Help Assessing JBL 2421B Diaphragms [Archive]

Jim Hodgson

11-03-2018, 06:51 PM

Ian Mackenzie

11-03-2018, 08:34 PM

I’m considering buying a pair of JBL 2421B drivers, which I’ve seen (but not heard) in person. I snapped a quick photo of one of the diaphragms, and I wonder if someone could guide me on both authenticity and condition, please?

My priorities are genuine factory aluminum diaphragms correct for 2421B. DCR readings were around 5.8 ohms—which I believe is “close enough”? How easily will those bits of urethane foam clean off the terminals and diaphragm surface?

I’d be most appreciative of any pre-purchase help. Thanks!

Here is an image l found of a 2421B interior so your image looks quite similar.

In terms of authenticity I don’t have a pair of these particular diaphragms to compare and they quite rare.

In terms of condition if they are the original they are quite old. If you search the forums there is discussion of the fatigue of the diamond surround aluminium versus titanium. It’s hard to know without using them as to the condition. Typically all diaphragms age wth use. The foam particles can be removed with gentle use of compressed air and a soft art brush. The foam will need replacing with either foam or felt.

Typically old drivers like this have a build up of dust, grit or dirt in the gap. That can have a big impact on performance so be prepared to pay someone to service them or get help from a friend who has cleaned a compression drive gaps. The diaphragm will require careful removal and then reinstalling are cleaning out the gap.

I hope this helps.