Speaking of 12 string players, I have a chance to go see Roger (Jim) McGuinn next week at a very small, local rec center. Only $35 bucks! I've got his 12 string video so it'll be fun to see him play live. Not sure if this is an all-acoustic gig or if he will break out his Rickenbacker 370/12. Do you guys realize he's pushing 70 pretty hard? How time flies!
A sound hole cover is designed to be used on an acoustic/electric guitar. One with an on-board peizo pickup, internal mic, pre-amp, etc. The sound hole cover is used to reduce or eliminate feedback. The downside is your guitar won't sound as good acoustically anymore unless you remove it. They are usually made of rubber and are a friction fit so they can be installed and removed easily.