4425 Re-Diaphram

[johnlcnm]

Looking for any input as to replacing the 2415/2416 diaphragm with a Radian 1225-8. Apparently Radian does not make the required back cap adapter any more. Does anyone have any suggestions for a substitute cap?

[johnlcnm]

Well, I think I have answered my own question: After obtaining the Radian Audio Engineering drawings of the C1225 Adapter Kit, thanks to Richard Kontrimas of Radian, I found that reproducing the back caps would cost about $400. I decided for less money I could buy used 2426 J drivers and replace the diaphragms with the 8 Ohm Radians. I have not received the both drivers yet, but will report the results.

[Earl K]

Hi,

Simply buying some used 2426 drivers ( to load with Radian diaphragms ) is a very reasonable way to go .

OTOH, "old-style" Altec loading caps ( used in many of their older alnico based,small format drivers ) will work over the Radian diaphragm, both bolted to a JBL magnetic structure .

They come up for sale on eBay from time to time ( prices really vary ) .

It's the item on the right-hand side of the following picture .

:)

[johnlcnm]

Hi Earl,

The main problem with the 2416 driver is the lack of mounting holes for a cap. The Radian cap mounts with the same holes and screws as the diaphragm. JBL did not machine the holes in the magnetic return plate on this driver to mount the back cap. I guess the holes could be drilled and threaded in the existing return plate. Man, I would hate to attempt a magnetic gap cleanup after the machine work. There is also a difference in the phase plug between the drivers. The 2416 has the nine concentric holes while the 2426 has the concentric rings. I think I read somewhere that the concentric ring configuration was an upgrade. I hope the new drivers are compatible! At this point I am waiting for the second driver.

Thank you for the reply. I really appreciate your input! Experimentation does not always result in an acceptable answer, Ha Ha.
John.

[Zonker92]

I made mine with $7 ABS pipe caps from the Home Despot. (Sorry for the sideways images.) Used "Amazing Goop" to seal the holes.

I put felt pads inside for reflection damping, and put steel shelf supports on the bottom edges of the plastic to "grab onto" the magnets: see:

https://s-media-cache-ak0.pinimg.com/236x/49/33/58/49335862bc944d393e81848eec375b98.jpg

(Not shown here; sorry). I pressed the pins into holes in the plastic to stabilize them, then let the 90-degree angled parts rest on the magnets; it sucked the cap down onto the driver and centered it.

[johnlcnm]

Zonker,

What did you use to seal the cap to the driver. Was the fit tight enough that the seal was not required?

[Zonker92]

It was a snug fit, but I wrapped a thin band of clear adhesive tape around the seam anyway. (I suppose I could have glued it closed with Amazing Goop, instead.)

[johnlcnm]

The replacement diaphragms were a successful match even though the phase plug is a completely different design. Last fall I was able to buy a new old stock Crown I-Tech 5000HD amp. I did need to equalize the 4425 response: 45Hz -4dB with a Q of 10, 110Hz -2dB with a Q of 4, LP Shelf @ 160Hz -3dB, 800Hz +1dB Q of 1.4, HP Shelf @ 5000Hz -3dB. These old JBLs really woke up! I have compared them to my 6332s which IMHO are very flat in my room. They are an excellent reference source. I have always considered the imaging excellent on the 6332s, but the 4425s are another step above. These things are incredible imagers. The mid range is very good for a two way system with a 12 inch woofer, and I understand why JBL has gone in this direction with there new designs: The M-2s and the 7 series.

A plug for the Crown I-Tech. If you have not heard this amp with a digital source connected to the AES input, seek out a demonstration. The transients and definition are much better then my Benchmark DAC-1 HDR and my Audio Research DAC-1.

John

[Zonker92]

Nice! I have my pair restored and mirror-imaged but I have yet to fire them up; they're waiting for me to finish my home office. Are you saying that the Radian diaphragms have a different response from the OEM diaphragms?

A buddy of mine has a metal fabrication shop and he's making stands for them; four square metal tubes running vertically between upper and lower horizontal metal plates.

[johnlcnm]

Zonker,

The Radians seem to be a little hotter then the JBL titaniums. But again, I changed the drivers to the 2426's, so I am not sure what effected what. I am running the pads at -4 for the 10kHz and -4.5 for the 2kHz, but the eq. in the amp is set to -3dB shelved at 5kHz. That is probably a preference thing on my part. I have hooked the baby checks up to my old Threshold 500. The sound is sweeter and a little laid back. I did not like the sound with the old titaniums when using the Crown amp. The measurement system I currently have only goes to 500Hz, so the rest of the equalization is by comparison to the 6332s. Certainly subjective!

But, the bottom line is, - I really like these old monitors. I used Event Opals for about 5 years before getting the 6332 JBL's. My opinion is: The JBL's are in a completely different league. If I were mixing, I know what I would be using.

John

[Zonker92]

OK; thanks; I think I understand.


I really like these old monitors. I used Event Opals for about 5 years before getting the 6332 JBL's. My opinion is: The JBL's are in a completely different league. If I were mixing, I know what I would be using.

Are you saying you like the 6332s over the Opals, or the 4425s over the Opals, or both?

[johnlcnm]

Zonker,

Yep,

I think both the JBLs are in another league. I really don't think they even compare. The Events have a pretty fuzzy mid. and the low end is not flat and can't be made flat. The upper end of the Events is wirey sounding and not flat at all. The Events image OK but not even close to the 4425s. I think the 4425s make a great video speaker also. They image so well you do not need a center channel.

Did you see the comment from Greg Timbers about the listening center of the 4425 being slightly above the speaker? He says that is where the crossover sum is the flattest. Below is the eq. that the Crown is feeding to the 4425's. I have one for the 6332's also.

Regards,

John

[Zonker92]

Very cool; thanks. I had not seen that comment about the 4425 listening center, but I'm glad to hear it, since I deliberately designed my stands a little low to keep the speakers less tippy. :D

[johnlcnm]

I'm not finished experimenting with the 4425s. I think the design philosophy concerning the frequency response was a little different then with the newer JBLs. The high end of the frequency spectrum was a collection of measurements taken in the dispersion pattern and summed for the newer designs? Or something a little more complicated then that. Maybe a sum of the direct and first reflected wave were summed. Anyway, the 6332s are considerably more "polite" at the top end. I need to purchase a measurement setup and haul everything outside to come up with a real eq. for these.

Zonker. I am looking forward to hearing of your listening adventures with these classics. I recently acquired a tired pair of 4333Bs. So I am working to get those guys restored and operating. At this point I am calling them the money sinks!

John

[Zonker92]

Yeah, can't wait to fire them up! Pictures here: http://www.audiokarma.org/forums/showthread.php?t=654308

4333Bs are way cool. I just finished some 4435s:

http://www.audiokarma.org/forums/showthread.php?t=654301

And earlier, some 4430s and 250Tis.

Eric

[johnlcnm]

Did download a program, "Fuzzmeasure". Ran a number of sweeps inside the house. Without amp EQ the pads were flattest with 2kHz set to zero and 10kHz set to min. Looks fairly flat and sounds good. I did not realize how much the 10kHz was up. Guess that is due to the new Radian diaphragms and maybe the difference in the 2416 and 2426 phase plug. Eric, I do remember you from Audiokarma. Sounds like you are overloaded with the 44 series. Maybe those 4430s would want to come to my place to live?--- Just kidding! The 4333Bs that followed me home came with one 2231H and one 2235H. I hope the efficiency at one kHz is the same. If not I may be on the hunt for another 2235H. Both had been re-foamed by the previous owner. He never got a chance to rebuild the rest of the speakers though. The cabinets had big holes gouged in the back for hanging I guess. The rats had also made a home in them at some time in their past. I removed the finish with a paint scraper and heat gun, filled and sanded the holes and gouges. The grills were in pieces. I rebuilt those. They need grille cloth and black paint. I sent the cabinets off to get walnut veneer. The 2405s were toasted so I replaced the series caps in both crossovers, even though they both read open. The caps look like they had been hot. A little on the brown side of the color spectra.

Man you are in the holy grail of JBL land!

John

[Zonker92]

Wow; you've had your work cut out for you! My 4435s were also a major project, with new veneer, refoaming, CCed crossovers, new grill cloths, new diaphragms, etc. Not that I'm complaining. :D

I sold the 4430s to a very happy man in SF; that was also for the best, as I'd run out of systems that could use them. I'll miss them, though.

[Rudy Kleimann]

Zonker,

The JBL's are in a completely different league. If I were mixing, I know what I would be using.

John

IIRC, Christopher Cross used a pair of 4425's in his studio, may still have them to this day. His first album, released in 1980, had superb sound quality. Still sounds good today IMHO

BTW- do you have a picture of your old driver phase plugs? You said they looked different. If they had 9 round holes in the phase plug instead of the annular slits, yours are probably early 4425's. I think those drivers were actually 2415H's. Diaphragm was not changed- only the part number changed, a la 2446,2447,2450,2451,etc.

Have you compared the crossover network components in your cabinets against the JBL Service exploded diagram? If yours had 2415H (round hole phase plug passages) The HF EQ filter section may be different in your 4425's than what was provided in the later models with 2416H drivers.

[Zonker92]

Thanks, Rudy. I have mine all buttoned up now and in service in my master bedroom system; no photos of the crossovers or phase plugs; sorry. They do sound very good to me, though.

The stands are a work in progress.

[johnlcnm]

IIRC, Christopher Cross used a pair of 4425's in his studio, may still have them to this day. His first album, released in 1980, had superb sound quality. Still sounds good today IMHO

BTW- do you have a picture of your old driver phase plugs? You said they looked different. If they had 9 round holes in the phase plug instead of the annular slits, yours are probably early 4425's. I think those drivers were actually 2415H's. Diaphragm was not changed- only the part number changed, a la 2446,2447,2450,2451,etc.

Have you compared the crossover network components in your cabinets against the JBL Service exploded diagram? If yours had 2415H (round hole phase plug passages) The HF EQ filter section may be different in your 4425's than what was provided in the later models with 2416H drivers.

Rudy,

I looked at the drivers. They are still in cold storage, i.e. the closet. They are the nine hole type. Date on the diaphragm is Sept 29, 1988. I don't think these speakers have ever been apart, at least before they came to me. No doubt the response with the 2426H and Radian diaphragm is a lot hotter on the top end. I do have the 12kH set to min. I also have a high frequency shelf of a couple of dB set up in the amp. Tried to photograph from the screen side but could not get a good photo. I will pull a diaphragm and get one from the back.

Regards,

John

[johnlcnm]

Thanks, Rudy. I have mine all buttoned up now and in service in my master bedroom system; no photos of the crossovers or phase plugs; sorry. They do sound very good to me, though.

The stands are a work in progress.

Zonker,

Looking good. So what position did your L-Pads wind up in? Did you notice an increase in the high frequencies with the Radian diaphragms? What do you think of the sound in comparison to your 4435s?

Regards,

John

[johnlcnm]

IIRC, Christopher Cross used a pair of 4425's in his studio, may still have them to this day. His first album, released in 1980, had superb sound quality. Still sounds good today IMHO

BTW- do you have a picture of your old driver phase plugs? You said they looked different. If they had 9 round holes in the phase plug instead of the annular slits, yours are probably early 4425's. I think those drivers were actually 2415H's. Diaphragm was not changed- only the part number changed, a la 2446,2447,2450,2451,etc.

Have you compared the crossover network components in your cabinets against the JBL Service exploded diagram? If yours had 2415H (round hole phase plug passages) The HF EQ filter section may be different in your 4425's than what was provided in the later models with 2416H drivers.
Rudy,

The photo, these are on an old 4430 horn, so disregard that. I got the horn with one of the 2426Hs that I bought for a replacement in the 4425s.

Regards,

John

[johnlcnm]

IIRC, Christopher Cross used a pair of 4425's in his studio, may still have them to this day. His first album, released in 1980, had superb sound quality. Still sounds good today IMHO

BTW- do you have a picture of your old driver phase plugs? You said they looked different. If they had 9 round holes in the phase plug instead of the annular slits, yours are probably early 4425's. I think those drivers were actually 2415H's. Diaphragm was not changed- only the part number changed, a la 2446,2447,2450,2451,etc.

Have you compared the crossover network components in your cabinets against the JBL Service exploded diagram? If yours had 2415H (round hole phase plug passages) The HF EQ filter section may be different in your 4425's than what was provided in the later models with 2416H drivers.

Rudy,
I did go back to some of your old discussion of the two HF drivers in the 4425s. I do appear to have early versions of the speakers. They have the five way binding posts. Diaphragms must have been replaced as the date on them was 1988. Need to find if the crossover was modified for the newer 2416 drivers.

Regards,

John