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Guido
09-20-2003, 03:41 AM
Hi JBL Maniacs!

Again I have to come with a problem:(

Today my second 2416H arrived:)

I connected it to the 4425 X-over (rebuild) and did realize that it has much lower output than my other 2416H. What to do?

I first cleaned the mash on the throat and as this didn't help I removed the back cover to see that everything looks like beeing ok.

While reinstalling the back cover I learnd that it is not self centering and the sound quality differs when moved slightly.:(
It doesen't matter how I adjust the back cover the output is still lower than that from the other one.

What the h... I can do or what can be wrong?

Any idea?

Thanks for help

Robh3606
09-20-2003, 06:48 AM
Is the diaphram a JBL or aftermarket?? Got a DVM?? You could measure DCR to see what it is and compare it to the good driver.

Rob:)

Guido
09-20-2003, 07:32 AM
DCR on both is exactly 3.1 Ohm!

When I loose the screws and move the back cover sometimes more mids and sometimes more highs appearing.

But in anyway the one driver have much lower output :(

HELP!!!

Robh3606
09-20-2003, 07:51 AM
Hmm Wish I could help more but??? I wonder if the voice coil is rubbing slightly on one. I imagine it would have a similar effect of reduced output and distortion. Gap looks clean? We need the Pro's for this one.

Rob :)

subwoof
09-20-2003, 07:27 PM
Easy - it's cooked from too much heat. When the varnish heats/burns it swells the adhesive bond between the voice coil and the paper former. You can feel small blisters on the inside.

Unfortunately there is no fix except for replacing.

The DCR info is irrevelant unless it is SO burnt that it shorts. At this point it would stink up the house....:)

I used to have a wall in the tech shop with 40 or so JBL diaphrams that were destroyed. This happens a LOT with lower power types. 90% of the 1.75" coils died from overheating.

sub

PS - sehr sclecht...:cooked:

Guido
09-21-2003, 10:55 AM
Hello Subwoof!

Tanks for popping in that thread.

I did attach a picture to let you check if it could be overheat or at least if it is a original coil.

Guido
09-21-2003, 10:56 AM
More

Guido
09-21-2003, 12:29 PM
Hallo Giskard!

What is this reply come reply go thing?

To Subwoof:

With your help I fixed it. I checked the coil for humps or blisters and found one, maybe two relevant ones.

I gently flattened them with sand paper. It worked:) :)

Sounds the same then the "good" one now!

subwoof
09-21-2003, 12:30 PM
feel the inside of the coil where the writing is.

if there are any "blisters" or bumps it is overheated.

I cannot tell with your picture.

danke

4313B
09-21-2003, 01:08 PM
Originally posted by Guido
Hallo Giskard!

What is this reply come reply go thing?

To Subwoof:

With your help I fixed it. I checked the coil for humps or blisters and found one, maybe two relevant ones.

I gently flattened them with sand paper. It worked:) :)

Sounds the same then the "good" one now!
I deleted my posts after I found out they were irrelevent.

So the coil had gunk on it? Or were the bumps on the coil former side?

Guido
09-21-2003, 01:13 PM
Originally posted by Giskard
I
So the coil had gunk on it? Or were the bumps on the coil former side?

No, the coil is absolutely ok. On the backside (coil former) there where one, maybe two relevant humps. I had nothing to loose and flattened them as posted. It really worked:)
Sounds perfect!!!
:rockon1:

4313B
09-21-2003, 01:31 PM
Originally posted by Guido
No, the coil is absolutely ok. On the backside (coil former) there where one, maybe two relevant humps. I had nothing to loose and flattened them as posted. It really worked:)
Sounds perfect!!!
Cool! Sometimes kits come with excess glue or varnish crystalized on the coil and that must be removed before putting in the kit. I've also seen those bumps in the formers on new kits and had to carefully remove them.

The DCR check can indicate if a coil has shorted turns and is out of spec. The DCR check can also indicate that a different diaphragm is in use rather than the intended diaphragm. JBL does not consider a DCR check irrelevent.

Mike Caldwell
09-22-2003, 03:05 PM
I have also had drivers that had a very low output
and the problem was were the lead attaches to the
speaker wire push terminal on the underside of the back cover.
There was just a bit of corrosion between the terminal on the wire
and screw, cleaning and tighten it up is all it took.

Mike Caldwell

GordonW
09-23-2003, 10:01 PM
Ah, the classic metal oxide resistor phenomena, huh, Mike? :duck: :D

Regards,
Gordon.
sounds like what used to happen to all the iginition points in lawnmower engines... dad used to fuss at what he called "superinsulation" that those things seemed to grow... :banghead: