At low frequencies, the transmission loss depends on the modal behavior of the partition wall (here a 18-mm plaster board partition). The elastic parameters of the partition wall (including the mass density) and the boundary conditions at the junctions with the floor and roof, are needed to describe the real behavior
of the partition (which appears in grey
on the graph between 63 and 1k Hz). The higher the amplitude of the partition vibration, the lower the transmission loss.
A rough estimation of the transmission loss at low frequencies can however be obtained by only considering the mass of the partition. This mass law modeling
, only valid at low frequencies, below the critical frequency, is depicted in black
on the graph.