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Jim Rogers JR149 DIY build

Discussion in 'd.i.y.' started by martinclan, Sep 13, 2022.

  1. martinclan

    martinclan Member

    I have been looking for a pair of JR149 speakers for a while now but mostly everything that has turned up is either in poor condition, overpriced (IMHO) or both. I suppose I shouldn't be surprised as the JR149 must be getting on for 40 years old now, and the fact they use the same drivers as the famous BBC Monitor LS3/5A makes them desirable.
    So - I am considering making a DIY version. I have the skills required, the only possible problem being the D shaped alumnium tube in which the drivers are mounted, but if I can't make that I know a man that can...
    The plan is not to spend a fortune just in case things don't go according to plan. My current thnking is to use the Vifa D27TG-35 tweeter and the Monacor SPH-135 as the midrange/woofer. The crossover is well documented so making these won't be a problem.
    Any thoughts anyone?
  2. Tony L

    Tony L Administrator

    I’ll be fascinated to see how you get on with this. I’ve always been baffled why no one seemed to follow-up such a logical low-mass and rigid construction technique. I guess one could argue their conceptual successors are Genlec, Neumann etc with their high-tech cast alloy cabs, but the simplicity and cost-efficiency of the 149 was very clever.

    PS I’m sure you are aware Jim Rogers started life as a metal-worker I think in the auto industry. The 149 cabs are rolled from a flat piece of aluminium using techniques he learned in that trade. The roller marks are always visible on the cabs!
  3. JensenHealey

    JensenHealey pfm Member

    I will be keeping an interest in this project - I have had a hankering about doing something similar myself. But have not diy-ed a speaker since I was a teenage student!
  4. divedeepdog

    divedeepdog pfm Member

    Avondale Revelation speakers are rolled sheet steel D with welded in baffles, probably not your idea of light, but hugely rigid and thin walled. Squint at Wilson Benech (spelling?) and there are similarities in shape at least.

    Les has ideas about recreating Revs with CF cabinet and SS baffle, modern materials of the day?
  5. S-Man

    S-Man Kinkless Tetrode Admirer

  6. Tony L

    Tony L Administrator

    Given the plethora of infinite baffle mini-monitors around at present I’d assume there were a fair few decent 5” mid-bass units knocking around. What do ProAc use in the Tab 10? I think their drivers are usually variations on Seas units. If I was embarking on a project like this I’d certainly be trying to take the basic 149 cabinet concept forward with modern driver technology. I’d be looking at the best bass-mid and soft-dome tweeter I could find that would work in the cab volume, not a direct equivalent of a B110/T27.
  7. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    There was the Dalesford D.

    The crossover may well be well documented but was designed for the B110 and T27.... Also the cabinet volume and amount of absorbent material are correct for the B110.
    Fatmarley and MikeMA like this.
  8. MikeMA

    MikeMA pfm Member

    This crossed my mind too. If the OP uses different drivers then he will almost certainly need crossovers tailored to match drivers and cabinets - probably the hardest part to get right unless you really know what you're doing.
    Fatmarley likes this.
  9. Tony L

    Tony L Administrator

    True, though good modern drivers should need far less crossover complexity than the Kef units.
    davidsrsb likes this.
  10. martinclan

    martinclan Member

    Thanks for all the input guys. I understand at least some of it.... Good points made about using modern drivers and that interesting thread on DIY audio.
    I have started the ball rolling discussing with a friend of mine, who is a sheet metal artisan, the construction of the alluminium D shaped tubes that form the main part of the enclosure. I wanted them made from 2mm aluminium which he thinks is beyond the capabilty of hand tools and needs to be machine made. The outcome being that he is going to give me a quote for making them.
    I now have plenty of reading to do....
  11. S-Man

    S-Man Kinkless Tetrode Admirer

  12. Tony L

    Tony L Administrator

    FWIW I’m convinced one reason JR149s sound so good is the lack of cabinet mass. They are not a heavy speaker for their size at all and the combination of thin alloy, deadsheet and foam makes for a pretty inert structure. You don’t get a ‘note’ when tapping a 149 cab and that puts them in a tiny minority of speakers and hardly any that also have the advantage of low mass. The original aluminium is not thick at all, I’d research its thickness before assuming you need 2mm. The secret is the effective lamination with the black deadsheet inside. That seems to damp them very well without adding much mass.
  13. Fatmarley

    Fatmarley "It appears my intelligence circuits have melted"

    I was always under that impression until I saw this measurement.

    Any problems with the frequency response would be caused by cabinet diffraction, internal reflections or reactance from the crossover.

    The best 5" driver that I know of, with a linear frequency response, that will also work well in a sealed enclosure was used by James in his Ergo IX -

    As said above, the crossover is by far the most difficult bit to get right. To do it properly you need to take measurements of the individual drivers, and model in software.
    MikeMA and a.palfreyman like this.
  14. S-Man

    S-Man Kinkless Tetrode Admirer

    The Monacor 145 is more similar to the B110 than the Revelator. It also has a smoother frequency response. Of course it will only play as loud as a B110, not the Revelator.

    It's also a lot cheaper!
  15. mik_rik

    mik_rik pfm Member

    I think it was the then Popular Hi-Fi ,back in '79,I think,that ran a d.i.y JR149 type project on how to make a "Builders Yard loudspeaker" using earthenware drainage pipe (possibly saltglaze pipe) as the cabinet material.Article may be found online somewhere,(haven't checked)
  16. martinclan

    martinclan Member

    Hmm - that looks interesting. Unfortunately the tweeter (Monacor DT-19SU) doesn't seem to be available in the UK. The bass/midrange (SPH-145HQ) seems to be available from Wilmslow.

    I guessed at 2mm from the only picture I have seen of a dissasembled JR149. If anyone knows any better please let me know. 1.5mm aly, or less, is generally workable with hand tools. Just look at my Avatar for how I know.

    I am old enough to remember it although my attempts at a network search hasn't found the article.
  17. Fatmarley

    Fatmarley "It appears my intelligence circuits have melted"

    S-Man likes this.
  18. davidsrsb

    davidsrsb pfm Member

    I would use a 28mm tweeter, which simplifies squeezing the top end out of the mid-woofer
  19. cpg

    cpg pfm Member

    S-Man likes this.
  20. Fatmarley

    Fatmarley "It appears my intelligence circuits have melted"

    That's interesting. The measurements show a peak at 1khz that is not shown in the dibirama ones. It's a different model b110 but even so, I'd imagine it's only the motor that's different. My Ciare HM500 didn't measure like theirs, so I'm starting to doubt their measurements.
    I'd imagine the falcon version has the same peak because although baffle diffraction will bump up this area, the measurements in stereophile show quite a sharp peak that's more than diffraction would cause.

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