The construction phase can be viewed in detail in the “verbouwing” category (sorry, in Dutch only), this is the sound isolation summary:

• Elimination of transmissions through the building structure are accomplished by using floating walls and floor.
• The floating walls are made up from a framed wood construction containing 12,5 cm Rockwool insulation layer on the inside and a double layer of 12,5 mm gypsum board on the outside.
• The floor is made up from Fermacell Estrich floor elements (insulation layer + double gypsum layer) on top of a new floor construction with transmission isolation (Auralex U-Boat construction) at the underlying floor & the adjacent neighbour walls.