Field replacing diaphragms

[stevem]

The spec sheet for the 2451 driver states that its diaphragm is "rim centered" for ease of field service. Does this mean that a new diaphragm can simply be correctly installed with a screwdriver without being sent back to JBL?

[edgewound]

The spec sheet for the 2451 driver states that its diaphragm is "rim centered" for ease of field service. Does this mean that a new diaphragm can simply be correctly installed with a screwdriver without being sent back to JBL?

In a perfect world, yes....but that hasn't happened yet . The diaphragm should always be replaced and centered in a properly equipped shop with a sweep generator and observing the correct voltages, cleaning, etc. You'll notice a warranty disclaimer packed with each diaphragm about tolerences, etc.

[Oldmics]

JBL diaphragms sold "over the counter" which are not installed by an authorised service center technician do NOT carry any implied warranty.

Only JBL items installed by JBL certified service center techs carry a warranty.

Oldmics

[stevem]

Rats. I knew it sounded too easy!

[johnaec]

I will say that when Zilch and I replaced the self-centering 2450 diaphragm in one of my 2446's, (factory stock NIB dia.), it appeared to me that there was no play at all - I don't see how it could've been tweaked even if you wanted.

Even if it can be minutely adjusted, (?), I'm sure it would be safe to install it yourself for now, to be possibly tweaked later. There's just not enough wiggle room to be concerned about the coil rubbing, even if it can be further optimized.

John

[stevem]

That's interesting. Your diaphragm is basically the same as the one in my 2450SL drivers (except yours has ribs and no aquaplas coating). Maybe it can be done.

[johnaec]

Whatever you do, keep control of the screwdriver - those magnets are STRONG in places! And be sure to look at positioning for correct polarity.

John

[Steve Gonzales]

The may be no side to side 'wiggle room' but there is the possibility of machining tolerences up and down that require shims, though not likely, I have known it to happen.

[Tim Rinkerman]

Even tightening the screws to varying tightness (torque) will change the sound of the diaphragm. We always enlarged the dowel pin holes (no more than .001")just so they weren't tight...and used as many different frequencies from 100 to 10,000+ and listened at varying power levels for a pure, un-colored, clean, sine wave tone. Put the diaphragm in, tighten the screws lightly, and go around the screws one at a time, tighten, loosen,(you will hear the tone change) put a bit of finger pressure near the screw while you are tightening it..( a non-magnetic screwdriver pays for itself real fast here). You will be able to "tune" the driver so it has no buzzes or overtones whatsoever if you are patient and dilligent. I have NEVER had a replacement diaphragm of any kind go in and work correctly just by cleaning the gap and screwing a new one in. A properly "tuned" one has decidedly more output than an "un-tuned" one as well.

[edgewound]

Nice addition, Tim. I always sweep way outside the test parameters too. Makes certain the diaphragm is really good and true.