Please understand that these are just my own thoughts on this subject. It’s not like I was tutored by the man himself about this. But based on my experience in designing and building midrange horns, here’s my thoughts on the Klipsch K400 horn used in the La Scala and Klipschorn loudspeakers.
In the beginning, Mr. Klipsch had a terrific folded horn design (Khorn). Compact and fitted in the corners of just the right sized/proportioned room, these bass horns produce solid bass down into the low 30’s and have a way of surrounding the room with bass that I’ve not heard from any other speaker. The Khorn bass horn cuts off naturally at about 400hz on the upper end, no crossover needed. Mr. Klipsch needed a midrange horn/driver combination that could reach down to 400hz to integrate with the bass horn. He chose a midrange horn size that would fit comfortably under the tophat design of the Khorn and then manipulated the design to lower the Fc of the horn by lengthening the throat of the horn, creating a long, narrow pathway for about half of the length of the horn. It is obvious to me that the unusually elongated throat of the K400 is ’pushing’ the horn beyond it’s ’comfort zone’ and causing the characteristic honky, colored, and harsh sound that the horn is known for. But it does reach down to 400Hz! The goal was met, but at a cost.
Twenty years ago or so, someone was building midrange replacement horns for La Scala and Khorns that had the same mouth size/shape to be a direct replacement. The horn was much shorter though. Still with a 1" throat, but not elongated. I tested and listened to a pair of these in my Khorns, and indeed they did sound less colored and harsh than the stock K400 horns. However, there was a problem. They didn’t extend down to 400Hz, leaving a ’hole’ in the response between the mid and the folded bass horn. Could be overcome somewhat in La Scalas, which have bass horns that can extend up higher than 400Hz to meet the midhorn with the higher Fc, but no chance with the Khorns. This exercise demonstrated to me how Mr. Klipsch took a ’normal’ exponential horn design and lengthened the throat to lower Fc. The replacement mid horn with a shorter/normal throat would get down to 600Hz and the longer throat K400 down to 400Hz - but at the cost of sound quality.
Nowadays, modern compression drivers are much more capable than they ever were. Machining tolerances, modern materials, and modern manufacturing processes enable compression drivers to produce lower mid frequencies with very low distortion. A modern compression driver with a 2" outlet and 3-1/2" diaphragm feeding into a 2" throat horn is capable of covering low-mid frequencies in a typical listening room with much greater ease. It is no longer necessary to push the design Fc of a horn by constricting the throat. A shallower design with a 2" throat that fits under the tophat of the Khorn can cover down to 400Hz with ease, and with no unwanted colorations, glare, or harshness that plague older and lesser quality designs. Think of it this way, the modern compression driver can cover more of the load, not requiring the horn to do as much.
Why does Klipsch still use the K400 horn in their speakers? It really is one of the worst sounding midrange horns ever produced. I just did the demo today for a customer who visited here to listen to my speakers. I spoke through the K400 and then spoke through my V-Trac horn. The difference is night and day. Charlie left here today with a pair of Lucera speakers in the back of his van and a big smile on his face. The demo of how different horns can sound I’m sure had a little to do with that. It certainly didn’t hurt.
So why? Perhaps it is because the Khorn has an iconic sound that Klipsch simply cannot change. People are used to a certain sound from the Khorn. Making a big change to the sound would be kinda like making Wonder Bread into a healthy slice of bread that you can no longer squeeze into a little ball in your hand. lol. Is Wonder Bread still made? Or how about New Coke? Remember that one? How did that go over?
I don’t know, it’s a theory.
Greg