Setting the Sub level. I use the Video Essentials test dvd and the Radio Shack SPL.... I have the Radio Shack Compensation chart in front of me, but just how do you use it? I'm having trouble figuring out those Hz numbers down the left column of the chart. For example, at "20Hz add 7.5 db." How and where do you get the "20Hz?" I'm using VE so is its test sound a constant 20Hz? The SPL doesn't measure Hz does it?