Monochromatic-emission-coefficient–weighted mean integrated spectral index at an emission frequency of ν = 150 MHz, including all shocks that occur at locations where the dark matter (DM) density ρ_DM is below some threshold. Larger thresholds incorporate shocks from a wider range in ρ_DM, eventually including shocks from both filament and cluster environments. To provide an idea of the uncertainty in , we use jackknife realisations that each contain 80% of the shocked voxels present in our Enzo snapshot at z = 0.025.