The problem
The client asked for the edge to disappear on all four sides — a level deck, water flush with the stone, no visible coping. That means the entire surface volume runs over the perimeter grating into a balance tank and is pumped back. It is the right detail visually and it is unforgiving acoustically: the tank is a drum, and the house was 9 m away with bedrooms facing the pool.
Commissioning measured 43 dB(A) at the nearest bedroom window at night, from water falling 900 mm into the tank. That is quiet in a plant room and loud outside a bedroom.
What we changed
Three changes, in the order of how much they bought us. We flooded the fall: the tank inlet was extended below the working water line so the return arrives underwater rather than dropping into air — 11 dB. We lined the tank soffit with a closed-cell acoustic panel — a further 4 dB. We put a night mode on the controller that drops the perimeter flow from 8 to 5 m³/h, which is still above the threshold where the edge starts to break into scallops. The final measurement was 27 dB(A) at the window, below the site background.
A note on the cantilever
Ninety-six cubic metres is ninety-six tonnes, and it moves. The structural engineer allowed 14 mm of deflection at the free end under full load. A level deck is only level within about 3 mm before you can see it. The pool is therefore filled and levelled under load, and the stone surround was set after first fill, not before. We now write that sequence into every cantilevered pool we specify.
