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Thread: JBL 4348 - Horns 435AI repair info needed

  1. #16
    Administrator Robh3606's Avatar
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    Quote Originally Posted by Earl K View Post
    I prefer the sound of my 2431h(s) without ferrofluid in the gap ( especially "cooked" ferrofluid ).

    So, I'll have to disagree with those who audibly prefer it's presence.

    I understand your preference but when the drivers designer says it should be there that's information the OP should have and he can make his own decisions.

    Rob
    "I could be arguing in my spare time"

  2. #17
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    Quote Originally Posted by Robh3606 View Post
    I understand your preference but when the drivers designer says it should be there that's information the OP should have and he can make his own decisions.

    Rob

    Agreed!


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    Thanks all for the input, regarding your post first Ian, that seems like an appropriate solution, but well beyond my capabilities in terms of technical knowledge.. and since we are in heavy lockdown getting anyone in to help is a no go.

    For clarity, i have tested the 2435Hpl in both speakers (i have a pair), & both produce the dull muted sound.. (The 2435 return an impedance of 4.0 (both of them).
    Ive also tested the one working 435AL & its performing well in both speakers, so its not a blown crossover.

    The reason the 435AL that is broken is not working is likely twofold, open circuit diaphragm, but also (according to a JBL tech in japan) the magnets are coated in neodymium and in this particular model the coating is known to not last very well, and peel off the magnet, probably causing the short in the diaphragm. I believe that is the case here (perhaps as these speakers lived in sydney & singapore the weather being a bit humid caused this to happen.. at least to one). So replacing the diaphragm would be a disaster otherwise i would have simply done that before jumping on here to ask questions.

    So, since i am not technically able to work with the crossovers to suit the 2435 and more to the point i'd like to keep these as original as possible, i was hoping that the 435Be which looks so similar in design and shape to the 435AL might be the answer for a plug & play solution..
    I had hoped this might be the case with the 2435hpl's but it definitely was not, so yes perhaps the pair are also damaged, or perhaps the crossover in the 4348 simply doesnt suit the 2435 (which is my assumption).

    Again thanks for all the input.

  4. #19
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    Hi oldbrowndog,

    Where did you buy those 2435hpl's from ?

    FYI;

    The "PRO" 2435hpl model more or less equates to the "CONSUMER" 435Be model ( both have Beryllium diaphragms, it's just that the 435 designation also means the diaphragm has a coating of aquaplas )

    The 2431h more or less equates to the 435Al ( since both have Aluminum diaphragms , the 435Al has an aquaplas coating on the diaphragm while the 2431 doesn't).

    Neodymium is more prone to corrosion effects ( especially if it's the sintered type ) if/when the surface plating breaks and exposes the magnetic slug to air.

    Normally, the slug is protected from the elements by encasing the slug in multiple passes of nickel type plating.


    If the plating fails the neodymium magnet core will eventually corrode, turning back into a pretty useless powder.



    All four driver models mentioned here share similar motor/magnetic structures. What I don't know is whether they are of a sintered or bonded magnet type.

    Your two 2435hpl motors could also be losing their magnetism > if so, that would certainly explain your sonic impressions of them if the neodymium is degrading/corroding.

    Those 2435hpl's really need to be properly tested.

    Many of us are in the same boat due to owning many of these variants .

    Chris Hagen ( a current speaker designer at Harman ) even made an off-hand comment some years back about returning to designs using ferrite magnet drivers > now that statement has a whole new perspective .


  5. #20
    Senior Member Ian Mackenzie's Avatar
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    Hi Earl,

    Your post was very insightful and explains failures in the 4344mk2 which used a neo driver.

    Do you think in your experience the gaps can be cleaned out and a replacement diaphragm and oil installed?

    To old browndog,

    If you are interested l could put a mock up filter together for you to try out with your 2435s. I can obtain the parts. I could also measure your drivers on one of the horns remotely and match the crossover to suit the 2435s.

    The other options of an 0435BE are very expensive and they are incredibly rare. I would not jump to that.

    Using an alternative 1.5 inch driver is an option however the driver would need to fit physically in the space and have the same bolt pattern. RCF, B&C snd 18Sound and others make excellent drivers.

    I would suggest waiting till Earl responds on cleaning out the gaps before considering your next steps.

    Ian

  6. #21
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    @oldbrowndog,

    The reason the 435AL that is broken is not working is likely twofold, open circuit diaphragm, but also (according to a JBL tech in japan) the magnets are coated in neodymium and in this particular model the coating is known to not last very well, and peel off the magnet, probably causing the short in the diaphragm. I believe that is the case here (perhaps as these speakers lived in sydney & singapore the weather being a bit humid caused this to happen.. at least to one). So replacing the diaphragm would be a disaster otherwise i would have simply done that before jumping on here to ask questions.
    - You heard this wrong. The plating///covering surrounds the magnet as a form of environmental protection ( not the other way around ) .

    Hmm,

    I've ( also ) conflated and mis-contrued Chris Hagen's words regarding Ferrite vs Neodymium.

    I believe this is the video that triggered my mis-direction.



    Quote Originally Posted by Ian
    Do you think in your experience the gaps can be cleaned out and a replacement diaphragm and oil installed?
    Ian, I don't have an informed opinion as to whether or not one can save a neodymium magnet ( once the protective covering has started to break-down and flake off ).

    OTOH, my understanding is that there should be a minimum of 2-3 platings ( and hopefully more ) if the magnet is of the sintered type, so losing only the outer-most covering might not be catastrophic ( if dealt with in time before rust sets in ).

    If the delamination process stabilizes ( or is stabilized/treated ) after the first layer of covering//plating has dis-integrated > then "YES" , maybe one could simply clean out the gap and install a new diaphragm ( along with ferrofluid ) .
    - OTOH, if VC failure was actually due to metallic ( plating ?? ) particles present in the gap shorting the coil then there's little guarantee it won't re-occur.


    I think it's worth noting at this point that the "JBL tech-in-Japan" didn't think that re-diaphragming was a viable approach.

    OTOH, one can always look to slow down the degradation process by applying some other protective covering ( I'm thinking along the lines of a "Cold Galvanizing Compound" as found in my link ).

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    I have no idea about the adhesion properties for these sort of products when applied onto any existing zinc plating.

    BTW, I just un-boxed 8, 2431h ( used eBay specials ) > that never made it into general use.

    3 of 8 now have the outer plating layer letting go ( all in various stages of delamination ). I'll look at the gaps at some point.

    Here's the worst example.

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    This actually looks more like silver paint that's giving up the ghost ( perhaps a bit of fraud was perpetuated towards JBL by their magnet supplier of the time ).


    All 3 have what appears to be a batch number of "92N-JBF" ( all 3 sport a silver colored plating > rather than the more typical black colored plating ).

    If I were to care about saving this example, I would first test it for output characteristics and then try the previously mentioned cold galvanizing treatment onto the remaining plating ( don't hold your breath for this to happen though ).


    Important quote ( reality check ) by sebackman ( for those who missed it the first time out ).

    Quote Originally Posted by sebackman
    Another topic I have not seen mentioned here at LHF is Neodym magnet rot.

    The older JBL drivers used Neodym magnet material that also tend to corrode/rot in certain environments.

    This
    materializes as small magnetic fragments in the coil gap and regardless how many times you clean they keep coming back.

    This means that the magnet is beyond salvage. I have had this on a few 2450SL/2451 drivers that had to be canned.

    I have also had it on a few older Neodym woofers like the 1400PRO (currently 3 dead basked in the shop). JBL knows of the problem and has also replaced a bunch back when.



  7. #22
    Administrator Robh3606's Avatar
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    Quote Originally Posted by oldbrowndog View Post
    Thanks all for the input, regarding your post first Ian, that seems like an appropriate solution, but well beyond my capabilities in terms of technical knowledge.. and since we are in heavy lockdown getting anyone in to help is a no go.For clarity, i have tested the 2435Hpl in both speakers (i have a pair), & both produce the dull muted sound.. (The 2435 return an impedance of 4.0 (both of them).Ive also tested the one working 435AL & its performing well in both speakers, so its not a blown crossover. The reason the 435AL that is broken is not working is likely twofold, open circuit diaphragm, but also (according to a JBL tech in japan) the magnets are coated in neodymium and in this particular model the coating is known to not last very well, and peel off the magnet, probably causing the short in the diaphragm. I believe that is the case here (perhaps as these speakers lived in sydney & singapore the weather being a bit humid caused this to happen.. at least to one). So replacing the diaphragm would be a disaster otherwise i would have simply done that before jumping on here to ask questions.So, since i am not technically able to work with the crossovers to suit the 2435 and more to the point i'd like to keep these as original as possible, i was hoping that the 435Be which looks so similar in design and shape to the 435AL might be the answer for a plug & play solution.. I had hoped this might be the case with the 2435hpl's but it definitely was not, so yes perhaps the pair are also damaged, or perhaps the crossover in the 4348 simply doesnt suit the 2435 (which is my assumption).Again thanks for all the input.

    Hello Oldbrowndog

    There is a measureable difference between the two drivers and when I built my Array 1400 DIY I used the beryllium drivers and had to make a value change in one of the inductors from the stock schematic. The Be puts out more energy from say 2-10k and rolls off faster above 10K. There is also a bit of gain sensitivity wise. So it should not sound muted.

    What the tech said?? They are not coated in Neo they are neo magnets. They have a paint or epoxy coating which has been know to shed. The voice coil is completely encapsulated in the kapton surround so the coil cannot be shorted by loose material. Another possible issue is that the magnet pole piece shifted either from a bonding failure or shock as in it was dropped. This is certainly possible with the 2435's as I actually dropped one and it jammed the VC in the gap so really muted output. I was able to fix it and there is another recent thread that could help if this is the case. I would send them back if you could.

    Have you opened the dead 435Al?? You should be able to get a replacement 2431 diaphragm. It won't be coated but it as close as you are likely to get. If it is jammed because of a shifted pole piece when you get the screws out it will not lift out.

    Normally when you open the drivers the clips that make the connection to the terminal push pins hold the diaphragm in the cover and you have to carefully pry the diaphragm free of the clips. The back cap should come right up in the dead 435Al as long as it's just an open VC .

    If it's jammed you can order a new 2431 from them as well as long as they will ship to you.

    Rob

    https://reconingspeakers.com/product...431-diaphragm/
    "I could be arguing in my spare time"

  8. #23
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    Here's a good web-page on the various coatings // platings applied to sintered Neodymium magnets.

    Magnet Plating and Coating Options

    Here's an example pic//chart.

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    I'm hoping that the "good" 2431h's that I have use one of the two black coatings seen above.

    I'm also assuming that the "bad" 2431h's that I just displayed pics of have the most common ( cheapest ) Nickel cladding ( Ni-Cu-Ni ).
    - The flakes shown in my pic are attracted to the internal magnet ( so that rules out the flakes being zinc plating ).


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    Conclusion ??

    One wants to own neodymium drivers having black epoxy enclosed magnets ( like the example seen in the left foreground might imply ).

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    PS; Rob's 2435h repair thread ( click the first pic );


  9. #24
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    Hey Rob,

    I tried an epoxy, got the shim out and just watched the top plate creep over to the pole in slow motion. I took a chance and used medium viscosity super glue. It worked like a charm.
    Regarding your successful repair ;

    Which epoxy didn't work for you ??

    Was it the 30 minute type ?

    Did you let it fully cure before removing that ( great looking ) shim ?

    Did you clean off this failed epoxy glue before the successful supergluing ?

    Thanks




  10. #25
    Administrator Robh3606's Avatar
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    Hello Earl

    Hmm that was a while ago. This may not be exact from what I can remember I used a 5 minute epoxy and removed it before using the supper glue. The pole piece shifted before it was fully cured so I was able to get it apart and basically clean it up. The epoxy was very thick and viscous probably used too much in comparison to the super glue gel. I pulled the shim when it was hardening up and not fully cured. I was concerned the shim could become jammed. With the super glue gel it was just a thin line and it bonded almost instantly. I followed the original glue line scar on the magnet.

    Hello Oldbrowndog

    Here are the measured differences between the 2431 vs 2435 of the Array 1400 horn. Red is the 2431 the other two are the 2435's I used in the build. You can see where the differences are in sensitivity and areas where the outputs are different.

    Rob
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  11. #26
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    Quote Originally Posted by Robh3606 View Post
    Hello Earl

    Hmm that was a while ago. This may not be exact from what I can remember I used a 5 minute epoxy and removed it before using the supper glue. The pole piece shifted before it was fully cured so I was able to get it apart and basically clean it up. The epoxy was very thick and viscous probably used too much in comparison to the super glue gel. I pulled the shim when it was hardening up and not fully cured. I was concerned the shim could become jammed. With the super glue gel it was just a thin line and it bonded almost instantly. I followed the original glue line scar on the magnet.

    Hello Oldbrowndog

    Here are the measured differences between the 2431 vs 2435 of the Array 1400 horn. Red is the 2431 the other two are the 2435's I used in the build. You can see where the differences are in sensitivity and areas where the outputs are different.

    Rob

    Thanks for the update Rob ( it's much appreciated ! ).

    Yes, great to see your comparison of the 2435H vs the 2431H ( I've been hammering away at this audible discrepancy since getting involved in this thread ).

    >> Again, a simple swap using the 2435H vs 435Al should have resulted in a reaction that was just the opposite of what oldbrowndog reported.

    His used pair of 2435H need some serious testing done on them to determine their relative health.



  12. #27
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    Hello Earl

    Your welcome! I am thinking that they were damaged in shipping and the pole pieces shifted pinning the voice coil. That would account for the muted response. Just a guess on my part though.

    Rob


    Quote Originally Posted by Earl K View Post
    Thanks for the update Rob ( it's much appreciated ! ).

    Yes, great to see your comparison of the 2435H vs the 2431H ( I've been hammering away at this audible discrepancy since getting involved in this thread ).

    >> Again, a simple swap using the 2435H vs 435Al should have resulted in a reaction that was just the opposite of what oldbrowndog reported.

    His used pair of 2435H need some serious testing done on them to determine their relative health.


    "I could be arguing in my spare time"

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    At this point its probably best to insert some photos of both the 2435 & the 435AL (which i have opened up).

    Ian, when you are back in town (assuming we will then be out of lockdown) and assuming i havent found a fix for this I would be very appreciative to take up your offer and happy to pay for your time.

    These are pictures of the 2435 which as mentioned has an impedance of 4.0 (the pair are matched).. i havent opened these up as yet.
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    & these are pictures of the non-working 435AL ( i have not opened the working one..). Note: I will need to include 2 more pictures in the next post as 5 is the max per post.
    The impedance measures 0, the short on the diaphragm is very hard to spot, so hard that i cant see anything that indicates damage.. The magnet as you can see is peeling.
    If it simply were that i could recoat the magnet and buy a replacement 2431 diaphragm, that would be a fantastic solution..
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    According to the technician I spoke with in Japan there were a few possibilities with the repair of this non functional 435AL.
    In all instances the quote for repair did seem high, but then the Japanese also usually do fantastic work, but i include this information below to show you what the insights were.
    At the worst case i could box up & send both 435AL to them for repair/inspection/matching, and the first 2 quote dollar amounts would be borderline worth it if i can get both in working condition again.. but if its the 3rd option thats a tad to expensive for my taste.

    The technician did intimate that the magnet coating being in the condition it was (via my pictures) that it may be the 3rd option.. hence my reluctance to send them as yet.

    Japan Tech Quotes
    [ In case possible to repair the disconnection point ]
    1 x 25,000 JPY

    [ In case impossible to repair the diaphragm ]
    2 x 39,800 JPY = 79,600 JPY

    [ In case there are issues on the Neodymium magnet coating and rust exists ]
    Either of above + 2 x 185,000 JPY (demagnetizing 40,000 JPY, making
    new magnets 90,000 JPY, remagnetizing 40,000 JPY, Voice coil gap
    adjustment 15,000 JPY)

  14. #29
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    2 more pictures as mentioned of the diaphragm connection points on the malfunctioning 435AL
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  15. #30
    Administrator Robh3606's Avatar
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    Are those tinsel leads touching the ring? That could short them they don't look like they are coated there.

    Rob
    "I could be arguing in my spare time"

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