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

Chapter 5Sound InsulationWhen considering the sound transmission between two rooms, a distinctionmust be made between airborne sound and impact sound. In airborne sound,asource (loudspeaker, singer, radio, music instrument, aircraft, car, machine,...) generates a pressure wave in a room which is transmitted through a wallto a neighbouring room. Contact noise, on the other hand, is generatedby vibration sources (generally impacts) which leads to structural vibrationsthat propagate to neighbouring rooms (e.g. a machine fixed on the floor ora wall, footsteps, elevator).The distinction between both types of transmission is important becauseboth the transmission mechanisms, the measurement procedures and thetechniques to prevent the sound transmission are completely different. In thenext paragraphswe will focusonthesimulationandmeasurement ofairbornesound insulation (contact noise measurements will be briefly introduced).5.1 Measuring sound insulation5.1.1 Measuring airborne sound insulationIn approximation one could think of describing airborne sound insulationbetween two rooms as :∆L p = L p1 −L p2 (5.1)with L p1 en L p2 respectively the sound pressure levels in the source roomand receiving room. This would mean that the airborne sound insulation isdefined as the attenuation of airborne sound arising from the first room (representedas the difference in sound pressure level). Not only the separatingwall plays a role in the transmission of sound, but also all other boundarysurfaces of these two adjacent rooms because they can all contribute to81