JBL 4348 - Horns 435AI repair info needed

[oldbrowndog]

Hi All, i really could use some help finding the right avenue to go down regarding a dead 435AI driver in my 4348 monitors, showing 0 resistance & no sound.
Who in the world is the best speaker driver repairer for JBL ? For this kind of rare driver i need the best, please recommend where it could be sent.

[Ian Mackenzie]

Pm sent for local options

[rusty jefferson]

Just saw your other post. That is a drag. I'm sure you're disappointed. Good luck getting it straight.

[Robh3606]

Keep us posted!

Rob

[oldbrowndog]

yessir! Will do, still in motion..

Keep us posted!

Rob

[oldbrowndog]

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.

[Earl K]

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 .

[Ian Mackenzie]

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

[Earl K]

@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.

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 ).



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.



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 ).

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.

[Robh3606]

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/

[Earl K]

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.



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 ).



Conclusion ??

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







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

[Earl K]

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

[oldbrowndog]

@oldbrowndog,

Thanks for the pics.

All 3 magnets you've pictured are badly rusting ( the 2, 2435H are the worst and beyond help IMHO ).

The Japanese pricing is typical ( for them ). IOW, prices that are much higher than the rest of us would entertain paying.

Personally, I would simply buy a new pair of 2431H ( from the link that RobH previously provided ) , then install the larger ( interchangeable ) backcaps ( of your existing 435Al drivers ) and call it a day .

PS 2; The "bad" 435Al might also possibly be salvageable >> if the gap can be cleaned of any debris in it and then possibly a new protective layer of thin epoxy laid into the bottom of the gap ( as a barrier to further migration of the magnet's cladding into the gap area ) .
- This would be a major "Science Experiment" ( due to the previous existence of ferrofluid there ) with the whole exercise possibly amounting to nothing more than a futile pain in the arse (with no real long term benefit ).

PS 3; In case it hasn't translated yet, all 4 models ( 435Be, 435Al, 2431h, + 2435h ) use a single type of interchangeable magnet. So that opens up your replacement options.

Thanks Earl, great and very useful info, seems like a feasible option to buy the 2431 and use that in its place, assuming you are 100% that this is the correct option for the 435AL?
I want to be doubly sure as this thread mentions the matching model is actually the 2430, but it could be incorrect?
The post is from 'vintage tubes' about 2/3 down the page & regarding the 4348 speaker, reads:

The bass driver is the new 1500Fe which uses the same basket as the 1500AL with a ferrite motor. Midbass is handled by the 10" pro 2251J which uses a differential drive motor. The midrange compression driver is the 435AL which is a consumer conversion of the 2430. This is the same motor as the 2435/435Be but uses an aluminum diaphragm instead of beryllium. The acoustic lens is gone, replaced by a small biradial horn. The UHF is the same 045Be from the S9800."

https://www.audioaficionado.org/archive/index.php/t-5637.html

Just want to be extra sure as if i go down this path and get the wrong driver im back to square one..

Assuming one of them is the correct model i would also assume:
1. no modifications to the crossover needed whatsoever?
2. how do u think the sound might differ from the 435AL?

[Earl K]

Sorry oldbrowndog .

I'm not 100% sure of anything ( regarding the "Plug-And-Play" substitution of 2431h drivers for your 435Al ).

It's really all just best guess since I don't own any variants of the 435 series ( 435Be or 435Al ) .

You'll need to continue to research this ( and hopefully others who have had those 435 drivers will offer-up their opinions and experiences so that you can move forward ).

[oldbrowndog]

Sorry oldbrowndog .

I'm not 100% sure of anything ( regarding the "Plug-And-Play" substitution of 2431h drivers for your 435Al ).

It's really all just best guess since I don't own any variants of the 435 series ( 435Be or 435Al ) .

You'll need to continue to research this ( and hopefully others who have had those 435 drivers will offer-up their opinions and experiences so that you can move forward ).

Ahh ok great good to know.
Yes its a bit of a mystery the old 4348.
I had hoped to simply buy another 435AL and not need to worry about all this but that hasn't proved easy, so its onto this search for info.
Many thanks for your input so far.