[savedbygrace]

If the numbers here:

http://en.wikipedia.org/wiki/Long_range_acoustic_device

are even close to accurate, you are correct. Those plugs will attenuate by more than 30dB, bringing the sound level at 300m and probably even at 100m down to a manageable level of 60 to 80dB.

[Lonesome in Massachussets]

You could wear the head phone style of ear plugs over them, too.