Transmission line speakers!

...I used to have a pair of those WTLC's...long ago, far away...

Ask me about the time we hooked up four Infinity Column IIs, and connected to a Phase Linear 700, in Pacific Stereo's big room. Even with the doors closed and way in the back of the store. They asked us to turn it down because they couldn't hear customers at the front of the store. I bought a quad for myself.   

@roxy54

bkeske,

I’m not sure of how a transmission line port differs from any other port, but that is only part of what a transmission line is

And logically, it would be hard to have a transmission line port without a transmission line behind it.

I grant you, I’ve never seen a good clear cut-thru image of the ‘transmission line’ to show what your rightly question, but Richard does use that verbiage when describing the bass design of the 1’s. And that lower cabinet does exist below the 8” driver. Is Richard misusing the term? Possible, but he is a pretty smart guy, so there must be a reason he has and is still using the term. Perhaps you could contact Richard directly, I’m sure he would respond.

Or, perhaps @tomic601 could clarify as he has had wide ranging discussions with Richard over the years, and this may have been one.

My DCM Time Windows were TL

uncleang

Those are beautiful speakers... impressive

Thank you.  I think they're fantastic speakers.   They do require quite a bit of power, so they wouldn't work well with small tube / class A amps, but they sound great and are easy to work within a room.  Another advantage of transmission line vs ported is that room placement is less critical, and mine are working in a functional living room (a less than perfect space) vs a listening room. 

Khorn. A transmission line with a fold or two. Just my interpretation, as I am no speaker designer. PWK could have ported it, but would not get the efficiency of a true horn, nor the quality of output. Transmission loaded, ime, always had folds within the cabinets, otherwise, it was simply ported. We can agree to disagree. All good.🙂

👍

A number of years ago I had a pair of PMC's FB1I, used in a small bedroom driven by a Bryston B-100. I remember them as being well built and very good sounding speaker. 

mrdecibel,

I don't think we can agree to disagree in this case. The transmission line is the opposite; it amplifies the rear output of the bass driver, and the folded horn of the Khorn amplifies the forward output of the bass driver. 

Roxy, do you understand that our ears are mini speakers, playing a role in reverse. Does not matter if the output is from the front.or the rear of the driver, imo. A mic is a mini speaker l8ke our ears in reverse.

Btw, I am a fan of isobaric loading, which is another way to do bass.

It's not a matter of opinion, they are different by definition, and what they do.

The bottom line of any design is how they perform and how musically satisfying they are.  

American made Acoustic Zen Crescendo Marl ll.  Great speaker.   

is a loudspeaker enclosure design which uses the topology of an acoustic transmission line within the cabinet, compared to the simpler enclosures used by sealed (closed) or ported (bass reflex) designs. Instead of reverberating in a fairly simple damped enclosure, sound from the back of the bass speaker is directed into a long (generally folded) damped pathway within the speaker enclosure, which allows far greater control and use of speaker energy and the resulting sound.

Inside a transmission line (TL) loudspeaker is a (usually folded) pathway into which the sound is directed. The pathway is often covered with varying types and depths of absorbent material, and it may vary in size or taper, and may be open or closed at its far end. Used correctly, such a design ensures that undesired resonances and energies, which would otherwise cause undesirable auditory effects, are instead selectively absorbed or reduced ("damped") due to the effects of the duct, or alternatively only emerge from the open end in phase with the sound radiated from the front of the driver, enhancing the output level ("sensitivity") at low frequencies. The transmission line acts as an acoustic waveguide, and the padding both reduces reflection and resonance, and also slows the speed of sound within the cabinet to allow for better tuning.

Transmission line loudspeakers designs are more complex to implement, making mass production difficult, but their advantages have led to acclaim for a number of manufacturers such as IMF, TDL, PMC. As a rule, transmission line speakers tend to have exceptionally high fidelity low frequency response far below that of a typical speaker or subwoofer, reaching into the infrasonic range (British company TDL's studio monitor range from the 1990s quoted their frequency responses as starting from as low as 17 Hz depending upon model with a sensitivity of 87 dB for 1 W @ 1 metre), without the need for a separate enclosure or driver.^[1][2]Acoustically, TL speakers roll off more slowly (less steeply) at low frequencies, and they are thought to provide better driver control than standard reflex cabinet designs,^[3] are less sensitive to positioning, and tend to create a very spacious soundstage. Modern TL speakers were described in a 2000 review as "match[ing] reflex cabinet designs in every respect, but with an extra octave of bass, lower LF distortion and a frequency balance which is more independent of listening level".^[4]

Although more complex to design and tune, and not as easy to analyze and calculate as other designs, the transmission line design is valued by several smaller manufacturers, as it avoids many of the major disadvantages of other loudspeaker designs. In particular, the basic parameters and equations describing sealed and reflex designs are fairly well understood, the range of options involved in a transmission line design mean that the general design can be somewhat calculated but final transmission line tuning requires considerable attention and is less easy to automate.

any of those wishing to differ..can..see how your corrections, edits and such fare on Wiki, or better yet on the….speaker market…. 

I had a rather lengthy conversation w Richard Vandersteen yesterday, we talked about other exotica like tanking circuits and Zobel networks, his use of transmission line didn’t come up…but when we get past Sunday the day of rest, i will certainly ask him….

Since 1977, not everyones cup o tea. How freaking boring that would be

Carry on

Pick your expert carefully….music is AC…. ha

tomic601,

I can't thank you enough. I was feeling like the odd man out. I appreciate your thorough description of TL design. Having owned the large TDL Monitors, I can attest to the scary extension of their bass. It didn't make itself known above other frequencies except when called for.

I recall a short while after I bought them in the 80's, I had a couple of friends over and we were listening to the first Enya disc at a lower level as we chatted in the living room. Suddenly, the synthesizer hit a subsonic note, and it felt as if a very heavy object had hit the floor. I'll never forget the first time I had that experience with them.

I started designing Transmission line speakers in the mid '70's. They can be real good for the money. These days I use a ported cabinet design because you can get a better final performance curve.

Though not a speaker designer, this meets with my experience. 

I had  pair of Spendor D7 which uses a quasi-transmission line bottom firing port.  The bass and sub-bass was so deep and effortless, a speaker with very special bass.  It improves the efficiency of bass response and makes them easier to position. 

No, I don't believe the Spendor D7 or D7.2 even qualify as "quasi-transmission line" (whatever that means). They are simply bottom ported. 

I had a pair of IMF TLS 80s in the mid-70s and loved the bass they produced. However, I found the midrange quite poor and they did not image very well. I sold them for a pair of Braun L810s - bass not as deep as the IMF but the midrange was far superior. 

My Acoustic Zen Crescendo II’s are a transmission line design...Best sounding loudspeakers I have ever heard or owned.

Nice demo!

Khorn. A transmission line with a fold or two. Just my interpretation, as I am no speaker designer. PWK could have ported it, but would not get the efficiency of a true horn, nor the quality of output. Transmission loaded, ime, always had folds within the cabinets, otherwise, it was simply ported.

The K-Horn does have some folds, but is not functioning as a true 1/4 wave T-Line. It’s more like a wave guide or horn to help amplify certain ranges of the bass for efficiency gains, as opposed to absorbing resonance and allowing deeper bass from a given driver. Very different principles with different purpose and execution of the folds.

...as opposed to absorbing resonance and allowing deeper bass from a given driver. 

Bingo.

@roxy54  thanks, i lifted it from Wiki. i should have been more clear about that. Best to you !

Jim

My mains speakers are some transmission line IMF RSPM mark IV. 

I bought them in great condition from a junk shop a year or so ago.

My magnepan .7's and Dalhquist dqm9 have been pushed into a corner ever since. 

The IMF's are huge and heavy but are so easy on the ear. 

I am sure that design difficulty, cost of manufacture and shipping, and shear size are the reasons speaker like this became rarities.

I’m still using a pair of KEF Transmission Lines that my late father and I built in the mid ’70s.

They are made of 1’’ ply and are a CJ Rogers design with a KEF B139 bass, KEF B110 mid, KEF T27 tweeter and an ITT-STC 4001G Super tweeter.

They sound really nice with any amp but could probably do with a crossover rebuild. And a refinish as the original glued laminate hasn’t aged well and has been removed.

I have tried to include a picture but it won’t stick for some reason.

I just got a pair of Alta Audio Alec’s - my first pair of speakers with a transmission line.  Have had them for about a month, they sound fantastic.  Bass performance far exceeds anything I’ve experienced in my set up.  Very organic and non fatiguing. 

This is a great post. I learned so much about this and similar designs today that provide direction of my next speaker upgrade. Thanks for bringing TL design to the forum and thanks to all those that contributed to the discussion.

My current speaker set uses a loose concept of the TL design but I was unaware of how the construction is classified and incorrectly thought I had stumbled across a unique design. I am enamored with this low frequency sound and today have found the path to take when upgrading. Thanks again!

Irving M (Bud) Fried of IMF and Fried became a good friend of mine, and I was one of the owners of Fried Products.  He graciously gifted me his own personal loudspeakers shortly before his passing.  Bud famously championed the transmission line loading.  No one came close to evangelizing the advantages of the alignment.

What few realize is as terrific as TL is in the bass, it's even better in the midrange, as the notes simply fly out of the speakers.

Recently finished a new pair of TL subwoofers for myself to replace Bud's.  Their lovely cosmetics fit right into my living room, play cleanly and powerfully into the teens, and cost me so little most in this day and age dismiss them immediately out of hand.  More than that, the quality of the low frequencies they produce leaves me happy like few, if any I've encountered when it comes to musicality.  They simply sound more like real music, and astonish people with their sound and modest dimensions. 

I knew Bud and spoke with him several times when he was still running Fried. He was a real gent, full of knowledge and eager to share it. I owned one of his large bookshelf speakers, a transmission line design, and I remember well that he was one of the very first to design a sattelite/subwoofer system, (Model J?) and it was really impressive.

@roxy54: Are you thinking of the FMI (Fulton Musical Industries) Model J loudspeaker? It was comprised of three separate boxes: on the bottom a transmisionline-loaded woofer enclosure, in the middle a small sealed enclosure with an 8" woofer and dome tweeter (marketed separately as the Model 80), and on top an RTR ESL tweeter array (6 ESL tweeters per side iirc)---the same tweeter Dave Wilson used in his original WAMM loudspeaker. I bought a pair of the Model J in 1974, when it was priced at $1200/pr. JGH loved it, putting the Model J at the top of his recommended component list.

Before ESS introduced the Heil AMT loudspeaker, their flagship model was the TranStatic I, which was also a three way: a KEF B139 woofer in a transmissionline enclosure, a KEF B110 5" cone midrange, and three of the RTR ESL tweeters mentioned above. It retailed in the early-70’s for $599/each, and was competition for the Infinity Servo-Static I. I have a pair sitting in my spare room.

bdp24,

Hi, I might be giving it the wrong letter, but it was definitely Fried. They were the first mini monitors I had ever seen, and they were really mini! A small two way, amd an rectangular subwoofer that was fairly large. I saw it demoed at House of Hi Fi in Trenton NJ around 1976, when I was considering my first pair of speakers. It sounded really good, but I was 19, and nothing was going to keep me from buying either Bozak Concert Grands (which they also carried) or Klipschorns, which their competitor Hal's Hi Fi carried. The Khorns won.

My main speakers are the Stax F-81 electrostatics. Difficult load and brutally inefficient, but with the most refined and realistic midrange that I have ever heard in a beautifully stable and realistic, but small scale soundstage presentation. Love those speakers. When I crave a larger scale presentation with a livelier rhythmic vibe and much better bass performance I rotate in a pair of Paragon Regent transmission line speakers.  

Paragon Acoustics was a relatively short lived company that produced some outstanding speakers. The 92 db efficient Regent, with its lead lined interior walls (140 lb ea.) sound like a more dynamic, fuller and more extended version of my Stax. The least “boxy” sounding box speakers that I have owned. They don’t have the beautifully refined and detailed midrange of the Stax, but are not too far off in that respect. I like tomic601’s description of TL’s in general and applicable to the Regent.

*** TL speakers roll off more slowly (less steeply) at low frequencies, and they are thought to provide better driver control than standard reflex cabinet designs,^[3] are less sensitive to positioning, and tend to create a very spacious soundstage. ***

As an aside, my Manley Reference 100W triode/200W pentode switchable amps work great with both. Should be obvious which mode I use for each speaker.

Not my pair:

https://www.hifido.co.jp/sold/11-62535-22980-00.html?LNG=E

                                       Everything tomic601 said, +1

     Below: a reprint of the article*, mentioned by MC, (01-06-2022 8:36 PM) written by Roger Sanders, who has since gained a certain amount of respect as a speaker designer.

     When I had my shoppe in Winter Park, FL (circa 1980): a customer wanted a pair of subs, to accompany his Acoustat Model III system.

     They worked so well, when loaded with the 10" drivers Speakerlab used in their Nestorovic bass system, crossed with a Dahlquist DQ-LP1 and driven by a Halfer DH-500; I built another pair for myself (and: bought a pair of Model IIIs).

     Then, built a few others, which I combined with passive crossovers, JVC ribbon tweeters, Audax dome midranges and very smooth, 10" Peerless woofers. Everything but the 10" woofers and their 5 Ways, were contained in moveable housings (for time-alignment and directivity), which sat atop the TL cabinets.

                           They sold as fast as I could build them.

     I’m still using my original pair, crossed/aligned with a TacT 2.2X, into a Hafler 9505 and: now sporting a pair of SEAS Extreme (not from Taiwan) L26ROYs.

     Their performance (measured and auditory): excellent, with a tube-driven pair of small, Emerald Physics speakers, crossed at 80Hz (10th order).

     Still have the old Nestorovic 10s, in a closet. (sentimental value, or: backup?)

           Whether just for the valuable insights/info, or: to build one’s own pair:

* http://sanderssoundsystems.com/downloads/speaker_builder_dec_1980_an_electrostatic_speaker_system_Part%20III.pdf

           More, from Roger Sanders and Speaker Builder/Audio Amateur, here:

                    http://sanderssoundsystems.com/audio-related-articles

                                                Happy listening!

One of the coolest transmission lines was the 1929 Stromberg Carlson Radio using a hand made coaxial driver (using a leather surround).  

I'll never forget the first time I heard TDL Reference speakers. I was simply blown away. For a kid still years away from a degree I couldn't even dream of laying out the dough. Eventually I did own a couple pair of TDL transmission line. A studio 1A, Studio 0.5. Should have never gotten rid of them. They were not the easiest to drive, mid 80's efficiency i recall. Needed some decent power to really make them sing. But what a sweet sounding and natural speaker they were. Beautiful, across the frequency range, amazing low end from such a small box. I still have a pair of TDL compact monitors (non transmission line design). Still a wonderful monitor using the same drivers as the bigger brothers.

TDL's are rare, and rarely mentioned here in forum, or for sale. If you spy one for sale grab it!

I'm always on the lookout. 

   All PMC speakers use transmission line designs.  Consequently, they seem to produce more and better bass than comparably sized speakers using other designs. 
   I really like my PMC Fb1i Signature speakers.  The only real knock on them I’ve ever heard is complaints about the cost, but apparently it’s not that easy to design and build good transmission line speakers.  I haven’t encountered any small 2-way towers that are better, certainly not in every parameter.  After a certain point, everything in engineering is a trade-off. 

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.