This part of IS0 717 a) defines single-number quantities for the impact sound insulation in buildings and of floors; b)gives rules for determining these quantities from the results of measurements carried out in onethird- octave bands in accordance with IS0 140-6 and IS0 140-7, and in octave bands in accordance with that option in IS0 140-7 for field measurements only; and c)defines single-number quantities for the impact sound reduction of floor coverings and floating floors from the results of measurements carried out in accordance with IS0 140-8. The single-number quantities in accordance with this part of IS0 717 are intended for rating the impact sound insulation and for simplifying the formulation of acoustical requirements in buidling codes. The required numerical values of the single-number quantities are specified according to varying needs. The rating of results from measurements carried out over an enlarged frequency range is dealt with in annex A. A method for obtaining single-number quantities for bare massive floors according to their performance in combination with floor coverings is described in annex B.