RMS-velocity (upper part) and characteristic radius (lower part) established in the SNe-driven convective phase. The left axis shows km s^-1 and pc. The right axis indicates the velocity in units of the central escape velocity and the radius in units of the half-mass radius. The solid black line is for the case when all massive stars produce energetic SNe. The dotted blue line assumes direct black-hole formation without energy release into the ICM for all stars with M > 25   M_⊙. The plot shows that in the latter case the onset of turbulence is delayed by 5.3 Myr. See Sect. 4.2 for more details.