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Regis
06-13-2005, 07:44 AM
I have chosen several posts from a couple of threads to create this "Sticky". I hope it will help people who decide to tackle the task of replacing their own diaphragms. For the record, while I have replaced many myself, I would recommend that you seriously consider having a professional factory authorized shop do the work. The money saved by your own installation is lost when you let the magnet pull your screwdriver into the new diaphragm. Going to a professional also saves you the hassle of dealing with JBL if you get an out of round diaphragm or one that simply won't fit your driver

With that disclaimer, check out these photos and comments below. These are of a small format driver, but the large format drivers are essentially the same.

Widget


Motor innards (without diaphragm). Note the three diaphragm body screws and the very small dual locating pins. The brass part in the center is the phase plug

Regis
06-13-2005, 07:45 AM
Remove the old diaphragms and put them in a safe place. Unbox the new diaphragm and find the two opposing holes in the black plastic body of the outer diaphragm ring. Handle the diaphragm with great care! With the dome facing up, match the holes to the locating pins and install gently.

Regis
06-13-2005, 07:46 AM
Gently tightening screws...

Regis
06-13-2005, 07:48 AM
Next, take the cap and locate the red or positive terminal and align the cap so that the red terminal is on the same side as the red screw head on the diaphragm. Install the wires underneath the lugs, snugging the screws down, just past being tight, again, do not overtorque or overtighten..

Earl K
06-13-2005, 10:33 AM
For the Record ( & perhaps it's just MO ), I also don't mean to offend but ;

#(1) I consider it a significant & major no-no :no: :no: :no: to suggest that the floor is a suitable work-bench for a diaphragm replacement .

- Your posted pics "telegraph" this message that "work-bench location" is unimportant.
- I strongly disagree that work-location is unimportant for this sort of work - as will any professional reconer .
- Again, The floor is not a suitable workbench !

#(2) Your omission from mentioning that you cleaned the gaps of your le85s' (ie ; using masking tape wrapped around thin/stiff cardboard ) suggests to me that you aren't aware of this critical cleaning step .

- FWIW, metallic derbis ( from the air / floor ) needs to be removed ( from the work-area & the gap of the driver-piece being worked on ) before replacing an old diaphragm or installing a new diaphragm or recone . Thankfully, some-one in your household does a bang-up job at vacuuming. :yes: :yes: :yes:

#(3) Humbly , I mention that I'd prefer to see you change the title on this thread to something incorporating or suggested by some of these words ; the L300s & the "easy & proper" Horn-Removal /Re-installation .

- FWIW ( & IMHO ); That's where the greatest worth of the included pictorials lay .

:cheers:

edgewound
06-13-2005, 01:20 PM
Please, EarlK, don't delete...that was excellent.:applaud:

Regis...I'm curious...did your diaphragm supplier inform you of the warranty disclaimer enclosed with your $244.00 part? No warranty when consumer installed due to tight tolerances, procedures, etc.

I'll just talk about the re-diaphragm. FYI...the RED terminal is NEGATIVE, black is positive. And this is addressed inside the crossover network. You really must have a debris-free work surface, a lighted bench magnifier, sweep generator and various other tools to make sure the new part fits properly...so many little things can go astray that will make your gennie part useless.

#1. You gotta clean the gap...and the slits in the phase plug....and the driver throat. Bits of dirt, metal chips, voice coil former residue...anything....MUST be cleaned out of the gap. Use 1" masking tape adhesive-side out folded outside of some card stock to dig into the gap. When the tape comes out clean after several times around the gap, then clean the gap again with some coffee filter paper dipped in acetone to clean out any tape adhesive bits left behind. Inspect the gap with a lighted magnifier to make sure it's CLEAN...there's only a few thousandths of an inch tolerance on either side of the voice coil when it's immersed in the gap, so this step is critical!...or you'll risk early mortality of the voice coil.

#2. Check the gap width uniformity with a gap guage (.031" on most 1" throat drivers) to make sure the top plate or phase plug hasn't shifted slightly. Alnico drivers can shift a little. The newer ceramic drivers are glued together...so any misaligned gaps are probably factory defects, which is rare...or it was dropped and broke loose. If you get adventurous and take apart an Alnico driver, the magnet will discharge, and subsequently need recharging.

#3. Clean the gap....again. Possibly metal chips from checking the gap tolerance found their way in.

#4. Inspect the new diaphragm. Check for high voice coil windings, check for roundness...sometimes they're not, right out of the box, and the consumer has not much recourse, because when the part leaves my shop in the box, I have no idea what went on from there...read the enclosed disclaimer...and the guy who put it in, NEVER does anything incorrectly...his dog ate it:bs:

#5. Trial fit the new diaphragm. Locating-pin holes are not always the same size as the locating pins. The diaphragm should fit snug on the pins but shouldn't need to be forced into place. If that's the case, the locating-pin holes need to be reamed out a bit....newer ceramic units have a relief machined into the top plate that the diaphragm drops into.

#6. Install the three diaphragm mounting screws...loosely....don't tighten down yet...just enough to hold down the mounting ring. Apply 3.5 volts(for 16 ohm, 2.83 for 8 ohm) test sweep tone from 500-1200Hz, and listen for any buzzing. Sometimes the diaphragm must be adjusted slightly to eliminate all buzzes. It's a good measure of thoroughness to sweep beyond the test frequency to ensure clean travel to lower frequencies, and adjust out any higher frequency anomalies. After all, these are always getting more program than the test frequencies...it's good to be thorough. Snug down the screws when it sounds clean and buzz and resonance free, while sweeping with test tone. BTW...polarity on the sweep test does not matter.

#7. Check the condition of the foam pad inside the loading cap. Get a replacement if its rotten. Check the condition of the lead wires. Make sure there are no short circuits to the loading cap from the outside spring terminals to the inner lead wires. Connect the lead wires to the properly colored terminals. Make sure the wires are lined up with the correct terminal. You don't want to twist and criss cross the wires when reinstalling the loading cap....cap needs to fit airtight. RED is NEGATIVE, BLACK is POSITIVE...yes that's right, it's backwards from what you're used to. Polarity conventions have been changing in the last few years to standardize with other mfr's products.

#8. Re-install the loading cap. Make sure it seats fully down to the top plate with no airleaks and the lead wires aren't resting on the diapragm dome...that doesn't sound good.

#9. Do a final thorough sweep test to the fully reassembled driver to makes sure it's good to go.

#10. It's cheap insurance to have the JBL Authorized servicer do the replacement. If the diaphragm fails due to user installation error....you're pretty much on your own.

Thanks...hope I covered everything:) ,

Edgewound

subwoof
03-29-2008, 02:22 PM
Do mount your own tires on the rims? Re shingle your own roof? diaphrams don't just *drop* in - the procedure for doing this has been posted a number of times on this site.

Perhaps a careful reading of those threads will assist...

sub

Robh3606
03-30-2008, 10:45 AM
#5. Trial fit the new diaphragm. Locating-pin holes are not always the same size as the locating pins. The diaphragm should fit snug on the pins but shouldn't need to be forced into place. If that's the case, the locating-pin holes need to be reamed out a bit....newer ceramic units have a relief machined into the top plate that the diaphragm drops into.


There are no pins in a 2425 so the alignment is basically inside the recess with the collored polarity pin lined up with either a JBL logo or a recess. The voice coil gap has a key to allow clearence for the return wire of the voice coil. When you look at the gap you will see a wider spot. Once you get the polarity mark, screws holes lined up and the coil in the gap Do Not Rotate the coil in the gap.

Rob:)

Malefoda
01-18-2019, 12:55 PM
Is that foam replacement mandatory? In other words, will the driver sound not as good as it should in a way?
30y.o. foam in sight...