Adjust the baseline shift by choosing a negative number. A baseline is a line that the text rests on.
Fonts are going to have different x-height or capital heights, etc. This will change the surrounding box based on how the font was made. You will need to adjusted the baseline depending on the font. Illustrator will vertically align the text based on the surrounding box.
Source : Link , Question Author : speeder , Answer Author : AndrewH