Ok, I see. As you say, it's already there so... Guess I'll ignore it for now and proceed. I should be able to generate a sweep test, hopefully that will tell me something. It's a backup, but I still hope it's working ok. I've found that vintage gear often needs some investment in time or parts, or both. And some self education, so thanks for your guidance and input :).
This guy is fixing a 2412h driver,
https://youtu.be/YNaTzoI-i7M
The 2412h uses a foam plug see 2:42-3:12. I wonder what they do to replace them? 2412h seems like a more current product?
And, they have "direct copy of 035Tia" which has "Foam plug behind dome to reduce unwanted ringing and resonance"
https://www.simplyspeakers.com/repla...-t-035tia.html
I sent them a request, maybe it could be possible to get plugs from them...