Crestron SPKA-PMK-IC6/IC8 Preconstruction Mounting Kit for In-Ceiling Speakers, 8 Pack

The preconstruction kit brackets the speaker position to the structure before the ceiling exists, which is the only way to get an even grid across a large open plan. Eight come to a box, matched to a floor's worth of positions rather than to a single room.

It fits the Reference and Ultimate in-ceiling speakers. The speakers themselves go in after the ceiling is finished.