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Thread: JBL 4348 - Horns 435AI repair info needed

  1. #1
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    JBL 4348 - Horns 435AI repair info needed

    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.

  2. #2
    Senior Member Ian Mackenzie's Avatar
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    Pm sent for local options

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

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    Administrator Robh3606's Avatar
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    Keep us posted!

    Rob
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    yessir! Will do, still in motion..


    Quote Originally Posted by Robh3606 View Post
    Keep us posted!

    Rob

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    Replacement instead?

    Hi all, im having difficulty with the repair option.. So ive started to investigate the option of replacing with a similar spec JBL driver. I have tried the JBL 2435HPL in its place which seemed to have very similar specs, but the sound was muted and very low. I suspect the 4348 crossover doesnt suit them.. I did try manipulatiing the crossover pot for the mid horn on the front of the 4348, but yeh no joy.. it sound dull & very low compared to the 4348 with the one working 435AL driver i have.

    So i am back to the beginning, short of finding a replacement 435AL driver I need a solution and I wonder if anyone here can tell me does the 435Be have the same specs as the 435AL? It looks exactly the same so i wonder if the Be is just a retagged version of the Al (or vice versa), if so it would be the perfect choice..?

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    Senior Member Ian Mackenzie's Avatar
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    Referring to the attachments below a guesstimate is to transpose the SE9800 horn filter schematic and try your 2435HPL. Some adjustments to the capacitor value at the input of the filter may be required.

    You can buy the parts from Wes Components or Speaker Bug in Aust then build out the schematic and bypass the 4348 horn filter. Layout the construction just like the schematic and it will work fine. Hot melt the parts to a strip of 12 mm ply or mdf. Hot melt gun from Jaycar.

    Without detailed measurements this is a good starting point.

    To reach an advanced level of response flatness with the 4348 horn and baffle location/ dimensions consider Downloading REW software and buying one of the recommended mics with calibration software. You can objectively dial in the measurements empirically just like JBL do with all their commercial loudspeakers. This ultimately is the preferred approach to so called simulation software that attempts to predict the response prior to building out the crossover. The SE9800 HF filter is a good starting point and accounts for the impedance magnitude and phase of the driver. Some variations are to be expected on the 4348 HF horn.

    The voltage drives are for reference only as they are used on different horns but they are both CD horns. You can see the 4348 filter provides more attenuation of the lower frequencies than the SE9800 schematic and this is mostly likely why your 2435HPL sounds muffled.

    Give it a try and take it from there.

    I am off the tools ⚒️ in far north QLD for a little while so l can’t give you more specific assistance.
    Attached Images Attached Images      

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    Quote Originally Posted by oldbrowndog View Post
    Hi all, im having difficulty with the repair option.. So ive started to investigate the option of replacing with a similar spec JBL driver. I have tried the JBL 2435HPL in its place which seemed to have very similar specs, but the sound was muted and very low. I suspect the 4348 crossover doesnt suit them.. I did try manipulatiing the crossover pot for the mid horn on the front of the 4348, but yeh no joy.. it sound dull & very low compared to the 4348 with the one working 435AL driver i have.

    So i am back to the beginning, short of finding a replacement 435AL driver I need a solution and I wonder if anyone here can tell me does the 435Be have the same specs as the 435AL? It looks exactly the same so i wonder if the Be is just a retagged version of the Al (or vice versa), if so it would be the perfect choice..?
    Really, your experience is just the opposite of what I would expect to encounter from a properly working 2435h driver ( substituted for a 2431h ).

    This "Be" driver is noted to be a bit louder and clearer sounding than the aluminum diaphragmed 2431h ( 435Al ) .

    I suspect its ( 2435h ) diaphragm is either after-market Chi.Com junk or there's something wrong with the OEM diaphragm presently in it ( +/or, the ferrofluid in the gap has dried-out and is locking the voice-coil within a mucky death-grip ).

    You should follow Ian's directions and download REW and run some tests on that driver ( build the recommended impedance jig and capture a raw impedance curve for that 2435h ).
    - It should look something like this;


    Used 2435h drivers of unknown provenance need extra attention paid to them to make sure they are performing ( at least close ) to spec.

    Additionally, I would ( if mine ) open it up and remove all the old ferrofluid within the gap ( using thin card-stock and something absorbent wiped/pushed around the gap ) .

    These drivers don't need any ferrofluid to operate within a home audio environment ( SR is a different story ).

    Years back ( almost 20years now ) I bought 16 used 2431h drivers from eBay. Each one that was opened ( for inspection ) has had the ferrofluid ( quite obviously cooked and ) splattered around the inside of the 3" aluminum dome.
    - Ferrofluid doesn't easily leave the gap area unless internal temperatures within that gap have climbed to excessive heights.


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    Administrator Robh3606's Avatar
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    Quote Originally Posted by Earl K View Post
    Additionally, I would ( if mine ) open it up and remove all the old ferrofluid within the gap ( using thin card-stock and something absorbent wiped/pushed around the gap ) .These drivers don't need any ferrofluid to operate within a home audio environment ( SR is a different story ).
    That's not correct. Take a look at Doug Buttons comments in Ian's attachment. Middle paragraph.


    Rob
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    Quote Originally Posted by Robh3606 View Post
    That's not correct. Take a look at Doug Buttons comments in Ian's attachment. Middle paragraph.


    Rob

    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.


  11. #11
    Senior Member Ian Mackenzie's Avatar
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    Failing the effort of a new filter simply pop in a replacement diaphragm

    https://www.simplyspeakers.com/jbl-r...m-d8r2431.html

    You would need to contact the supply to confirm it will fit.

    If you end up replacing the diaphragm try putting a polymer loudspeaker protection component in series with the crossover to future damage from power amplifier clipping. They have a positive temperament coefficient which increases the temperature with signal current above a threshold value and the series dcr.

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    Quote Originally Posted by oldbrowndog View Post
    Hi all, im having difficulty with the repair option.. So ive started to investigate the option of replacing with a similar spec JBL driver. I have tried the JBL 2435HPL in its place which seemed to have very similar specs, but the sound was muted and very low. I suspect the 4348 crossover doesnt suit them.. I did try manipulatiing the crossover pot for the mid horn on the front of the 4348, but yeh no joy.. it sound dull & very low compared to the 4348 with the one working 435AL driver i have.

    So i am back to the beginning, short of finding a replacement 435AL driver I need a solution and I wonder if anyone here can tell me does the 435Be have the same specs as the 435AL? It looks exactly the same so i wonder if the Be is just a retagged version of the Al (or vice versa), if so it would be the perfect choice..?
    @oldbrowndog

    The current problem might just as easily be that the HF portion of the crossover ( within the bad speaker ) is also cooked .

    Whatever event blew-up your bad 435Al could just as easily stressed the network right out of spec ( making the sound of anything now connected to it dull + muted ).

    I'd recommend installing your 2435HPL into ( your known ) properly working 4348 ( iow; this "dull" 2435hpl now needs to be checked out on a properly working speaker ).

    Next, install the good 435Al into the 4348 that's had all the problems.

    Now compare to see which channel has the "Dull + Muted" sound .

    This will help determine whether the "bad 4348" also has a properly working crossover.



  13. #13
    Senior Member Ian Mackenzie's Avatar
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    One of the diaphragms is open circuit.

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    Quote Originally Posted by Ian Mackenzie View Post
    One of the diaphragms is open circuit.

    The way I read his posts is that he has one working 435Al and one ( iffy//sketchy//unknown quality ) 2435hpl and a open-circuit 435Al ( for a total of 3 HF drivers ) .


    Whatever,


    To kill a 435Al takes at least 40 watts sustained power ( which a horn driver within a home setting should never ever really see ).

    Still. there's a blown driver here and some untoward event has caused it's failure ( implying the driver did in fact see more > than 40 watts ).

    So, here's a power dissipation chart for the HF portion of the 4348 network ( with a full 40 watts applied ).

    Name:  Wattage Dissapation of 4348 network-HF portion_ .jpg
Views: 185
Size:  87.4 KB

    One can see the stress that the 7.5R resistor is operating under ( represented here by the black line in the above chart ).

    The initial LC components within this horn circuit form quite a resonate circuit ( peaking at around 2500hz ).
    - This resonance ends up drawing more than the applied 40 watts.

    Name:  4348 HF + UHF network_.png
Views: 185
Size:  175.1 KB

    I don't think JBL used 50 watt resistors in that location .


  15. #15
    Senior Member Ian Mackenzie's Avatar
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    We talk about it a month or so ago on pm. The driver is definitely blown. The problem is how to repair the driver or implement new horn crossover filter.

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