Please read Alexey Sklyarenko's annotations on Pale Fire, Ada and other Nabokov works here.
In his Foreword to Shade's poem Kinbote (in VN's novel Pale Fire, 1962, Shade's mad commentator who imagines that he is Charles the Beloved, the last self-exiled king of Zembla) mentions two ping-pong tables that he installed in his basement: