Francesco Lamperti was known to declare that /a/ was the "father of all vowels."

Reading old voice manuals, articles and newspaper discussions (they did back then in the paper what we do now on Facebook), it becomes apparent that he wasn't alone in asserting the importance of this vowel. 

The Old Italian School believed that every fault of the voice was revealed by /a/, an assessment with which I am inclined to agree. 

It is also the vowel in which Americans do not excel, our language being guttural in tint. This becomes clear when one compares current vocal styles with early 20th century ones, the latter heavily influenced by the "pure" /a/ of the Old Italian School. 

I've not forgotten the teaching of Anne Wiggins Brown, who was George Gershwin's Bess in Porgy and Bess. She told me she was taught to speak with a "Juilliard Ah," which gave her speech a kind of class now only heard in black and white movies from the 30's and 40's. Where do you think those movie stars got it from? Old School voice teachers and singers who settled in Hollywood to make the most of a new industry.