In a recent application, DEICON was asked to further improve the structure-borne noise reduction of two large transformers (9000 pounds, each) installed in a multi-story residential building. The transformers were housed in sound proofed rooms and isolated from the floor via mounts (compressed fiberglass mounts for one transformer and cork/neoprene mats for the other). In a preliminary study including some laboratory tests it was concluded that the compressed fiberglass mounts had too much damping deteriorating their high frequency vibration isolation and the cork/neoprene mounts were too stiff to effectively isolate the transformer. It was decided to change the isolation schemes from compressed fiberglass and cork/neoprene to air. More