View Full Version : JRX1125/SR25 Driver transplant help needed

04-22-2012, 05:46 AM
Dear all,

I need some crossover ideas / calculation help on combining dual JBL 15” with a 2417/2370 for PA use.

I bought a used pair of JRX125 (same as SF25) the other day and both of the 2412H drivers were burnt. There is a pair of M115-8A (8ohms each) woofers in each cab and they are ok.

Since the 2412 is probably not the best drivers JBL ever made and I happen to have 2 2417 & 2 2426 driver cores, 2 new H (8ohm) diaphragms and 2 aluminum “2370 horns” my idea is to upgrade instead of buying new diaphragms for the 2412’s. Se picture below to compare size.

Many seem to just throw in a Selenium driver and keep the plastic horn and the crossover intact, but I’m not sure that would be the way for me and also I’m not sure the plastic horn can take the extra weight without breaking over time. I’m aware that the phase plug in 2417 and 2426 are slightly different but either should be fine with a standard diaphragm, albeit a little less treble coming out of the 2417.

I believe my 2370 horns are JBL clones from different brand as they are in aluminum, but they look and measure very similar to the 2370 when comparing to the JBL originals in my SR4725’s.

The JRX system sensitivity is stated at 100db 1w@1m, so the 2417 should be fine and also a reasonable upgrade from the 2412. The best of all is that the 2370 horn actually fits in the JRX125 cab with very minor changes.

The original JRX filter has a simple 2kHz 12db HP filter for the drivers and uses different LP’s for the two 15” units. Both do bass but only the upper 15” is allowed to do mid’s. JBL calls it a “quasi 3-way system”. Se filter below.

Has someone seen a JBL filter for dual 8ohm 15” woofers and a single (2415/2416/2417/2425/2426) 2426 driver in a 2370 (or similar) combination?

All the filters I can find from JBL for dual 15” cab’s are made for 2” drivers with too low crossover points for the 2426 to survive.

Do I need to retain different crossover points for the woofers even if I lower the XO point from 2kHz to say 1,3kHz? Most other JBL dual 15” systems have both woofers in parallel.

I though about using the filter from the SR4725X (2226/2426/2370), but since it is calculated for a single 15” (2226 @ 97db 1w@1m) the driver levels will be wrong and the XO since the filter is for 8ohms as opposed to 4 ohms here. The use of 2417/2370 should also allow for a lower HP point, like in the SR4725X (1,3kHz). See filter below.

Can someone recalculate the SR4725X filter for dual woofers (4ohms LP) and increase the driver sensitivity 3db to compensate for the dual 15” drivers @ 100db as opposed to the single 2226 @ 97db.

Or any other passive ideas?

Best regards and thank you

04-22-2012, 07:02 AM
compare the attenuation circuits between the 4725 and the 4725A. the woofers changed to 4 ohm from 8 and that difference might be all you need to do. The woofers you have are small coil / midrange types and will be brighter in the crossover region too.

all in all if you just added a L-pad you can make it work.

04-22-2012, 11:09 AM
Hi Subwoof,

Thank you for the answer.

I looked at 4725, 4725a and 4725X again and they are all 8ohm filters (single 2226H) ... Please explain.

I think the 2426 circuit in the 4725X makes more sense in the way it is made compared to the older 4725 and 4725a with a bunch of resistors.

My problem is that I am not skilled enough to recalculate the 4725X filter for +3 db higher level to the 2426 driver and change the woofer circuit to 4ohms with the same xo frequencies. All a result of the dual woofers.

Or find a JBL filter for dual 8ohms 15” woofers and single 2426/2370….

-Any ideas?

Best regards

05-02-2012, 09:15 AM
Here is what I did.

I swapped the pretty thin 2417 driver and the waveguide for a 2426H/2370 combination.

I kept the original filter for the lower 15" and since the M115-8A driver TS parameters are reasonable close to the 2226H, I made a SR4725X (which is based upon the 2226/2426 combination) filter for the upper woofer and the 2426/2370 combination and just combined them. Some initial measurement and listening shows that it works pretty well. It’s like a pair of SR4725X with a built in sub J .

While I was at it I reinforced the cabinet a little and added some dampening….

Not as violent as my SR4725X clones with separate subs, but decent.

All the best