PMC's Toby Ridley on Transmission-Line Loudspeaker Loading - SoundStage! Real Hi-Fi (Ep:37)

Professional Monitor Company (PMC) was established in England in 1991. Originally, PMC made studio monitors, but later he company began making home speakers as well. One of the hallmarks of all PMC speaker designs is the use of a transmission line for bass loading. In this video, SoundStage! founder Doug Schneider talks with PMC speaker-designer Toby Ridley about how a transmission line works, as well as the pros and cons of implementing one in a loudspeaker.
#audiophile #hifi #speaker

[@philvale5724]

Hi 👋, Not sure if you will see this transmission, 😂 . About 40 years ago, I built a pair of transmission line loudspeaker cabinets with a help from a friend who was into electronics., he built the crossover, I supplied him with a special microphone and some equipment, but I make the boxes, they are 1 inch thick, MDF, They are approximately 10 inches across the front, 12 inches deep and stand dust over 5 feet high, it has a line length approximately 14 1/2 foot from what I can remember, I just recently had to replace the driving units it had peerless in before, I’ve now put, SEAS 8” 150w and 3” tweeters , I can’t remember the model numbers of the components, And they fire out the bottom, and it’s approximately 4 inch gap under the cabinet from the floor, I play classical to heavy metal to blues and Nordic Viking war music, play sound, amazing, I even have some friends when they’re near me in the summertime on holiday spent hours listening to various types of music, I got the design out of a hi-fi magazine from the early 70s , I cannot remember the article, but I do have the magazine I haven’t seen it for many years, My equipment is what they call mediocre, I play vinyl on a Linn Sondek LP12 , play CDs on Pioneer, I played cassettes on Nakamichi D2 , and I stream music from my iPad through a Bluetooth device, and my amp is a NAD, very interesting subject transmission line. Phil from the moulin France .

[@SuperMcgenius]

Yes, so many benefits to a transmission line. Mid bass and low base. Have a great quality.

[@matthewrond7386]

Nice! We need more videos like this in hifi. Well done.

[@soundstagenetwork]

Great to hear!

[@dougschneider8243]

I appreciate that feedback. Obviously, I think technical subjects are important as well.

[@onebylandtwoifbysearunifby5475]

There really isn't much available on TL speakers. Boom boxes are too easy with computer software now, so few people look elsewhere. This was a good discussion, informative and useful in a technical way. Group delay was interesting, as one would assume it would be more towards ported than sealed, not in the middle. Kind of like a passive radiator in a way. TL are interesting.

[@dougschneider8243]

Glad you enjoyed it!

[@ReferenceFidelityComponents]

Boom boxes may be easy to roughly calculate but people frequently underestimate how to perfect the designs for limiting excursion, keeping bass linear, and minimising group delay. It is easy to let software spit and answer out but it seldom is the right answer because each driver will have specific requirements for tuning system q and this is always affected by port design, positioning and internal damping. Anyone can design a ported enclosure using software but few can design a really good one. That takes development, understanding and time.

[@juststuff5216]

kzbin.info/www/bejne/Y4aWiYpsibtssKs - it's this simple!

[@billywindsock9597]

I have a pair of those Twenty5.23i tower speakers. Love them.

[@dougschneider8243]

The company definitely has its fans.

[@martinarscott3524]

Seen a few interviews with PMC staff and the one thing that comes across is their enthusiasm, which is great! My 22i's are currently in transit and I can't wait to hear the difference from the Twenty 21's.....

[@gdwlaw5549]

Any good then?

[@martinarscott3524]

@@gdwlaw5549 yes definitely, I love them :)

[@picassoimpaler3243]

TL boxes can sound great when designed well, but they are also incredibly difficult to design well. I believe hornsrep does a pretty good job at simulation. But make sure you measure the driver via DATS or something similar before building, because small variances in the manufactures stated parameters vs the actual speaker parameters can make a massive difference in having a good sounding speaker. By their nature, you often get several peaks and dips in the response in the range of the line contribution. They can be mitigated somewhat by doing things like having the speaker not play at the beginning of the line, but further down, roughly 1/3 the way down the line tends to work well. Stuffing the line in certain spots and tapering the line can also go a long way in making the output of a tline much more linear.

[@soundstagenetwork]

Thanks for the input!

[@juststuff5216]

I've been designing t-lines exclusively since 1990, and I think they're the simplest enclosure to design! When audiophiles chip in their 10 cents worth ... is the only time t-lines seem to get complicated … but they're really not! Headphones on for the demo kzbin.info/www/bejne/Y4aWiYpsibtssKs

[@jonathansturm4163]

In 2000 I purchased a pair of VAF DC-X transmission line speakers and I love the bass extension. They’re down only 3 dB at 29 Hz. When Rolling Stone reviewed them in 1995 they said they were the first speakers they’d heard that didn’t benefit from a sub-woofer. I can confirm that. I just ordered the latest version of the DC-Xs from Phil Vafiadis out of curiosity. My existing pair are worth the same amount of dollars that I paid in 2000 and are only rarely available second-hand. Phil says the company has manufactured more than 10,000 pairs since 1995. VAF are located in Adelaide, South Australia.

[@soundstagenetwork]

Thanks for sharing that!

[@dougschneider8243]

Very interesting!

[@lorindamikaela]

I brought speakers from Adelaide Speakers [Ascension Speakers] they are also TL and have incredible bass. I also own another TL speaker built in the early 1970's called IMF and they have a cult following and for very good reason.

[@asilva781]

As a amateur speaker designer. I can tel you this is very interesting info. Martin J. King made fabolous research about TL bass lines. But yes. I try a couple of TL designs. But is very hard to get good results if you don't measure well. And many other difficulties that are there.

[@soundstagenetwork]

Thanks for the input!

[@dougschneider8243]

Appreciate you sharing.

[@okkinokki9366]

How you doing Doug?Great to see SoundStage still doing it! Dave Duvall

[@JodyM2]

Hexibase did a fun series on this subject years ago called what's in my Trunk where people whould guess the size & number of speakers but it was usually a little 6" driver in a Transmision line.

[@soundstagenetwork]

Very interesting!

[@dougschneider8243]

A name for me to look up!

[@JodyM2]

@@dougschneider8243 kzbin.info?search_query=hexibase+transmission+line

[@juststuff5216]

I assume you mean this video kzbin.info/www/bejne/iJC0hqBvbMSegM0 one of my favourite PWK transmission line builds. I did buy the sub and have a go myself, and I have to say, easily, the Hybrid I6SW is my favourite sub, and it replaced my DD12"!!! He did this home audio version with a 3.5" Fostex drvier. Headphones on for the demo kzbin.info/www/bejne/Y4aWiYpsibtssKs

[@TannhaeuserGate]

Missed on the downsides: the peaks and troughs that are produced by TL designs within the lower frequency range. It would have been interesting to hear how PMC deals with those.

[@soundstagenetwork]

You might be interested in this video then... kzbin.info/www/bejne/j4jZqqGkmM5ra7Msi=TMZQy1-O94mkfIpO

[@andrewmcmillan8110]

Those are easily fixed by adjusting the CSA or by adding filling/stuffing. The only downside to TLs are the size but if you model it correctly you can make the CSA smaller than the speaker SD and eliminate the first peak without stuffing

[@PAC-fp9hy]

Surprised that the engineer did not mention the output from the vent being in phase with the bass driver as the way to soften the roll off at the -3db point. That is surely the point of a TL speaker, to add/sum the output in the bass in order to compensate for roll off.

[@6643bear]

Very interesting and informative re 1/4 resonances and Lines etc . Regards mark

[@georgebartolo8856]

Yes would have to agree their design do sound like sealed speakers. Lean.

[@dougschneider8243]

Does that mean you like them or not?

[@georgebartolo8856]

Well I own the 23 model that was behind you. It’s very matter of fact which can be come fatiguing after awhile. They need subs for sure and don’t play very loud. Let’s say I have a love hate relationship with them.

[@dougschneider8243]

@@georgebartolo8856 Fair enough!

[@speakerman1093]

I have been building and listening to Fried transmission line satellites and subwoofers for 30 years.

[@ReferenceFidelityComponents]

Pmc seem to do it better than most, but I still hear some delay with some models. There is another elephant in the room which becomes all too apparent with smaller classical ensembles and that is TL’s just cannot compete with a well designed large baffle ported or sealed design for bass timbrel accuracy and part of this is down to the very narrow baffle and ironically the low system q. I think the group delay stated for ported designs was over exaggerated. A poor ported design might be 25m/s and that is audible. However, when designing distributed vent Helmholtz tuning (a sort of port using multiple vents) the models don’t seem to predict the tuning accurately so you have to use tools like speaker software for measuring and plotting impedance with frequency, testing excursion bandwidth limits and output. As with a TL, internal damping and position of the openings all affect”q” and group delay. I have got my own vented designs as low as 12m/s but more often an average would be 15 to 18m/s which is barely audible in delay terms. It takes a lot of development and learning to perfect this type of Helmholtz tuning, so the assumption “ports are straight-forward” simply isn’t true. Back to bass timbre. Recreating a cello or double bass to sound like one and not just have cab resonances play along is a fine art. There is no doubt that a well designed, well controlled, wide baffle cab can do this better using a higher overall (narrower)q. This means picking a larger more efficient driver with low fs and low distortion, and making the baffle angled to avoid direct reflected edge refraction affecting direct radiated sound. This approach is out of fashion but boy does it deliver realism in upper bass registers. This is why I prefer to use large high efficiency low fs and low excursion drivers over modern long throw small diameter drivers. The TL approach using a low q system helps in reducing distortion by limiting driver excursion which is a good thing but I still think that purely from a sound quality perspective that the immediacy and efficient air impedance coupling to the room of a big driver convinces more but this also requires the use of high quality drivers.

[@Digibeatle09]

What you state is, pretty much, “above my head” but the “take away” for me, as someone who loves the sound of the cello, is that I would need to think carefully about acquiring a pair of TLs - that said, it’s great that a company like PMC is committed to that type of technology and, from what I read, is earning a lot of plaudits for a number of their models.

[@linandy1]

That was very interesting

[@soundstagenetwork]

Seems many are finding this video useful

[@samuelsalins8309]

Great track 🧿..

[@jepryx]

New subscriber

[@g7vqedave2]

A folded 1/4 wavelength... so why is this a "transmission line" and not a folded horn..? It's a folded horn with a little bit of exponential folded horn thrown in to broaden/fudge the resonant frequency of the horn.

[@RennieAsh]

I thought that horns vent at the big side , and "transmission line" vents at the little side.

[@g7vqedave2]

@@RennieAsh In each case the added free energy is reliant on the air in the Helmholtz resonator being excited to act as an additional but out of phase driver at the horn/transmission line resonance. The horn transforms the air impedance from being fairly compressed behind the driver to a lower pressure but larger area wave at the exit whereas in the transmission line the path is stuffed to reduce the harmonics supported within both types of pipe, the reduced area of the TL could potentially be where chuffing would occur.

[@hugoberdeja9283]

Bla bla bla bla.........., just play it to be tested

[@pedrocols]

Very cute little cheap looking speakers.

[@andrewwalker7214]

Nothing cheap looking about them.

[@willmac5642]

EQ makes TLs fairly pointless. Just use a good quality sealed design with EQ .. most streamers have it built in or will do soon

[@soundstagenetwork]

One of the worst things you can do is boost the bass on any design too much. You can overdrive the woofer I to distortion or even damage.

[@andrewwalker7214]

EQ isn’t better. I haven’t had it for years. My bose has bass and treble but you have to adjust it depending on the volume. Doesn’t sound as good as my Naim pmc combo

[@RennieAsh]

​@@andrewwalker7214modern Bose products actively change EQ based on volume level. You can get this loudness compensation on some DACs and amps.

[@RennieAsh]

​@@soundstagenetworkyou can do that by turning up the volume too, and many people blow up woofers and tweeters

[@Alicatt1]

When I auditioned the speakers for my home cinema, I had picked out a few to try, the hi fi shop also put in a pair of cheaper speakers to compare with. Blind testing and it was down to two sets of speakers, a set of TAD by Pioneer and the unknown set of cheaper speakers, it took quite a while to decide but the unknown speakers eventually prevailed they were PMC OB1i, not cheap but less than half the price of the Pioneers, been using them in my cinema since 2008 and love them, the difference was subtle but the PMC just had that little bit more clarity and extension. My cinema front speakers OB1i left and right, CBi centre speaker and REL Storm2 sub: i.imgur.com/OHnqT6V.jpg