Differences Between Folded Horn Speakers and Transmission Line Speakers

Quarter wave back loaded horns have a constantly expanding cross section to the folded horn.  That expansion prevents standing waves from developing in the horn.  A transmission line has a more constant cross section and has to have a lot of damping material in it to reduce standing waves.  This damping greatly reduces the amount of acoustic energy that back wave can contribute to the sound, hence the much lower efficiency of transmission lines.  But, it is a much harder trick to make that back horn have the properly expanding size and the opening has to be quite large.

@larryi Thanks. I could kind of see it, but I wasn't sure if it was just the one folded horn I had seen or it it was generally the case. I definitely didn't know the reason for the shape of the folded horn.

Additionally, how would you compare the sound of the folder horn verses the transmission line speakers? I haven't heard the TL myself, but I understand that they are very good at producing the lower frequency range. Like I said, I know nothing about folded horn or how they sound.

Thanks.

The transmission line speakers I heard had very tight bass and sounded quite good.  They were also reasonably compact and did not require a lot of depth.  The various folded horns, like the Tannoy speakers, sound really good, although the bass did not go extremely deep in frequency, and most were quite lively sounding.  In recent years, I’ve heard single- driver backloaded horns systems, like those from Charney Audio, that blew me away because they sounded so lively, rich, and smooth—so much more complete and free from peakiness than most other single driver systems.  The Charney speakers were compact in width and height, but were quite deep to allow for the back horn.  A big plus with backloaded horns is that the high efficiency allows for use of low-powered tube amps thst are my favorite amps.