Could any body tell me why the number of holes on a silencer should be at least 30% of the surface area
and the diameter of holes 4-6 mm,is there any formula in this case,I know these are Helmholz resonators
but I have not come across any particular formula which gives delta=function (d,n),delta being the
noise reduction and d the diameter of holes and n number of holes per unit area of the silencer?
I did not find the right solution from the internet.