The sound level decreases as the distance from the sound source increases. The design of the room (shape, furnishing, surface finish etc.) influences the extent to which the sound level decreases along with the distance.
Speech at 1 m distance
Speech at 4 m distance
Speech at 8 m distance
To characterise the propagation of the sound there is a parameter that describes the extent to which the sound decreases when the distance is doubled. This parameter, designated DL2 and measured in dB, determines the slope of the sound propagation curve. Another parameter, DLf, also measured in dB, shows how the sound level at a certain distance is related to the sound level at the same distance in a free soundfield, i.e. without reflecting objects. A high DL2 and a low DLf ensure limited disturbance between work places.
AC is a classification of suspended ceilings according to their ability to contribute to the acoustic privacy between work stations. This method provides measurements of the sound reflective characteristics of ceilings used together with screens.