The sub isnt good on the floor if you have carpeting underneath. The carpet absorbs the sound. If you have it sitting on hardwood or linoleum, then you will get a fuller deeper sound.
If you have it on carpet, and want more, you can get a piece of plywood to sit it on.
Edit: Also, I would hope that Logitech would NOT make computer speakers that arent magnetically shielded. Not only for the parts in your computer, but the monitor as well.