Hello forum,

I am "restoring" a pair of 4333A I've had for quite a few years now. They have always been sounding great ever since I got them, but during some free time I finally pulled myself together to take the basses, drivers and tweeters out for further investegation. I started measuring the DC resistance on all the units. Here are the results:

2231A: one measuring 6,0 / 6,1. The other 6,3 / 6,4
2420: one measuring 7,2 / 7,3. The other 5,7 / 5,8
2405: one measuring 6,2 / 6,3. The other 6,4 / 6,5

The 2231A are 100% original. On both the cones it writes "2231" on the underside. They were refoamed at a qualified JBL shop about 1½ years ago and they both sound great.

The 2405 are also with the original blue diaphragms and both sound great. Though, I noticed when I had them apart that on one of the diaphragms there were 2 tiny tiny "lowerings/holes", like if you had touched the diaphragm with a small needle or something like that. It's not holes all the way through the diaphragm at all, just 2 tiny lowerings. Perhaps 0,02 mm lowerings or something like that. But as I mentioned, they both sound great. It shouldn't be a problem I take it?

Well, so far so good for the 2231A and 2405. My real concern here are the 2420. First of all they measure very differently. The 7,3 vs. the 5,8 I think is too big a difference. One of the 2420. The one measuring 5,8 has that red paint on the screws on the backpanel. I can see the previous owner has tried to unscrew the back panel, but with no luck. All 4 screws are totally ruined on the top, so it is impossible to just loosen one of the screws just 1 mm. Therefore I take it that this driver has never been taken apart and has the original alu D16R2420 diaphragm. Apart from that it sounds fine, and has always sounded fine to my ears. I have never noticed any kind of distortion etc. not even at high levels. But my concern here is that I read somewhere on this forum that a healthy D16R2420 diaphragm should measure betweem 5.9 and 7.0. Could this be a problem with a DCR of 5,8 on this driver?

The other 2420 driver measures 7,3, which is more than the 7,0 a healthy 2420 should max. measure. I took the driver apart and saw that the diaphragm does not look like an original D16R2420 diaphragm. As far as I am concerned the original D16R2420 alu diaphragm have a "silver" or "shiny metal"-like look. Am I right here? The diaphragm has the excatly same shape as the D16R2420, but it is grey, infact what I would call dark grey. There was no text on the diaphragm. At least that I could see. Hmm, this diaphragm have the same shape, but not the same looks as I know an orignal D16R2420 should look like. Apart from that it measures 7,3 DCR. Could this be some kind af cheap/bad aftermarket diaphragm? Or which diaphragm could it be, with the same shape of the D16R2420, but with that dark grey color?

I know that the sound of the drivers naturally is the most important thing. I must admit that I have not ever noticed any great difference on the sound of the speakers. This really puzzles me. How can a pair of 2420 that measure that differently, and most likely have different diaphragms sound so relatively much alike? Or at least what I can hear. With these dfferences I would expect them to sound much more different. The only real difference I can hear is that the driver measuring 7,3 plays slightly lower than the one measuring 5,8 at the same volume. The difference is hearable if you practically put your ears directly into the horn. I have just turned the L-pad about a mm up to compensate for the lower volume.

What are your thoughts regarding the 2420 situation? Is it me having very bad ears, as I am not able to hear a radical difference? Also, what do you think about the DCR on my 2231A and 2405. Should they be OK? As I mentioned i have never had any problems with them.

Just before posting this, I have another question regarding DCR. I also own 3 2441's where I will be using 2 of them for a future speaker project. The DCR situation with these are even more strange. They all have the original 2441 diaphragms. One measure: 7,6/7,7. Another measure: 6,1/6,2, and the last measure 8,0/8,1. I have tested them all and to me they all sound fine on a 2350 horn. But 3 so different measures should result in, at least noticeable, different sound, should it not?

Finally I can tell I have been searching this forum over and over again for threads regarding DCR, replacement diaphragms etc., but I feel i must fully describe my situation in order to get some inputs, and hopefully some answers regarding my situation.