Do a simple test. The tunes (ring tones) distort due to the cover vibration. To fix that, that ring tone again with the back cover off...or prress down on it.

2) For all your doubters. Play a song with your cover on sitting speaker facing up on a table or counter. Then take the cover off and play it again with the cover off, speaker facing up on a table.

3) Then come back here and say there is no diff...haha

Give it a try. You'll see. The sound is awesome for a cell phone.