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Thread: 2234 Butyl Surrounds from Japan

  1. #1
    Senior Member 1audiohack's Avatar
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    2234 Butyl Surrounds from Japan

    Hi All!

    I have in my office a pair of 4435's that were built in 08-1986. They are original and the surrounds lasted just a few months shy of 30 years. One of them just started to crack, yeah I know, terrible design, only 29.5 years of trouble free service.

    I have never re-foamed a speaker, I have always just re-coned them but I had seen on the bay these butyl surrounds from Japan and I figured if anyone was going to get this right it would be them. What the hell? What have I to loose? If they don't behave I will just re-cone them anyway so I bought four.

    The first thing I learned is that if you value your time, just re-cone!

    I haven't taken pictures yet but the roll is slightly smaller than the JBL surround. It fits the cone perfectly but leaves a slightly wider flat between the outer edge of the roll and the front foam gasket. This may not be noticeable to the average person but most of us would see it.

    Other than that? Pretty close to perfection.

    Name:  JBL  2234X3.jpg
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    The graph curser numbers didn't display so here is the rundown:

    17 Hz Fs is with the original surround removed, no surround at all.

    21.6 Hz Fs is with the original failing surround.

    24.0 Hz Fs is with the new butyl surround installed.

    Because I didn't want to be without music at all I re-coned four 2235's to 2234's while I went through this experiment. I swept all four of them of course and the average Fs of four of them is 24.4 Hz.

    I will get these back in their original homes tomorrow during lunch and see if I can hear any difference from the new ones going back to these.

    All the best,
    Barry.
    If we knew what the hell we were doing, we wouldn't call it research would we.

  2. #2
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    Interesting!

    Quote Originally Posted by 1audiohack View Post
    They are original and the surrounds lasted just a few months shy of 30 years. One of them just started to crack, yeah I know, terrible design, only 29.5 years of trouble free service.
    Maybe it is a desert thing... I've noticed that the environment has a large effect on when exactly the foam surrounds fail. I think it is quite interesting how we forgo alleged superior performance for functionality. Greg mentioned a couple years ago how fantastic lans-a-loy was from a performance perspective but it had no longevity, hence the foam surrounds of the 2231/2234/2235, etc.

    As an aside, years ago I purchased a whole bunch of recone kits from JBL that all contained foam surrounds in a very advanced state of rot. I should have kept the photos. In any case, JBL ended up crediting me for the kits and they all ended up with Rick Cobb refoams. A few months later when I went to order a few more of these kits I was told that the remainder had been destroyed. I could have simply refoamed them.

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    Senior Member Flodstroem's Avatar
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    Quote Originally Posted by 4313B View Post
    I was told that the remainder had been destroyed.
    Oh my god

    Flodstroem

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    Senior Member hsosdrum's Avatar
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    Quote Originally Posted by 4313B View Post
    Interesting!

    I've noticed that the environment has a large effect on when exactly the foam surrounds fail.
    That's for sure. Here in smoggy L.A. they have a considerably shorter lifespan than in areas that are comparatively smog-free. The same is true for the rubber drive belts on turntables and cassette decks (remember those?). Butyl rubber surrounds seem to be relatively impervious, thankfully—I've had my rubber-surrounded HT speakers for 20 years with no apparent degradation.

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    Quote Originally Posted by 1audiohack View Post
    I have never re-foamed a speaker, I have always just re-coned them but I had seen on the bay these butyl surrounds from Japan and I figured if anyone was going to get this right it would be them. What the hell? What have I to loose? If they don't behave I will just re-cone them anyway so I bought four.

    The first thing I learned is that if you value your time, just re-cone!Barry.
    I cannot imagine why on earth you would do such a thing to such beautiful drivers, makes not one iota of sense to me when the closest to the original you're going to get is readily avaluable and is of a known quantity as well as being supplied from a well established and known to be excellent vendor
    Especially as you claim that you value your time

    And who knows, with a quad of Rick's surrounds those bad boys might just meet or exceed specs, you never know, but regardless, definitely a heck of a lot less of a gamble involved and at least they'd look correct

    Bizarre

    Hope it all works out

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    Senior Member 1audiohack's Avatar
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    Hi Joseph;

    This was an experiment, nothing more. I wasn't looking to save money or time, simply to try a surround made from a material that is widely used by JBL and many others. Normally I wouldn't even bother to re-foam these, I would do the most correct thing and buy new JBL C8R2235 cone kits and keep them all 100% JBL.

    Meet or exceed factory specs? Being within a couple of Hertz Fs is plenty close to me.

    The truth is that these 30 year old speakers as great as the are/were, have been absolutely eclipsed by the new large format JBL monitors. That's why they ended up in the office.

    I have thought about gutting the crossovers, replacing the woofers with 2216's and making throats for the 2344's that would use an 1.5" throat driver like a 2451 or D2430K but your still left with a 35 year old horn and that would be a waste of an otherwise near pristine pair of 4435's.

    It is likely that I will soon re-cone these anyway because I like things proper. If the re-cones last like these did I will be 84 when they get weak again and I doubt I will care much by then.

    So here is the intended value in this experiment, there is for those who hate the foam thing, a butyl surround that performance matches the 2234/2235 stock surrounds. Cobbs not the only game on the planet. There is a good non foam option, not for purists maybe but these guys have butyl surrounds for many others as well.

    All the best,
    Barry.
    If we knew what the hell we were doing, we wouldn't call it research would we.

  7. #7
    Senior Member Ian Mackenzie's Avatar
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    The T/L parameters have nothing to do with the suround,

    The surround minimises reflections back into the cone and provides air tight seal and centres the cone. Nothing else. In modern drivers a foam surround is not considered part of the radiating area.

    In pleated paper surrounds the surround may form part of the radiating area.

    The Driver relies on the spider and the coil, mass and profile of the cone for the LF and mid band response and of course the gap and Vol of the enclosure.

    Provided only the suround is rotted l would not use an after market reconsider kit as a solution.

    Talk to your pro reconvert first. If a recone is all that is required then do that.

    But I do not see by butyl would not work and it would be useful to do some real measurements and impedance plots

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    Senior Member 1audiohack's Avatar
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    Red face

    Hello Ian;

    Did you read the first post?

    The impedance graph is one I took of the same 2234 with the old surround, then no surround, and finally with the new surround. Although I didn't post them all, I measured all four in the same way. The suround does affect the Small signal Fs as is shown.

    I also measured the four 2234's that I just re-coned with new JBL C8R2235 kits (with the mass rings left out) as a comparison.

    My best,
    Barry.
    If we knew what the hell we were doing, we wouldn't call it research would we.

  9. #9
    Senior Member Ian Mackenzie's Avatar
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    I understand but what is the fs if a run in stock 2234.

    According to JBL the Fs of a 2234 is 23 Hz, the 2235 is 20 Hz.
    The Qts is .22, the Qms is 2.0

    I am not discounting your measurements , obviously no surround is going make a difference. That is not what l meant .

    If the butyl is really Stiff because it's new it might make a relative difference but your measurement is 24Hz. Compared to 23 Hz that is fuck all difference in production so l would not get too excited about that.

    I am talking relative differences of surround types.

    The effect of a different surround is more noticeable in the midrange than the bass.

    What l am trying to explain is that the compliance of the spider (QMS)and the mms of the cone sets up driver in a working box along with the electrical QES.

    The QTS or total Q is a lumped parameter based on half a dozen other parameters.

    If the FS is up or down a bit it is normally compensated by another related parameter and you end up with the same Response in a enclosure.

    James Bullock discussed this in his book Bullock on boxes Which is very detailed study of bass reflex designs and the impact of variation in T/L on box tuning.

    Losses QL (box losses )have a bigger impact than small variation is FS.

    But if you can do it reliably measuring the QTS is a great way to optimise a design.

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    Quote Originally Posted by 1audiohack View Post
    This was an experiment, nothing more.
    Cobbs not the only game on the planet. There is a good non foam option, not for purists maybe but these guys have butyl surrounds for many others as well.
    All the best,
    Barry.
    I realize that, and to be honest, it's your business. But in my view, it is a waste of time and a mistake to experiment with a part not considered as part of the original design, so completely different in so many ways when there is one that's pretty darn close, if not possibly an exact match to what was called for by the designers of the driver and is readily available

    And it takes the same amount of time to install either one, not to mention the hit you may take if you decided to sell them for whatever reason if ever

    Outer compliance does make a difference in driver behavior, especially after you have some hours put on them

    The unanswered variables, the "what ifs" would drive me nuts, but that's just me unless you do one with rubber and the other with foam and then take your measurements and compare behaviors then you'd know something for sure relatively speaking especially after you have so hours on them

    And you are right, Rick's not the only game in town when it comes to foam edges, but based on experience, he definitely is the best game in town when it comes to coming even close to selling a product that is in the same ball park with what JBL used originally. Good example of that is what he sells to replace Lans-a-loy surrounds, they exceed even the parameters as defined when the drivers and the Lans-a-loy were new! And the fit of every surround I have ever bought from him, quite a few, is second to none, ID", OD", roll width and compliance

    I have tried more than a few of the other vendors and nothing comes close, some were almost close, as in close enough to function but there was always some compromise either in material, appearance or fit ergo my loyalty to Rick's product

    Good luck and I hope you results make you happy

    Best wishes
    Joe

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    Quote Originally Posted by Joseph Smith Jr View Post
    I cannot imagine why on earth you would do such a thing to such beautiful drivers, makes not one iota of sense to me when the closest to the original you're going to get is readily avaluable and is of a known quantity as well as being supplied from a well established and known to be excellent vendor
    Especially as you claim that you value your time

    And who knows, with a quad of Rick's surrounds those bad boys might just meet or exceed specs, you never know, but regardless, definitely a heck of a lot less of a gamble involved and at least they'd look correct

    Bizarre

    Hope it all works out

    Man, they are just 2234s, not some rare and irreplaceable masterpieces. Recone kits are still available. You make it sound like he painted a butyl moustache on the Mona Lisa. JBL is moving away from foam surrounds in favor of rubber, I'm not sure any of their new production designs still use foam. He clearly stated it was an experiment, and he certainly has the skill and resources to perform an inexpensive experiment on some extremely common drivers.

    Quote Originally Posted by Joseph Smith Jr View Post
    Good example of that is what he sells to replace Lans-a-loy surround, they exceed even the parameters as defined when the drivers and the Lans-a-loy were new! And the fit of every surround I have ever bought from him, quite a few, is second to none, ID", OD", roll width and compliance
    Wait - now you are advocating replacing surrounds with something other than what JBL used?

  12. #12
    Senior Member Ian Mackenzie's Avatar
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    Storm in a tea cup!

    I have to say when a foam surround starts to go it's very annoying.

    I am in favour of challenging the convention.

  13. #13
    Senior Member Ian Mackenzie's Avatar
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    What interesting is the 2235h found its way (and the 2235 recone ) into many 2231 based boxes and no one gave a rats about the specs (16 Hz versus 20 Hz)just bolt it in and let it go. Ie the 4343.

    But most people agreed the 2235 sounded a bit different.

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    Strangely I ended up with J.M's cloth surrounds on all my LF transducers (2216Nd and 1501AL-2). Full circle. Cloth - Lans-a-Loy - Foam - Rubber - Cloth - The End.

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    Senior Member 1audiohack's Avatar
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    This was meant to just share some discovery, at my expense.

    I assumed there would be some conversation about it and I welcome that. Criticism does not offend me, at all.

    I have more measurements including the new 2234's and I can sweep them again now that they have had a month of play while I re edged the originals and see if they have changed although I doubt it as they don't get loud often or long in the office.

    I also get that Fs is a weak force when in a vented box and or driven with a constant voltage source.

    As for the different surround types that 4313b mentioned, I had a discussion with JM and GT during my last visit to Northridge about the 1500Al verses the 1501-1Al and GT said the cloth accordion surround knocked down a mid band ripple about a dB. I know there is a cone fiber material difference as well but they really were sweating the small stuff and making the best driver possible.

    The 2234-2235's don't knock me out and never have. I don't hate them but A 1501-1Al with an Fs of 19 so far outshines a 2235 that it is nearly comical.

    I will post a few more measurments when I get a minute that are not so zoomed in, they will look a little more familliar. I will do better at the notation as well.

    All the best,
    Barry.
    If we knew what the hell we were doing, we wouldn't call it research would we.

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