To recap here, there are three primary ways you effect sound transmission, a. you reflect it, by increasing the rigidity of the surface b. you slow it down/lower its frequency by increasing the mass of the barrier, c. you absorb a portion of it, which is usually very frequency dependent, ie Fiberglas does well on higher frequencies, asphalt/lead does well on lower frequencies, with a lot of options in between, and finally d. a mixed combination of all the above as buyer chooses. There is no magic here, just some guess luckier then others.