Count Vowels

Hi, I've got this problem I wasn't able to solve. I need to count the total count of vowels inside a single cell. For example i have:

John Davidson = 4 (I need to display 4 because of "o", "a", "i", "o").

Thank you.

Assuming the cell is A1

=SUM(LEN(A1)-LEN(SUBSTITUTE(LOWER(A1),{"a","e","i","o","u"},"")))