Quoting Akhilesh Pillalamarri <[log in to unmask]>:

> Everywhere I've read, it says the sound [a] is the most common sound in human
> speech; my personal experience with language agrees with that. I wonder now,
> is the sound [a] found in every language?

As others have indicated, no, not every vowel has [a], or even a vowel closer to
[a] than to any other cardinal vowel.

I've, however, never seen a vocalic inventory of a natlang without any low
unrounded vowel, far as I can recall. Some folks apparently reconstruct
Proto-Germanic as having the set /i e o u/, but I wouldn't accept a
reconstruction as evidence here.