Here's one for ya...

[turnitdown]

I have a 2425J and a 2425H. Both work and both have a DCR of 6.3. Is this the famous "JBL swung both ways" and I can assume 8 ohms when using an 8 ohm JBL crossover made for this driver?

[Earl K]

I have a 2425J and a 2425H. Both work and both have a DCR of 6.3. Is this the famous "JBL swung both ways" and I can assume 8 ohms when using an 8 ohm JBL crossover made for this driver?


In JBL parlance both your diaphragms are "J"s .

One always needs to Sim these things to see if the resulting FR meets expectations ( when using stock networks ).

:)

[jbl4ever]

I have both 2425H and J's. The H's read like 3.6 to 3.9 on DCR and 6.1+ on the J's. Possible that someone changed the diaphragm. Take the 3 screws out of the back carefully take the cap off. Now look at your foam disc on back of cap to see if it has deteriorated. Also JBL marked the + led with red for 16 ohm or green for 8 ohm on the diaphragm screw.

[turnitdown]

EarlK. You have taught me to run the sims on EVERYTHING. Haha. Thanks

JBL4ever - I will check the cap and terminals.

This will be my first foray into 16 ohm drivers. Should be fun.

[turnitdown]

Free air impedance sweep of one of the 2425Js. What does this tell me with regard to its behavior at 1kH?

[1audiohack]

Free air impedance sweep of one of the 2425Js. What does this tell me with regard to its behavior at 1kH?

Not much, directly. A horn will change the impedance dramatically.

However, the magnitude and the sharpness of the fs peak lets you know that the coil is not dragging. If it were, the axtra dampening of the friction would broaden and nearly obscure the peak.

Also, if the peak were say twice as high it would indicate coil separation from the diapragm either at the glue joint or a broken diapragm.

Barry.

[turnitdown]

Thanks. Good. I'll mount them and sweep again.

[Ian Mackenzie]

I have a 2425J and a 2425H. Both work and both have a DCR of 6.3. Is this the famous "JBL swung both ways" and I can assume 8 ohms when using an 8 ohm JBL crossover made for this driver?

I would confirm the diaphragms installed.

Typically the measuremed dcr is lower on the H than the J

The Ac impedance of the J is typically 12 ohms above 3 khertz.
The Ac impedance of the H is around 8 ohms above3 khertz

The difference in sensitivity is approximately 3 dB

[Earl K]

Free air impedance sweep of one of the 2425Js. What does this tell me with regard to its behavior at 1kH?


If that trace is indeed from a bona-fide 2425J diaphragm, then I think you need to recalibrate your DATs system ( IOW, the trace should read higher ).

I'll post a 2425j impedance trace a bit later for you to compare yours to ( made on a 2344 horn ).

Mine will be done using my WT2 setup.

In the meantime here's an ancient set of traces for you to ponder ( from LHF member Guido ).

83493

:)

[turnitdown]

OK. Before I mount them on a horn and sweep test them, I will pull the diaphragms and post pictures to be sure they're JBL, etc.