Yes - that's a tline.

some more stuff I've dug up on high fidelity scoops - these are 15" loaded with Tannoy HPDs, design based on the GRF in both instances - the contour and folding may be of interest to some of you chaps, especially with regard to 'small scoop' concepts:

Dual HPD Monster! - well worth a look
Single HPD - look down for the original GRF plans, accompanied by measurements

Now reading my posts, I find it's not clear to the reader what I refer to as a BVR (big vent reflex).

I'll first display a few quotes:

Scottmoose:
End-correction? It's not really about trying to extend
the bass. These boxes are just regular BR or MLTL cabinets, and I
design them as such initially, then replace the usual small vent with a
larger flared one (or more than one) that gives the same Fb. The rapid
decrease of pressure you get from the flare reduces noise and any
peaking at Fc, should either exist. As you've coupled to more air you
get a larger scale to the presentation & they help act as
waveguides to an extent so they sound a bit like BLHs, albeit a heck of
a lot smoother most of the time as they operate over a much narrower
passband.

</font>Design a BR or MLTL for it with a slot vent (same CSA
and length as a round vent, as you know). Then apply a flare to the end
of said port. Best sheet to use is the BLH sections, though in a sense,
it's not too critical. Have a play -you'll soon find out which things
make the most effect.</font>

Just found this thread and it got me thinking. In this design is the horn o/p in phase with the driver o/p?