The Danish National Wind Tunnel is at the moment being established in Denmark at DTU Risoe Campus close to Roskilde dedicated for wind energy purposes. The wind tunnel has a cross sectional area of the test section of 2 m * 3 m with a maximum flow speed of 105 m/s and a turbulence intensity of below 0.1 %. The wind tunnel is dedicated to measurements on blade sections for wind turbine blades. Customers in the tunnel will be wind turbine manufacturers, but could also be the industry that needs the support from wind engineering such as bridge cables and houses. Acoustic measurements are very important and will be a key element in the tunnel. This tender comprises the establishment of the anechoic chamber surrounding the test section. The anechoic chamber has to be designed for free field condition down to 100 Hz.