But if the proposition is that different screw materials, in being
softer or harder, can affix speaker materials more or less loosely than
others, and that it is the changes in vibration to THOSE materials as a
result that people can hear (e.g. vibrating speaker cabinet parts or
whatever), then that would be measurable.
I was taught that the copper screws were used as little tuned shock absorbers for the speaker baskets. And they were to be loctited at the specific tension. The driver was simply going to click and you go in a star pattern until all were done up and checked with a second pass.
Mike never told me that the screws made a specific sound. Some people may have heard the improvement without understanding why - even so, the improvement exists despite not understanding how it works.
Kind of like gravity, it works even if you are totally ignorant of it.
Also I believe ( I was not told this by my employer) that the rate at which kenetic energy can be transferred into heat, will affect the shock absorber properties in this particular device. Softness is not the only consideration in the dynamic properties used in this particular application.
I cannot confirm whether or not Mike used Clio measurements or simply tuned by ear, or got the calculations form an engineer - I simply don't know.