  We show that dissipative effects during cosmological first order phase
transitions lead to a frequency-dependent suppression for the usually dominant
gravitational wave production from sound waves, through an analytical modelling
of the source based on the sound shell model. This damping effect is more
pronounced for high frequencies or small scales, and modifies the spectral
shape and possibly the peak frequency. These modifications can be used to
reveal more information about the underlying particle interactions, serving as
a way of breaking the parameter degeneracy that plagues particle physics
studies based on the perfect fluid approximation.
