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Thread: Another Troels Gravesen Jenzen build.

  1. #1
    Join Date: Apr 2012

    Location: United Kingdom

    Posts: 2,136
    I'm Richard.

    Default Another Troels Gravesen Jenzen build.

    I thought I ought to start my own thread here instead of kibbutzing Phil's.
    This build started last year, and the speakers have been running since midnight on 22nd December. If that sounds rather precise, it's because I was having an operation on my hand on the 23rd, and if I didn't get them running before then, it would be several weeks before I could continue!
    Anyway, I made it, but haven't touched the crossovers since then, and they WILL need some tweaking. I won't post all the pics, as some of them are very similar to Phil's, so I'll mainly document the differences.
    My cabinets are 24mm, 18mm birch ply plus 6mm MDF, with the fronts 18 + 6 + 18mm. These are screwed on at the moment, but will be glued when I have finished routing the edges. At the moment I am veneering the new sand filled side cheeks, which is a pain. My veneer is old and splits easily, but it was cheap!
    The tops will be 15mm sandstone set into oak framing.
    The carcasse is biscuit jointed, glued AND screwed. I believe in overkill!





    I started out using some SEAS bass units I had, but quickly found they weren't suitable, so bought the specified type.

    Phil sent me some reticulated foam for the ports, which wedge in easily.

    I stained the fronts black, just to see how they would look (they will be covered with black leather similar to Sonus Fabers), and put bars over the drivers to protect them from grandsons with rucksacks! It turns out my wife likes the look so they will be staying. They may all be brass in the end.

    After a while I felt the midrange could be improved, so I earned enough to replace them with the Nextel W18NX001 drivers. Crossover is still the same for now, but I emailed Troels with some questions, so it will soon be modified, as they are a bit brighter than the old mids.

    When the sand filled sides are ready to fit, I will trim the front panels, rewire and modify the crossovers. Then work on the TL stuffing.

    I have had some success with Townshend style stands, so will make some to fit these speakers and see how that works. I use 2 inner tubes, which means I can adjust for tilt.

    At the moment Massive Attack is rattling away, but these speakers seem very sensitive to cabling; I've changed the speaker cables from silver plated stranded to Polk Cobra litz, quadrupled. Makes quite a difference, so I will try changing the internal wiring too, and run direct from the crossover to the drivers with no breaks.
    Well, that's where I am at the moment, and as soon as they sound half decent I want to host a bake-off to try different amps. I need to know what the limiting factors are before I try to fix problems that may be nothing to do with the speakers!

  2. #2
    Join Date: Feb 2011

    Location: northern ireland

    Posts: 288
    I'm ron.

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    Looks superb mate well done can't wait to see them when completed

  3. #3
    Join Date: Apr 2012

    Location: United Kingdom

    Posts: 2,136
    I'm Richard.

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    Progress is slow, partly due to trying to work out how to apply the veneer without visible joins. Changes in humidity mean the veneer expands and contracts, and matching filler is hard. I am now trying to pre-lacquer the veneer to stabilise it and then cut and glue it. Anyway, here is what they should look like when they are fixed; these are only propped up to have a look. My wife still likes them, and that is half the battle. The stands/bases will match, and there will be a solid oak trim around the top, with a 15mm limestone slab inset.




    The fronts need the edges chamfering and the black leather applying before the sides are glued on. Which will be very heavy when they are sand filled!
    From where I sit, nearly face on to the right speaker, they look rather muscular with the curved sides, almost like hunched shoulders. I rather like that, it gives them presence, especially with the grills. I am quite surprised that my wife likes those!
    I am waiting for drier weather before I lacquer the veneer, so it hopefully won't shrink anymore, so I think the next job is to make the new larger crossover boxes to go on the back, with sloped sides to make them less visible from the front, and I guess I'll veneer them too. Crossover changes mean I want extra room for more or bigger components, like C core inductors or Russian PIO caps.

  4. #4
    Join Date: Apr 2012

    Location: United Kingdom

    Posts: 2,136
    I'm Richard.

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    I've been looking at other TL designs, including ones I have built myself, and one thing stands out compared with Troels'; the port is generally at least as big as the line. Troels makes his smaller, and I wonder if this is causing back reflections at some frequencies. Of course, this may have all been taken into consideration, and if it's working OK then there is no need worry about it. However I am not satisfied with the bass performance, and I stress this is in MY room with MY amplifier (a temporary one at that), with MY speaker positioning (with which I am stuck), so I plan to widen the port slot out to full width. At the moment it has an area of 150 sq/cm, the line is 270 sq/cm, and the bass driver is 350 sq/cm. The relationship between the driver and line is reasonable, but I am dubious about the port. If I recut it to better match the line, I could easily add fillets to reduce it again if I am wrong, without disturbing the front finish, but not increase it after the leather is applied.
    Also I will stuff the line like the Chris Rogers PRO9TL, a design I built many years ago, and which worked well. Of course that was in a different room, etc. I still have plenty of wool, so it won't cost me any extra, just time and effort!
    Phil is happy with his performance, so it may just be my room, and as I am pretty much stuck with the positioning, this could work for me. I have built enough TLs in the last 40 years to know how good they CAN be, but never in this house.

  5. #5
    Join Date: Aug 2012

    Location: Hartlepool UK

    Posts: 1,512
    I'm Alan.

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    Very nice build
    How do they sound
    Alan
    Turntable - Garrard 401/Jelco 750L/Ortofon Kontrapunkt B, Pioneer PLC 590, SME 3009/2 , Denon DL103R - DIY Paradise Phono stage - Reel 2 Reel Studer A810, Otari MX55,Tascam BR20, Revox A77, B77, PR99, TEAC X1000 & 3440, Technics RS1500 - Digital HTPC / Young Dac - Preamp - DIY B4, 821, Power Amp's DIY Voyager Mono Block, Speakers Tannoy precision 6.4 / Wilmslow Kit Volt BM220.8 / Scanspeak D2905/9500

  6. #6
    Join Date: Apr 2012

    Location: United Kingdom

    Posts: 2,136
    I'm Richard.

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    Well, the bass isn't right yet, and the treble was a bit fluffy and sibilant. But yesterday I looked at the grills over the tweeters and wondered......... They are about 18mm from the dome, and I worked out that wavelength equated to 17-18 kHz (I think!). Half wave is 8.5-9 kHz, and a reflection would try to cancel at that. Anyway, I took the 2 outer bars off and what do you know, it sounds better! Now I may be fooling myself here, but if it makes me happy, who cares? I'm definitely getting somewhere now, but until the cabinets are finished I can't really tune them. I will do some measurements then and move them around, just to see what happens. I just hope I can finish them before I get to old to move them!

  7. #7
    Join Date: Apr 2012

    Location: United Kingdom

    Posts: 2,136
    I'm Richard.

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    Not fooling myself after all. How can removing 2 little brass bars (2.3mm brazing rods) make such a difference? Reflections? Refraction? I don't know, but these speakers are far more sensitive to small changes than I expected. I am hoping that adding notch filters as Troels did to the NEXT version will clean it up further, without killing it. The new crossover boxes are nearly made; I will veneer them next. Do I use matching oak, or wenge? I have both, and dark may look better round the back. Decisions, decisions.

  8. #8
    Join Date: Nov 2011

    Location: Wantage

    Posts: 265
    I'm Frank.

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    There is a good chance that those rods are buzzing away when excited themselves by the music just next to them. Metal has pretty well zero internal damping.
    Try touching them very lightly when playing music and see if you can feel any vibration. If you can feel it at all you will be able to hear it. (try lightly touching the mid-range unit when playing to get a feel for the level of vibration you can hear).
    I was amazed when I first tried it.
    That is when I became a fan of extremely dead speaker cabinets.

  9. #9
    Join Date: Apr 2012

    Location: United Kingdom

    Posts: 2,136
    I'm Richard.

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    Hi Frank, I thought of that, and the bass bars have enough tension in them to ring if I flick them, but the little brass rods on the tweeters were not tight in their holes; not under tension, and damped by the fluffy nature of the ply. So I don't THINK they resonated, anyway I couldn't feel any, but who knows, you may be right. They're staying out anyway, one is enough to protect the tweeters, but I will try removing that one too when the crossovers are upgraded.
    A question, for anyone really, is it worth using Mills non-inductive wirewound resistors instead of Jantzen MOS or Superes 10w resistors, especially in the tweeter section? I know some people think it is an improvement, but I have no experience with them. Z foil resistors made a difference in my DAC, so I know resistors CAN sound different, but that is a different application.
    I agree about killing cabinet vibrations, that is why I am making the sand-filled side panels. And if I can isolate the top cabinets from the bass cabinets, I will do that too. Plus some new Townshend style isolation plinths. It costs me very little to do these things, mainly time.
    Anyway, I have been busily veneering the crossover boxes today (I decided on oak; it was easier!), even though they will be unseen round the back of the speakers. I intend to hang them on rubber rings, to isolate them from cabinet vibrations; I don't know if it matters, but it's another doubt out of the equation, and easy enough to do. If I can find some chunky handles to use for hanging them, they will double up as transport handles.

  10. #10
    Join Date: Apr 2012

    Location: United Kingdom

    Posts: 2,136
    I'm Richard.

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    Crossover boxes made, veneered and lacquered. I should get out more!


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