Sound in a concrete basement

[sjbluray]

I was sitting here and started to wonder about sound and how it bounces of materials. One thing I wondered was how a (finished) concrete basement would effect the sound in my feeble home theater. My house was built a bit strange, its made from formed concrete, top and basement. The basement is underground and between the two floors we found a steel plate and I assume the reason for the steel plate is because there is a layer of concrete between the two. Now, I am just talking about the outer walls, the inside walls are basic sheet rock.

So, what kind of stuff will the concrete do to sound?