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]

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

[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?

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]

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/...421-diaphragm/ )

while D16R2425 is titanium 'diamond shape suspension'

(looking like: http://reconingspeakers.com/product/...425-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/show...number=294-720 )

Regards
Ivica

[martin2395]

Afaik, the D16R2421 was also available with diamond surrounds like these:
http://www.audioheritage.org/vbullet...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.

[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.

[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.