Many people who learn Vietnamese will learn or will want to learn the Vietnamese of the northern dialect (Hanoi) but when they encounter people from the South there may be some confusion such as with the way some tones and vowels are pronounced. Here are some things I have noticed at least among some people in the South.

I think that in the North they pronounce ‘ô’ as more or less the pure European ‘o’ and they pronounce ‘o’ as Americans pronounce ‘aw’ as in “law”. In the South when the vowels aren’t at the end of the word the two vowels are pronounced more similarly with the ‘o’ being pronounced closer to ‘ô’.
In words that end with ‘nh’ such as “anh” it is pronounced like “ANgst” in the North and “lAWN” in the South. And in the South words like “tin” and “tinh” are both pronounced like Americans pronounce “tin” although much shorter whereas in the South the first would be pronounced “teen” and the second would be pronounced “ting”. The same happens when ‘i’ is followed by ‘t’ or ‘ch’.   And some people pronounce the vowel in ‘ic’ somewhat differently from the rest.

And sometimes in words like “tên”, “hết”, “nên”, or “trệt” the vowel is pronounced slightly differently in the South. In these situations the ê sounds closer to ơ or â.

yên: in the South I hear “een” and in the north I hear “eyen”.

There is also some difference in the way the tones are pronounced.  In the South the hỏi and the ngã tones are pronounced similarly.  I also think that the nặng tone is much less distinct from the huyền tone in the South whereas in the North the nặng tone results in much more pronounced glottal stops.  I also think that the rising and falling tones are slower to rise and fall in the North.

I’m sure I’ve left out some differences so please feel free to leave a note in the comments. Next time I will talk about Vietnamese consonants and the differences between consonant sounds in the North and South.