Each ring compose of 10 to 12 enemies distributed equally. There are 3 rings total in a wave, that makes them 30-36 in total. On its basic form, these compose of chickens having a different color on each ring. The feat of this wave is when these three rings combine each other to form one ring. The expanded form looks like a Venn diagram, hence the wave name.
A 2-ring variant can also be added on lower difficulties: