Each source radiates a real circular wave, y = (A/√r)·cos(kr − ωt + φ), and the total displacement at every point is the exact sum of both waves (the superposition principle) — nothing here is faked or pre-drawn. Where two crests (or two troughs) arrive together, they add up into constructive interference (bright bands); where a crest meets a trough, they cancel into destructive interference (calm, dark bands). Try setting both sources to the same frequency with a 180° phase difference to flip every bright band into a dark one, or use different frequencies to watch the pattern drift as the sources fall in and out of step.