Damaged 4430 driver?

[Lancer]

Oops! My fault! I goofed and posted this in the Technical Help forum!

[sfellini]

Tell us what they are once you remove them....

Not having any AC/DC, I resorted to a putty knife. Worked nicely.

Steve.

[Zilch]

Those are the correct OEM drivers for late production 4430's, looks like.

We'll soon know if they are O.K. or not. You probably have several factory service centers there.

A pic of the room you're playin' them in would be helpful, too. There's members here whose specialty is room alignment.

[sfellini]

We'll soon know if they are O.K. or not. You probably have several factory service centers there.

I just got a call from the local JBL service center and he says the
drivers "sound" ok to him. I asked if that meant they measured
within spec or not and he said he didn't have any special equipment,
and just does a frequency sweep and listens.

I guess this isn't what I expected . I did want them measured,
right? Isn't that what these guys do? Should I try someone else local,
or ship them off to a service center that someone can recommend?

Steve.

[Regis]

I'd have to say (from a service center perspective, as I used to be a technician) that a JBL Service Center is likely well-equipped to repair your equipment, but as far as actual measurements, that's almost in the realm of the laboratory. I understand that you're trying to set up optimum room eq using the equipment you have on hand, but even Zilch's equipment shows minor differences between the left and right (maybe I'm wrong and feel free to correct me, just playing the 'Devil's Advocate').

Have you tried switching the two as Zilch suggested? Secondly, was there a noticable difference between the two before you got the measuring equipment? If you didn't have the equipment, is the difference noticeable? Zilch did point out L-pads and X-overs as possible culprits and these would have some contribution. I would do an A/B test with both speakers L-pads carefully labeled, to see if there's any differences as well. As far as the passives, try measuring the individual components in the x-overs and see if there's any glaring differences. You'll have to pull the caps to measure capacitance if you can, I don't think you can measure that with the caps in the circuit. Just some thoughts and good luck.

[Zilch]

While I give some credibility to a tech who works with these all of the time saying, "Sounds fine to me," I doubt he could hear a difference in the frequency range of interest here. Ask him to open them up and verify that they have JBL stock diaphragms in them, at least, and that there is nothing apparent amiss in there. For a nominal charge, he might also clean the gaps for you while they're open.

At risk of sending you on a wild goose chase, I'd then call the other nearby JBL service centers and inquire if any of them have means to compare the performance of your drivers to known good ones above 10 kHz.

Another option would be to tell this tech to go ahead and put new diaphragms in them. That'll be about $300 for the pair, probably, and may not solve the problem. At least you'll know the drivers are to spec then, though. I've seen other members here recommend this as standard practice with any acquisition of used compression drivers.

The one case in which I did that here, I concluded there was probably nothing wrong with the old diaphragms in the first place. I did have success with returning a different pair to the JBL factory for evaluation and rehab, but that was after I had obtained definitive performance measurements by Mr. Widget indicating they were not up to spec.

I'm convinced there's a problem somewhere there. Once you get them back, move that "Int/Ext" switch on the crossovers back and forth a couple of times. It may be that the contacts of that switch are dirty, is all....

[edgewound]

A real easy first test to find out if they're JBL diaphragms is to measure the DC resistance of the voice coil with a ohmmeter. D8R2425 should measure 3.2 ohms dcr +/- 8%. This is what's in a 2426H driver. Maybe it's a JBL diaphragm but possibly 16 ohms? which would measure 6.2 ohms dcr +/- 8%. If it's an aftermarket 8 ohm it'll likely measure close to 8 ohms dcr. Lotsa people all over the place are peddling aftermarket diaphragms and claiming they're identical to the JBL...well....THEY'RE NOT!!!! They sound different....darker..usually because thery'r pulling less current due to the higher dcr.....whew!!


I know...those 4430's are big and heavy.....but it's best to have them tested as a system...visually and sonically...by someone willing to open up and take a peek to check the innards. I'd venture to say that most Service Centers don't have sophisticated measurement facilities...me included, but I do have an RTA and test mic that works ok.

Hope this info helps

[Don Mascali]

May I ask Where you sent them?

I am near you and inquiring minds want to know.

[sfellini]

A real easy first test to find out if they're JBL diaphragms is to measure the DC resistance of the voice coil with a ohmmeter. D8R2425 should measure 3.2 ohms dcr +/- 8%. This is what's in a 2426H driver.

Thanks for the suggestion. I picked up the drivers yesterday and
was able to measure them. One is 3.5 ohms and the other is 3.6.
That's more than 8%, but just barely.

I also mounted the drivers on their horns and sent pink noise
through them and measured (R & L respectively shown below).
This will take the crosover out of the picture.

There is a notch at 4k in the R driver which corresponds to the
dip in the near field response that I first posted. So I think something really is off with this driver .

Is this likely to be fixed with a diaphram replacement?

Also for your amusement, I'm including a pic of the test rig here
at Fellini Audio Labs.

Thanks for all the help I've been getting...
Steve.

[sfellini]

May I ask Where you sent them?

Hi Don,

Joe Rodgers PAS
12401 Twinbrook Parkway
Rockville 20852
(301) 984-3822
Transducers, Electronics, EON, LSR & 6208, JRX, MPro &
SoundFactor

I would not reccomend these guys based on the condition
of my drivers when I got them back: each had a chip or
two taken out of the magnet .

Steve.

[Zilch]

Pull the mic up outta the horn throat a foot or so. Repeat test.

http://audioheritage.org/vbulletin/s...page=1&p=64864

I see your protection capacitor there. Good job!

[johnaec]

Pull the mic up outta the horn throat a foot or so. Repeat test.

I agree! 'Way too many anomolies when jammed in the throat. I'd suggest 1-3 feet, though the farther away the more likely getting some room interference.

John

[sfellini]

Pull the mic up outta the horn throat a foot or so. Repeat test.

and

I agree! 'Way too many anomolies when jammed in the throat. I'd suggest 1-3 feet,

Ok, at 12 inches the notch is gone and they look pretty close (R, L).

Thanks!

Next they go back into the cabs.

[johnaec]

Wow - that's about as perfectly a matched pair as I've ever seen. It also looks like you've got a real smooth standard 6db/octave bi-radial rolloff, (5db graph divisions?). If the crossovers are in spec, I'd think they should sound pretty good!

John

[Zilch]

Next they go back into the cabs.

Nope. Now run a wire to them from one of your crossovers. Substitute an 8-Ohm resistor for the woofer in that cabinet. Test both drivers on that one crossover. Then repeat with the other crossover. Small wilre nuts will facilitate this process....

Click that crossover "Int/ext" switch back and forth a couple of times to be sure dirty contacts there aren't a problem. Maybe test first, then click to see if there's a difference. Set controls at "0".

This is SCIENCE now at Fellini Labs....