On a completely-somewhatly related note, some boffins have made a superb low-frequency sound insulation material out of latex and buttons. It's no thicker than a ceramic tile and can nullify even bass frequencies
http://www.newscientist.com/article/mg20527485.400-latex-could-silence-noisy-neighbours.html
I have used a rubber underlay but this one was not it is just a foam underlay.