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Donald
12-05-2004, 06:54 PM
Took the H91 horn off its LE85 because I wanted to remove the bracket that held it in a L200. Planning to get the LE85 re-gaussed. Saw something sitting in the throat and tried to use a pair of tweezers to get it out. But the magnet wanted them more. Now I have 2 holes from the tweezer tips in the screen that covers the diaphragm.

1. Since the unit is normally used in a horizontal position, is there a great danger in just leaving the 2 holes?
2. Can just the screen be replaced? I know it means breaking the seals.

Bestsmurfs
12-05-2004, 07:35 PM
I know what you mean, I had a phillips screwdriver yanked out of my hand and down the throat of a 375! You're only dumb if you did it twice. Maybe it didn't need to be re-gaussed after all. I would sweep test it with a CD at volume and if it doesn't buzz don't worry about it. I have said a few times on this site (to the dismay of some) that the JBL horns are not all that accurate or distortion free anyways, especially if the diaphrams are 30 years old. Relax...... Enjoy..... PS: sorry I couldn't answer the question. :smthsail:

Robh3606
12-05-2004, 07:46 PM
Those magnetic fields are a real surprise! I had the back off a 2425 and damn near had a screw driver yanked into the diaphram. We have all had our disasters and close calls so don't beat yourself up. As long as it's working and doesn't buzz I would leave well enough alone until sometime down the road when you have no choice but to opener up.

Rob:)

johnaec
12-05-2004, 08:06 PM
But the magnet wanted them more.At least others, (particularly me), will benefit from your experience. I had no idea the magnetic force was so strongly focused in that area. Especially with Alnico magnets and the refined JBL magnetic fields we're so used to, it's really easy to become complacent working around their drivers. Thanks for the heads up!

John

honist_bob
12-05-2004, 09:53 PM
Thanks for the heads up on the intense magnetic field. I too, have an LE85 with a lot of dust on the screen. When I attempt to clean it, I'll remember, now, to use a plastic brush, or a new flux brush (from the plumbing department at the hardware store) that is made with an aluminum shaft.
I know that the screen is made of a very, very fine mesh. Is it sturdy enough to stand up to a brushing/vacuuming?

Tim Rinkerman
12-05-2004, 09:55 PM
$30.00 was too much money for a non-magnetic screwdriver.......till I did that a second time...:banghead: Beryllium or stainless steel..(any bone doctor friends?). As the old TV ad used to say,"it takes the worry out of being close"...Tim

Zilch
12-05-2004, 09:58 PM
Same problem here. I have a "Mini" vacuum accessory kit by Eureka here somewhere. Has adjustable suction, and attaches to my "Mighty-Mite" vacuum. We'll see....

http://store.yahoo.com/eurekaservice/minitoolset.html

$12.99, heh, heh.... :cool:

Alex Lancaster
12-06-2004, 05:37 AM
:) Ive used compressed air at about 60psi, (4Kg/cm2) from both sides, with the diaph removed, with no problems, just dont ram the airgun in the hole.

Also, even Stainless S. is not completely amagnetic, so I use my left thumb and forefinger to guide the screwdriver, and do it slowly; Ive busted some diaphs too.

boputnam
12-06-2004, 08:40 AM
:rotfl: And not at you, at the scene! I felt like I was watching me... Like John sez, this a good thing to have posted.

1) I don't think so, at all.
2) Maybe the folks at JBL Pro have a suitable replacement part (from the Pro version of the driver). Call 'em! 818 894-8850 - ask for Dave, or Karla.

Oh, one other thing - I've twice had the laptop on the work bench TOO dang close to some H drivers. :eek: Been lucky, twice...

Mr. Widget
12-06-2004, 10:44 AM
The fine mesh screen is to keep bugs and dirt out of the driver. Having a couple of extra holes in it will not hurt a thing. Many tweaks carefully trim the entire screen out from their drivers as it supposedly sounds better.

The only concern I would have is that perhaps a bit of screen sheered off and fell into the phase plug. If I were really concerned, I would remove the diaphragm and blow low psi compressed air from the diaphragm side and see if anything collects against the screen. You may want to tape off the gap first as a bit of metal getting in there will be a real problem.

Widget

John
12-06-2004, 12:33 PM
I am not sure how the screen is secured in the jbl driver but in the altec small format driver i think it is sitting in a small circuler groove. I have never removed them from my jbl or altec drivers,but heard a pair of 19,s out in calgary that had them removed from the compression drivers. I have to say they did sound very open and smooth,althought i had nothing to compare it to,no A-B sound off.:D

subwoof
12-06-2004, 04:55 PM
I have a disasembled 2420 with a discharged magnet that I use to explain how drivers are made / work to sound engineers ( as part of their client-ordered probation when they blow too many )

:)

The screen is *under* the bottom of the cast metal conical throat and unless the throat is removed, inaccessable.

I would cut it out and ( as previously described ) clean the driver and take care to align the diaphram when reinstalling it with a good oscillator.

use a new exacto knife with a SS blade ( #11) and aluminum handle. There's not enough ferric material to cause grief. Do this while holding the driver facing *down* so gravity is in your favor.

Then you can use a simple copper mesh at the driver's exit to keep out the inquiring insects and the occassional flying screwdriver / mounting bolt.

sub.

And I agree - magnets suck. it would be a lot more fun if they pushed.

Charley Rummel
12-07-2004, 08:07 PM
Many moons ago, when I was new at this crazy interest of mine (ours), I openned up a 175 to change a diaphragm, and I gave no thought to the scattered iron filings all over the work bench left over from a project my father had done. :banghead:

This one went back to JBL in California for help.....

Regards,
Charley

Zilch
12-08-2004, 05:41 PM
The little Eureka kit worked perfectly to clean out a nasty LE85 here today. The 3/8" diameter plastic tools, one with brush, easily reached the 2+ inches into the throat to vacuum the screen. It also has an adjustment to vary the suction as required. A highly recommended accessory.

The driver is off to Mr. Widget now for testing.... :)