Hi all, Normally the floors between condos are made out of concrete right? If the units are separated by a layer of concrete, how can you still hear people walking around?

Not sure if some condos have other materials instead of concrete between floors. Have a friend staying in a condo, he owns a subwoofer, and when he plays music or movies, he don't seem to get any complaints from neighbors. I would imagine a subwoofer to produce more vibrations and sound compared to footsteps right.