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Thread: Opinions wanted: 240Ti vs L-150A

  1. #61
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    Quote Originally Posted by SEAWOLF97 View Post
    looks nice ...
    for foam, I just went through old packing boxes and found some pliable, but firm open cell foam that was older, but didn't seem to deteriorate at all.

    the hardest part (for me) was getting all those blades inserted and hoping "the plinth" would not break or crack ... seems like you did fine. .... I like to mark 'the plinth" and the mag with a marker in the same spot when separating so to get correct (original) orientation when reassembling.

    OH, and don't forget to blow out (with compressed air) the gap , sure some foam dust got in there ... can see in your pic.
    Hi, and thanks again guys ! Good idea, I must have some old foam somewhere. Matress foam, maybe?
    Next one I'll use less/narrower leverage and more patience, even if it worked out without breaking. The double sided tape will let go, eventually. It is beginning to deteriorate too, btw (made 1987). The rear of the plinth may need some cleaning, the tape isn't sticky anymore. I'll post a pic of the rear too when I can take one. I did mark orientation just like you, and will do the dust job once I get my compressor out of storage . But the tricky part is done, - couldn't have done it without the help I found here.

    For reassembly I intend to follow described procedure: put som guides in the screwholes and lower into position using the guides. Since the tape isn't that sticky anymore, I wonder if I should replace it? The cleaning may be difficult/risky near the coil, and I wonder if extra tape may put it out of position?

  2. #62
    Senior Member SEAWOLF97's Avatar
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    Quote Originally Posted by Dagfinn View Post
    Hi, and thanks again guys ! Good idea, I must have some old foam somewhere. Matress foam, maybe?
    Next one I'll use less/narrower leverage and more patience, even if it worked out without breaking. The double sided tape will let go, eventually. It is beginning to deteriorate too, btw (made 1987). The rear of the plinth may need some cleaning, the tape isn't sticky anymore. I'll post a pic of the rear too when I can take one. I did mark orientation just like you, and will do the dust job once I get my compressor out of storage . But the tricky part is done, - couldn't have done it without the help I found here.

    For reassembly I intend to follow described procedure: put som guides in the screwholes and lower into position using the guides. Since the tape isn't that sticky anymore, I wonder if I should replace it? The cleaning may be difficult/risky near the coil, and I wonder if extra tape may put it out of position?
    >>Matress foam, maybe?
    I would GUESS that kind of foam is CLOSED cell ??

    I would not bother with the tape/glue ... it's the 4 bolts that hold & center it. The tape just makes it more difficult as once the dia is in place & stuck, cannot adjust.

    IF you can't get to the compressor, maybe a wood toothpick could do it, but NOTHING METALIC into the gap. , but still blow it out afterwards
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  3. #63
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    Quote Originally Posted by SEAWOLF97 View Post
    >>Matress foam, maybe?
    I would GUESS that kind of foam is CLOSED cell ??

    I would not bother with the tape/glue ... it's the 4 bolts that hold & center it. The tape just makes it more difficult as once the dia is in place & stuck, cannot adjust.

    IF you can't get to the compressor, maybe a wood toothpick could do it, but NOTHING METALIC into the gap. , but still blow it out afterwards
    Hm, I'm not too well informed on foams . But, looking at https://www.foambymail.com/open-cell-foam.html, which would you choose?

    It's not biking season, so I have to move some stuff to get to the compressor, but I will. I see minute fragments in there, and possibly space where dust could hide. The glue from the old foam plug is not so easy to remove after the plug has powderized, it seems. For other surfaces I would use a solvent to remove it, but since you mentioned non-metallic, maybe that is a bad idéa?

    Also, out of curiosity and ignorance, what would happen if you used something metallic in there?

  4. #64
    Senior Member macaroonie's Avatar
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    You can buy comp air aerosols for cleaning electronic stuff.

    Or CO2 canisters for beer , watch for frosting.

  5. #65
    Senior Member SEAWOLF97's Avatar
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    Quote Originally Posted by Dagfinn View Post
    Hm, I'm not too well informed on foams . But, looking at https://www.foambymail.com/open-cell-foam.html, which would you choose?
    I'd go for the Speaker / Filter Foam (30 PPI) , but you only need about
    1 cubic inch per speaker.

    https://www.foambymail.com/SFF-/spea...am-30-ppi.html
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  6. #66
    Senior Member grumpy's Avatar
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    tape, sticky side out, on a stiff piece of plastic... e.g., part of an old credit card.
    new tape, clean gap, inspect gap and tape, repeat until clean.

    You don't want to add any abrasive or metal bits in there.

  7. #67
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    Great, I should get it clean . I have a few foams available I've found, now that I know what "open cell" is.

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    I very, very gently brushed off some powder sticking to the rear of the dome with a very soft art brush. A little is still left, but I don't dare pushing harder on the brush. Double sided tape is hardly sticky anymore, so I'll just remove what is loose and comes off easily...

  8. #68
    Senior Member grumpy's Avatar
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    That should be fine. The charcoal pick&pluck foam from the same vendor might be worth checking too (nice sized chunks pre-scored). Whatever is used should compress -very- easily. The foam plug that came with the factory diaphragm replacement was a bit taller than the height of the installed diaphragm at it's highest point on the dome, so there should be some foam plug compression when installed. There may be pictures in the 044 thread. I'd shoot for it just touching the top of the dome if unsure about the squish-ability of the foam.

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    Looking closer at foam specs, they have huge variance in "typical lifetime", from very short up to 18 years, as best I could find.

    https://www.foambymail.com/hd36-hq-foam-sheet.html - typical lifetime 12 to 18 years. High density, support factor 1.9. Medium feel.
    https://www.foambymail.com/charcoal-reg-foam-sheet.html - typical lifetime 8 to 10 years. Low density, support factor 1.9. Medium feel.
    https://www.foambymail.com/speaker-f...et-30-ppi.html typical lifetime 5 to 10 years. No support factor data, but medium/firm feel.

    , makes me wonder how long the random stuff I have would last. Perhaps best to buy something with spec, would be sad to do it again in two-three years...

    Alas, no shipping to Norway .

  10. #70
    Senior Member macaroonie's Avatar
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    One of the things that has always perplexed me about these foam plugs is that the idea is to control or reduce unwanted resonances.
    To that end JBL set it up so that the foan would be touching the back of the dome under compression. I would assume that the amount of compression would have been established through testing. Maybe.
    Lets take another look at it. The dome itself has rhat hydroformed pattern on the surface that is intended to break up ringing modes. In many tweets there is a felt damper behind the dome but not touching.
    What we do know is that Ti diaphragms can have a tinsel kind of sound about them. This is the payoff for the light weight.
    Now lets have a look at the dia in the 2450SL. 4" Ti with no ribs BUT it dous have a coating of magic dust ( fine grain Aquaplas ) This driver is known to sound excellent without harshness.
    I wonder why JBL didn't just go this path and put a felt damper not touching the dome.
    If it were me ,knowing what I know now having treated my own Ti Dias the transformation is very positive indeed.
    I would be heading down this path if it were possible.
    As you have spotted , there is foam and there is foam. All different never mind the thickness and hence compression.
    Anyone have some magic dust out there ?

  11. #71
    Senior Member SEAWOLF97's Avatar
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    THE MAN speaks .... :)

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    Quote Originally Posted by gtimbers View Post
    All 250 models were made in Northridge. All models had exactly the same enclosure dimensions and were built basically the same way. The woofer and mid bass were the same in all models. Only the 5" and tweeter changed. The best sounding model was the Jubilee and the weakest one was the original L250. From the 250Ti through to the Jubilee, this sonic difference was pretty small with each newer model sounding incrementally better. None of them had charge coupled networks, to my recollection.

    it is true that there is a foam damping plug under the titanium dome. It does take a set after time and doesn't damp as well. Changing the plug usually brings the tweeter behavior back to original conditions. The biggest issue with the 250's is the failure of the woofer surround. If you can get the unit reconed or refoamed things go back to original. The LE 14-3 has a rubber surround which doesn't wear out. Although it uses a thicker frame, it will mount into the enclosure. The grille may or may not fit, however. The problem with this substitution is that the -1 woofer is about 1 dB lower in sensitivity. The LE 14H-4 is too loud by a dB.

    The original L250 used first order crossovers with a lot of Zobel filters to true up the transducer impedance curves. Although a nice idea, the resulting sound was not as clear or detailed as all of the subsequent models. On those, I used a second order topology, but done differently than ever before. The sound was improved in clarity and detail. The 250Ti was the last of the series to use an in house built network. After that, we outsourced the networks from Taiwan since management closed down our network lines.

    The Jubilee was the best sounding model by a little. It was just slightly smoother and a little more open than the previous model. We made 500 pairs which were ordered by and sold in Europe. I hope this helps a bit.
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  12. #72
    Senior Member Odd's Avatar
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    Very interesting information, thanks for posting this.

    Quote Originally Posted by SEAWOLF97 View Post
    .
    43XX (2235-2123-2450-2405-CC 3155)5235-4412-4406-4401-L250-18Ti-L40-S109 Aquarius lV-C38 (030) 305P MkII

  13. #73
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    Hm, I think if I could get the 12-18 year material, I'd start there and maybe try to measure my way to the right foam compression level. Long process perhaps, but maybe possible using a UMIK-1 and REW? Since the glue no longer sticks (at least on the spare), it is easier and less nervewrecking to disassemble...

    Hi, Odd, sent my first order to Trestokken, nice guy - thanks for the tip! He's making some turntable parts for me already .

  14. #74
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    So I'm considering using these for plugs, unused Thorens spring damper foam from recent replacement. Very soft and easy to compress, and I know they will not powderize over time. How long they will work is unknown, but after 40 years I know they will deform if heavily compressed. I have an old, used set with varying degree of deformation depending on compression, so I'm aiming for minimum compression. Not that I think they will last 40 years, but I have hopes for a few .


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    I think maybe trim them so compression is maybe 2 mm, or height is about 2 mm above the wood plinth? Judging pressure required is difficult, but in my mind they only have to touch lightly, compress only enough to maintain pressure and stop any "ringing"...

  15. #75
    Senior Member grumpy's Avatar
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    Sounds like a good plan. A few mm of 'squish' is probably safe, vs more for the original. But not being able to compare makes being conservative a likely wise move. Don't want to deform/damage the dome. You may also consider pre-shaping the portion that fits into the dome.

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