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Any experience of IMF loudspeakers? I got a pair today!

Discussion in 'classic' started by beammeup, Apr 30, 2019.

  1. beammeup

    beammeup pfm Member

    Never heard of IMF speakers before - they look very 70's - on the back label it reads IMF SC.

    They look well built, and quickly hooking them up to a system in the garage (at low volume for now playing continuously to work them in) all the drivers seem to be working...



  2. Stunsworth

    Stunsworth pfm Member

    A friend had a pair in the late 70s/early 80s. It’s a long time ago, but I remember liking the sound even if it was a bit bass heavy.
  3. Snufkin

    Snufkin pfm Member

    Looks like a good buy and I expect they sound good. IMF produced some well respected speakers in their day.
  4. Tony L

    Tony L Administrator

    Never heard the little ‘uns, but TLS80s and the Reference Monitor are excellent IMO. Surprising sleepers to my mind, clearly undervalued on the used market given the quality of sound they kick out.
  5. sp25

    sp25 pfm Member

    You have a pair of Super Compacts. My first experience of HiFi was hearing a pair of these in a coffee shop in High Wycombe (where they were made) in about 1968. Couldn't believe the bass from that size of box.
    Niel Blackwood and Rockmeister like this.
  6. JensenHealey

    JensenHealey pfm Member

    Lucky buy!


    IMF were famous for Transmission Line style of speakers. You can read up about Transmission Lines on the internet. Successors were TDL - who became very well known. I had a pair of TDL for many years and thoroughly enjoyed them.
  7. retrospective

    retrospective pfm Member

    Enjoying Als30's as i type ..enjoying it while it lasts the missus hates them! that said she's gone a bit quiet since i bought her a new car so you never know.
    I would like to try the smaller 'Compacts'
  8. beammeup

    beammeup pfm Member

    The ALS 30's are MUCH larger. Are these your main go to speakers after hearing many others?
  9. snowman_al

    snowman_al pfm Member

    Yes I had a pair of Super Compacts back in their day. Mid 70's about 89 Guineas or there abouts...
    You need loads of power to move them, 40 plus watts minimum and heavy stands. They did not stay long they were rather 'muddy', especially if (when) the Peerless tweeters fail. The first Wharfedale Diamonds were way better. Here is the inspection card from mine, I cannot find the receipt.


    And more here:
  10. ToTo Man

    ToTo Man the band not the dog

    They're isn't much size difference between the Super Compacts and ALS 30 IMO, both are positively pint-sized compared to IMF's genuine transmission line models. In fact even the entry-level TLS 50 transmission line looks rather dainty compared to the likes of the Professional Monitor mk3 and RSPM mk4!

    I had a pair of Super Compacts for a while when I was fully obsessed with IMFs. They were the mk1 version but I suspect were made just before transition to mk2 because they used the mk1 bass and mid drivers but mk2 tweeters and also sported a veneered front baffle that matched the cabinet exterior.


    Unlike @snowman_al I found them exceedingly open and detailed in the upper registers with a very similar presentation to my ALS 40 mk2a (unsurprising really given they shared a tweeter in common). However I found the mid-frequencies rather thin/recessed meaning vocals lacked weight/body. I had a similar criticism of the TLS 50 mk1 that I also owned.

    The published frequency response does show a dip at 500Hz, but it appears to be quite narrow in bandwidth which I wouldn't have thought would be that audible:

    The mk2 iterations used a different mid driver and are apparently the superior sounding model but I cannot comment as I haven't directly compared them.

    The Super Compact I owned was still an excellent sounding speaker though with a bass punch and extension that belies their size. But the TLS 80 mk2, Professional Monitor mk3 and RSPM mk4 is where the real IMF magic is at! ;)
    Big Tabs likes this.
  11. davidsrsb

    davidsrsb pfm Member

    That graph is flat, look at the dB scale 1dB steps when most tests are 5dB steps.
    If anything there is a hint of excess around 300Hz
  12. ToTo Man

    ToTo Man the band not the dog

    So it's definitely a 1dB scale? I was a bit confused as there appears to be two different scales on the left y-axis and a third scale on the right.
  13. Tony L

    Tony L Administrator

    Could well be issues with the mid-driver surround/spider. Old IMF mids can look decidedly crusty these days, the surrounds seem to go very weird indeed. I don’t know what units they used. I’ve seen some with what look like Kef B110s, but whether they were factory fitted I've no idea. If so those models would be far more serviceable as they are still obtainable (Falcon).
  14. davidsrsb

    davidsrsb pfm Member

    Well spotted, the top hand written note says 50dB range, so the leftmost scale, 2dB per division.
    ToTo Man likes this.
  15. davidsrsb

    davidsrsb pfm Member

    TDL used Elac and there seems to be some similarity
  16. ToTo Man

    ToTo Man the band not the dog

    I might be mistaken but the first generation mids IMF used in the Super Compact, ALS 30 and 40, and TLS 50 were made by ELAC and had a rather unattractive wrinkly rubber surround that dipped inwards. (Is convex the correct terminology? I always get convex and convex and concave mixed up!).


    The second generation mids I think were made by Peerless and had bird-poo / khaki coloured foam surrounds which start to crack and eventually disintegrate with age. (My ALS 40 mk2a are still waiting to be refoamed, I bought the foams 10 years ago but still haven't been brave enough to tackle it. In fact I've had the 'new' foams in storage for so long now I probably ought to toss them out and buy fresher ones!)


    I compared an original TLS 50 mk1 to a recapped TLS 50 mk1 and the latter sounded like a grainy veil had been lifted from the speakers, though the recessed mids still persisted. I'd have loved the opportunity to compare the mk1 to the mk2. The TLS 50 was in fact my first introduction to IMF, and also my first introduction to transmission line bass. It was one of those jaw-dropping moments when I realised it was possible for an affordable and practically-sized loudspeaker to generate effortless and visceral bass free from the usual enclosure limitations and colourations I had previously grown accustomed to.

    IMF's bigger transmission-line models, starting with the TLS 80, used the KEF B110 as the mid driver (they later changed this to their own 5" mid driver called "5/36" that looked almost identical to the B110), and these models to my ears have a fuller, richer and more satisfying midband presentation than those with the smaller mid units.

    Last edited: May 2, 2019
    Big Tabs likes this.
  17. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    By far the best transmission line bass I've ever heard was from the Leak 2075... awesome! Considerably larger than even RSPM's though and has 15" sandwich woofer.
  18. davidsrsb

    davidsrsb pfm Member

    A 15" will make good quality deep bass in a sealed cabinet, a TL to suit must be really long.
  19. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    Just the TL section must be at least as big as RSPM's and then there is a head unit on top with the upper and lower midrange drivers and tweeter.... not exactly high on WAF!
  20. demotivated

    demotivated pfm Member

    trick cyclist likes this.

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