Every material our there has pores in it, and thus contains air. With some materials out there, like lead, these pores are so incredibly small, they are hardly noticeable under a microscope. But they are there.
Right, I hate the way that metal things aren't airtight. Oh wait... they are.
noise is able to travel through the material much like the way electricity travels through copper wire
Ah, that's a bit more like it. Different materials have different conductivity for sound, for vibration. Masonry, including concrete, stone, and brick, conducts sound very poorly. Metal, including rebar, is "sonorous", which is to say that it conducts sound very well, despite being denser than masonry. (Church bells are made of metal, not concrete. They aren't made of lead, because lead's too soft, but if they were made of iridium or osmium, the densest metals, they'd work fine. Until they were nicked by metal thieves, of course.)
It'll be all the steelwork, not the concrete, that's conducting all the sound-waves through Doug's apartment block.
Peter
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