Well, fellas... don't know what to say
I guess I'll be pullin' diaphragms in my cabs to see what I've REALLY got. Happy to report, I've only replaced diaphragms in JBL compression drivers that were abused by others.
Robh, you are certain? Notice however, the drivers in both cases were advertised as "2416H". Note also the "-1" written on the magnet plate with a sharpie. Maybe 2416H-1? I have seen similar markings on 4" compression drivers too, with "-3", "-1", etc. I recently read somewhere (I think there was a posting on this forum) that these markings, as well as similar markings on the inside of the voice coil formers on diaphragms, were markings for production variations to optimally match drivers and diaphragms. I don't know; I've apparently been wrong once today already.
After all the drivers I've seen apart, JBL or others, I've only round holes once before, on a cheap no-name speaker with a 1" diaphragm where the sound wave did not pass through the magnet. ALL the JBL drivers I've had the diaphragm off of used the annular slits.
After finding this site several years ago, and learning of Jim Lansings' fight with Western Electric over rights to the annular slit phase plug design, and Altec going with thr radial slits, I never thought I'd see the day...
As for sympathy towards the JBL Tech support guy over his ignorance and the misinformation provided, should he suffer for his ignorance? :dont-know