  We present ongoing investigations of the first-order confinement transition
of a composite dark matter model, to predict the resulting spectrum of
gravitational waves. To avoid long autocorrelations at the first-order
transition, we employ the Logarithmic Linear Relaxation (LLR) density of states
algorithm. After testing our calculations by reproducing existing results for
compact U(1) lattice gauge theory, we focus on the pure-gauge SU(4) theory
related to the Stealth Dark Matter model.
