Trouble with 2421A line-up pins

[Ed Zeppeli]

I have the 2421A drivers in my 4430s and am trying to install new OEM D8R2425s into them. The issue is that the holes for the line-up pins in the new diaphragm don't seem to be large enough and as such the diaphragm won't sit down.

I have tried gently pushing down but will not go any further to force it in.

I was under the impression that these were interchangeable. The 2425 doesn't seem to have the line up pins to contend with.

Has anyone else encountered this?

Thanks,

Warren

[Ed Zeppeli]

[Ed Zeppeli]

Drilled 'em out and sine-aligned the diaphragms.

[Ed Zeppeli]

The two on the right came out of the 2421As and the left one is new OEM 2425.

Do the old two look like JBL original?

[hjames]

At a casual glance - looks like the pair on the right are like the one on the left, if it was rotated 180 degrees.
It does look like the larger pair of holes on the 2421A pair are somewhat larger than the old pair of larger holes -
but from here, the pattern appears to be similar ...
Certainly I would check by physically positioning the diaphram on the other driver and checking the fit that way.

The two on the right came out of the 2421As and the left one is new OEM 2425.

Do the old two look like JBL original?

[Ed Zeppeli]

Yes thanks HJames. I kept searching and found that some have had to drill out the line-up pin holes so that's what I did. Everything is installed now and functional.

Now onto further troubleshooting as to why one speaker has lower output than the other....


Cheers,

Warren

[ivica]

.....Everything is installed now and functional.
Now onto further troubleshooting as to why one speaker has lower output than the other....
Warren

Hi Ed Zeppeli,

May the magnet has to be "recharged". The best would be to measure the magnetic flux in the top-plate gap.

regards
ivica

[Ed Zeppeli]

Thanks Ivica.

I went through the whole network and swapped out the l-pad and re-touched some solder joints. I also tightened in the screws on the backside of the binding posts. I guess those can loosen over time and I'm glad I checked. Things seem to have equalled out now between the two speakers; output-wise.

I ran some pink noise into my minidsp and used REW and an RTA to get them tuned in a bit. I think I have them up to snuff now.

I am curious though; how does a hobbyist go about measuring flux?

Cheers,

Warren

[ivica]

Thanks Ivica.

I went through the whole network and swapped out the l-pad and re-touched some solder joints. I also tightened in the screws on the backside of the binding posts. I guess those can loosen over time and I'm glad I checked. Things seem to have equalled out now between the two speakers; output-wise.

I ran some pink noise into my minidsp and used REW and an RTA to get them tuned in a bit. I think I have them up to snuff now.

I am curious though; how does a hobbyist go about measuring flux?

Cheers,

Warren

Hi Ed Zeppeli,

I have no exact idea how to measure the flux without proper tools, but one idea is (may be even useful for the hobbyist):
You need one driver (call it reference driver) of the same type the driver you want to test, and one driver as a source.
You have to 'connect' source driver with the reference driver (face-to-face) using a kind of pipe between.
While applying, say, sinusoidal signal to the source driver (over amp) , You can measure the signal level on the reference drives binding posts.
It would be good to repeat the measurements using more different frequencies.
Then you have to remove reference driver, and use DUT (driver-under-test) equipped with the same diaphragm as is in the reference driver ( removing from the reference driver and installed into the DUT-driver, or using additional diaphragm that behaves almost the same as the one in the reference drive).
Install DUT-driver instead of the reference one, and repeat the whole measurements.
If magnetic flux is almost the same as in the reference one, then the measurements would show ALMOST the same level of signal measuring over DUT-driver binding post.
But if the magnetic flux is weaker, the level would be less (then when reference diver has been used), and I believe that would be much more "visible" using higher frequency. So you can start from say 500Hz up to 12kHz...

The same "method" can be done for the cone-type drivers too, but then the frequency range has to be 'adapted' to the expect-able driver's frequency range of use.

regards
ivica