Borimer leads the way into the northern room (32d).
This room looks very familiar. It is another Crystal Focus Room. On the first floor, you saw an identical room (32a), except that the strange device was pointing up. This time, the device is pointing from east to west across the room.
The east side of the wall has carved out of it an octagonal shaped indenture, from which a mechanism sticks out (parabolic dish). The mechanism consists of a parabolic dish carved and smoothed out of the face of an octagonal block of granite, all mounted inside a framework with eight metal tracks. A large, screwlike device moves the granite block along these tracks. At the front of the tracks, eight rods hold a crystal in place in front of the granite dish. The crystal pulsates with light.
On the wall adjacent to the crystal focus device, you see another 12 digit display (transfinite repeater display).
There are exits to the north and west, as well as the one you came through to the south.
The humming sound you heard was the humming of the device. It issues a constant, low pulsing hum almost inaudible.
You don't remember hearing the low hum before, which leads you to only one conclusion: The device must have been recently used, and these reverberations are like the echows of a vibrating sword after it has struck the ground with some force.