Transmission line speakers!

I owned the model right below the TDL reference speakers twice. I sold the first pair under duress because of their size and always regretted it. Quite a few years later when I finally had a dedicated listening room and had been through a number of other speakers, large and small, I found another used pair online and traveled a couple of hundred miles to buy them. I had them for a very short while when I read some glowing things about Klipsch Epic CF-4 version 1 speakers. I bought them on a guess, and suddenly the TDL's didn't sound good anymore. The Epics were so much more coherent. I sold them at a loss and never looked back. 

Sometimes it's true that you "can't go home". 

Transmission line use a long internal pathway. for the bass and are ported as I recall. IMF (Irving M Fried) were doing this back in the late 1980's and their floor standing speaker did indeed have deep, articulate bass. I think the design usually results in a low efficiency speaker. The few times I've owned or heard these types I always liked the bass but often it seemed somewhat disconnected from the mid and highs - almost as if the bass were too goo or too present for the rest of the speaker if that makes sense. Worth exploring though.

Okay the year was 1982, and my roommate put the Infinity monitor jr. outside on top of the porch. The Urbana IL police came by and tried to confiscate the Infinity Monitor Jr. with its transmission line loading. The complaint was that neighbors from 2 to 3 blocks away did not like the extreme deep bass. When I came back from class I heard the story and believed it.

Bose also uses transmission line designs and holds several patents on them.  The little Wave Radio uses a transmission line.   BTW,  transmission line applies/impacts typically only the low end portion of the speaker- not the midrange or above (other than its bass output is in phase with the overall system).  So like bass reflex or passive LF drivers or other boosting strategies, they attempt to reduce the normal 12 dB per octave low end roll off you get with a sealed box.  Since most home hi fi speakers need to be smaller, the port helps us get low end that would otherwise not be possible from that size [sealed] box.   The trade off/cost is usually a more rapid roll off of bass after the designed "boost" point of the port or passive driver, usually a roll off of 24dB per octave (that's rapid).  But compared to the 12dB per octave sealed box, it is possible you could get more deep bass out of a sealed box system than a ported system, especially if you are willing to go larger. So the "boost" from all these different strategies always has a price, the price is some other negative that you cannot avoid if you want the boost.  

As the engineers at ATC constantly explain to me, everything in speaker design is a trade off.  You can't get "this" without "that".  

These deeper performance values are good to know when you are speaker shopping.  It's what usually differentiates one company over another, the choices they make and the price of those choices;  how do these choices align with your choices?  It's good to know what you value, which is to my way of thinking, what a speaker demo is all about.  If you value low distortion, you usually also avoid bass boosting strategies because they generally increase distortion.  If you value bass, maybe the ported/transmission line speaker is the right idea?  Depends on what the rest of the system sounds like but porting is one low cost way manufacturers deliver "more bass".    What if you have a small room?  Deep bass is not supported in a small 10x15 room, wavelengths are too long.  A sealed box speaker may be perfect for you after all since you can't pump a lot of bass into the room anyway- even if the speaker will do it.

Brad 

Above I mentioned the ESS Transtatic I, introduced in around 1970. As I said, it consisted of a transmissionline enclosure (20" w, 16" d, 42" h) housing a single KEF B139 driver (also used by David Wilson in his original WAMM), a short transmissionline (the depth of the enclosure) behind a KEF B110 5" dynamic driver, and three RTR ESL tweeters (firing ahead and behind off an angled inner panel). I have a pair in my spare room.

Shortly before ESS introduced the AMT model (with the Heil driver), they offered what I believe they were calling the Super Quad. It was the same transmission line/B139 enclosure and RTR tweeters, with a Quad ESL for each speaker in place of the KEF B110, sitting side-by-side with the transmissionline enclosure. I saw a pair in the flesh, but didn’t hear them. If I remember correctly, ESS was selling them for $2,000/pr. (a fair amount of money in 1972).