Dispersion and attenuation of acoustic plane‐wave disturbances propagating in a ducted combustion system are studied. The dispersion and attenuation are caused by fuel droplets and soot emission from a jet engine combustor. The attenuation and dispersion are due to heat and mass transfer, and viscous drag forces between the emissions and the ambient gas. Theoretical calculations show sound propagation at speeds below the isentropic speed of sound at low frequencies. Experimental results are in good agreement with the theory.