Uplift the existing floorboard / chipboard floor to expose the joists and cavity. Clear the cavity and install 100mm RWA45 Rockwool into the cavity at the bottom leaving an airgap at the top of the cavity. Friction fit the insulation tight within the cavity and infill any small gaps with insulation. Replace the floorboards or install a new timber, chipboard or ply subfloor. Mechanically fix with screws into the existing joists to create a sound level subfloor.
Around the perimeter of the room install the Acoustilay perimeter strips. Push the expanding foam side of the strip tight to wall so it compresses. Screw the strip in place into the subfloor. Do this around the entire perimeter of the room. This strip will then receive your gripper rod, the height of the gripper rod will match perfectly with the heigh of the Acoustilay underlay once installed.
Install you Acoustliay 15 tightly up to the perimeter strips. Install in a brick bond pattern. Cut the matting using a straight edge and a stanley knife, scoring the matting repeatedly to get a clean cut. Bond down the matting using Acoustilay adhesvie. Use a 3mm notched trowel to apply the adhesive. Your carpet can now be installed over the matting onto the flush gripper rods.