I've known them as duplexes all my life and more recently as semi-detached; my neice in Toronto now owns one.

Phillipe, the low bass the EP350 plays, as Alan recently pointed out, travels horizontally more so than vertically, this would be why it doesn't sound as loud upstairs.

Jason
M80 v2
VP160 v3
QS8 v2
PB13 Ultra
Denon 3808
Samsung 85" Q70