While changing diaphragms at my 2426 Driver last night I realized for the first time that there are slight milling groves at the top plate exactly where the mounting ring of the diaphragm lays on the top plate!
This means that the mounting ring does NOT seal the rearchamber of the driver from the phase plug!
When I put the D16R2421 dia in I realized that these dias have thin metal plates where the mounting holes are. I suspect that these thin plates provide the same “gap” between dia and top plate in a 2420/2421 driver by “lifting it a bit” as this driver does not have the milling groves.
Mounting the D16R2421 dia in a 2426 will consequently increase the “gap” as we have then milling groves + thin metal plates.
If you look at my measurement in the “Playing with a 2426” thread this does not lead to any anomalies in impedance which make me wonder.
The 2416 for example does NOT have this “gap”
What for the heck is this JBL mystery again? I’m confused as I always thought that the rearchamber of an compression driver is airtight sealed from the phase plug section? Shouldn’t it?
Any explanations would be MUCH appreciated.