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Revisiting Jim Rogers JR149s

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Just for clarity if anyone is playing along at home: when I said I had the pots set by ear to 29-30 Ohm (this value measured with the pots out of circuit when I was swapping them over) this is between the wiper (VR1) and the pin that connects to the 4R7 resistor.

PS I accept acoustic measurement in a perfectly controlled condition is of great value, it is just far harder to do in reality as moving the mic just a cm in any direction or getting the speaker a degree or two difference in axis (getting a round JR149 perfectly square on the stand) often impacts the plot more that the thing one is trying to measure! Ears seem far more useful unless one has an anechoic chamber to hand! In my close near-field listening setup leaving the mic in position between changes would just impede the listening space too much, it would inevitably get knocked out of position. I’ll do a measurement right at the end of this process once I’m happy.
 
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Just for clarity if anyone is playing along at home: when I said I had the pots set by ear to 29-30 Ohm (this value measured with the pots out of circuit when I was swapping them over) this is between the wiper (VR1) and the pin that connects to the 4R7 resistor.

PS I accept acoustic measurement in a perfectly controlled condition is of great value, it is just far harder to do in reality as moving the mic just a cm in any direction or getting the speaker a degree or two difference in axis (getting a round JR149 perfectly square on the stand) often impacts the plot more that the thing one is trying to measure! Ears seem far more useful unless one has an anechoic chamber to hand! In my close near-field listening setup leaving the mic in position between changes would just impede the listening space too much, it would inevitably get knocked out of position. I’ll do a measurement right at the end of this process once I’m happy.

It's been a while since I acoustically measured the effect of the trimpot, but I recall each quarter-turn affecting a 0.75dB change in output above 4kHz. though the first evidence of change appears to be from just above 2kHz.

If you're making adjustments of just one or two degrees, I'm not convinced this would show up as an amplitude change on a FR graph, in which case I would indeed defer to trusting your ears over measurements.

Unfortunately I took these measurements at a time when I was unaware of comb-filtering when measuring at close distances. Also, the measurements were also made with the speaker turned upside down, allowing quicker trimpot adjustment. I suspect the combination of these two factors is responsible for the rather peculiar HF response. One day I'll get round to making fresh measurements!...

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It's been a while since I acoustically measured the effect of the trimpot, but I recall each quarter-turn affecting a 0.75dB change in output above 4kHz. though the first evidence of change appears to be from just above 2kHz.

If you're making adjustments of just one or two degrees, I'm not convinced this would show up as an amplitude change on a FR graph, in which case I would indeed defer to trusting your ears over measurements.

I’m certain the thing a listener is more sensitive to is the balance across the crossover region, not the ultimate treble level, hence my feeling the really important stuff is around violin bows, orchestral string balance etc rather than really high treble (or as high as I can hear anyway). It is all about getting the changeover between drivers absolutely seamless. I seem especially sensitive to crossover issues, there are many well-liked speakers I just can’t deal with as I don’t like the driver integration, so it makes sense I’ll be pretty critical here. A tiny movement is very noticeable IME. Your graph, whilst I’m not convinced it accurately represents the 149s tonal balance, does indicate a good bit of change across this crossover region. It correlates with what I’m hearing.

I will certainly measure mine again at some point fairly soon as all my previous measurements date from before I discovered the resistor error on my crossovers.
 
The changes around 3kHz are the most important, especially female voice.
Music has far more power there than above 10kHz
 
Ok, curiosity once again got the better of me and I stuck the two Mundorf 3.3uF on the tweeter in the ‘known good’ crossovers. It was very interesting and certainly made the treble more prominent, so I backed it off with the level pot until I got a good natural balance. I assume this is the ESR effect. Even when I’d knocked it back quite a lot I still felt something wasn’t quite right, though I’m sure a lot of people would prefer it. If one were to draw a ‘speaker voicing graph’ with say Quad ESLs, proper Tannoys, BC1s etc at one end (this being where I live), and a modern lean bright forward speaker like say a JM Labs at the other, then for my taste it shunted the 149s in the wrong direction. Wonderfully open and clear, but just too analytical and spotlit for me to ever enjoy.

As such I have learned my lesson and now reverted the crossovers back to the Alcaps, i.e. I even pulled out the poly 1.5uF notch filter I did several months ago. These speakers are just right how they were originally voiced by Jim Rogers and I would recommend anyone with a pair simply restores them to as close as NOS as is possible. A fascinating experiment though and I’m really pleased I did it with two sets of crossovers as I’m sure that speeded up my error-correction. I’m now happy they are as good as I can get them and I’ll just leave them be.
 
Ok, curiosity once again got the better of me and I stuck the two Mundorf 3.3uF on the tweeter in the ‘known good’ crossovers. It was very interesting and certainly made the treble more prominent, so I backed it off with the level pot until I got a good natural balance. I assume this is the ESR effect. Even when I’d knocked it back quite a lot I still felt something wasn’t quite right, though I’m sure a lot of people would prefer it. If one were to draw a ‘speaker voicing graph’ with say Quad ESLs, proper Tannoys, BC1s etc at one end (this being where I live), and a modern lean bright forward speaker like say a JM Labs at the other, then for my taste it shunted the 149s in the wrong direction. Wonderfully open and clear, but just too analytical and spotlit for me to ever enjoy.

As such I have learned my lesson and now reverted the crossovers back to the Alcaps, i.e. I even pulled out the poly 1.5uF notch filter I did several months ago. These speakers are just right how they were originally voiced by Jim Rogers and I would recommend anyone with a pair simply restores them to as close as NOS as is possible. A fascinating experiment though and I’m really pleased I did it with two sets of crossovers as I’m sure that speeded up my error-correction. I’m now happy they are as good as I can get them and I’ll just leave them be.

Is it possible the Mundorfs have a break-in period?
 
Very unlikely. High ESR from aged bipolar electrolytics is the main reason for the changes. Subtle shifts in resonances due to tolerance is also possible
 
Is it possible the Mundorfs have a break-in period?

I did consider that and felt I should leave them in for a month or two, but the difference in perceived level is significant, so I concluded I’d actually changed the circuit in an unpredictable way. To get a treble balance I felt was balanced I was having to turn the level pot about 8 minutes or so (higher attenuation).

Very unlikely. High ESR from aged bipolar electrolytics is the main reason for the changes. Subtle shifts in resonances due to tolerance is also possible

For clarity the Alcap electrolytics are not aged/vintage, I put them in fresh soon after I started this restoration project. As such they are very comfortably within their expected lifespan, though are certainly ‘burned in’ or whatever. They should be good for another 15 years or so hopefully.

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They are now back looking exactly like this earlier pic aside from being a bit cleaner and with better condition level pots! Thankfully the boards have nice quality tracks and pads so no issues at all with reworking, looking at the back of the board there is no evidence of my tampering at all.
 
A couple of measurements of where things are right now:

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This from my listening bean-bag, so quite low down below tweeter axis. I used a 'psychoacoustic' smoothing for the both trace just to make things more readable. Very happy with this, its a nice natural balance in practice reflected in the measurements. The L & R are surprisingly closely matched given they occupy different environments in the room, the L being fairly close to an Ikea record rack, the right far less impeded as there is a door to the right of it.

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Here's a more 'purist' measurement of the right one at one metre on tweeter axis. Again I'm very happy with that, very smooth over the crossover region and one isn't conscious of the bass cancellation which I assume is an interaction with the front wall (they are about 8" from it).

The aim of doing these measurements now I'm happy with the cap choices etc was just to see if I could dial the tweeter pot in any better, but looking at the plots I've nailed it by ear, I don't really see how I could improve on that 2-4kHz range. Its flat!

This is just using the default settings in REW, I don't understand it well enough to do anything more clever at this point! The test tone was running passively from the MacBook headphone out into the Audio Synthesis attenuator and Leak as for some reason I couldn't get the Mac to talk to my Marantz SA8005's USB input. No idea why and I just couldn't be arsed wasting time faffing with it. Whether that has had any effect on the response I don't know.
 
@Tony L, is the 'both listening seat' measurement with both speakers playing at the same time as a stereo pair or is it the averaged response of the individual left and right measurements? I often run into problems when measuring both speakers simultaneously and end up with erroneous cancellations/peaks showing in the upper-mid and high frequencies. I presume this is because the mic struggles to cope with two competing sound fields as the frequency increases. I therefore average the left & right responses and use that as my 'stereo' measurement instead. Your stereo measurement however looks very well behaved and traces the individual responses pretty well, so I'd like to know what your secret is?!
 
Both is both playing together at the same time, not averaged. Here it is without the 'psy' smoothing:

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It does show some 'adding' or whatever to my eyes. I have no idea how to generate an average from multiple plots! I think I knew at one point years ago, but I certainly can't find an option now! If you can refresh my memory I'll do so from the L/R plots.

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Here's a waterfall from the same trace. No idea how best to set that one either. It certainly sounds clean as the listening seat is well away from any room boundaries and the room is well damped.
 
Go to the "All SPL" tab to the right of the "SPL & Phase" tab and you'll be presented with all the measurements you took. Uncheck all measurements bar the ones you wish to use in the averaging, then click the "Average the responses" button in the lower left corner of the graph. (FWIW it took me a few years to find this feature! :rolleyes:)

EDIT - The waterfall plot looks good with no audible resonances lasting longer than 350ms-400ms for the most part, which is allowing you to hear a clean/agile sound whilst retaining enough room ambience to avoid it sounding dead/unnatural. The decay times begin to increase below 100Hz, as they do in most typical living rooms, but the JR149's inherently curtailed low frequency extension and your preferred listening levels means this probably won't excite the room enough to have an audible impact.
 
Cool, here we go:

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Looks a bit flatter, but I assume the 'both' is more accurate as that is what you'll actually be listening to in-room as things will add/subtract with two speakers producing output.
 
but I assume the 'both' is more accurate as that is what you'll actually be listening to in-room as things will add/subtract with two speakers producing output.
I'm not sure how equatable a single mic in a single position is to a pair of ears a few inches apart. I'm inclined to hedge my bets and say that the lower frequencies on the stereo measurement, and the higher frequencies on the left & right averaged measurement, are the more accurate indicators of what your ears experience, but I'm happy to be corrected!
 
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Another day, another measurement as I wanted to see exactly what the level control does on my pair. This is the right speaker (it is slightly further from boundaries, so possibly the better measurement candidate). The measurement is at 1m on tweeter axis (not how I listen at all), the speaker the correct way up on the stand. It is quite a subtle setting for sure, but still very audible in practice. The red trace is where I had the pot set, which is just a smidge below the mid point, probably about ‘12:30’ (confusingly clockwise is cut, anti-clockwise boost).

I’ve just reduced the setting to about ‘1:30’ as I think I still had it just a little ‘hot’ for my taste. I’ve also been searching the internet for pictures of JR149 crossovers and I have a feeling the pot tended to be set about 2:00-3:00 on the old red-label pairs, i.e. quite a bit of cut. I’ve not seen enough consistency on later crossover types like mine so I’ll just carry on doing it by ear very slowly over many CDs and weeks. Once I’m really happy with the basic tweeter level I’ll then have a go at pair matching using the same stand. My feeling given my drivers are so well matched the visual pot position is likely pretty much bang on, but I will eventually check. They certainly sound balanced!
 
@Tony L, I'm presuming you dialled-in the optimum tweeter level setting with the foam grilles still on the speakers? I took measurements as I was convinced I could hear a subtle difference between grilles on and off, and sure enough the ribbed foam has an effect on the response above 2kHz, providing almost 0.5dB attenuation from 2kHz-8kHz and about 1dB attenuation between 9kHz-20kHz, as shown in the first graph I uploaded in post #445. It's pretty minimal in the grand scheme of things, and thankfully the effect is very linear, but worth being aware of.
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I wish my Ditton 66 grille had such a benign effect on its response, - it knocks an average of 2dB off everything above 4kHz (I say average because the effect isn't linear, - the metal grid structure must be diffracting certain frequencies more than others!).
 
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Yes, grilles on. In fact I haven’t disturbed the grilles for a couple of years now! They are a couple of mm over-sized length-wise so I try to do nothing that will stretch them!
 
I've got a pair of early 16 ohm JR149s, they're a bit battered. The grille has long since disintegrated and the wooden top is worse for wear, in fact I think they've been painted more than once, poorly.

I swapped the old bell wire with some cat 5 cable I had lying around, the crossover is all original.

I can appreciate their industrial chic, but my wife really dislikes the look of them - I've been thing of transferring the bits over to a LS3/5A cabinet (made in Moldova).

I know they'll fit into domestic life a lot better that way, I've probably sent some of you into an apoplectic reaction ;-)
Am I right to assume the drivers will fit ok?
 
I've been thing of transferring the bits over to a LS3/5A cabinet (made in Moldova).

Am I right to assume the drivers will fit ok?
Yes. You might struggle to fit the crossover in though. And of course the crossovers are different electrically/sonically as well.
 
Sadly tatty 149s are commonplace, a shame as a mint pair with correct fluted grilles like mine are timeless design classics IMO.

If rehousing the drivers to LS3/5A cabs you really need to use proper LS3/5A crossovers. Falcon can supply them either built or in kit form.
 


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