Results of the echo threshold level (filled symbols) and the masked threshold level (open symbols) given as means and 95% confidence intervals. The influence of the scattering coefficient s is examined with conditions A ^s , the influence of the angle θ ₀ is examined with conditions A ¹, B ¹, C ¹, and the influence of the directional spread is examined with the hybrid condition A ^⋆, which combines the temporal characteristics of a diffuse reflection with the directional characteristics of a specular reflection. For all conditions the delay is constant with ΔT = 20 ms.