I'm glad to see Paul Kittinger and Dennis Murphy both responded to an earlier post. I'd like to add one more observation about transmission line speaker design. Earlier TL designs, such as Bud Fried's, involved a significant amount of trial & error (guesswork) that produced reasonably good results, but were not optimal.
Martin King and George Augspurger, two researchers and designers, independently succeeded in creating the first successful mathematical models of TL speaker behavior in the early 21st century. Their work realistically predicts TL speaker behavior without trial & error with lumber & sawdust, and allowed for improved TL designs.
See this Wikipedia article on Transmission Line Loudspeakers for more. https://en.wikipedia.org/wiki/Transmission_line_loudspeaker
"However from the 21st century, Martin King and George Augspurger (both separately and referencing each other's works), produced models which show these to be "generally less than optimal" designs which "did a good job of approaching what was possible in their day". Audio engineer Augspurger had modeled TL using an electrical analogy, and found it to agree closely with King's existing work, based on a mechanical analogy. D'Lugos concluded in his overview of TL modeling and design theory: "I think that using modern drivers & tools such as King's software you can build a better TL easier today"."
All the Salk TL speaker cabinets were designed by Paul Kittinger who uses Martin King's software combined with his own expertise and experience.
Instead of spinning in his grave, I suspect Bud Fried might smile in approval.