I think nearly everyone has ear plugs laying around? If not, they are nearly free...
You know the foam kind that you compress and shove into your ear?
Like this:
The sound tube isn't all that big. Just take a pair and chop one of the ear plugs off leaving some line so you can retrieve it later from the tube. Roll it in your fingers to make it skinny and stick it in the sound tube as shown:
The foam will expand filling the tube. I spent a half hour in home depot looking for a 7/8" cap. It is way easier to find ear plugs!
