Free electrons density contrast power spectrum for a box filled with enough bubbles of radius R = 15 px = 5.5 Mpc to reach a filling fraction f = 1%. Points are results of a numerical computation of the power spectrum, compared to the theoretical model (solid line). The dotted vertical line corresponds to k = 1/R, the dashed vertical line to 9^1/4/R, the dashed horizontal line to 4/3πR³/f and the tilted dashed line has slope k⁻⁴.