I like the idea, but too bad the chart doesn't include Borla and Magnaflow.
You can pick up a digital SPL meter from Radio Shack for $70.
If you're lucky, you can get the old (back stock) analog meter for $14 - Radio Shack put them on clearance a few months ago.
Most of us turbo guys won't run anything under 3", so we need a whole new chart for 3" mufflers?
-Ted