OK, After studying this sit-chee-ation, I don't think that would help. If you look close, the cover isn't touching the speaker. I had the backround sounds for Angry birds playing and put my ear around the phone. The sound comes from around the cover as well as from the speaker. I'm guessing it's like a folding speaker that expands, the open space between the cover and the interior acts like an amplifier of sorts.
Put your ear against as it makes sound, you'll see what I mean. Also, I didnt notice any difference in volume with the cover off.