Hello!
with so many questions about real/fake silver coins, I suggest attaching a “ping” test sound spectrum to each coin page (not the actual spectrum photo - which would be too “heavy” for the site - rather just peak values).
For instance, the spectrum for N#8120 looks like this:
peaks at 5.6/5.8 kHz & 12.7 kHz
(Taken with “Advanced Spectrum Analyzer PRO” for Android phone)
Another coin I've tested is Austrian 10 Schilling (N#1941).
Here are the results (peak frequences) of the 4 coins tested:
5.6 kHz & 12.9 kHz
5.7 kHz & 13.2 kHz
5.9 kHz & 13.6 kHz
5.9 kHz & 13.4 kHz
Metals like Cu-Ni, steel… all have only one (or two, shadowing each other) peak frequency.
The only metal, besides silver, with pronounced double frequency is copper (higher than silver: 8 kHz & 17 kHz).