I'm not sure about the volume, but felt strips are generally used to help muffle a bass drum head i.e. you could make and emperor sound more like a PS3 or SK2 head. What you would do is cut a strip about 2-2 1/2" wide and about an 2" longer (or more, you can always trim off the extra) than the diameter of you bass drum. Place it on the bearing edge of you bass drum and then place the head on top of it and kind of stretch the material a little so it's actually contacting the back of the head while you out the hoop on and tune it. This can be done on the batter and reso sides.
Check the vid below. At ~4 seconds, if you look at the reso head you'll see a thick white line running down the diameter and off-center of the bass drum.
http://www.youtube.com/watch?v=LMqHqADnREY