Acoustic Guitar Question (Duct Tape)?

Question

I was watching this video (http://youtube.com/watch?v=QeVhNNR37fA) and I noticed that Matt Costa has duct tape over the hole in his guitar. What does that do?

Thank You

Answer 1

To cut down the possiblity of feedback from the vocal mic is my best guess. He most likely has a piezo in the bridge which is the audio source for his guitar. In fact BB king's lucille guitar was originally es-335 where he stuffed socks into the F-holes to reduce feedback. Subsequent models of lucille now has no F-holes at all.