http://www.mini-iac.com/pages/SoundT...gSchematic.pdf

Here's a link showing you how it's done at the contests using a digital sound meter which is purchased through radio shack. (about $60)

Yes all contestants planes are required to go through the process. Like Diablo said above, overall it doesn't have a whole lot of meaning. Meters aren't really that accurate, same setup can read different from day to day depending on temp, wind, humidity, etc, etc. This was implemented because the ama required a solid number.

What you really need to do is aquire a setup that will be quiet in the air. IE, no ripping props, a quiet muffler system (most are now using cans). Your smaller engines, say 100cc and under may not require any special setup at all. You can also control it with your left hand, get out of the throttle when you don't need it. Your in flight air score will be your biggest factor.