What can anyone say about Quarter Wavelength transmission line enclosure design ?

I have read, but am no authority, that the math for TL's is not very well established, unlike say creating a sealed or normal ported enclosure.

This makes getting it right a lot harder.

@erik_squires - Experimentation(a lot), back in the early Eighties and DSP, now. Wasn’t all that hard!

I came across a design for a 10" TL back in 1981 that I built using the 10" woofer from my JBL L-26 speakers. The result was a lot bigger than the JBL speakers, roughly 14" wide, 20" deep and 48" tall and heavy being made of 1" HDF. But they had MUCH better frequency response, not only flatter but a LOT deeper, way more than I ever expected, honestly deeper and flatter than anything I ever heard back then and frankly few I have heard since. Even more surprisingly they seemed to be about as sensitive (efficient) as the original ported JBL factory enclosure.

I forget the details but the folded taper design was not that complicated or hard to build. Basically it tapered from being a little bigger than the driver which was at the top front of the enclosure to maybe about 1/4 where it ended in a rectangular port at the bottom front. The taper went first from the front to the back, then folded down to the bottom, up again then back down and out the front. The whole thing was stuffed full of dacron fluff.

Never got the impression there was anything terribly difficult involved in the design either. In general, starting from about 125% of the driver area you taper down to about 25%, over a length of about 10'. The actual math I think has to do with the wavelength of 20Hz but that's just very old memory this was after all 1981!

@millercarbon- Did you happen to find that design in the Speaker Builder Magazine articles(circa- early 1980’s), written by Roger Sanders? In them, he outlined building a 10", TL woofer system, closely matching your description, to compliment his(then home-built) electrostatic panels.

Bingo! Exactamundo! Pre-internet days!