Hi-Fi History: The IMF Reference Standard Professional Monitor | The Transmission Line Speaker
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- เผยแพร่เมื่อ 7 ก.พ. 2023
- In this episode of Hi-Fi History, Tom Martin talks about the IMF Reference Standard Professional Monitor, its history, and why transmission line speakers, if they're so effective, are no longer in vogue.
The seminal 1965 work that I mention and which appears to have triggered John Wright and IMF to pursue transmission line speakers was written by Arthur R. Bailey in Wireless World magazine:
diyaudioprojects.com/Technical...
Bailey for this paper, and subsequently in 1972, did some nice reasoning and empirical measurements to help guide the design of TL speakers. Very importantly, he realized that the wool fiber in the line could slow the rear wave and hence allow shorter lines - a significant element in practical designs.
When I mention in the video that the mathematics of TL designs was not fully characterized, I have this in mind:
en.wikipedia.org/wiki/Thiele/...
Many people contributed to the “full” models of ported and closed-box speakers, but the work culminated in a series of papers in the early 1970s by Richard H. Small extending the work of A.N. Thiele. These parameters have henceforth been called the Thiel-Small parameters.
My main point, as you may intuit, is that it is one thing to have some mathematics applied to a speaker concept and quite another to have a full parameterization of a design concept. Bradbury, for example, attempted the former in the late 1970’s for transmission line loading and he described the results as “unsatisfactory”.
As far as I can tell, a Thiel-Small type characterization of the transmission line speaker was not published until the 1999 work of George L. Augsperger of JBL. Around this time, others were involved in this “project” including Locanthi, Dickason, and King. A very nice summary is here:
transmissionlinespeakers.com/...
This kind of mathematical work is challenging, and I intuit that the IMF and related products were so good that they spurred slow but continued work in this area.
About Tom Martin:
Tom is a long-time audiophile. He began his reviewing career after acquiring the The Absolute Sound magazine in 1997 and then hi-fi+ magazine in 2002. He has worked closely with Harry Pearson and Robert Harley at TAS and with Roy Gregory and Alan Sircom at hi-fi+. Since Tom and his teams expanded the TAS and Plus platforms in the digital domain, he has served as Chief Content Officer.
For more product information visit:
www.theabsolutesound.com/arti...
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I had a pair of IMF ALS40 speakers in the 90's. I was given them by a widow when I did some work for her. They were amazing. The bass was just biblical but in a controlled deep way. It was like waves coming over you. When I left home I left them at my mums for future renovation. Mu brother in law gave them away. I've never forgiven him.
Wow, how generous of him. 😮
I had been obsessed with good quality sound from a very young age to the extent that I would wonder why the Scottish horn would be heard so far away and at the same time we had our own "ABUU" a local African musical instrument made up of a biiig guard with a hole at one end and a tube at the the other used to blow into this very big guard.I would wonder how deep and how far the sound would go.Another experience was with our prayerful grandmother who would wake up in the wee hours of the morning with a horn and seemingly singing in low voice would be heard miles away.I therefore later in life tried bringing these together and the result was wonderful.
@@midastouchinteriors8058 omg….I’m still waiting to hear your choice of speakers amp n set up or are you Hamish?
Their black and white exploded/cutaway ads are a thing of legend!
Mid-century black and white cutaways revolutionized an era. Those big detailed drawings ... you could look at them forever.
Very nice review! I have a pair of RSPM Mk IV Improved with the Elac Woofer, kef mid and celestion s tweeter and supertweeter that my late father bought in 1981.
I decided to put some TLC on these beauties so, I changed the old plastic RCA terminals with the most expensive WBT terminals, recap the crossovers, replaced all inside cables from WBT to crossover and from the crossover to each drive with Transparent Audio drives cables and serviced the tweeter and supertweeter to top factory performance without ofcourse changing diaphragms, just cleaning the old ferro fluid and more.. I couldn't believe my ears..!
Everybody that listens to them now cannot believe the sound that they produce... Friends that they have spent tens of thousands for their speakers are amazed and very ...unhappy with their purchase...
All I want to say is that they had a vision and created speakers that after 50 years are still standing with pride!
Terry,
Athens,
Greece
Are you sure its a Kef mid and not a 5/36 ?
In the Netherlands there was a man called Hans Baan, who made transmissionline speakers based on the IMF tls 50 and 80. The brand was called HB and the models were named HB1 and HB10. I owned a pair of HB1's. They were produced from around 1977 to 1980. Great speakers and I regret selling my HB1's in 1988.
I had a pair of TDL's and not only was the bass jaw dropping but so was the imaging which was stunning!!!
I own a pair of Fried Studio IV speakers and love them. Had the original tweeters reproduced by Oskar Wronding with ferro fluid and foam rings just like the originals. Crossovers were rejuvenated at Quest For Sound in Bensalem PA . Wiring was replaced with Silverline Audio cabling. Very powerful pair for sure.
Had a pair of IMFs in the first "aspirational" stereo system I owned in the late 1970s. Put on "The Jungle Line" from Hissing of Summer Lawns, there is a four beats of low base part that repeats, it was one of the things that system did that showed what it could do, though I much more enjoyed listening to "Harry's House"; those speakers sang. Funny thing about those speakers, they were also beautiful listening to Voodoo Chile, or anything from Electric Ladyland, for that matter. Or "Please Be With Me" from Duane Allman an Anthology. The most beautiful sound I could find back then. Crown DC300A amp (200W/ch), Radford ZD22 Preamp was pristine clean. Shure V15 Type 3 cartridge. Great times! :)
In 1974, a company by the name of Audiionics, located in Portland, Oregon, sold transmission line speakers with British (Goodmans woofers and midrange and Peerless tweeter) components. You could buy the drivers for their TL-90 as a kit as well as complete speakers. (They also sold the TL50 and the TL30 only as completed speakers, I recall.) I built cabinets based on the factory design, which was much simpler than the design shown in this video. The transmission line was formed by a diagonally placed divider in the cabinet, which was about 52" tall. The port was on the back near the top. The stuffing provided was dacron fiber (pillow stuffing) to be placed in a graduated density. It was a pain to try to get the stuffing placed properly but the bass response was quite good considering I had a tube amplifier. I got rid of the cabinets years ago , but saved the drivers and cross overs. I could make another set of cabinets.
l had the TLS mark 1’s for 34 years. All types of amps used. Even 2 Armstrong 6 watt valve amps. Interesting moving house a few times and hearing in different acoustics i.e. concrete or wooden flooring. l realised as l grew older l needed better treble from them. The race-track ABR’s rubber started to deteriorate but the bass still sounded great. l had earlier a pair of B&O 5702’s which had these ABR’s. But the IMF’s produce some wonderful moments.
I love that Lincoln Mayorga record and I play it through my electrostatic speakers quite frequently. I have a lot of Sheffield Lab records.
My parents bought IMF super compacts in about 1980 always loved them. I eventually found a pair of TLS80 mk1 a number of years ago.they had played classical music all their life.I like a lot of electronic music bass heavy,which these do amazingly well!
Doing a refurbish,sanding them down today.
I’ve changed the capacitors on the crossovers,bought all replacement drivers,new diaphragms for the coles tweeters.Can’t wait!
They have foam and soft wool fiber for the mid tubes.
Nice video thanks.
@@TAS - I miss those days - I met Bud Fried's son while I worked as a teenager in an Upper End HiFi store near San Jose called Avant Garde. The owners Ernie and Alan were not just bosses, they were friends that allowed me to experience the truly magical days of audio. Yeah, maybe there is some magic left in the HiFi industry, but at the price of a house for a set of cables. Thanks, though for keeping this part of the HiFi history alive.
A nice walk down memory lane. I still have my well worn Missing Linc album.
Arthur Radford should be getting the credit for the transmission line as he worked with Bailey but was more the tech genius behind the TL design. He was also the first to bring the TL design into a commercial product. Radford had said many times he was disappointed people didn't recognize his contribution to the loudspeaker art (especially the TL design) as much as his amps and electronics. He said he was more proud of his speaker designs than his amplifiers.
Radford did do transmission lines and originally Bud Fried was going to import them But every time Bud was told the speakers were ready Radford pulled back. This went on for years which is why Bud turned to John Wright and what became IMF speakers.
Totally agree. Fried was the distributor for Radford and they made a reference monitor identical to the later IMF.
Allegedly Fried asked John Wright to make a speaker similar to the Radfords and improved the design over the next 10 years.
A footnote: After Fried broke up with the English group, he continued to sell the drivers and crossover for a transmission line. The line was in its own cabinet (the first subwoofer?) with a separate line for each channel. It was relatively easy to build (using Fried's plans) because the line had only one turn. The mids and tweeters were in small "bookshelf" cabinets. The crossover was an enormous and very heavy steel box. Fried recommended placing the sub in the mid of the space for speakers with the smaller boxes on stands on either side or hung from the wall. I had this setup for several years. My only complaint was that it produced too much bass.
The H2 subwoofer, dual 10" transmission lines in one 8 foot wide enclosure.
I had what I believe were the same speakers. The Fried Super Monitor. Bought the kit and had a furniture maker build the cabinets. I subsequently added Decca ribbon tweeters and to this day I miss them. The bass was fast, tight, articulate yet too much for the smaller room I had.
I just watched your video while listening on my pair of IMF TLS50 Mkii's. I love these speakers! Not as much as my 80 Mkii's that are scheduled to be redone... when I get the time. I was really happy to come across someone talking about IMF, in depth. Thank you for this video! New subscriber.
How come I only just discovered this channel?! Great video. Subscribed!
I heard TDL speakers in their room at the Hifi show at heathrow in the mid 80s. I was especially taken with the bass coming out of their speakers. They were playing monty alexander live in montreux and it was amazing. I had always wondered what happened to them.
Did you know that Marantz sponsored that record? As a Marantz rep I had a box of them to give to my retailers for demo. It is a gate fold with a gold label seal with Marantz name on it and a letter inside from Marantz to their dealers. I still have my copy.
Fascinating story and beautifully explained.Well done, sir.I wondered why the technology never gained traction, now I know.
@5:00 It was powerful, it was deep, it was detailed, it sounded REAL - awesome description of a good transmission line speaker
It's still very very good today - I have a refreshed (crossover and NOS drivers) pair of RSPM Mk IV and they are phenomenal!
TDL studio 3. Best thing I've ever heard. In the day :)
I have a pair of Studio 3 and Monitors. They must sound good as I still have them. The integration of the lower bass right through into the midrange is what makes them sound realistic, - much better than a reflex design plus subwoofer combination.
Great video. I often think IMF speakers are not talked about enough in the realm of vintage greats, because to me, and in my experience, they are up there with the best. John Wright really was a genius to be able to make such an excellent, marketable product when the idea was in its infancy. I understand well what you say when you talk about how great they sound - I have owned several pairs of IMFs myself, all the way from the Super Compacts up to the RSPM Mk IV. Currently I own a pair of the original Reference Standard Professional Monitor, when the company was called "Transmission Electronics Ltd", and a pair of TDL Super Compacts. The other thing impressive about IMFs is not just the bass, but also how they managed to get the voicing similar amongst all their models. If you buy Super Compacts, you are getting the same character of sound of the RSPM.
Thanks for this nice recap and for bringing to light IMFs to more people. I thoroughly enjoyed it.
My uncle built "labyrinth" speakers back in the late 70's when I was a kid. I still remember his impressive reel to reel deck, probably where I got the audio system bug.
What was the name of the speakers he built or were they diy?
I believe the recommended stuffing for DIY projects for this was the long fiber wool.
It was also referred to as the Folded transmission line.
There was also a design described as a straight transmission line enclosure (no folds) and could be as long as 7 ft. It was impractical commercially
Yes correct, the long fiber wool ave not been beat yet!
I believe these designs were 1/8 wavelength calculated by the bass drivers resonant frequency. The Kef B200 used in the TLS50 had a higher resonance than the B139 used in the larger models therefore the length of the wave was longer and needed the increased cabinet size to suit the labyrinth. Great designs, imagine what they could do now with custom built drivers.
They are actually referred to as 1/4 wave length design.
Thank you for the discussion. Difficult area to be sure. Best wishes from NZ.
At the beginning of the 1980s I replicated the IMF RSPM. The speaker systems were easy to obtain as they were available on the DIY market. They were the legendary KEF B139, B110 and Celestion HF1300 and HF2000. There were DIY suggestions for the crossover, one of which I chose based on gut feeling, as I didn't have any measuring equipment. The speakers had an incredibly deep and totally airy bass, but they also needed a lot of amplifier power, which unfortunately wasn't available to us at the time. It came as it had to come. When the speakers were misused as party speakers, the underpowered amplifier died and took one of the B139s to its death. The B139 was replaced, the amplifier was replaced by a more powerful one and the speakers played for many more years without any problems. Later, IMF replaced the bass speakers with more powerful ones. I listened to the RSPM on Accuphase 600 W mono amplifiers and it was an overwhelming experience.
amazing video!! I learnt a lot! 🙌
Great video. Demoing the speakers with a great sounding record isn't cheating, it's just doing a demo the correct way. The Mayorga album has it's flaws, but in the early 70s I can see how a beginner audiophile would be blown away. I used to flip gear back in the 90s, and people would bring over the same reverb soaked "female vocals" that we're still hearing at high end shows. I guess I "cheated" a lot since I always chose late 50s jazz or well recorded 70s rock to sell gear. Believe me, it's easy to sell gear when you play decent music, and it's sad that the people who spend the most on high end gear listen to garbage music that's drenched in digitally synthesized reverb.
All the gear and no idea springs to mind 😊
A very interesting video, I am in the UK and I own a pair of LNB Paralab 20, these seem to be loosely based on a spendor BC1 but with a transmission line, they were built in Loughborough England in 1974 and I can tell you they sound sublime, I use them everyday and I love their sound from top to bottom. The story goes that the designer was tone deaf so he had them voiced by a local musician through trial and error, I will never part with them because they are the only speaker I’ve ever owned that stopped me looking for anything else and I’ve owned speakers in the past such as Thiel 3.6, 2.3 and 1.2, there’s just something about these that just sound right! Thanks for the IMF history, I found it very informative!
Had a pair of TLS 50’s in the 70’s great speaker . Heard a pair a few years ago, they still sounded great. The crossover networks were some of the best at the time .
I purchased a pair of IMF Studio speakers from Lyric Hi-Fi in Manhattan, in 1971. I was and remain an avid fan of TL woofers. Shortly thereafter, I built a pair of speakers to mimic the IMF Monitor, which was my heart's desire but which I could not afford. The dimensions of my speaker were nearly exactly the same as those of the Monitor. (All the details are supplied in an article published in the 50s or 60s in a journal called "Wireless World". Author is Bailey. I do also recognize that Arthur Radford was an early developer. As in the Monitor, I used KEF B139 woofers and the same KEF midrange driver as used in the Monitor (B10, I think). For tweeters, I used four RTR ESL panels per side, the same panels used by Infinity in the Servo-Statik One. The results were great and crushed all local competition. However, I later became an ESL fan, and I sold my home made Monitors in favor of KLH Model 9 ESLs; I used two pair, full range. Twenty years (and several more ESLs) or more later, I re-acquired my home built KEF-based speakers, and I cut away the part of the cabinet that housed the midrange and tweeters. I now use the TL bass cabinets to supply bass below 80Hz for my Beveridge 2SW speakers (another vintage stroke of genius). The lower you place the low pass filter, the less stuffing you need in the TL cabinet. The Brits originally used "long hair wool" and the current recommendation is a synthetic fiber called "polyfil". Easy to find. There are on line guidelines for how much fiber you need (in terms of weight) and where it needs to go (in terms of where in the transmission line), depending upon the desired bandwidth. Since I am rolling off at 80Hz with a steep slope, very little filler is needed. The TL woofer blends wonderfully with the Beveridge speakers, and incidentally the KEF B139 is one of the great woofers of all time in terms of its capacity to deliver detail in the bass frequencies.
I heard these in a tiny HiFi store in Sheffield, UK @ 1973/1974. I couldn't afford them, but they must have sounded nice for the memory to have lingered.
Bud Fried was indeed a genius. I worked for him from about 1976-80. His C/2-3 satellites were outstanding as were his M/2
and C/2-3 satellite super monitor models.
But I heard he would freak out if someone pronounced his name wrong.
I heard them in the 70's and I was blown away! The model had two small 2 way satellites and a central transmission line box which was rather large, housing two oval woofers. I seem to recall it was called the Model M(?). I couldn't afford them and seem to remember they were about $3000. They offered for sale a plan for the speaker for home builders ... as a student I couldn't afford the plans either. I remember it had a most impressive large crossover in a separate box with huge air core coils ... it was explained to me that this crossover was a major part of the secret sauce. I remember how impressed I was at the time!
Really enjoyed the history of IMF speaker.. in 1977 at Custom Sound in Montreal was the first time I heard them, they were connected to an SAE amp and preamp with a Linn Sondek turntable .. the sound was overwhelming.. a moment of sound in high fidelity that is not often repeated. Shame the company didn’t hold together like other long standing manufacturers who are still around today.
Wow, the explanation here describing the working principle of transmission lines has the power to even make you forget what you know about the transmission lines.
I have had my PMC FB1 speakers for 21 years now. As you said that Bass depth & control from an ATL just blows your mind. It’s difficult for me to find alternatives that aren’t PMC and more particularly ATL without resorting to Subwoofers. Thanks for sharing your experience with IMF as I didn’t know about them before watching your insightful video. Thank you.
Same for me….PMC is unreal and nothing better so far.
I have several Fried T-lines as well as one pair of TDL RTL2's, the imaging is fantastic as is the natural, extended bass!
That's funny that you choose Focal as an example of picking off the shelf driver, because Focal made a woofer that was marketed and recommended as appropriate for transmission lines. It was an 8" clear polypropylene woofer with a stamped basket and large motor from probably the early to mid 1980's. I built a very large TL based on an article in Speaker Builder magazine. I think the woofers model number was 8P501.
I bult a pair WEBB t-lines back in the mid 70s. They were similar. Amazing performance. Wish I still had them.
Imf was just down from the road from me and they later became TDL. I had a small audio company and an enginneer from IMF/TDL worked with me and we corrected the transmission line limitations as its a single air movement design. We also created the forrest filter that projected frequency beyound the normal internal soundstage. We were at the london international show for several years showing whats possible. We used 80 thousand components in the filter that was housed in its own case.
Clive anther engineer went on from IMF and firmed Wizard, you can see his design in PMF but they never improved on the design.
The high units you mention are Elac. All drivers were mstched and the idea was to use the correct air movement and volume in an internal dead space. They only used basic isolation and not a combination of different density material.
Its not just air movement you also have to work out volume with foam and its air absorption. Angles must be correct too.
Had a pair of 80's for 30 years, very goog until cabinet developed a rattle. Here we are a few years later and have just bought a pair of tdl speakers which l am very pleased with. Consider myself very fortunate to have had speakers of this quality. Good transmission line speakers are a thing of beauty.
This was really interesting 😊
At one time I felt the TL was the grail. That was until I heard Isobaric designs with their very tight and extended bass and low distortion. Enclosures were ridiculously small, and the bass that came out of them seemed to defy physics.
Dang it now I gotta find some iso to listen to! 😇
@@robjones8733 I built two ISO subs years ago with 10” woofers. The cabinets were really small, but the bass was tight and very deep.
@@ChicagoRob2 dang I'd like to try building something....I'm usually trying to keep cars going though--congrats on your sub build!
@@robjones8733 I’ve heard transmission line bass and the isobarics I built were tighter.
Good speech about the legendary speakers. I have had TLS 80 mkII, RSPM mk.IV and now RSPM mk.VII. You can read a lot about the speakers but i had at some time both mk. IV and mk. VII and had a chance to test them against each other and i must agree with you about the mid range on mk.IV.
The mk.VII is a completely different speaker sound wise, in my ears better. Bass is tighter, mid is in to my ears really natural and the ferro tweeters also very natural and not harsh as the HF1300/2000 combo in mk.IV.
It is a matter of taste, and a lot of people have never heard mk.VII, thats why they always talk about mk. IV as the «holy grail imf».
I built am IMF copy back around 1972 with 3 KEF drivers dampened with the recommended horse hair and many years later bought a pair of Castle Winchesters a 2 way transmission line speaker. The mid-woofer unfortunately didn’t blend well with its tweeter but needed no subwoofer. It’s still pumping out some awesome bass to this day.
IMF didn't use long hair wool. The early designs used fiber glass hung so the edges faced the back of the driver to minimize reflections. Later IMF Monitors from the Monitor 3 used egg crate shaped foam.
I have a pair of PMC TB1 and jean Marie Reynaud Cantibile . Pure magic
I bought a pair of IMF TLS80 in 1976, along with a Harman Kardon Citation 11 preamp and a Harman Kardon Citation 12 amplifier. I was 18 at the time and had worked two summers to buy that equipment, after hearing it in a store. I gave all of it to my daughter and son in law last year (2022). The bass was still good but not as quick as it once was. My son in law rebuilt the crossover and the whole system sounds fantastic. Some of their friends are into hifi and have paid upwards of $20k dollars for a system that they say does not sound as good.
That is an amazing combo
I too had the Harmon Kardon Citation 11/12 combo-- superb. I too was a teen who worked for 2 years in a factory in 1974 to buy that stereo with JBL Century 100's.
Pretty sure they had a pair at Goldsmiths College London where I went to University. Sounded pretty good as I recall, I remember being intrigued by the design.
I heard some imf's decades ago early 70's loved them could'nt afford them so I made some using kef b200 kef b110 and t27 tweeters still sound amazing today
Not to take anything away from Fried's interest, effort, and diligence in getting the transmission line to market; but if we're going to talk about IMF. TDL, PMC, etc. it should be noted that the small American company DCM produced some fantastic TL speakers with a *value* quotient that couldn't be matched in that era. I still have a pair of Time Windows in my game room that sound sublime through refurbished SAE electronics!
I'm grinning right now. Because a tiny polish manufacturer called Closer Acoustics sells lovely transmission line speakers (with smiley faces!) for under 2k€. I have been using them daily for 2 years. They're brilliant! And NOBODY cares! Because the dogma today is "single driver = BAD!".
I will briefly discuss the Time Windows when I cover the Vandersteen 2a
@@user-xg6zz8qs3q under 2k? Did you buy them new?
@@Phloored yeah just look them up
@@user-xg6zz8qs3q oh now i see, you have the ogy model. So cool. I would love to have those! I am a firm believer in transmission line speakers. Congratulations on those, they are beautiful. I was looking at the floor standers. They are way out of what i need for a small listening room. I am going to contact them because unlike conventional thinking, i think single driver speakers =good, very good 👍
Sanders’ Sound bass unit is an active, transmission line.
I think there is a White Paper on Roger’s site re this topic.
My old man uses a pair of Lentek Transmission Line Speakers the 70s. They’re seen better days now and could do with a tidy up, but they’ve always sounded outstanding.
I have a pair of Fried Model R Signature Series transmission line speakers built in England 1974. I love them.
The Model R is not a transmission line in the bass, It is a line tunnel, stuffed port. The mid range however is in tube reaching the back of the box and is a short transmission line.
We’re the Definitive Technology BP10 speakers transmission speakers. Those were designed by Sandy Gross.
My Meadowlark Blue Herons are transmission line speakers, they are a gem the only issue with them is the issue with the unique HD3P Audax tweeter.
Easily the best speaker that I have ever heard. Sadly way beyond my budget.
It's interesting why Bud Fried got into transmission lines. He was in England and with Arthur Haddy of Decca records. Arthus told him he had to change his beloved Quad electrostatics because Decca could now put 30 dB of dynamic range on a record and the Quads couldn't handle that. Bud asked him waht to do and Haddy suggested transmission lines and I believe sent him to Radford who was working on lines, Unfortunately Radford took many years to finally produce transmission lines which led to the hookup with John Wright who Bud knew from some of his importing products from England.
WHO wrote the 'seminal' paper?
What was that record shop named?
THE ABSOLUTE SOUND .... Details matter!
Lol, my first “audiophile” speakers were a pair of Advents, around 78’ish. They were bookshelf sized so they weren’t of this design. I was 17 and starting recording engineering school (SoundMaster.)
I first saw the IMF RSPMs in the 1970s but I was very young and never listened to them. I did however listen to the TDL Electronics Reference Standard M monitors much later (1990 maybe?) which were fantastic but too big and expensive for me. Eventually I bought a pair of John Wright's small TDL Studio 0.75Ms which I've owned over twenty years. They are still amazing for their size.
I love my DCM Time Window transition line speakers.
I built a pair of Bailey transmission line speakers from a Wireless World article in May 1972, using KEF Kit 3 drivers and crossover. They used a simple internal baffle giving triangular cross section to the line. I loved the uncoloured sound and deep bass. They had some issues with a dip at 100Hz and poor imaging, but for the time we're great. I added a concrete lining to the large back panel to stop it resonating!
The 1st IMF monitors according to what Bud Fried told me were a KEF Concerto kit(KEF kit 3) put into a transmission line by John Wright. Bud had announced a transmission line for a show produced by Radford and as happened many times before Radford failed to produce. Bud went to John Wright for suggestions and the KEF kit 3 in a transmission line box was the solution. A name was needed since the original show proposal was a Radford speaker so since Bud used IMF a name he had trade marked. With later mods these became the original IMF Monitor speakers.
Cool info ...have some TL 2000 aka r50s @@nobelstone9714
IMF never used wool for their lines. Baily in his seminal articles suggested wool and many other line designers did use wool. IMF used fiberglass sheets hung so the edges faced the woofers for minimal reflection in the 1st and 2nd generation versions. Then they switched to foam probably because it was simpler and more consistent to deal with.
The fourth IMF partner was named David Brown(not the DB od Aston Martin). The breakup of the English and Bud Fried probably came from personality and business differences. Bud knew it was coming and designed the first version of the model R, a modified KEF Concerto in a line tunnel( aperiodic stuffed port which he never claimed was a transmission line, but a second best alternative) so he'd have something to sell in case there was a breakup. The English claimed Bud was making cheap speakers hurting the IMF name. In reality the 1st IMF speaker was just a KEF Concerto in a transmission line box, about the same quality. The split went to court and Bud retained the IMF trademark but the English got the right to call their speaker company IMF Electronics only as long as they stayed in business.
The mid range of the IMF speakers was a tube from front to back of the speaker, a short line, with careful damping. It worked OK. Lter Bud produced a Model G with a line tunnel bass and short line mid range. In the third version the mid range became a longer, double folded line that improved the mids considerably. Bud demoed the difference to me with a prototype.
I bought two years ago a pair of new PearlAcoustics Sibelius SG speakers: single driver 1/4 wavelength TL speakers. I very much like them for their focused sound and great sound stage, and no lack of bass. Had B&W CM6SII before. The clarity and lack of midrange bloat of the Sibelius is wonderful. Tried adding a sub, but while a REL T9i adds bass, it also loses focus, so I took the sub out again. Not a fan of big bass anyway. And for a bespoke speaker, they are very affordable (I think $3.5K for a pair).
Wonderful cautionary tale…
Best speakers ever made in my opinion.
Went on the hunt for IMF TL but happened find and get some TL 200 aka R50 ..about 100lbs each , good take on TLs
Doug Sax has mastered for me. He was amazingly nice human and a historically great mastering engineer, a giant in the field.
I have owned a pair of IMF TLS 50 speakers for over 40 years, even today very few modern speakers come close in sound, would i sell them no not a chance, they just dont build quality like this any more , just outstanding quality
Mr. Martin, let me please share with you the system at all I listened together with the IML at this time in 1979 (I don't remember numbers man 😉) , but remember my first serious pod together at this event 🤣Besides, how much crazy you was at this time? Well, Mc Intosh amplification , Vacuum Thorens turntable with wood tonearm and Grado woodshell.... Hell, it was the heaven! Passion at the first look, listen!
I have a pair of TDLs bought in the late 90's. They are in regular use. I agree with others that they cant handle power. Ive blown a few drivers and with the demise of TDL I'm being much more careful.
But the bass is strong and fairly natural. Good imaging. Compared to modern designs that pay careful attention to phase alignment id say that the bass punch is not quite there. But im comparing to PA rigs from D&B, Martin Audio etc costing substantially more.
I own a pair of B&W DM2
Few people know about these speakers and they come up in the UK at quite reasonable prices due to the fact that they are rather large in size.
I had a pair of Infinity WTLC…. They also were great…
Does TL line speakers not require greater cost and engineering? I assume that's a major reason they dropped out of favor but for a few companies such as PMC. I have never had the chance to compare a TL line to more typical modern designs myself.
I still listen to a pair of TLS80 MKII
Fantastic speaker
It's not JUST a transmission line, but a mass-loaded transmission line to help dampen resonances within the cabinet. Neat idea, but the arrangement of the drivers seems a bit odd. Reminds me of some of the early cabinet designs from Bose, where they were initially using transmission line and carefully tuned ported enclosures with unusual speaker arrangements to achieve their desired sound characteristics before they entirely gave up on that and went full tuning network ham on everything instead. I would love to have an opportunity to listen to some of these vintage speaker designs and see if we've really made as much progress as we think we have.
Absolute Sound never actually reviewed the IMF RSPM. Harry Pearson did review it's smaller brother the TLS 80 II that sported the same drivers in a somewhat smaller but still large enclosure.
Harry did review the Monitor 2 full size speaker in issue 3 I believe.
I have two pairs of DCM TimeFrame TF-700 speakers that are "transmission line" speakers. I only recently learned what that meant. Cool tech, and they have always sounded good.
I believe they weren't true transmission lines but stuffed ports sort of like the Dynaco A25 bass loading or what IMF called a line tunnel.
Running TF 600's here. DCM called the design a hybrid staggered transmission line. I'd like to find an orphaned one and have a look inside. Mine sound pretty good.
@@robjones8733 I suspect they were' transmission lines' like the Infinity 2000, really just a ported speaker with the port stuffed with lots of damping, a variant on the Dynaco A25 loading.
The effective length of the "folded line" is calculated as 1/4 the length of the frequency at which the woofer resonates in free air.
The reason being is to save space, since the ideal would be the full length of the wavelength at the woofer's free-air resonance. We are talking 32 feet wavelength, or more.
My friend built one full-wave length line, we called it "The Whale"!
I remember the small IMF speaker. Unique signature of them was the use of the KEF B139 speaker. Looking online, the speaker has been revived by Falcon in the UK. So popular to be revived so many years later , since KEF had quit manufacturing. Worthy of a history for this woofer model.
I think it is possible the B139 was part of why the IMFs worked. One element may be the happenstance matching of driver parameters with TL needs. The other is that the B139 had excellent response into the midrange.
@@thomasmartin2219 That’s right it was the KEF B139. The flat cone I believe was styrofoam but laminated with black paper (my guess) and it was very rigid and light. The was very compliant. I think it was the same driver they used in the KEF105B
@@flormanjr The KEF B139 was termed ‘Bextrene’ in the original description, a combination of the materials polystyrene ( the rigid core) and butyl rubber which was the thin skin covering the polystyrene. I think the Falcon Acoustics ( UK) re manufactured units employ a thin skin of anodised aluminium.
Doesn't Bose do a lot of waveguides/TLs in their small speaker units?
It would seem that with CAD/CAM design and manufacturing they would be somewhat easier and less costly to build woodworking wise esp. if it is possible to use MDF for the interior channels
Probably, in fact almost certainly. I suspect the problem then is almost cultural: the IMF was a “thing” in the ‘70s, the math models of TL operation and the CAD/CAM for small companies weren’t available until 25 years later and by then the entrepreneurs in audio had no direct experience with TL speakers. And, even if they did, conventional speaker design had made progress so the TL advantage had waned. Not sure that tells the whole story, but maybe…. Chris used MDF in the ‘70s for the Audionics TL kit he built, so that is certainly doable. And with easily available FEA you could optimize the resonant character of the structure?
I have a pair of dual transmission line Castle Winchester speakers-- $4,200 USD (1990) absolute immaculate condition. Found them across the street by a little old lady who wanted to get rid of them. I didn't know what they were, just that they were gorgeous. Bought them for $400. probably $20k in today's money. Sometimes you just get lucky... now I almost always buy used and look for "the deal"
Where does Transmission Electronics come into the timeline, before or after the split? I own a superb pair of speakers labelled Model 738 Transmission Electronics Ltd. 495/9 Oxford Road Reading Berks
1×Woofer Kef B139, (1973 stickered)
1×Passive Kef
1×KEF Tweeter
1×Celestion Mid
They are very well made.
Sound fantastic.
The transmission line components Fried sold were called the "Model H".
Its more a steep collapsing volume folded horn bass wave guide than a transmission line
Alta Audio makes transmission line bookshelf speakers today, but they are really expensive.
Very interesting video! I recall hearing IMF speakers just once in a hifi shop near University of Buffalo when I was in my late 20s. I’ve never forgotten that sound - the bass felt limitless, clean, natural, more accurate than anything I’d ever heard outside of Kleinhans Music Hall. It spoiled me for a lifetime until over a half-century later when technology made it possible to afford subwoofers with “smart” 500+ watt integrated amplifiers (SVS) coupled with a system employing Dirac room compensation software.
Roger Sanders also uses TL for the bass in his electrostat Sanders Sound System speakers. They sell for $20K including one power amp for the ES panels. So, reasonably priced by today's standards.
Roger knows a thing or two…
Yes his panels are extremely transparent but Sanders likes hyper directional sound. Too directional for me. Images and sound field don't sound like they're in the room but ping pong inside my head like headphones. This happens with extremely directional speakers. And if you sit off axis even a few inches they sound muted in the highs.
Steve eberbach who owned DCM and designed DCM was a real master at Transmission line design and did many versions eventually getting into the 90s who had a smaller footprint transmission line speaker which were the famous time window seven speakers and the TFv line. Steve started DCM in the 1970s to 1999 when the company was sold to Mitek which is known for there MTX brand which of course slowly killed DCM over time making one good flagship speaker TFE 200 which was a transmission speaker as well then the company was sold it officially was killed. steve eberbach was why DCM speakers where so good he understood detailed speaker design. I agree with you that the speaker design is probably a little bit more difficult I don't think that's why they're not made. I think they're not made is actually because they're cheaper passive radiators cost more money and you could just throw them right in the cabinet. B aW's hundred-thousand-dollar speaker using transmission line. bose waveguide is technically a transmission line version as well. it's used just not talked about much which makes it the odd part. Why they uses and not talk about it should be the question
They are still good today!
I can relate with this aspect of past loudspeakers that bucked the trend with unique loading designs with the product I have recreated, based upon a system that was launched back in 1980 on the back of the company's previous smaller loudspeaker designs. Theirs was a quarter-wave with considerably altered internals that gave the broadest bandwidth imaginable from a large stand-mount three-way system using a very simple yet elegantly designed series crossover, together with almost no internal damping to create a most wide dynamic, broad bandwidth system that sounds utterly neutral and transparent. A speaker that rather upset a few of the big players back in the day with a sound so far ahead of the rest. So much so that it can still show the way to this very day. An interview, conducted by Steve Harris of Hi-fi News & Record Review can be seen here: th-cam.com/video/8RV5kYKVrMY/w-d-xo.html
Isn't the Bose "wave" essentially a quarter wave transmission line type of design?
Yes they are.
I have the tls 50s,imf super compact 2, and Fried Model Rs. They sound better than a lot of Hifi today
The TLS design is my favorite bass design
Btw.. Kef and peerless still make drivers for the application
I think that we *should* have a lot more transmission line speakers. With 3D acoustic modeling programs like Hornresp - designing a "modern" transmission like is much, much easier. They can be much simpler - and they can avoid the biggest issue that was often present in "old school" transmission line speakers.
The key to designing a better TL is to move the driver away from the closed end of the TL by about 1/4 to 1/3 of the length. This allows the response to be much more even, without a big dip/trough. And it can allow better mass loading of the driver, that with the right amount of taper - the size of the enclosure can be reduced, and the complexity of building the cabinet can be greatly reduced.
The bass quality of a mass loaded transmission line is fabulous - they can use a much smaller driver, so much lower Mms, but still deliver low bass, because they progressively add mass to the driver as the frequency goes down. And you are using the output of the back of the woofer, while minimizing the excursion; so distortion is often very low.
And because there is much lower cabinet air pressure, the midrange is pretty close to an open baffle - and cabinet resonances are also greatly reduced. The interior baffles act as braces, and are asymmetrically placed in the cabinet, so resonances are not a "common mode".
I have designed a stand mount mass loaded transmission line speaker with a 6" nominal paper cone woofer that is essentially flat in my room to ~32Hz. And I am building a MLTL-6 Tower that should have a fundamental frequency of ~28Hz with the same driver. It is an SB Acoustics driver with 13.8 gram Mms; and is also fairly sensitive.
To add to my comments - the MLTL-6 speaker has only 3 additional pieces to form the transmission line. And it only requires two small dowels to retain the polyfil in the portion where it needs to be. The polyfil is the same density throughout that area, so it is not a "skill" that can't be quickly learned.
The MLTL-6 is a mid-sized stand mount - 9" wide x 16" deep x 21.5" tall. I have a tower version that is slimmer - 8" wide x 13" deep x 1 meter tall (39.375"). The tower uses the same drivers, and is tuned to 28Hz fundamental frequency.
So, the idea that transmission lines are too complicated, and too big - is based on the "old school" designs from long ago.