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84 CHAPTER 5. SOUND INSULATIONand thus :R = L p1 −L p2 +10log S A(5.3)where the sound pressure level measurements are performed in tertsoctavebands (according to the international standard ISO 140). Also thetotal absorption A of the receiving room must be measured in terts-octavebands. Above equationis onlyvalid forthelaboratorymeasurement of soundinsulation of a wall (or door, window, panel, ...), whereby no flanking transmissiontakes place. The problem of the measurement of sound insulationbetween two rooms in a construction still persist. Although in this case onehas flanking transmission, it is proposed in international standard to usethe same expression (Equation 5.3) in that case, but with the surface of theseparating wall S replaced by A 0 = 10m 2 open window area :R = L p1 −L p2 +10log A 0A(5.4)Now one can compare different constructions independently of the receivingroom total absorption. The expression T is also used instead of A 0,0.5 Awith T the reverberation time of the receiving room (0.5 sec is a referencereverberation time that is typical for small rooms).5.1.2 Measurement of impact soundThe international standard ISO 140-6: 1978 describes the measurement ofimpact soundinsulationinalaboratory. Animpact device isused(see Figure5.3). It has 5 small steel hammers with normalized mass of 0.5 kg and aradius of 3 cm (the final radius is 50 cm). These hammers are aligned (0.4 mtotal length). At impact of the hammers one measure the normalized soundpressure in the receiving room :L n = L+10log A A 0(5.5)with L the A weighted SPL. Such as was the case for airborne sound insulationone measure also the standardized level (according to ISO-7 140) :L ′ nT= L+10log0.5T(5.6)