I have been googling like a mad thing. apparently 40-50psi will make a honky tonk loud sound. From this you can then increase up to the loudness of a jet taking off …around 100 psi. The suggestion being move up in increments of 10 until the desired eardrum decimation has been reached, monitoring your air horn as you go. All sites do not recommend greater than that for air horns (perhaps that is because they can’t hear you or your eardrums have been punctured) Happy honking