where c is the speed of sound in air (see chapter 1, equation (1)), t is the partition thickness (m)
and cL is the longitudinal wave speed in the panel given by cL = (E/)1/2, where E, and are
Young's modulus of elasticity, density and Poisson's ratio respectively for the partition material.
The lower frequency limit of validity of equation (3) is twice the lowest resonance frequency of
the partition which is usually well below the audio frequency range for most constructions used
for machine enclosures. Means for estimating the transmission loss of partitions at frequencies
outside of the mass law range are discussed in the literature (Bies and Hansen, 1996, Ch. 8).