One downside of Moscow and SPb metro that perennially bothers me is how loud it is in the trains. In Helsinki or Stockholm metro (iirc) you can easily talk to s

One downside of Moscow and SPb metro that perennially bothers me is how loud it is in the trains. In Helsinki or Stockholm metro (iirc) you can easily talk to someone at nearly normal indoor volume. Notably, the noise almost disappears if the track leaves the tunnels for open air—so I have to wonder what's special about tunnels in those foreign systems.