This is topic Swap a JBL driver in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.
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Posted by Antonio Marcheselli (Member # 373) on 06-03-2002, 01:23 PM:
Hi everyone.Seems that one of our theater has blew a HF driver. Which channel? Center of course... 
While we have it replaced I'm going to swap it with the one of the left or right channel tonight.
I never disassembled a driver. Is there anything that I should know? Special tools required, some particularly attention...
Any suggestion will be precious!
Bye
Antonio
Posted by Manny Knowles (Member # 1171) on 06-03-2002, 05:10 PM:
The 2446H driver is heavy. Be careful.I believe that regular 7/16" bolts mount it to the throat of the horn.
Did I mention that it's a heavy object?
Posted by Steve Guttag (Member # 268) on 06-03-2002, 06:15 PM:
The JBL 244x series drivers (where x can be from 0 to 6)mount with 1/4-20 hardware...four of them in fact. What can blow is the diaphragm (replacement for a 2446H is a D8R2450...accept no imitations or substitutions. Also, one thing to check is the tightness of the "push" terminals...they have been known to come loose and cause intermittent or apparent failure types of response.Steve
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"Old projectionists never die, they just changeover!"
Posted by Manny Knowles (Member # 1171) on 06-03-2002, 08:51 PM:
And JBL's diaphragms come with stern warnings regarding its proper installation (by trained JBL techs).
Posted by Randy Stankey (Member # 64) on 06-03-2002, 10:04 PM:
So, what is it about those diaphragms that is so special? I have replaced several of them with no problem. I just carefully remove them and put in the new one. I'm careful to make sure that nothing's hitting where it shouldn't be.Done carefully, it only takes 10-15 minutes to change one. I have even changed one out between shows on a Saturday night.
Is there some secret that eludes me, here?
Posted by Manny Knowles (Member # 1171) on 06-03-2002, 11:59 PM:
I wondered about that, too..."the device is not self-centering" or something like that...goes on to say something about requiring special gear and training.Beats me.
Maybe somebody can explain if this is for real or just a corporate disclaimer.
Posted by Paul G. Thompson (Member # 655) on 06-04-2002, 12:06 AM:
If you are going to change the diaphragm, DO NOT USE A FERROUS METAL SCREWDRIVER!! When you have the magnet suck your screwdriver from your hand and punch a hole into your new diaphragm, then you will know why.Use a copper, brass, or aluminum screwdriver, or any appropiate screwdiver that is not attracted by magnets.
Posted by Antonio Marcheselli (Member # 373) on 06-04-2002, 02:45 AM:
Thanks to all for the suggestions.
However I didn't swap the driver. Seems that was the CP500 was kidding. My colleague reset it many times and the problem disappeared.It is VERY strange because that problem (a cawing from the center channel) was there since yesterday and from the THX monitor cannot be heard (he tried with a pair of Grado headphones too!).
But then the problem disappeared... I really know that CP500 can cause so strange problems, but why on two differents day... ??
We will follow this. Thanks for your help.
Paul,
You're right, I put few times a screwdriver near a driver... 
Bye
Posted by Steve Guttag (Member # 268) on 06-04-2002, 07:50 AM:
The 2446 DOES use a self centering diaphragm (it is pinned for registration). I guess, you can install it rotated by 180 degrees so the extra space for the in/out leads don't line up. Also, you should make sure the air-gap is cleaned out really well. One thing a genuine JBL certified technician will have is an appropriate gap gauge to verify that the magnet structure hasn't shifted. The 2446 should be able to pass a .036" gap gauge all of the way around.Steve
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"Old projectionists never die, they just changeover!"
Posted by David Koegel (Member # 25) on 06-04-2002, 10:10 AM:
And when replacing the diaphram, make sure that you are working in a fairly clean area. Most important is to clean around the edges of that diaphram before you remove it. That gap in the magnet can easily suck in some tiny pieces of magnetic material (read: metal filings), and once in they are in there, I imagine they are very difficult to remove.
Posted by Manny Knowles (Member # 1171) on 06-04-2002, 10:24 AM:
Sounds to me like this is one of those "simple procedures" where there is only one way to do it correctly and over a dozen ways to screw it up.Usually, I need to SEE somebody do it correctly at least once before I feel comfortable doing it myself.
Pictorial guide, anyone?
Posted by Antonio Marcheselli (Member # 373) on 06-04-2002, 05:26 PM:
Uhm... Luckily I had no need to touch that driver!!
Bye
Antonio
Posted by Michael Gonzalez (Member # 593) on 06-05-2002, 01:12 AM:
The hard part isn't replacing the Diaphram it's climbing behind the screen and putting the Driver back by yourself. Try holding a 25lb driver in the air with one hand while trying to screw it back on to the base with ther other hand. Not Fun. Oh and you have to be really careful not to drop the horn and tear a hole into the screen because our screens were not really design for anyone to climb behind them. There are wires everywhere and not very much room to work back there. I got lucky and was able to get it done and it isn't an expirance that I would like to relive any time soon.
Posted by Manny Knowles (Member # 1171) on 06-05-2002, 06:59 AM:
I had to b*tch and moan to get an extra 12" of space and an AC outlet behind the screen. Good thing, too because I later upgraded one of those screens to speakers with much larger horns.It's always good to have help replacing or installing one of those heavy drivers. I usually try to get two helpers if I can.
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~Manny.
"The brown acid that is circulating around is not specifically too good."
-- An announcement in the film, "Woodstock: 3 Days of Peace & Music."
Posted by John Walsh (Member # 168) on 06-05-2002, 05:26 PM:
It would also be a lot nicer if the driver had 4 studs sticking out to hold it in place, (while you screw nuts on) rather than the way it is actually designed (you have to hold the damn thing up while trying to get the bolts to thread through.)
Posted by Randy Stankey (Member # 64) on 06-05-2002, 09:51 PM:
Sheesh! You should see some of the screens I had to replae drivers/diaphragms in!20 feet off the floor. NO scaffolding! Just two pieces of angle iron welded to the screen frame at right angles. Two pieces of metal grating laid across those and the 10 foot tall, 3 way speaker stack sitting on top of that catwalk. No ladders and only enough room to squeeze the horn in the space. In fact they had to cut holes in the insulation to fit them in!
We had to replace all three mids in one and two mids and a high in another! Then about a month later, had to do it all over again when they blew up a second time.
I did find out that the crossover was programmed incorrectly, sending the wrong frequencies to the horns. I fixed that, realigned the B-Chain and lowered the master gain inside the processor (so the kids couldn't turn it up too loud.) Didn't have any more trouble out of those houses.
If you didn't have the agility of an orangutan and the guts of an Indian steel worker you wouldn't be able to do these. In fact, we hired the job out!