I see where the ZYX Web site cites both silver and copper with the same coil wire diameter (.035mm) and same weight (5.0gm)You're reading too much into that 5.0g weight specification.
If both cartridges weigh the same and have the same wire diameter, maybe its not extra mass on the silver's cantilever that accounts for the sonic differences.
First, it's only nominal. I've weighed six ZYX's to the closest 0.01g and they were all different. The variations were larger than could be accounted for by any differences between the coils.
Second, a specification to the nearest .1g is too imprecise to capture any coil variations. You'd have to go out several more decimal places to measure that.
Third, even if you did that, variations in other components would swamp coil variations.
The coils are so tiny compared to the rest of the cartridge that the only way to know anything useful about their mass/weight would be to measure or calculate it directly. Coil weight cannot be deduced from overall cartridge weight, no matter how accurately that is measured.
Maybe its fewer windings of the heavier metal. (??) ).Given identical magnets, more windings = higher output. Since the output of each cartridge is the same, the number of windings should be the same.
Could a different number of windings between silver and copper yield different signals?
Good questions, but I think my hypothesis is still valid.