Thanks for the test. Regardless of sound meter it sounded like the Gamo was the quietest followed closely by the Stoeger then Xisico then Walther being the loudest.
Do you have a Walther LGV Competition Ultra or HW77 or 97 or HW30s or Beeman R7 or FWB300s to side by side comparison for relative loudness?
These are the quietest springers I recall shooting.
My newly acquired Canadian spec 500fps 177 Crosman F4 Nitro Piston seems pretty loud fprvots relatively low power it really surprised me.