I suspect that Effenberger derives from Essenberger. There is a city in Germany called Homberg-Essenberg on the east bank of the Rhine River near Essen. Esse(n) means chimney or relating to chimney in German.This would mean that Essenberger means someone from Essenberg; and Essenberg is the hill with chimneys. This is consistent with the industry of the region (iron smelting).