The whole kit and kaboodle for sound dampening...

speedfreak28

to put it in simple terms, dynamats and butyl based deadeners are essentially mass loading to stop resonance and vibration, a good second defense is the use of a foam deadening pad to abosrb sound waves. people who use multiple layers of dynamta re wasting money, really if applied properly you dont even need to cover entire areas, jsut areas prone to resonance and vibration.