Dunno...
I live in a town with a quiet zone on the main line thru town.
For the most part the quiet zone works, you don't hear the horns as the trains approach the multiple street crossings, you do hear the speakers at the x-ings themselves when you are at the x-ings,
but...
you do hear the passing trains, when the engineer determines an extra warning is needed and especially on cold days when the air transmits the sound of the steel wheels on rail.
We also have a sub-division that isn't part of the "quiet zone". So, twice a day we have GP-15s going south/north honking horns at every x-ing. Not bad until it is a hot summer night, the windows are open, and at 3 am the local is working its way north.