Question: why aum instead of om?
Answer: Meditation experts say that the Sanskrit word 'Aum' has, over a period of time and owing to the ravages of spread and travelling, has become 'Om'. ... Against this, Aum is pronounced as aa-uu-eemm. In Sanskrit, 'O' is a diphthong sound. This means that it is formed by combining the two sounds 'A' and 'U'.