For the numerical example in Figures 7–13, in the frequency range which used two secondary sources: (a) The transfer function magnitudes G_front and G_rear for the SS 1← SS 1 combination. (b) The relative error for the G = G_front + G_rear transfer functions, when either only GA, or GA+first-order diffraction is included. (c) The relative error for the v_SS secondary source amplitudes (due to symmetry both secondary sources get the same amplitude).