Differences Between Folded Horn Speakers and Transmission Line Speakers

Transmission lines have the reputation of excellent deep bass, but they are also very, very inefficient.  They need a big amp.  

Iʻm not fond of those transmission line designs that have only an 8" bass driver, or even two of them.  You need surface area to move a lot of air.  Thereʻs no replacement for displacement. 

Just because you donʻt have the tools to build from scratch doesnʻt mean you canʻt do a project.  Go to any local cabinet shop with a diagram of what you want and they can cut the parts for you.  They could also assemble the enclosure for you if you need it.  It wonʻt cost as much as you might think.

As for horns, the enclosure stops acting like a horn based upon the size of the horn mouth.  The lowest frequency that it acts like a horn is based upon the quarter wave length. If your horn mouth is 3 feet across, then that quarter wave length is:

The speed of sound
===============
full wave length

The speed of sound is 1100 ft/second.  If the horn mouth is 3 feet, then the wave length is 12 feet.   1100/12 = 91 hz.   The reason that Klipsch made corner horns is that they use the room corner as part of the horn.  Thatʻs how you get a horn mouth that is 8 feet across, which is the quarter wave length at about 34 hz.

@dynamiclinearity is mistaken.  When a Klipschorn loudspeaker is placed in a room corner, the walls do act as part of the horn.   From Wikipedia:

"Utilizing the room walls and floor boundaries as extensions of the bass horn helps extend the speaker's frequency response down into the 35 Hz range, considerably lower than would be possible otherwise. Because of the folded horn, the woofer cone moves no more than a few millimeters."

@panzrwagn I remember seeing old stories and photos of home audio systems in rooms with opposing corners.   Thereʻs really no point in having K-horns  unless you have two corners to put them in.  Way Back When, Klipsch tried promoting the 3 channel setup with K-horns in opposing corners and a single Cornwall in the middle.  The Fisher 500C receiver had a mixed, line level center output that youʻd run to a monoblock amp to drive the Cornwall with.

It has been a long time since I listened to K-horns, but my memory was of a mid-range that had a nasal quality to it.

Iʻm not at all against transmission lines because they need a lot of power to run.  I just donʻt like the designs with 7" bass drivers in a transmission line.  You may get very deep bass, but not a lot of level.  Thereʻs no replacement for displacement.

Back in the late 70ʻs, sub-woofers were mostly DIY projects.  The Holy Grail sub from that time was an enormous transmission line with a single 24" Hartley bass driver.