[quote=Jimbo;200330]My father-in law's 075 tweeters need the diaphragms replaced. I contacted JBL and was told that he could use the 2405 diaphragm if the phase plug was milled down to create the proper air gap.
I am having the same issues and I believe the thread is wrong about the 075/2402 and 2404/2405 diaphragms being interchangeable. I am building some floor monitor speakers modeled after the Cabaret 4602A but in a smaller cabinet. I have a bunch of 2402's that need new diaphragms and am looking into aftermarket diaphragms They are 1/4 the price and I need 6, besides these are floor monitors and it is rock'n'roll. I exchanged email with Eric Sunda at Orange County Speaker about their aftermarket diaphragms and was told they were not interchangeable because of some dimension mis-matches. Being brave and having experience as a machinist, I went ahead and ordered one to check it out. And you know what, Eric was right. The problem is with the back profile of the bullet itself. It has a slight angle to match the profile of the diaphragm and the lip of that angle touches the diaphragm.
The first two photos are the back profile of the bullet.
The second two photos are a real 2402 diaphragm. I believe it is out of a 2402, not a 2402H. Note how there are 3 rings in the diaphragm profile.
The last photo is the after-market 2405 diaphragm. Note how it does not have the inner ring in the diaphragm profile. If you look closely you will see a whitish ring just inside the bottom of the profile where the voice coil attaches. This is where the edge of the bullet rubbed against the diaphragm itself.
As to whether or not this can be worked around, I am still trying. First off, milling the bullet would not make sense because you would loose the slight angle to match the profile. You could turn it on a lathe, but it would be tricky to get the same angle. What I am going to try is a shim between the front of the inner ring of the diaphragm and bullet to push it away from the diaphragm. This is the simplest solution and would not modify the driver. This would allow me to go back and use the 075 diaphragm if I want to.
Stay tuned for further results. It will be interesting testing this because the 2402 is crossed over at 3 K or so and my hearing dumps at about 12 K on a good day (:-), so I will be listening in the upper 2 - 2 1/2 octaves of my hearing.
I hope this helps
RLH