The shocking, sustained, mechanical roar of rocket engines. The sound of Simi Valley during the cold war. If you grew up in Simi Valley during the 60's, 70's and 80's you remember this sound. Each firing produced enormous acoustic energy — sound levels above 150 decibels at the test stands, enough to register for miles. By the time those waves reached the neighborhoods below, the sound had become a deep, steady vibration: low-frequency pressure that made windows rattle, and the ground rumble. Re