VRIJE UNIVERSITEIT BRUSSEL Acoustics - the Dept. of ...

86 CHAPTER 5. SOUND INSULATIONFrequency Ref. value (in dB)100 33100 33125 36160 39200 42250 45315 48400 51500 52630 53800 541000 551250 561600 562000 562500 563150 56Table 5.1: Reference values for sound insulation of a wall from ISO 717.5.2 Airborne sound insulation of a wall5.2.1 Simple lawConsider a plane sound wave which is incident ona(simple) wall. We assumefollowing conditions are met :The wall is characterized by its mass per unit area (isotropic material).It is assumed infinitely long.The wall does not absorb sound (a = 0).The wall has no stiffness and no damping. On the source side a planeharmonic wave is normally incident on the partition wall. There is nodeformation within the wall: it displaces as a whole.On the source side one can write that the air particles have a zero velocityon the wall because this wall does not move and does not absorb sound (seealso Section 4.1). Because of the acoustically hard reflection if no absorptionis present the pressure doubles at the incident side 2p i . Applying thefundamental equation of dynamics on the wall surface :2p i −p d = ma (5.7)