On Thu, 19 Nov 2009 22:26:43 -0500, mm
wrote:

If the cinderblocks are filled with cement, that much mass
could be an effective sound barrier also.

I hadn't thought of that either, but wouldn't that slow down
construction a lot? I doubt they did that.

Perlite would be nice too, Oren, but how do I find out if it's there?

Drill a 5/8" hole in one of the cavities?