Aluminum diaphragms

[Dwight]

I have two new aluminum diaphragms for my 375's. One has a smooth roll on the edge where it attaches to the outer ring and the other has small diamond shapes on the outside edge where it attaches to the outer ring. Are there measurable differences
between the two? Is one "correct" and the other for a different
model number driver?

[4313B]

The one with the diamond patterned surround is newer and is preferred. It was the final generation of the old aluminum diaphragms and was standard with the 376/2441. The other one was standard with the 375/2440.

[scott fitlin]

And the newer diaphragm with the diamond pattern surround definitely sound nicer! Better at its upper end response! And to my ears smoother sounding midrange!

[boputnam]

Originally posted by Giskard
The one with the diamond patterned surround is newer and is preferred.

That is exactly the version I just installed, and they are a sublime improvement.

[Mr. Widget]

Originally posted by Dwight
I have two new aluminum diaphragms for my 375's. One has a smooth roll on the edge where it attaches to the outer ring and the other has small diamond shapes on the outside edge where it attaches to the outer ring. Are there measurable differences
between the two? Is one "correct" and the other for a different
model number driver?

Yes they do have very measurable differences! The original 375 diaphragm is the 2440, you can see an idealized response on page two of this pdf.

http://www.jblpro.com/pub/obsolete/2440.pdf

The original "new" diaphragm with the diamond pattern is the 2441. They are both currently available. You can see an idealized response on page two of this pdf.

http://www.jblpro.com/pub/obsolete/2441.pdf

I looked in the Lansing Library for the technical document discussing large format drivers vs. small format as it had actual plots of both diaphragms on the same 2350 horn. Here you could really compare them. Unfortunately, I was unable to find that document. It may have gotten lost in the transfer from the posted thread it was on.

As far as correct goes, if you want the original vintage sound of the 375, use the 2440 diaphragm, if you prefer a more linear sound that is a touch more extended without a HF bump at 9KHz go with the 2441. In either case I certainly would not use one of each.

[Mr. Widget]

Bo, are you saying that you replaced a pair of smooth surrounded 2420 diaphragms with the diamond surrounded 2421 diaphragms? If so that would put the improvements in your 2421s more in the camp of technology improvement rather than metal fatigue.

While JBL has decided to continue to produce both the 2440 and 2441 diaphragms as there are those who appreciate and specify each, in the case of the 2420/LE85 they discontinued the 2420 diaphragm long ago in favor of the 2421.

[4313B]

Originally posted by Mr. Widget
I looked in the Lansing Library for the technical document discussing large format drivers vs. small format as it had actual plots of both diaphragms on the same 2350 horn. Here you could really compare them. Unfortunately, I was unable to find that document. It may have gotten lost in the transfer from the posted thread it was on.

Technical Notes Volume 1, Number 8

http://www.audioheritage.org/vbullet...=tech#post5344

I just added in the last page (6) as well to finish up the post.