I was wondering that how was the pronunciation of the word "about" in 16th century England. I know that it is different now and is this difference occurred because of The Great Vowel Shift?
The main change happening at this time was, as you mentioned, the Great Vowel Shift. Before the GVS, the second vowel in "about" was
/u:/; this went through something like
[əu], before turning into modern
In the 16th century, it would probably be somewhere between
This diagram (from Wikipedia) might help, though it writes the diphthongs a bit differently than I do.