The Surname Dum or Dumm Thumm decendants of Casper Thumm
The decendants of Casper Dum/Thum spell their name either Thum Thumm Dumm Dum Thumme Dumme Dom Domm Thom
All surname spellings are the same sound.The use of German Grim's Law of saying it can use either "D" for "T" sound or "TH" for the hard "D" or "T" sound You also see "DT" for the hard "T" or "D" sound.