From what I think I know... it is bricks, air gap, bricks, air gap and then bricks... with no insulation. I'd assume it would be quite sound proof. I've no idea why they built like this or how the floor joists are tied into the structure. The ground floor joists may actually be tied into the foundation somehow. From a very quick inspection, it would appear that the walls are almost 12" thick in total... the foundation is massive.
cheers and thanks,
cheers and thanks,