Om …..aum

అ a

……….. is just opening the mouth, breaking the silence, original unmanifest silence starting to manifest

ఉ u

……...is bending

ఓ o

……...is making into ring

ఓ oo

……...is cylindrical shaping

ఔ au

……...is blowing into balloon. spherical shape

When combined with dhathu ..m ..

It is becoming a spherical shape,…….ie,  a perfect beauty, poornam……so it is a great full sound……..rather the greatest full sound ……..pleasing, shraavya, sonorous, good, beneficial, auspicious, and further flowing into infinite swaras and ragas,