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

Too bad you can't hear my pair, regardless of what I type(8', tapered, folded, w/10" Seas L26RO4Y D1004) .   Are you ever around the Indianapolis, IN area?

Of course, those are being actively bi-amped.  Only producing between 80 and 20Hz(60dB/Oct cutoff).   

This design is why folks swear by PMCs, including me. TLs are actually very complicated to design right, but when they are they're delish. 

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!

That, Glass Audio and Audio Amateur, were my favorite rags(back in the day).   Inspiring!

Ohm Walsh speakers use a transmission line. The bass has real impact and slam. Nothing polite about the bass it produces.

Salk Sound also uses TL. Never heard them but the bass measurements are impressive for the speaker sizes.

Quarter wave is popular in the DIY community. Tabaq is a popular DIY quarter wave design. A company named Kvart & Bolge made a really cool and low priced commercial speaker from this design called the Sound Sommelier. I have a pair and they really disappear.  

Acoustic Zen loudspeakers utilize the transmission line design. They sound phenomenal!!! 

I built the electrostatic panels too, rodman. Just the way Sanders described. They sure looked like they would work! But being a starving college student it took me a while figuring out how to find and buy everything for the power supply to make them work. In the meantime I for some unfathomable reason decided to remove the woofers from the TLs.

Now if you ever do this be sure to use a cap or something to cover the speaker mounting bolts. Because the whole thing is stuffed with dacron. If you don't cap the bolts then when you go to remove the bolt the dacron gets wrapped around it so tight you're never getting that bolt out without destroying the cabinet, or the driver, or both.

And that will be the end of your glorious Speaker Builder Electrostatic TL project. Sigh.

I built a pair (in 1981), per Roger’s design, to go with a customer’s Acoustat Model IIIs. He wanted something that could match the speed and definition, of his electrostatics. They worked so well, powered by a Halfer DH-500 and crossed over via a Dahlquist DQ-LP1, I duplicated the system for myself(and my Acoustats) and another customer. Back then, I used a 10" woofer that Milo Nestorovic employed in his woofer systems. In answer to the OP’s original query; TLs(at that time), were the only woofers systems around, that many of us had experienced, able to blend well with electrostatics. I used bi-amped TLs, in concert with various planars, for 36 years. Now, with an Emerald Physics system. The trusty DQ-LP1 was replaced by a modded TacT RCS 2.2X(and Hafler Trans-Nova 9505), about 12 years ago. The TacT’s DSP(time-alignment/room correction/EQ) was the finishing touch, to an already stellar bottom end. Guess I’m a TL believer!

I am very fortunate to have a pair of T+A Criterion 210 speakers that are transmission line designs that are done right!  They have exceptional response from top to bottom and absolutely no overhang in the bass. They are very heavy speakers due to the transmission line enclosure, but that is a small price to pay for wonderful sound. 

Fried, and his IMF(Irving M Fried) designs, got me interested in TLs.  Man; that's been awhile(I'm dating myself).

Found it! https://sanderssoundsystems.com/downloads/speaker_builder_dec_1980_an_electrostatic_speaker_system_P...

Exactly what I built! Excellent deep bass. Is this the same design you used too Rodman?

@millercarbon- Affirmative. Built three pair of those. Excellent, extended, authoritative, articulate and tuneful bass. The system did a good job of extending the dynamic range of the electrostatics too, relieving them of the longer excursions, demanded by the bottom freqs.

These ARE, by definition, "transmission lines" and have been found wonderful designs for bass reproduction, by the experienced and dedicated. http://diyaudioprojects.com/Technical/Papers/Non-resonant-Loudspeaker-Enclosure-Design.pdf Good stuff, regarding why they work so well, for the knowledge seekers: http://www.quarter-wave.com/TLs/TL_Anatomy.pdf

That's what I remember. But it was so long ago, conditions so crazy, and other equipment so much different it was hard to be sure. But they were definitely the best bass I ever heard back then, probably ever. A few deeper,  but none of them were as articulate. Even my Talon Roc sub doesn't seem as good as I remember these being.

Which come to think of it the last time I used the 10" woofers from my JBLs. This time I could use the much better drivers from the Talon sub. Already have more than enough MDF just sitting in the shop. And a proven design. Now if someone can just help me find the time... lol!