Yes, My Mad catalog has it as a 6".

I put up this link because Akhilesh asked about why the
shape vs. standard BR. As a design, I think even a 4"
will give the effect in a less huge enclosure. TC may
disagree. His posted design of TQWT at the full range
forum is called Bigger Is Better."

Since Martin King still has some information to add to the
report, more will follow.