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Revisiting Jim Rogers JR149s

It is very easy to measure speaker impedance with REW, a 10 Ohm resistor and a PC soundcard. Impedance is sensitive to leaks and is not so fussy about exact room positioning as trying to measure LF bass extension.
A serious leak turns a sealed box into a bass reflex. I found a speaker surround glue had come unstuck like this.
 
I haven't touched mine apart from replacing the fuses and cleaning the fuse holders. The electrolytics, though not as old as mk1 JR149s, are probably old enough to warrant replacing but I've left them be as the speakers sound absolutely fine to me as they are (I've got more than one pair of mk2 so have a good frame of reference if something wasn't right with one of them!).

If you're twiddling your fingers and want to experiment with something, try replacing the fuses like for like (2A IIRC?) and also with 50A ones (which are pretty close to what a hardwire bypass would be) and see if you can hear any difference. :)

http://rover.ebay.com/rover/1/710-5...0001&campid=5338728743&icep_item=331759443681

Well the Mk2s have been back for a couple of weeks, caps and fuses changed. This was very good advice. The image is extremely impressive, there is no sense of box, or rather cylinder, at all, and I’d advise anyone with Mk2s to do likewise. As we’ve kind of said before, they don’t efface the fond memory of the special tone of the midrange of the Mk1s at all, but when listening to the Mk2s, I don’t miss the Mk1s either. I guess it’s good to have both, I just need to buy a bigger house with more rooms.

Just looking at Tony’s musings about the crossover in his Falcons, and the sort of real presence he says the image has in the midrange, I wonder if the crossover in the MK2s uses the lessons learned while designing the LS3/5a.
 
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Just looking at Tony’s musings about the crossover in his Falcons, and the sort of real presence he says the image has in the midrange, I wonder if the crossover in the MK2s uses the lessons learned while designing the LS3/5a.

I suspect it is more that the problem the LS3/5A and MkI 149 had to address (the known resonant peak in the low-treble region of the B110) may not have existed at all in the Focal unit, which was obviously a later generation of driver.
 
I suspect it is more that the problem the LS3/5A and MkI 149 had to address (the known resonant peak in the low-treble region of the B110) may not have existed at all in the Focal unit, which was obviously a later generation of driver.

I think you should treat yourself to a pair of Mk2s sometime. Then you can do a big compare and contrast project.
 
I’d love to try them, but I have to admit they make me nervous as, as can be ascertained by this and my other threads in this room, I have weapons grade OCD when it comes to vintage audio and those drivers are just not available. If a very close to mint and ideally boxed pair turned up I’d certainly be very tempted though. There is no such thing as too many mini-monitors, right?
 
Got round to fitting the Falcon cap kit today, before & after pics below;
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Falcon sent a slightly different set of caps to the last set they sent me (see post #919), all electrolytics this time.
I measured the old caps after removal, they were all on the high side, the 3.3uF caps vary between 5.7uF & 21.1uF.
The ribbed foam has also arrived from America, just had to reglue the velcro strips which were peeling in places so will fit them tomorrow & post some pics.
Set them up in my main system for the moment while the new caps bed in, sounding really good so far.
TS
 
That set of Falcon selected caps looks exactly the same as the set they sent me a few months ago. Having lived with the re-capped crossovers for just over a month I have to say they made a very positive difference. I use my JR149s in an edit suite setup – so for near-field monitoring – and they work superbly for my video and audio editing needs, as well as being very enjoyable to listen to music on.
 
Yes, they definitely make a positive difference. I also substituted the crappy bell wire speaker cable while I had them apart, fitted some generic 2.5mm ofc with banana sockets to make moving the speakers into different set ups easier.
The tweeter trim pots were set about 3/4 the way round (I had noticed this pair sounded a bit toppier than my previous pair) so I gave them a squirt of Deoxit & reset them about 1/2 way, sounding much more even now.
Fitted the new grilles this morning as well, they look much nicer than the plain foam, they are dark grey rather than black which makes them look less imposing but also more interesting.
Overall, despite the cost, very pleased with the results.
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Graham Hartle’s grille foams here on eBay. If you message him via eBay I believe there are options for the other JR models too.
 
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If you bear with this post you’ll eventually find it relates (loosely) to the JR149. :)

I finally dug my IMF MCR2A mini monitors out from the back of my wardrobe to measure; they haven’t seen daylight for about a decade! I’ve mentioned the MCR2A on this thread before, it’s one of the last models IMF ever produced and is their smallest, measuring 382mm x 198mm x 184mm (HxWxD), with an internal volume of 8.4L. It’s supposed to use a 5/36 mid-bass driver (IMF’s answer to the B110) and a TW2100F tweeter, but my pair are one of a handful that were fitted with KEF B110 and T27 units. This was done around the time IMF were being wound up, circa 1986. (It took me a few years to piece together the full story behind this and I don’t really want to go into the somewhat unsavoury details here).

I bought them in the late 2000’s and they arrived in NOS condition, complete with original box and packaging. They even still had their original, laser-cut brown foam grilles that still looked brand new (I’ve stored these in a dry, dark cupboard for the past 12 years in an attempt to preserve them!).

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They have a similar aesthetic appearance to the KEF Reference Model 101. The 5/36 and B110 share the same PCD so the B110 fits into the MCR2A’s rebated baffle cutout perfectly. The TW2100F was flush-mounted and screwed in from the rear (like the HF2000 in the RSPM), but the T27 is much larger than the TW2100F so the countersunk pocket was drilled out and the opening enlarged to accommodate the T27’s magnet. No rebate was routed, this means the T27’s face plate sits proud of the baffle. (I also have a pair of unadulterated MCR2A enclosures in my cupboard that I bought a couple of years later which are fitted with the correct MCR2A crossovers and 5/36 drivers but no tweeters. I've been looking for a pair of TW2100F's to install in them for 10 years without success; they are evidently rarer than rocking horse sh!t...)

When I originally received the T27/B110-equipped MCR2A's I removed the drive units to have a nosey inside at the crossover. I had great difficulty finding it as the enclosure is crammed full of long hair wool and I would’ve needed to removed a lot of it to create some space, and I decided against doing this at the time in case I disrupted anything. All I managed to eyeball was a small blue ALCAP, nothing resembling the proper MCR2A crossover. That’s not to say there weren’t more components inside, just that I did not see any more at that time. I could remove the drivers again and do a deeper dive, this time removing all the wool, but I’d rather not disturb them again as the solder tags on the B110 have a habit of breaking off with age. Besides, I was hoping you might be able to tell me something about the crossover from my measurements! :D

My original impressions upon first auditioning these T27/B110-equipped MCR2A were that they were very dynamic and revealing but rather forward-sounding and bass-shy compared to my JR149. I also noticed a ‘lispy’ quality to the treble. I don’t recall what made me try it but I fitted a pair of LS3/5A tweeter grilles onto the T27 domes and this had a marked effect on the treble, removing the ‘lispy’ character and adding more incision, detail and air higher up the spectrum (note this was all subjective impression, I had no measuring kit in 2008!).

I’ve been meaning to frequency sweep these speakers for years but never got round to it, until yesterday. I set each enclosure on a 60cm high stand and placed it hard against the wall to give it the best chance possible, and then proceeded to take measurements from 1 metre distance and at three heights: T27 axis, B110 axis, and the midpoint between the two. I set the volume for 80dB SPL at 1kHz.

IMF MCR2A measurements:

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IMF MCR2A commentary:
  • Pair-matching looks very good to me for aged KEF drivers that presumably were not hand-selected to go into these enclosures.
  • LF starts to shelf down from 400Hz and ends up around -7dB down in level from MF and HF.
  • The most linear HF response is obtained when on-axis with the T27. As you move toward B110 axis, a 5kHz cancellation emerges. What does this reveal about the crossover design?
  • The distortion plot looks fairly innocuous, though there is a slight in increase in 3rd order distortion around 1.5kHz. This may simply be due to running the tests at 80dB instead of my usual 70dB-75dB or it could perhaps reveal a low-order crossover or low crossover frequency is being used?
For a comparison I also repeated the tests on my JR149 mk1 and JR149 mk2. As luck would have it, the driver height and spacing in the JR149 mk1 and mk2 is exactly the same as the MCR2A. Note I did NOT change the volume on the amp for the JR149 mk1 and mk2 tests so any difference in sensitivity you see vs the MCR2A is due to the JR149 crossover.

JR149 mk1 measurements:

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JR149 mk1 vs MCR2A commentary:
  • The LF response of the JR149 is very similar to that of the MCR2A (similar dB output level), but the JR149 crossover’s baffle-step correction is attenuating the MF and HF by almost -5dB to achieve a more balanced frequency response.
  • The JR149 MF/HF is far less affected in the vertical axis than the MCR2A, there is no cancellation at 5kHz.
  • The JR149 has a less-forward response than the MCR2A between 800Hz and 3kHz, and also has less energy between 5kHz and 12kHz (though the 5kHz-12kHz difference is greater when the JR149 is measured on T27 axis and lesser when the JR149 is measured on B110 axis).
  • The JR149 does not exhibit the 3rd order harmonic distortion at 1.5kHz that the MCR2A does. This may simply be due to the lower SPL, or it might indicate that the JR149 is crossing over to the T27 at a higher frequency or with a steeper rolloff than the MCR2A crossover?
JR149 mk2 measurements:

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JR149 mk2 vs MCR2A commentary:
  • The LF response of the JR149 mk2 is very similar to that of the MCR2A (similar dB output level), but the JR149 mk2 crossover’s baffle-step correction is attenuating the MF and HF by around -3.5dB to achieve a more balanced frequency response.
  • The JR149 mk2 MF/HF is far less affected in the vertical axis than the MCR2A, there is no cancellation at 5kHz.
  • The JR149 mk2 has a more forward response above 1.5kHz that's quite similar to the MCR2A but does not exhibit the resonance at 1.1kHz.
  • The JR149 mk2 does not exhibit the 3rd order harmonic distortion at 1.5kHz that the MCR2A does. This may simply be due to the lower SPL, or it might indicate that the JR149 is crossing over to the tweeter at a higher frequency or with a steeper rolloff than the MCR2A crossover?
Further thoughts:
I’m going to try listening to the MCR2A with a few dBs of bass boost and see how they compare with my JR149s.
I’d also like to repeat the measurements with the metal grilles removed from the T27 domes, but I’m not sure if I’ll be able to remove them safely (I stuck them on with blu tac in 2008 and haven’t touched them since!).

So what do I have here, folks, something that's better or worse than a mk1 Kan? You have to admit they do look rather beautiful in their American Walnut veneer!... ;)

PS - If you feel this strays too much off-topic Tony please move it to another thread, I was reluctant to create a specific MCR2A thread for this as they're not MCR2A's as originally designed.
 
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They look really nice, chunky little things! I assume infinite baffle again, though obviously IMF were known for transmission line loading?

Looking at the differences between them and the 149s they might be a proper half-space speaker like a Kan and be designed to sound right hard against a wall or on a bookshelf. Certainly a lot more efficient in the mid/top, which I suspect again puts them more in Kan territory (though obviously the Kan never had a T27). Are the B110s SP1003s or one of the later variants?
 
They look really nice, chunky little things! I assume infinite baffle again, though obviously IMF were known for transmission line loading?

Looking at the differences between them and the 149s they might be a proper half-space speaker like a Kan and be designed to sound right hard against a wall or on a bookshelf. Certainly a lot more efficient in the mid/top, which I suspect again puts them more in Kan territory (though obviously the Kan never had a T27). Are the B110s SP1003s or one of the later variants?
Yes, they are chunky things! Sealed enclosure with 18mm thick walls. It's been too long since I removed the drivers to remember if the B110 are the SP1003 or the later SP1057 version. If you look closely at the photo you'll notice the surround on one looks different to the other, more matte/powdery in appearance. I'm not sure of the reason for this, but given their FR's are so closely matched they must be from the same era. The shelved-down LF response reminds me of the Goodmans Maxim I measured which had a 6dB differential between its lower and upper octaves. I remember you commenting that the Maxim would've been designed to go into a bookshelf and be flanked with books to help curtail the baffle step loss so perhaps a similar installation would benefit these MCR2A's. Would be a shame to cover up all that lovely walnut though!

Incidentally, when they're placed up against the front wall and you sit not too far from the rear wall, you get a very surprising kick from these thanks to the 42Hz room mode!
 
I think the matt aspect is just a little dust or damp. I gently cleaned up my original very grey and mouldy JR149 B110s quite successfully with a microfibre cloth and a little AytoGlym Vinyl & Rubber Care. I’m not necessarily saying I’d recommend this, and I’d certainly avoid the coated Bextrene which has a reputation for not liking liquids, but I tend to find it works wonders on tired rubber and plastic. It is amazing on old turntable mats too, really brings the supple aspect and life back. Helps UV protect too.
 
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I've added JR149 mk2 measurements to post #972 as another interesting reference for comparison. The mk2 model appears to bridge some of the gap between the T27/B110-equipped MCR2A and JR149 mk1, with the mk2's upper mids and lower treble being more forward than the mk1.
 
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Just parking this so I can compare on the same page (I’m on an iPad), but I’m curious as to how far from a boundary you are measuring? It certainly looks like your mids are relatively more loud compared to the bass than mine, so I’m assuming they are way out in free-space? Mine are about 10” from the wall.

PS I hadn’t read the scale properly. How have you got stuff at 40 Hz? Sub?
 
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Just parking this so I can compare on the same page (I’m on an iPad), but I’m curious as to how far from a boundary you are measuring? It certainly looks like your mids are relatively more loud compared to the bass than mine, so I’m assuming they are way out in free-space? Mine are about 10” from the wall.

PS I hadn’t read the scale properly. How have you got stuff at 40 Hz? Sub?

No sub, just the JR149. I'm measuring the speaker tight against the wall behind my listening chair and about 1.4m away from the side wall (it's now the only free space I have in my room to take 1 metre nearfield measurements without other objects in the vicinity!) I'll post a graph tomorrow of the MCR2A's and JR149's moved into proper listening position from my listening seat, then we'll see how deep they dig!...
 
That is interesting. As stated I’ve got the speakers about 10” from the wall, but the listening seat is pretty much middle of the room so I get no lift from the rear wall, I actually suspect I’m in a null there. It isn’t an optimal setup as it’s upstairs in the ‘record shop’ so there is vinyl & CDs piled up everywhere. The whole house is like that to be honest!

I must measure the LS3/5As downstairs at some point. Plonked in front of the Tannoys they had a surprising amount of bass, but the listening seat is close to the rear wall there so gives some LF reinforcement (can be a bit much on modern rap stuff with the Tannoys!). I suspect they’ll dig a bit deeper down there.
 
That is interesting. As stated I’ve got the speakers about 10” from the wall, but the listening seat is pretty much middle of the room so I get no lift from the rear wall, I actually suspect I’m in a null there. It isn’t an optimal setup as it’s upstairs in the ‘record shop’ so there is vinyl & CDs piled up everywhere. The whole house is like that to be honest!

I must measure the LS3/5As downstairs at some point. Plonked in front of the Tannoys they had a surprising amount of bass, but the listening seat is close to the rear wall there so gives some LF reinforcement (can be a bit much on modern rap stuff with the Tannoys!). I suspect they’ll dig a bit deeper down there.
Yes, if you're sitting in the middle of the room it'll completely suck out the speaker's low end response that coincides with your front-wall/rear-wall axial mode, which in my case is 42Hz (you can see how drastic the effect is in the REW Room Simulator).

When I was in my larger room I effectively had three different hifi setups (one on each side wall and a third on the front wall!). One of the side wall setups was JR149s on my computer desk, and it was great because the speakers were about 12" from the wall (couldn't get them any closer than that due to a pesky radiator) and I was listening no more than a metre away, so the room didn't have chance to mangle the bass response. I'd love to have a nearfield setup again but multiple systems in a 4.2m x 3.8m room is far less practical than it was in a 7m x 5m room!
 
JR149 mk1 measurements from my listening seat. Speakers on 60cm high stands, 1.8m apart, 1.1m from side walls, 20cm from front wall (I presume you're measuring this from the back of the end cap, Tony, not from the front baffle?). Distance from speakers to mic is 2.5m, mic is 1m from the rear wall and 104cm high (i.e. my normal listening height). This is 20cm closer to the rear wall than I listen to my Tannoys/Dittons at as it excites the 42Hz axial mode too much with full range speakers, but in the case mini monitors that are spec'd as -4dB at 55Hz some room mode support is useful!

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This listening distance is more to demonstrate the effect of the axial mode. I think it's too far away to obtain an immersive listening experience from a mini monitor like the JR149, it sounds rather undynamic and lost at this distance, even in a relatively small 4.2m x 3.8m room. I reckon a 2m equilateral triangle is probably the upper limit for a speaker like this, and suspect a smaller 1.5m equilateral triangle is the sweet spot. The latter, sadly, would put my listening seat slap bang in the middle of my room and devour all bass below 53Hz...
 


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