A: Aluminum hat channel is used for 2’ x 4’ acoustic drop in ceiling tile systems, allowing the contractor to pre-install a flange for the track and incorporate the hat channel into the ceiling grid system. The ceiling tiles actually rest on this flange.
The hat-channel can only be used with the standard "U" channel track, the hat-channel is not available for the acoustical doors.
When measuring for doors utilizing hat channel, the finished opening dimension should reflect the distance from the surface to which the hat channel attaches to the finished floor rather than from the finished surface of the acoustic ceiling.
Why the strange term? Hat channel looks like a top hat, hence the name.