Not out of fashion in terms of users but maybe production.
I nearly went PMC but the infinite baffle of ATC edged it for me.
You’ve got a good memory 
Best Peter
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At the end of a long period of auditioning new speakers for my system (552 / 300 / CDX2 / Acutus) I finally went for PMC FACT8. Signature over Kudos 606, YG Acoustic Tor (new Peaks series standmounter) and the truly wonderful FinkTeam Kim.
I chose the FACT 8 because they are incredibly fast, and that transmission line delivers bass that challenges the perceived laws of physics beyond anything I have ever experienced. Try a favourite piece with plenty of low end and they deliver stupid levels but with stop-on-a-penny agility and with superb ‘tightness’. And all from two tiny midrange drivers firing through their transmission line. As others have said, I can well imagine that it must be a Herculean engineering challenge to get terrific musicality combined with such bass and in such a small enclosure…. Strongly recommended
!!
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Pmc fact 12’s are certainly a good speaker to see how transmission line works and it took the titan 808’s to show up there short comings
I had read that the smaller pmc’s are not a true transmission line as they are too small. They are more of a folded quarter wave pipe, but I guess the bigger ones have enough line length to absorb the rear bass frequencies.
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I have used PMC’s for 20 years now, had the FB1 + for nearly 16 years, I believe this was their first proper domestic speaker, definitely a transmission line. I now have the Twenty 26 which for me exceeds my previous speaker with its excellent PMC Midrange drive. If we go back in time, my very first floorstander was a TDL RTL 2, again a transmission line speak, these were great on bass and very exciting budget speaker but lacked detail and finesse!
Fashion? Yes they’re out of fashion, and always have been.
(Today’s hifi fashion appears to be small speakers and all-in-ones with a Turntable attached…)
As already mentioned by someone, TL speakers are difficult to design - even with greater in understanding of the physics and development of design software a lot of trial and error is involved in design, and then they are complex to make, and as a consequence of both factors they tend to be expensive, and therefore not popular (even less so with the “source first” philosophy when equated to speaker cost). But they do bass like no other design, and for many people once hooked nothing else will do - certainly that was the case with me, hooked since my first pair acquired in 1975 or 76.
However I think there is a greater range of TL speakers to choose from today than ever before: Back in1960s/70s there was IMF, who at any one time only had 3, briefly 4 TL models in their range, Radford, withI think one, and Cambridge, with I think one design, and perhaps another I’ve forgotten. Over the decades that was probably a fairly typical average. Today PMC have, I think, a dozen domestic ones in their range, not including their in-and on-wall models (they also have studio models), Castle have about 8 models in their current line-up, and Kerr have maybe 4. Then there’s the B&W Nautilus, which is a form of transmission line. A company called IPL used to do one or two kit form TL designs, but they wound up a few years ago, however Wilmslow Audio do two of three today in kit form.
Whils many TL designs are large, nowadays some are available that are not - though I’m unclear about how well they work (I haven’t heard. PMC, Castle and Kerr all do some small models - but of course bass will be limited, perhaps making the benefit of TL less obvious. When I bought my first IMFs, the TLS50ii, it was bottom of their TL range, and although still a large speaker they said it was the smallest they could get the TL loading to work properly, their smaller models not TL.
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Hi Dunc, any chance of posting a photo of your set up please? ATB Peter
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Hi peter its the same really as it was with the fact 12’s apart from the rossini has gone.
The facts would resonate my cabinet at a certain volume and bass, now i get better bass and no resonate, so the facts must have been doing something the 808’s aren’t
Resonance is a matter of hitting a resonant frequency. Ergo they hit one the Titans don’t or at least with more energy.
Always correct to find the right speaker for your room and it appears you have.
Thanks for all the replies. I had not known that PMC speakers used a transmission line.
I am interested in the topic because I am considering the purchase of a stand-mount speaker made by Falcon Acoustics that is based on the BBC LS3/5A but incorporates a transmission line. I can find very little information about it online. (It’s a ‘DIY-kit’ speaker so I would probably have to purchase it unheard).
I assume you mean the IMF 100 kit? Looks like an interesting speaker! IMF were a manufacturer of TL designs as @Innocent_Bystander says above, intrigued what relationship falcon acoustics have to them, as I assume the name isn’t a coincidence. And the design looks superficially similar to the IMF compact monitor 2??
Anyway, the FA site has links to some positive reviews, and like any DIY speaker, at least part of the fun is the unknown factor 
But if TL then only superficial as the Super Compact wasn’t a transmission line design.
But Falcon are good, and if they’ve designed it I would be surprised if it is rubbish, though how good is another matter.
Aye, I noticed after doing a bit of reading up on the compact 2. I haven’t heard of a resistive reflex design before.
The IMF 100 does looks like a good value kit as the TL cabinet comes pre made, be interesting if you go ahead with it @Bonang - how’s the decision making going??
Back in the 70’s, when I was first interested in HiFi - and before the Linn/Naim thing was a ‘thing’ - I recall the IMF TLS80’s being touted at the speakers to aspire to.
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I bought the bottom of the TL range, the TLS50ii, above that was the TLS 80 and then the RSPM (at that point in time I think the IV). Some 15 years later I came across someone selling a pair of RSPMs at a very good price - though an older model, no other number so might have been Mk 1. I snapped them up and they did me the next 25 years, till I changed them for PMC EB1i, and then PMC MB2.
I recall a Hifi magazine review back in early 1970s when they set a pair of IMFs - I don’t know if RSPM or TLS80 on a stage, High Wycombe Town Hall for some reason comes to mind but I could be wrong, and they compared a live performance with a recording through those speakers. The reviewer was impressed. (I’d love to see that article again!)
Then there is this: What's the best-sounding system you've ever heard? - #25 by Innocent_Bystander
I once had a pair of IMF reference standard speakers that sounded and felt amazing. Unfortunately I had to let them go as I was travelling overseas for a number of years. I eventually settled down and brought a pair of TDLs Studio 3 speakers that I still have, they are over 30 years old and still going strong. They are made by the late John Wright who was also part owner of IMF Electronics. If you want to feel the bass go thru you get a good pair of transmission lines and play some Bob.
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The “IMF 100” kit is indeed the speaker I am thinking about.
I am glad to hear that transmission-line speakers are still considered a viable option.
I have not come to any decision yet, and I probably won’t do anything this side of Christmas.
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The kit looks like fun and well made.
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