1.1 General This part of ISO 15186 specifies a sound intensity method to determine the in-situ sound insulation of walls, floors, doors, windows and small building elements. It is intended for measurements that have to be made in the presence of flanking transmission. It can be used to provide sound power data for diagnostic analysis of flanking transmission or to measure flanking sound insulation parameters. This part of ISO 15186 can be used by laboratories that could not satisfy the requirements of ISO 15186-1, which deals with laboratory measurements with no or little flanking transmission. ISO 15186-3 deals with measurements under laboratory conditions, at low frequencies. This part of ISO 15186 also describes the effect of flanking transmission on measurements made using the specified method, and how intensity measurements can be used — to compare the in-situ sound insulation of a building element with laboratory measurements where flanking has been suppressed (i.e. ISO 140-3), — to rank the partial contributions for building elements, and — to measure the flanking sound reduction index for one or more transmission paths (for validation of prediction models such as those given in EN 12354-1). This method gives values for airborne sound insulation, which are frequency dependent. They can be converted into a single number, characterizing the acoustic performance, by application of ISO 717-1. 1.2 Precision The reproducibility of this intensity method is estimated to be equal to or better than that of the methods of ISO 140-10 and ISO 140-4, when measuring a single small and large building element, respectively. NOTE 1 If sound reduction measures made using this method are to be compared with those made using the conventional reverberation room method in various parts of ISO 140, then it will be necessary to introduce an adaptation term that reflects the bias between the test methods. This term is given in Annex A. NOTE 2 Some information about the accuracy for this part of ISO 15186 and its relationship to the sound reduction index measured according to ISO 140-3 and ISO 140-4 is given in Annex B. NOTE 3 Flanking transmission is discussed in Annex C.