Differences Between Folded Horn Speakers and Transmission Line Speakers

@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."

@russbutton  Great explanation of horns, but i would add that a 40Hz horn quarter wave is just over 7Ft, so a full-range horn is impractical in most domestic settings.

The Klipchorn 'cheat' of 1/8 space loading the woofer is so room variable that its hard to predict the actual perfomance. In a purpose-built room the LF can perform admirably, but the MF and HF are still mediocre compared to other higher quality horns. 

Where our opinions diverge is on Transmission Lines. Properly calculated and damped they are capable of superb bass. Yes, they give up the backwave reinforcement and so are lower in efficiency, but unless you are designing a low-power or max output system, that's not much of an issue. They are larger and more complex (expensive) to build than a traditional ported or sealed design which accounts for much/most of their lack of popularity commercially, but relative popularity for DIY projects.

@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.  

In my opinion, the JBL Hartsfield is a better sounding corner horn then the K-horn. Also, they were the first powered speaker see here and here. 

Mike

A local dealer who builds custom horn systems has a 70hz horn with a square opening and a 90 degree bend in the horn throat.  Even with that bend, the horn is well north of six feet long so it is very hard to work all of this into a single cabinet.  He has the drivers meant to work with the horn and they have a practical operating range from 60hz to 1,000 hz.  This is something wildly impractical to work with.  To me, the best sounding nearly practical horn he has used was a Japanese wooden replica of a Western Electric 22A horn, which all who have heard it agree that it sounds better than an original Western Electric 22A horn.  The wooden 22A horn system I liked had the horn suspended above a cabinet that held the woofers (twin 18" woofers) and horn tweeters.  THIS is what horn systems should ideally sound like: huge and enveloping soundstage (large scale to the presentation), macro and micro dynamics with a sense of ease and a relaxed sound, sense of power and weight even when playing at low volume.

By horn system standards, mine is a mini, with twin 12" woofers in a "compact" Jensen/Onken bass reflex cabinet.  That cabinet is 24" wide, by about 20" deep and about 30" tall.  On top rests the tweeter (bullet tweeter) and a Western Electric 12025 multicellular horn (24" wide) driven by Western Electric 713b drivers.  This is, to me, one of the best sounding compression drivers ever made.   My system delivers extremely good dynamics, particularly at low volume, and very little of the peaky or rough sound one hears with most horn systems.  But, it cannot deliver the sense of scale of the big boy horn systems.