Upgrading from 2421B to 2425J

[martin2395]

I'm thinking about replacing the 2421B's (JBL Al diaphragm's with diamond surrounds) in my 4343 to the newer 2425J driver, is it a drop in replacement or does it require modifying the crossover?

Also, what is the difference between 2425J and 2426J?

[Robh3606]

Why?? No crossover mod required. The 2425 has a solid throat while the 2426 has a screw on adaptor that when removed allows you to use threaded horns like a 2342. For your application you could use either one. Just make sure the 2426's have the adaptors. Rob:)

[martin2395]

Thank you for your reply Rob!

I thought the 2425/2426 would be an improvement over the old 2421? ;)

[grumpy]

You might want to hang on to the 2421's, in case (after a good long listening span)
you decide that the Titanium is not actually an improvement in sound -quality-.

[Mr. Widget]

I thought the 2425/2426 would be an improvement over the old 2421? ;)Ti diaphragms have more objectionable distortion characteristics than the aluminum diaphragms. They are an improvement in durability and that is why JBL moved towards Ti, especially in pro applications.

These comments are assuming both drivers/diaphragms are operating within specs.


Widget

[martin2395]

That's true, my concern is that titanium diaphragms may sound too harsh...

BTW, the 4344 and 4345 also came out with 2425J installed - did they have Ti diaphragms or still aluminium ones equipped?
Actually that was my first idea - to buy a pair of broken 2425J's and put my aluminium diaphragms in.

How can I spot the difference between alu and Ti dia's since they both seem to have a smooth surface and diamond-style suspension?

[ivica]

That's true, my concern is that titanium diaphragms may sound too harsh...

BTW, the 4344 and 4345 also came out with 2425J installed - did they have Ti diaphragms or still aluminium ones equipped?
Actually that was my first idea - to buy a pair of broken 2425J's and put my aluminium diaphragms in.

How can I spot the difference between alu and Ti dia's since they both seem to have a smooth surface and diamond-style suspension?

Hi,

I am not sure, but aluminum diaphragm (that is acceptable durability) D16R2420 that has 'tangential aluminum suspension'

(looking like; http://reconingspeakers.com/product/jbl-2420-d16r2421-diaphragm/ )

while D16R2425 is titanium 'diamond shape suspension'

(looking like: http://reconingspeakers.com/product/jbl-2425j-d16r2425-diaphragm/ )

Not to mention that the color of aluminum is "less dark" then titanium.

Concerning the price may be "Radian 1225" aluminum diaphragm with 'Mylar' (looking like polyester) suspension be acceptable solution.
(looking like: http://www.parts-express.com/pe/showdetl.cfm?partnumber=294-720 )

Regards
Ivica

[martin2395]

Afaik, the D16R2421 was also available with diamond surrounds like these:
http://www.audioheritage.org/vbulletin/attachment.php?attachmentid=17004&stc=1&d=1153844854

The diaphragms have now:
Front - http://tinypic.com/r/2vjx8d4/5
Back - http://tinypic.com/r/2mrzeki/5

[4313B]

The LE85/2420/2421 with aluminum diaphragm is a very desirable compression driver.

And plenty of people have put the D8R2421 or D16R2421 aluminum diaphragm into a ferrite 2425/2426 core.

Conversely, plenty of people have put the D8R2425 or D16R2425 titanium diaphragm into the LE85/2420/2421 alnico core.

What these cores really need though is an Mg or Be diaphragm. It's 2013 and it's well past time.


We will have to see what JBL does with the smaller diameter D2-type compression drivers. They could potentially marginalize everything else on the market providing they are priced right.

[martin2395]

I guess there always will be two camps - Alnico vs ferrite :D

My 2421B's look mint but I was thinking about 'upgrading' to 2425/2426 core because of stronger magnets.

p.s
Are mine diaphragms actually genuine D16R2421's?

[4343]

I guess there always will be two camps - Alnico vs ferrite :D

My 2421B's look mint but I was thinking about 'upgrading' to 2425/2426 core because of stronger magnets.

p.s
Are mine diaphragms actually genuine D16R2421's?

They look like it to me. Can't see the red or green mark on the positive wire, but the diamond surround is properly coated with damping goo.

[martin2395]

They are marked but the connectors are covered with goo from detoriating foam damping.

Can I buy the new damping pads somewhere?

[ivica]

They are marked but the connectors are covered with goo from detoriating foam damping.

Can I buy the new damping pads somewhere?

Interesting, but no JBL numbers at the bottom side, as I would expect....http://reconingspeakers.com/product/jbl-2425j-d16r2425-diaphragm/


Regards
Ivica

[martin2395]

The one from reconingspeakers look strange, they seem to have a copper inlay on the inside?
Mine have some text wrtten by hand on the inside of the voice coil, it's written with a pencil or a grey marker (?)

[grumpy]

The surface texture appears to be aluminum (vs Ti) at least.
They look pretty convincing for older 2421 type JBL dias.

[jbl]

[QUOTE=4313B;352925]The LE85/2420/2421 with aluminum diaphragm is a very desirable compression driver.

And plenty of people have put the D8R2421 or D16R2421 aluminum diaphragm into a ferrite 2425/2426 core.

Conversely, plenty of people have put the D8R2425 or D16R2425 titanium diaphragm into the LE85/2420/2421 alnico core.


Grass is always greener.:D

[martin2395]

Does the 2421B 'suffer' from JBL's inverted polarity madness? :)
I tested a 2121 midbass yesterday and it turned out to have the positive signal on the black terminal....

[Mostlydiy]

I believe they do, page 2, specs 2/3 down

http://www.jblpro.com/pub/obsolete/2421ab.pdf

/Mostly

[more10]

If you want to upgrade you will have to look for even more modern JBL drivers which are unobtainable, or look for other brands. TAD 2001 or 2002 (http://tad-labs.com/en/professional/unitspeaker/unit2.html) are better but also much more expensive.

[martin2395]

I believe they do, page 2, specs 2/3 down

http://www.jblpro.com/pub/obsolete/2421ab.pdf

/Mostly

I tested the 2421 yesterday with a 1.5V battery and noticed that the diaphragm actually moves upwards with positive voltage applied on the red terminal so it looks like it has de "modern standard" connection. Or should it move to the other side? :dont-know:

So far the conclusion is: 2121, 2235H, 2405H = Black(+) at least in the 4343. Now i rewired them so that i can normally connect the 4343 to the amp with the red terminal being the (+).

[Mostlydiy]

If it moves "upward" with positive to red then It moves towards the phaseplug when positive is to black, so its reversed as the pdf says. If I caught your meening with upward that is.

/Mostly

[martin2395]

If it moves "upward" with positive to red then It moves towards the phaseplug when positive is to black, so its reversed as the pdf says. If I caught your meening with upward that is.

/Mostly

It's exactly as you say - positive signal to the red terminal makes the diaphragm move upwards = towards the back of the driver.

That would mean that the 4343 is fully negative, all units having the positive signal on black connectors.

[JMD]

Hello, help me please.
I need to replace diaphragms D16R2421 in the speakers JBL2421B in my loudspeakers systems 4345 from JBL.



I found an expensive genuine parts D16R2421 with an aluminum diaphragm from JBL. I also found a newer and cheaper titanium diaphragm D16R2425 genuine from JBL. These titanium diaphragms are also available in unbranded version and are very cheap.


When I see the images the new titanium diaphragms well, so there missing thin spacers / metal strips under the three mounting screws. These spacers shall ensure an air gap, and thus the air permeability between front and rear wall diaphragm. Air permeability in original parts is very small but it is there. I do not know why it matters. IMHO I think that this permeability is undesirable. Please, whitch replace diaphragms should I chose?

Thanks very much

Bohdan

[1audiohack]

Rudy Kleimann and I have tested more than a few inexpensive aftermarket diaphragms on a proper plane wave tube and have yet to find any that are even close to the JBL's. At the very least buy the genuine JBL Ti's if not the Al's.

My two bits.

Barry.

[badman]

Rudy Kleimann and I have tested more than a few inexpensive aftermarket diaphragms on a proper plane wave tube and have yet to find any that are even close to the JBL's. At the very least buy the genuine JBL Ti's if not the Al's.

My two bits.

Barry.

Did you test the Radian Al phragms? I keep thinking they might work nicely for me.

[more10]

Did you test the Radian Al phragms?

I have those in 2420 and they sound good. I have not measured them.

[JMD]

I did measure JBL2421B. The result was very good. The curve at the end of the spectrum is smooth. I assume, that titanium dome will not be as smooth. Break up can cause hard sound.

Bohdan

[1audiohack]

We did measure a couple of Radians in the small format drivers and they were decent. Without pulling up the data and going by memory they (more than one/all that we measured ) had a dip in the frequency response with a corresponding wrinkle in the phase response around 7kHz. Not major but non of the JBL's exhibit this. I attributed this (correctly?) to a surround resonance.

I do not really lump the Radian's in with the cheap replacements as they are better and significantly more expensive than the crap that simply makes noise and looks the part. I have no long term listening experience with them. Right or wrong I still bleed orange.

Barry.

[more10]

The Radians are ok replacement diaphragms, but not an upgrade to a JBL aluminum diaphragm. If you want to upgrade get an Altec driver. JBL did not do anything with the one inch phase plugs for 50 years or so. Altec have worked with the phase plugs a lot.

[kawasakitech]

I have Altec-Lansing 808-8As with 811B horns and Radian diaphragms.
They sound great but need to be crossed over at 1.2k.
I use a bi amp system with a DBX crossover.
They have also proven to be very durable with a 3B Bryston driving them sometimes to clipping they haven't failed in over 20 years:cool::cool:

[badman]

The Radians are ok replacement diaphragms, but not an upgrade to a JBL aluminum diaphragm. If you want to upgrade get an Altec driver. JBL did not do anything with the one inch phase plugs for 50 years or so. Altec have worked with the phase plugs a lot.

They would be used as an upgrade to the JBL Ti phragms in 2426h.

[frank23]

I would consider changing from 2421+alu to 2425+titanium a downgrade. I have had a number of horns, drivers and diaphragms over the years and always returned to the 2420+alu combination for home sound quality.

I just read a great research paper on beryllium diaphragms as compared to aluminium and titanium and it clearly shows that aluminium has about the same waterfall as beryllium whereas titanium has a worse waterfall. Alas the researchers do not mention the exact brands / types they have tested.

Another aspect that is tested is surround fatigue. The titanium diaphragms tested show great fatigue after an endurance test of 100hours at 25W pink noise from 500-5000Hz. I must admit that this seems quite a severe test to me to say the least, at least when considered from a home audio perspective. The beryllium diaphragms do not show fatigue. But the difference has nothing to do with diaphragm material. The difference is because the titanium diaphragm surround is titanium whereas the beryllium diaphragm surround is a polymer of some sort. And as you might know aluminium shows far greater fatigue problems than titanium, that is why JBL changed from aluminium to titanium. So I expect my old aluminium diaphragms to by now also show fatigue problems in the surround. The fatigue caused a 5% distortion figure after the endurance test wheras before it was about 0.1%, same as the berylllium ones with the polymer surround. But the polymer surround stayed at 0.1% and did not get worse.

The fatigue test was only published on the titanium and beryllium diaphragms. I suspect they did not publish those figures for the aluminium diaphragms, because they may have used Radian aluminium diaphragms that use a mylar surround and the fatigue tests might just have turned out just as well as those of the beryllium diaphragms with their polymer surround, which is not good for the beryllium manufacturer as he wants to state beryllium is best… :-)

So I have just ordered a pair of Radian alu+mylar diaphragms, for an optimal combination of "alu waterfall" and "mylar fatigue free" just to see how they sound being fresh and hopefully stay fatigue free with use. The only problems I can think of with these Radians is that the surrounds are not the optimal termination for the aluminium. But JBL also uses polymer surrounds with their own beryllium diaphragms, so there must be something ok with them...

[martin2395]

Hi Frank,
I was only considering replacing the motors but kepping my D16R2421's as I'm not a fan of titanium dia's. Replacing the alu 2421B to ti 2425j's would be indeed a side/downgrade.

[ivica]

....... But JBL also uses polymer surrounds with their own beryllium diaphragms, so there must be something ok with them...

IS IT ????
As I have remembered, JBL 4"-Be has Be surrounds

Ivica

[martin2395]

Found this pic:
http://www.audioheritage.org/vbulletin/attachment.php?attachmentid=28170&stc=1&d=1189868511

Well, it could be mylar.

[frank23]

IS IT ????
As I have remembered, JBL 4"-Be has Be surrounds

Ivica

No, it has a kapton surround, here I found it:
http://www.audioheritage.org/html/projectmay/technology/435be.htm


While the switch to beryllium addressed distortion and extension issues, it would not address the requirement for high output since a surround formed out of this same material has much less fatigue resistance than the titanium it replaced. Doug addressed this in a very innovative way, with a unique composite design. He specified a kapton surround that would be immune to fatigue failure. However, previous composite designs always proved problematic due to the need to have the diaphragm, voice coil former and surround all attach at the same point. Doug solved this issue by having the kapton surround formed into a deep well just before the point where it attaches to the diaphragm. The voice coil was dropped into this well, which eliminated the need for a former, and thus, only the surround had to be fastened to the diaphragm. This resulted in a very robust design with reduced moving mass.

[ivica]

No, it has a kapton surround, here I found it:
http://www.audioheritage.org/html/projectmay/technology/435be.htm


Hi,

for 3"-inch diaphragm You are right, but here I have mentioned ONLY 4"-inch JBL diaphragm suspension

example JBL 476Be driver.



Regards

Ivica

[JMD]

Hello,
I bought an aftermarket diaphragm for JBL2425/2426 16ohm to driver JBL2421 of JBL4345 loudspeakers. I am disappointed, because a measurements THD are very bad compared to the original membranes. THD 2nd and 3rd are about 20dB to 30dB worse than the original driver. Another problem is the decreasing sensitivity towards the lower frequency of about 15 db at 1kHz. It looks like as though the coil does not have correct dimension. Although the view of the membrane seem to be the same. I will try to check and possibly correct the membrane.

Best Regards

Bohdan

[martin2395]

Why bother with aftermarkets, they are rubbish.

The only good and worthwile replacement dia's are Radian - model 1225-16 (for 16 Ohm drivers)

[JMD]

Thank you very much, I did not know this product. Do you have any measurements?

Thanks

Bohdan

[JMD]

My measurements aftermarkets are similar to those...
http://www.audioheritage.org/vbulletin/showthread.php?31988-JBL-4425-Questions-JBL-2416H-vs-RAdian-1225-8&p=325397&viewfull=1#post325397 (http://www.audioheritage.org/vbulletin/showthread.php?31988-JBL-4425-Questions-JBL-2416H-vs-RAdian-1225-8&p=325397&viewfull=1#post325397)