At the Norwegian Building Research Institute (NBI), sound insulation measurements have been carried out in the frequency range from 50 to 5000 Hz since 1997. A major part of our experiences are from field measurements, but for some years we have also studied floor constructions in two different experiment set up at the laboratory. Since 2002, also ordinary sound transmission laboratories have been available at NBI in Oslo. The most common mea¬sure¬ment objects at NBI are floor constructions between dwellings, especially timber floor constructions due to complain about impact sound insulation at low frequencies. Therefore, this paper present experiences with the spectrum adaptation term and extended frequency range for different types of floor constructions. Main results are also compared with Nor¬wegian requirements, sound classes from NS 8175 and recommendations from NBI. Some results are also given for impact sound insulation measurements with both the ISO Tapping machine and the Japanese rubber ball.