TL606 is a Electro Voice cabinet design
it sounds like a zillion other ported 1x15 cabs
pretty common volume for a live sound 15" driver will be around 3 cubic feet
and tuned around 40 to 55hz
Ironically for a EV15B or EVM15L
EV used a volume of 3.2 cubic feet. and the baffle you noticed is a unique function of the TL606
it has a removable plate for 2 modes for the reflex or port tuning.
55hz without the plate installed which is for PA use or music play back
40hz which is step down mode for lower tuning of 40 hz recommended for extended bass transient or musical instrument use.
Its just a well known pre made design and sounds like any other 3 cubic foot ported cab tuned to 40 or 55hz
3 cubic feet being a very common volume
basically any well known classic bass driver works very well in the enclosure.
such as peavey black widows, JBL D, K and E 140
Eminence legend 158, beta and deltas
and a million other live sound 15" speakers which usually end up in 3 to 4 cubic feet and tuned to 40 to 55hz
you can follow the EV design exactly, or you can build a cabinet to your dimensions.
as long as your have 3.2 cubic feet and tune to 40 or 55hz using whatever port type you like. the TL606 uses a slot port. but you can use round ports, flared ports , square, triangle etc etc. it just has to be calculated to have a reflex or tuning or Fb of 40 hz
the box is just a set volume, and the port is designed to resonate at a certain frequency.
no specific " sound" just a standard ported/reflex box designed for typical high sensitivity 15" live sound drivers