passed by the enclosure), as the typical application is a car applications for people who want to be as obnoxious as possible ;).

The Bose acoustimass bass module (not a true subwoofer BTW) is probably the most popular application in the home; It does not give flat, deep bass. Just like in car stereos, it's tuned for a mid-bass hump to impress the lay-person. Most HT afficienados want deep, tight bass, and the most common approaches to get that are sealed, or a large ported, enclosures.