Just want to add that this is one of my biggest gripes with the iPad. I have to position things behind my iPad to hear things sometimes. It's by far the worst part of the iPad.
I think it should have one speaker at each of 3 corners at least.
Also it would be nice if they invented some cleaver way of directing sound towards the user because now when I use iPad I have to user my hand as a makeshift reflector to hear anything.