6dB is half of the sound pressure. You don't need to explain logs to me. Commercial firearm suppressors typically have reductions of 30 to 40 decibels. Spring air guns generate a lot of sound from the vibration of the rifle. You can't use a suppressor for that. The air gun silencers are pretty ineffective because there isn't a lot of super sonic gas to slow down. If the pellets are super sonic, that's what you're going to hear anyway and a suppressor can't do anything about the super sonic crack.