quick follow up on my previous post regarding CS 3.5 midrange replacement drivers. Perusing the Madisound website, they have this
https://www.madisoundspeakerstore.com/approx-5-midrange/scan-speak-13m-midrange-replacement-speaker/ which is probably closer to the original Scanspeak midrange found on the 3.5s, and it has the custom mounting plate. The 12W/8524G speaker that I have in my 3.5s will fit, but its a 4 screw mount, as opposed to the 3 screw mount with the flange. From Madisound website regarding the 10F/8424G replacement...."
The specifications and response curve of the 10F/8424G is very close to the original and long discontinued Scan-Speak midranges. PBN Audio uses these as replacements for the 13M/8636 in their legacy speakers and speak glowingly of the results."
There seems to be a significant difference in the curves for these speakers. I guess the thing that makes the 12W/8524G speaker attractive is a price of @$60 vs $220 for the 10F/8424G. Unfortunately what I don't have is the curve for the original midrange Scanspeak driver.