KEF Concerto vs IMF Super Compact

[luvmusik]

Comparison sonically of the two models. In particular, interested in the KEF Concerto system model SP1006 with SP1003 mid & SP1032 tweeter drivers and SP1004 crossover (up to 1977) vs the IMF Super Compact MkII (@1978-1985). Or, also comparisons of any versions of the two mfr's models here. Concerto has slightly larger, heavier cabinet with the exquisite character of the B139 woofer. Super Compact does it with a smaller cabinet, 100 db efficiency, possibly handling more a little more watts - not sure there.
May be the ultimate speaker shoot-out. Your thoughts, please, on the sonics compared on these two models. And, has anyone owned/heard both to weigh-in ?

 

[luvmusik]

Realizing also that the IMF "Compact Monitor III" (and maybe IIIa) @1980 - 1987, is very similar, so that model too should join the mix to round out a TRIO model shoot-out. Interested in audio/sonics thoughts on these 3 models...KEF Concerto vs IMF Super Compact vs IMF Compact Monitor III, any versions, in any order of comparison.

 

[surv1v0r]

What are the three drivers in the IMF?
What are the dimensions?
It looks like a transmission line - anyone know what the line looks like?

As you say, the Concerto uses the B139 bass driver and I can't see the IMF matching that with what look like a much smaller driver.

 

[luvmusik]

UK/Worldwide input needed

Although looking for sonic comparison, here is the technical data.

KEF Concerto (1969-1977) system SP-1006 version (2 earlier types differ)
3 way
B-139 woofer flat oval A-6171
B-110 mid 5" bextrene cone SP-1003
T-27 tweeter 3/4" melinex dome SP-1032
bass reflex
isolated mid internal enclosure
db efficiency not sure
28 x 17 x 12"
50 lbs (I think each, but maybe pair)
8 ohm
30 w, maybe more
cross at 400 & 3500 Hz SP-1004
30-30,000 Hz range

IMF Compact Monitor III (1980-1986) and also IIIa version
3 way
8" woofer plastic cone
4" mid plastic cone
1" tweeter soft dome
bass & mid each in seperate tapered cabinet internal sections
84 db efficiency
24 x 12 x 12"
29 lbs ea
8 ohm
20 to 150 w
cross at 375 & 3000 Hz
29-to inaudible (minimum 20,000 or better) Hz range
not sure of model or type #'s of drivers & crossover

IMF Super Compact (1973 to 1980 version I) & (1979 to 1985 MK II)
3 way
8" woofer bextrene cone
4" mid cone (I think bextrene)
tweeter soft dome (?size?)
bass reflex
midrange short transmission line
100 db efficiency
18 x 11 x 12"
20 lbs ea
4 to 8 ohm
20 to 50 w, maybe more
cross at 375 & 3000 Hz
30-20,000 Hz range
not sure of model or type 's# of drivers & crossover

Spec-wise it's a shootout, so curious for sonic impressions comparisons

Best help may be our UK friends here which may have heard any of the 3

The exact model & type # of drivers and crossovers not listed is probably found on AK - IMF Owners Thread or IMF Yahoo group for details

Any of 3 Concerto versions and 2 Super Compact versions info welcome

Any thoughts ? Eager to learn of the sonic comparison & impressions of the 3

 

[surv1v0r]

Thanks for the data. I have found out a little (very little and certainly less than you) about the INF Compact Monitor III speakers:
The drivers may be from either Dalesford or Elac?
Cabinet dimensions: 22½" high x 11" x 11¾" - 13½ kilos
It seems that the crossovers would probably need to be refurbished due to ageing.

I didn't realise that the Bass & Mid drivers were each in separate tapered cabinet internal sections - are they both transmission lines?

Am I right in thinking that these speakers are likely to be very inefficient? Up to 150 watts seems a lot for twenty years ago.

29 Hz seems amazing (i.e. unlikely) for such a small speaker.

 

[luvmusik]

Hope this may help in some way.

Lots of info on these models can be found on the imf-electronics webpage, the imf Yahoo group, and the kef museum - explore kef pages. I'm not sure of the mfr of all the drivers, as imf changed mfr's a couple times, even throughout different production years of the same models, many in their line-up. Some folks from the 2 imf sources mentioned know exact driver mfrs for particular years of specific models.

Here on AK, in the IMF owners thread, I'm pretty sure someone posted he newly owns Compact Monitor III, and may know the internal cabinet design and also driver mfr types. I think this model is either a T-line or a bass reflex overall, based on photos. Not sure if a t-line and if so, if that is for the woofer only or combined mid or seperate for both if a t-line. May want to shout out a message on that thread to owner, or pm him.

Many IMF speaker models are relatively inefficient compared to highly efficient loudspeakers.

The 150 w rating on CM III does seem high, yet is printed in IMF technical sheets - owner as said may know more there. Agreed it seems high though.

29 Hz is likely. IMF are known for achieving deep bass - some thunderous models (like my RSPM MK IV). It's in the internal design of the speaker system. The Super Compact Mk II is a model I also own & they certainly reach the 30 Hz mark, and these are the smallest of the 3 models posted. I remember when they emerged on the market and we were all stunned by the bass in such a small enclosure. Others AK owners also attest to this. It is a bass-reflex design with a short mid t-line and gets lower than anything I've heard in this size. As with IMF, the detail, speed and seemless integration is very tight, defined and accurately clear - no booming reflex type enclosure with IMF. The SC MK II was IMF's biggest seller, and a sensational speaker, holding it's own easily today. Possibly one of the smallest speakers to reach such low frequency at level db; surely they're aren't too many others.

Noted is any measurements done in anechoic chambers or how those figures differ vs in testing in real-room acoustics where wall/floor interplay greatly can affect values (for good or worse). But, these specs all give us a starting point of the ballpark numbers.

My preference is a B139 SP1044 woofer for IMF and KEF designs, yet I think the 3 posted models are very close in sound signature and characteristics and would like to learn how some describe their audio sonic impressions that have owned or heard any 2 or 3 of the 3 models. Seems to be a great runoff; all 3 are great, have fans for each model and surely there are folks that have heard 2 or 3 of the models - possibly more in UK. Maybe some folks switched from 1 to the other, or even swap back & forth in listening preference. Would like to know more.

Hope at least some of this may be of some help.

Wish we get some feedback too, on how some find the sonic impressions; seems interesting.

 

[BilboBaggins]

I can talk about the Concerto. First, I would like to say I love these speakers. They are the kind of speaker that sits in the background and delivers. Not in your face, but subtly gives superior sound. And they go very low accurately. And they look great doing it! They are hungry for high current. I recommend an amp with at least 50 Damping Factor like a Kenwood Supreme, Yamaha M-40, or a beast such as that. They can take more than 30 watts if it is clean. How much, I don't know.

 

[luvmusik]

Nice loudspeakers ! Do the Concertos weigh about 50 lbs each or 50 lbs for the pair ? Were they hard to find in North America ? It looks like they pop up in UK for sale on occasion, and maybe less often in Canada & the states, not sure. Those are keepers !

 

[JimPA]

There were some Kef Constructor kits very similar to the Concerto model sold by Madisound and Falcon Acoustics up until the early 90's.

 

[luvmusik]

Hey Jim ! Good to see you (and Heidi) here ! Great point about the KEFKIT. We should open it up to a 4 speaker model sonic comparison. Is it the KefKit3 the applicable one ? I'll try to attach a file of it here, may need to clic on thumbnail to enlarge. The speaker is spot-on what we're discussing. Nice low frequency too as per file.

 

[JimPA]

I once read that some of the Kef B110's that were rejected for the Ls3/5a's were used in some of the Kef constructor kits.

Miss Heidi and I are very busy now with customers coming out to our tree farm to cut down and purchase Christmas trees. :wave:

 

[luvmusik]

Another similar occurance recalling from some time ago is that the B139 SP1044 woofer differs slightly from the same labelled as Konstruktor (Constructor) series. Also read the Konstruktor series of drivers were not the 1st run-1st quality drivers (instead as rejects) as said in preceding post. Recall the actual B139 Konstruktor specs from KEF themselves were slightly different than the standard B139 - both same year SP1044. The Konstructor did not reach as low Hz in print and in room yielded disappointing thinner bass frequencies. Forums have posts of users actual measurements confirming the Konstruktors lesser characteristics - higher Fs and higher frequency response at bottom- although it's not to say we may find some good ones.

Those forums also had fellows modding them to get improvements closer to expectations. I looked into it deeply long ago as I bought some SP1044's and almost jumped on Konstruktors (they sell for less), until I found out these details and waited to buy the real-thing B139 SP1044. Also, it' said, not sure if true, that in the 70's and 80's KEF's QA/QC was slacking; maybe some lot runs went thru with loose spec tolerance and don't sound as good as others. With the real-thing SP1044 I've been lucky getting all good ones.

Still, we may see some excellent Konstruktors that measure out well and sound great, so the KefKit3 is a good contender for the loudspeaker run-off. It's a good thing to keep in mind if buying drivers or making replacements - the upgrade may be to replace kits with standard non-Konstruktor versions if those supplied drivers don't pan out well.

KEF Concerto vs KefKit3 vs IMF Super Compact vs IMF Compact Monitor III !

 

[luvmusik]

On the DIY site forum thread about B139, a fellow stating he worked at KEF about 22 years speaks about the KEF specs for B139 SP1044 ..."the 'nominal' resonance of 25 Hz was always wishful thinking by Marketting", however admits he was not part of that production or testings.

In the '70's some mfr's highly exaggerated measurements to sell product & compete, especially if having a lesser product (some had fantastical claims spec-wise), but the more humble, very concerned mfr's tried to get it right as tested to print. KEF impresses me more as a rightious manufacturer. Their drivers such as the B139 SP1044 mounted in some cabinets, particularly t-lines, yield incredible low range response testing. The drivers alone usually test out well too.

It's possible that although the worker also dismisses the notion of "seconds" for Konstruktor drivers... - it's possible the QA/QC tolerance may have been in spec - but at the widest in range variation point and thus delegated to the Konstruktor line. This practice is common in all types of manufacturing & distribution. Same spec range of deviation - just different levels of either tighter or wider (looser) tolerance within that accepted variation. Who knows ? It's interesting. Maybe QA/QC has more options in technology now-a-days too.

 

[c-atle-79bay]

The super compact is not a transmission line rather just vented, if I recall correctly. The sound is very much like it's larger IMF kin, very good placement and depth of sound stage as well as width too. Also nice and musical with a extended mid range, but a really warmth in the mids. I just put in some pioneer 52's by andrew jones, and was struck by just how much mid range richness exists in the IMF's.

The thing that strikes me the most about the super compact is it has no business sounding as big as it does.

 

[luvmusik]

Yes, the IMF Super Compact versions are a bass reflex design for the woofer, and nicely done for this speaker cabinet is a short transmission line only for the midrange alone. It is a tube enclosure seperating the mid going to the rear of the cabinet wall, in an isolated section, and thus travelling downward to the bottom out the front vent on bottom.

There is a brief description in better wording about this, with a real nice internal construction diagram arrowed at page bottom on the imf-electronics site page for the SC. Careful examination and enlarging that diagram shows the passageway of the midrange t-line. What I'm not sure of, is when the tube outlets to the back wall, if that space simply combines below with the bass reflex vent, or if the mid t-line continues seperated alone then down and out. I never took mine apart. There must be some folks that have, however, that can fill us in on the bending passage and ultimate outlet of that mid line, when they took theirs totally apart.

This mid arrangement helps establish that wonderful midrange presentation described in preceding post. These are remarkable speakers. For this size, just incredible - exhibiting a sound attained by much larger competitors. At this small size, they impressed me along with 2 other favorites as bookshelfers - but for much different reasons - the original EPI/Epicure M100 for the phenomenal tweeter and full bandwidth lifelike linearity and also the Legacy Audio Studio HD for sensational overall presentation, wow-factor and sparkling ribbon tweeters - 2 other gems for small speakers. Noted is the IMF SC does this as a 3-way in a small cabinet, the others mentioned-EPI & Legacy are 2-way models mentioned; some prefer either design approach, each has its attributes. All 3 perform uber-exceptionally.

Not to stray from thread, but just placing the IMF SC among other well-liked bookshelvers - one that is priced less, the other priced more, with the IMF price in the middle. Price not important, just mentioning the fine level the IMF perform at, and also as a reference point for those not familiar with IMF, but maybe having heard some other fine very small speakers that really stand out from the pack of many.

 

[surv1v0r]

Hi luvmusic, you refer to various sites (e.g. "imf-electronics webpage", "the imf Yahoo group" & "the imf-electronics site page for the SC"), would you be able to quote the URLs for these references please?

To summarise your technical specs for the IMF speakers, I think the attached image consolidates what you have gathered + a few changes - if anyone knows different, please say so and I will correct and update

​

 

[luvmusik]

KEF Concerto/KefKit3/IMF SC/IMF CM III runoff

http://www.imf-electronics.com/

proceed to Super Compact and also Compact Monitor III
lotsa goodies thru-out the site
be sure to vote in IMF transmission-line babe contest for your fav while reading.
IMF, TDL & Fried info.



http://kef.com/html/en/explore/about_kef/museum/1960s/Concerto/index.html

Concerto info.


https://groups.yahoo.com/neo/groups/imf-electronics

free to join - sign up & follow procedure - may take a week or two until notified of group acceptance - site has oddly been dormant last month or two, yet very active up to then - 10 or 15 of the most imf-knowledgeable in the world post & discuss in the group to the finest detail & are helpful to all. Site also welcomes TDL, Fried and other t-line mfr speaker owners too.

Nice chart & format ! Please add the 2 models from KEF = Concerto and KefKit3 - all info is in posts #4 and #10 here to complete the full 4 speaker runoff.
Modifying to include all 4 speakers in chart in your format would make nice side-by-side analysis for all to see specs, and help to make a comprehensive thread.
These 4 models are so closely similar in so many respects & is a great shoot-out. Possibly one of the closest loudspeaker comparison runoffs for sound.

Enjoying the comraderie !

Hope this helps !

 

[luvmusik]

KEF Concerto/KefKit3/IMF SC/IMF CM III

I guess a next step could be the exact listing of the drivers and crossovers - both model & type # where applicable and years production for each of the 4 speakers. This can get involved, as some drivers changed during certain production years. I only have some of the numbers, not all. I think there are only 2 or 3 tuff ones to pin down for all drivers over the years. Maybe someone is willing to contribute specifics.

We got a nice start on some sonic impressions from posts. Greatly appreciated. Hopefully some more will come along & even some comparisons among the 4 speakers. Very cool if anyone ran A-B tests anytime & can help out. We reach out to our European friends here on AK that may be well-versed in this subject.

 

[luvmusik]

KEF Concerto/KefKit3/IMF SC/IMF CM III

Although looking for sonic comparison, here is the technical data.
Updated info is here:
KEF Concerto (1969-1977) system SP-1006 version (2 earlier types differ)
3 way
13 x 9" B139-A6171 woofer flat oval
5 " B110-SP1003 mid bextrene cone
3/4" T27-SP1032 tweeter melinex dome
bass reflex
isolated mid internal enclosure
db efficiency not sure
28 x 17 x 12"
50 lbs
8 ohm
30 w, maybe more
cross at 400 & 3500 Hz
crossover DN12-SP1004
30-30,000 Hz range
including the earlier two Concerto versions - the 3 versions complete arrangements are:
System A6614- woofer is B139-A6171 & mid is B110-A6362 & tweet is T27-A6340 & crossover is A6606 earliest version
System SP1005- woofer is B139-A6171 & mid is B110-A6362 & tweet is T27-A6340 & crossover is SP1002 mid-era version
System SP1006- woofer is B139-A6171 & mid is B110-SP1003 & tweet is T27-SP1032 & crossover is SP1004 latest version (most interesting to me !)

KefKit3 (1969)
3way
13 x 9" B139-SP6171 early & SP1044 later, oval woofer
5" B110-SP1003 mid
3/4" T27-SP1032 tweeter
bass reflex
96 db sensitivity
28 x 14 x 10"
28 lbs ea
8 ohm
15 to 50 w
cross at 400 & 3500 Hz
crossover DN12-SP1004
25 to 40,000 Hz range


IMF Compact Monitor III (1980-1986) and also IIIa version (1981-1987)
3 way
8" IMF-branded KEF B200, or Dalesford or IMF-branded Elac woofer plastic cone
4" Elac 4/200 mid plastic cone
1" Audax 12 X 8 (or X 9) D 25 SP or IMF-branded TW1500 = a rework of Peerless DT 10 HFC tweeter soft dome
bass & mid each in seperate tapered cabinet internal sections
84 db efficiency
24 x 12 x 12"
29 lbs ea
8 ohm
20 to 150 w
cross at 375 & 3000 Hz
29-to inaudible (minimum 20,000 or better) Hz range
not sure of model or type #'s of crossover=likely IMF-branded in-house built

IMF Super Compact (1973 to 1980 version I) & (1979 to 1985 MK II)
3 way
8" IMF branded KEF B200 (large magnet version)=version I then IMF-branded Dalesford 8/22 SP1014=version Mark II woofer bextrene cone
4" Elac 4EM/101 or some EMI=version I then Elac 4/200=version Mark II mid bextrene cone
1" IMF-branded reworked Peerless DT 10 HFC=version I then Audax HD 12 X 8 D 25 SP=version Mark II tweeter soft dome
bass reflex
midrange short transmission line
100 db efficiency, but about 84 db at 1 w
18 x 11 x 12"
20 lbs ea
4 to 8 ohm
20 to 50 w, maybe more
cross at 375 & 3000 Hz
30-20,000 Hz range
not sure of model or type 's# of crossover=likely IMF-branded in-house built

Spec-wise it's a shootout, so curious for sonic impressions comparisons

Best help may be our UK friends here which may have heard any of the FOUR speaker models

The exact model & type #'s of crossovers not listed (for IMF speakers) is unknown so far

Any of 3 Concerto versions and 2 Super Compact versions info welcome

Speakers are in no particular ranking order - each owner has preference(s) for 1 or more models !

Any thoughts ? Eager to learn of the sonic comparison & impressions of the FOUR speaker models

Updated info appears.

 

[luvmusik]

KEF Concerto/KefKit3/IMF SC/IMF CM III

Ran out of time, but still need to dig up the exact IMF model & type #'s for the drivers-woofer, mid, tweeters and crossovers for the IMF Super Compact version I and Mark II and also IMF Compact Monitor III/IIIa. Some production drivers may have changed during certain years of the lines' run. I can add the correct #'s to the data sheet of the FOUR speaker models in the previous post to make a comprehensive technical spec sheet comparison, but running short on time & need to dig deep. If anyone wants to list the #'s, I can re-enter updated data into the spec sheet for the 4 speaker models. I am in process of gathering missing data now, asking help also on other AK "IMF Owners Thread" & make take some time.