I was at Shure's webpage reading up on some stuff. ( http://www.shure.com/app-impedance.html ). I always thought that impedance matching was important. But they say here that the load should have a greater impedance than the source. These are the guys at Shure so I am not gonna argue. But that brings up some important questions. What is the input impedance on a guitar amp? What is the output impedance of a guitar? In addition to that... If an amp head has a 4ohm Output impedance does that mean that the cab should be greater? I was told that is was important to match so the head can transfer all its power to the speaker. For the love of god can someone clear all this up? Thanks and praise in advance!!!