EN ISO 10848, of which this is Part 4, specifies measurement methods to be performed in a laboratory test facility in order to characterise the flanking transmission of one or several building components. The measured quantities can be used to compare different products, or to express a requirement, or as input data for prediction methods, such as EN 12354-1 and EN123542. This Part 4 is specifically referred to from Clause 4.4 of EN ISO 10848-1:200X, as being a supporting standard to the frame document. This part applies to a T or X junction when at least one of the elements that form the construction under test is not a light element. A light element is defined in Part 1. The relevant quantity to be measured is selected according to Clause 4.4 of Part 1 of the standard. The performance of the building components are expressed either as an overall quantity for the combination of elements and junction like Dn,f and/or Ln,f or as the vibration reduction index Kij of a junction. Dn,f and Ln,f depend on the actual dimensions of the elements, while Kij is in principle an invariant quantity. For general application of the test results, Dn,f and Ln,f are the relevant quantities to measure for characterizing the transmission between two light, well damped types of elements - for example timber or metal framed stud walls or wooden floors on beams. For characterizing the transmission between two heavy elements with reverberant vibration fields Kij is the relevant quantity to measure. It is not possible to give general guidelines about which quantity to select for transmission between light and heavy elements.