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IMF Professional Monitor IV

S

skyebridge

Registered User
hello all:

i have heard/seen no mention of these speakers for years. does anyone else remember them? in the days when only my schoolfriends who were smart enough to leave asap and set up businesses like importing grado cartridges could afford to buy them, they were reckoned by many to be THE ultimate british loudspeaker; and as an impoverished student visiting the converted barn houses of my really successful mates i was able to make comparisons between tannoy, IMF etc. the IMF PM-IV made a life-long improession for its ability to spread sound and to get RIGHT DOWN into whatever base the most expensively set-up LP-12-based system could produce. anybody else got similar (or different) memories? do these speakers continue to exist anywhere? thanks in advance for all responses. hugh
 
Where's DSJR when you need him :p

Yes, I remember IMF's of one sort or another. In their day they were about as good as it got but only the very. very large ones, whatever the model designation was. Oodles of (slow) bass, realistic SPL's and huge sound stage, very impressive.

Didn't they metamorphosise into TDL ? which weren't nearly anywhere as good. The IMF name is probably owned by some Chinese manufacturing consortium now with a range of sub/sats on the way as we speak. :D
 
IMF... Designed by John Wright. A man with a passion for transmission line speakers. Spoke to him in the '70s at a show ( somewhere?) . I heard the range ( not in the best setting ) and I loved the IMF compact best of all. The big speakers were a bit 'slow' for my taste. Quite low in coloration and ' impressive ' , that is deep bass and high levels . A friend bought a pair of smaller monitors in the mid '70s, but I can't remember the model. May have been the Domestic Monitor. Much better in a home setting than the show setting I thought, but a little excessive in the bass. I suspect they would sound better on modern digital programme. The friend sold them eventually and bought something completely different. Quad ELS speakers. I loved those, but never had the room. I did consider the IMF Compacts, but a pair of Spendor BC1s arrived for me to try out. Still with me after 28 years... Martyn .
 
I WANT SOME!!!!!!!!!!


...But I'd need a divorce first...


In my first life based at KJ Watford and London a million years ago, we sold a huge number of IMF models, all shapes and sizes and for some years they were a major brand for us.

Apart from a little sting at the top end, these LARGE speakers could show PMC how to properly align and acoustically damp a transmission line today, thirty two years later! They ran from 1976 to the early eighties I think.

This DOESN'T apply to the Mark 3 models (remember your ATC 100a customer Dave?) which, without a Crown/Amcron style power amp with massive damping factor, wallowed all over the place and got your ears pumping in and out with the pressure.

The Mark 4 and TLS80 II were on low frame stands, slightly angled back as I remember. A friend once had some RSPM mk4's and sold them for DMS 'Briks, a HUGE mistake we both now acknowledge.

During the IMF years (and the life of the above speaker - late seventies), a drive unit manufacturing facility was started called TDL. A guy named Clive Gibson, who was ex Elac IIRC, was involved in the design of these new drive units as I remember.

When IMF folded, TDL found themselves with drive units and noone to supply them to, so Clive (and I think, John Wright too) started designing new speakers for them. TDL as "we" know them was born. I think I've got that right............. Clive went on to start Musical Technology specialising in trianglular tube style cabinets and metal cones. he continued to make some drive units for TDL also, or repaired faulty ones, I cannot now remember. Sadly, MT, like early Epos, were more a labour of love rather than a money making business and they eventually folded just when the £550 Harrier Evolution model finally came together - sad! Ironically in this story, Musical Technology's remains were purchased by PMC...

The TDL Studio 1 and 1m were very successful for us (6" bass/mid floorstander) and the size, sound balance and basic shape lives on in the totally unrelated Spendor S6e, a speaker I have high regard for (alone here on this forum it appears).

We sold a couple of pairs of the TDL £2.5K model - can't remember its name - and I was rewarded after one of these sales by my customer complaining about the unconventional bass response (up at 40 - 60Hz and severely down at 120 - 140Hz approx) in HiFi News, not a problem for TDL as noone read HFN even twelve years ago...

Transmission Lines live on, courtesy of PMC, who's boss Pete Thomas was highly influenced by the IMF Pro Monitor 3's he had/still has. I find their domestic models a bit floppy in the low bass, with corresponding suckouts in the upper bass/lower mid - a price paid for all this bass extension. They've got new models now, which may have ironed this out for all I know.

I think I have the basics right and I know there's at least one other on here who could tell more and correct me if I've got it wrong.

P.S. The RSPM mk4 name was a sort of melding of two prior models, the Reference Standard (Robin Marshall of Epos fame once owned a pair) and the Professional Monitor, itself derived, I think, from the IMF Domestic Monitor.
 
What became of TDL? I've just acquired some RTL2's, which appear to be a well-built and pretty good sounding little budget box.
 
The RTL 2 (with full length grille) was a Clive Gibson design (John Wright may have "voiced" the tweeter level) and, apart from lousy bubbly vinyl print finish, the mk1's were a truly superb box, available for peanuts nowadays.

The mk2 RTL2's were much better finished and styled, with the grille being curved on its underside 2/3rds down the cabinet, but the tweeter was several db down on the bass/mid, just like the AE109, which was a competitor - perfect for the PM66 KI SSSSIGnature amp, which was a godawful screamer of an amp that no dealer liked. The tweeter level can be returned to flat by replacing the in line resistor feeding the tweeter cap with a lower value.

TDL suffered by not being pro-active enough. They set up an enthusiastic US distribution and didn't follow it up regularly to continue its nurture for example. John Wright succumbed to cancer some years ago and the company was bought out before going over to the Richer Sounds group as just another brand name IIRC.
 
Mine have the solid full length grilles, and sound pretty well balanced up top. In fact the more I listen, the more I like (they hadn't been used for a while). I'm tempted to whip out my box of Bennics and T20 and see what they can do.

I've been inside AE109's and I can see certain similarities, both seemingly engineering-led rather than marketing-led designs. The integral port arrangement of the TDL is clever and effective as it braces the box as well.

Thanks for the info.
 
RTL 2s... Yes, a friend bought a pair and I thought they sounded OK, on his system at least. I would have liked to try them on my familiar equipment, but he moved away. I seem to recall Hi-FI News ( when it was a 'proper' Magazine) tested the TDL range and liked the '2. Not that they were the final arbiters...
 
RustyB said:
Mine have the solid full length grilles, and sound pretty well balanced up top. In fact the more I listen, the more I like (they hadn't been used for a while). I'm tempted to whip out my box of Bennics and T20 and see what they can do.

I've been inside AE109's and I can see certain similarities, both seemingly engineering-led rather than marketing-led designs. The integral port arrangement of the TDL is clever and effective as it braces the box as well.

Thanks for the info.
Click to expand...

Change the tweeter cap (4.7uF?) for a better one and ADD half an Ohm to the tweeter restor value to balance it up. That's all...
 
I used to work for IMF Electronics based in High Wycombe, Bucks in the late 70's, I was the x-over supervisor and had to handle around 13 young ladies, hey what a job, NOT, they used to wind coils, assemble x-overs, measure inductors, select caps for the RSPM MkIV, oh!! "those were the days my friend" hey we all know a song about that, don't we.

The TLS80 was the best floor stander they made IMHO, they had great dynamics and a huge soundstage when compared to the slightly more accurate RSPM's, these lost their ooomph due to the overly complex x-over, there were literally rows of caps used for the filter slopes, all reversible electrolytics, YUK!!! although they were all hand selected to be within 5% tolerence, the inductors were wound on an old hand machine and mounted over steel laminate strips to form the core for the LF stuff, while the HF section had air cored inductors, all the cabinets were also made at the local factory, that was when we had an industry. Oh yes those were the days, havn't I heard that somewhere before, happy memories are all we have now :O)
 
Pulse Studio said:
I used to work for IMF Electronics based in High Wycombe, Bucks in the late 70's, I was the x-over supervisor and had to handle around 13 young ladies, hey what a job, NOT, they used to wind coils, assemble x-overs, measure inductors, select caps for the RSPM MkIV, oh!! "those were the days my friend" hey we all know a song about that, don't we.

The TLS80 was the best floor stander they made IMHO, they had great dynamics and a huge soundstage when compared to the slightly more accurate RSPM's, these lost their ooomph due to the overly complex x-over, there were literally rows of caps used for the filter slopes, all reversible electrolytics, YUK!!! although they were all hand selected to be within 5% tolerence, the inductors were wound on an old hand machine and mounted over steel laminate strips to form the core for the LF stuff, while the HF section had air cored inductors, all the cabinets were also made at the local factory, that was when we had an industry. Oh yes those were the days, havn't I heard that somewhere before, happy memories are all we have now :O)
Click to expand...
I have a pair of the TLS80 Mk 2 brought in 1982, to this very day. Driven with Lux amplification, they produce real low bass, not some false imitation! Built like big solid battleships, unlike some many of the flimsy constructed speakers of today. Large 32ft organ pipes , when reproduced, cause it no hint of distress. The sense of physical air pressure going up in the room, is amazing. You actually feel it, either low or somewhat loud. They also show what soundstage imaging is all about. Wide , big and deep. Although the cabinets were originally teak, over the years I have lovingly treated them with rubbing in Bees wax and a mixed blend of mahogany and oxblood red strains to create a stunning reddish brown mirror finish. I have found that they have a sound closely akin to B&W's DM2 if A/B'ed side by side, except the IMF's go a full bass octave lower. At times I feel I am in heaven surrounded by the IMF's in front topped with a pair of Time Windows 1-A's, (when used together, making possible height columns of 7ft of sound) then B& W's DM2a's at the back of the room (all 3 brands used the transmission line principle) plus 2 big NHT subs and an array of other ancilliary speakers for AV theatre. A total of 13 speakers in the one listening room. Case of 'climb into the cockpit' for the adventure. :)
 
WOW!!!!!!! do you live in the Albert Hall ?? and for my meagre by comparison system is:
2 pairs of 3/5a's with a Paradigm sub and modified Kef coda centre speaker with obviously B110 & T27, and yes I do miss those beautiful low end TL bass notes, no sub could ever reproduce.
 
We had all the IMF models to demonstrate and I also loved the TLS80 mk2. I dunno, I think I might have liked the adjustment possibility of the RSPM IV. I'm not sure if all these caps were always in circuit or could be switched out though, it's so long ago and in a life I thought I'd left behind....

I remember one very happy afternoon when JM Jarre's Equinox had just come out, playing side 2 and really getting in to it (I'm a sucker for electronic bass sequencers/arpeggiators). That controlled "push" in the chest on the bass notes and no boom on these, not even with a "bolt up" 250, which didn't quite have the damping factor on paper these TL's were supposed to need (it sounded awful in combo with the previous generation though, all wallowy Booooooom!!!!!!!).

If I try to play Dark Side of The Moon on CD on the ATC 20aSLpro's I have to almost catch the cone as it shoots out on the *heartbeats* :(
 
TLChris I have the x-over circuits if you need them, and a few caps from the RSPM, sadly no longer have any inductors, but then these should all be OK, nothing to deteriorate.
Paul
 
I did have the chance to also audition a pair of the IMF 50's for a few days back in the 80's.. In some ways there were a 'littlle more rounded' musically IMHO but there was a 'reason' why I finally chose the 80's for their more robust heft and power. I happened to be experimenting at the time with a then new top of the line Teac casette deck that had 'dbx' noise reduction. I recorded high level test high frequencies. Inadventantly I forgot to make sure the 'dbx' decode was on, on playback... which meant an added further boost of 10db to the signal ! Luckily I only 'killed' one of the IMF super tweeters in the process. The tape alignment against the playback heads was probably not truly 'spot on' to give the other tweeter the full 'blow'. I paid for the IMF 50 replacemnt tweeter and closed the deal by saying "You better give me the bigger model 80' IMF! I have respected amp power / speaker usage, ever since. Lesson learned.
 
very many thanks to all for this informative thread! i now understand much better the contention between PM-IV's and TLS-80's than at the time - i thought the PM-IV's were clearly superior, but of course never owned a pair; whereas one or two friends whose opinions i valued switched from the PM-IV's to the TLS-80's.

over the past twelve years i have mainly been running ruark speakers - though i had a pair of B&W DM somethings (6?) at one stage.

has anyone got any experience in comparing the bigger ruark's (solstice and excalibur) with IMF or TLS speakers?

also, how do the older IMF and TLS compare with the current generation of transmission lines made by PMC etc? opinion so far seems to say that more recent examples of this design are poorer?

and, is there a used market for the older IMF and TLS if one wanted to go there?

lastly, DSJR mentioned running LS3/5a's. this is another speaker i have greatly admired since first hearing a pair in canada in 1977. as it happens my wife is currently chafing me to acquire a pair of stand-mounted monitors. i have been looking fitfully and wonder if the older BBC-type still stands favourable comparison with what else is 'out there'. maybe this should be another thread, but any advice/opinion would be appreciated.

thanks again,

hugh
 
DJSR is right on championing the LS3/5a, but you could get into a lot of controversy re. which to buy. The only true new LS3/5a is the Stirling Broadcast V2 model. As you probably know, 2nd hand ones go for BIG money, especially Chartwells. In my opinion, they all sound much the same. After all, the BBC wouldn't have been pleased if they didn't, if they drew a spare from stockto use. The Harbeth ( M40? ) is another BBC influenced design. I have a lot of respect for Harbeth for having followed their path and not succumed to Hi-Fi 'Fashion '. I've never heard a bad Harbeth. Come to that nor have I heard a bad Spendor, another BBC 'type' sound . Both Harbeth's and Spendor's LS3/5a type speakers are very good... Hope this helps al ittle. Martyn .
 
Without being too biased or disrespectful either way (!!!) I'd say the Ruark speakers of my acquaintance can sound just a little "tight a*sed" in the bass (a bit like someone I knew who always walked as if he had a carrot stuck up where the sun doesn't shine).

Traditional early seventies IMF's let it all hang out big time. The B139 bass unit of the bigger ones could flap about uncontrollably and get everything not tied down in the listening room flapping about too. In my first life (at KJ Watford), we sold bucket loads of Crown/Amcron power amps, which back then were the only models with enough control (damping factor) over these wayward bass units (and this was with bell wire through a relay switched comparator as well!). The little D60 was a stonking power amp, brick walled at 35Watts, but it had the control and, more recently, sounds musical too with a modern source and pre-amp. We sold a lot of D150's too with the IMF's - more power - and we had the fear inducing (back then) DC300A as well!

The mark 2 models had a MUCH tighter bass and the RSPM IV was the first to come out. That's why I still have very fond feelings for it. The TLS50 models were ideal for typical UK rooms but looked tiny by comarison so we unfairly overlooked them, as with a push uf a button, we could show how much bigger and more imposing the sound was on the bigger ones

Favourite tracks/albums? Dark Side Of The Moon, Tago Mago (by Can), Anything by Mandingo (highly percussive jazzy stuff recorded in Abbey Road - we had a copy master tape) and Frankenstein, by the Edgar Winter group - I once had a round of applause after demonstrating this track through IMF ALS40's!

IMF's are of course over thirty years old now. The drivers may have aged and will almost certainly be irreplaceable with new ones. I wonder whether the internal sponge line damping will have disintegrated too? I'd love to hear a pair with modern gear, but to ever own some - I'd need a divorce and a big detached house.......

PMC are where it's at now, but the only ones that even begin to get where the big IMF/TDL models are the MB2 and BB5's to be honest. All the lower caste PMC's are but childrens toys by comparison.
 
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