I was wondering what the most non-sound-conductive materials are, especially where those materials are abutting materials that are sound conductive. For example, imagine a long bar or block, and sound is being conducted through one half, but the sound needs to be killed so that it doesn't flow through the other half. What materials would be best for the latter?
the least sound-conductive materials are dense (so most of the incoming sound wave reflects off without being transmitted) and have lots of internal friction (to dissipate the transmitted wave). a good compromise for engineering purposes is a product called quiet steel, which is two thin sheets of steel with a layer of rubbery material laminated in the middle.