DALI PHANTOM K-60 LP in-ceiling speaker, 36.5 mm mounting depth and a 6-inch aluminium woofer. Sold individually.

The K-60 LP needs 36.5 mm behind the ceiling, against roughly ten centimetres for a conventional ceiling speaker. It therefore fits under a concrete slab, in a shallow false ceiling or between low joists. This is the case where available space decides before sound quality does.
The anodised aluminium cone stays rigid despite the short travel the flat format imposes. The speaker reaches down to 52 Hz at plus or minus 3 dB and up to 26 kHz, with a low 2400 Hz crossover that hands the treble early to the 25 mm dome. Its 84 dB sensitivity asks for an amplifier with something in reserve.
The grille lifts off by hand, with no visible screw. Design and classic versions come in white and black, so several rooms with different ceilings can be matched. The frame takes paint when the speaker has to be forgotten.
Connection is a single-cable terminal, which limits the wiring pulled through an already crowded ceiling. The dog-leg clamps tighten from the front, so installation finishes without access from above. On a multizone system the 8 ohm impedance makes parallel wiring simpler.
Data sheet
Specific References