I don't know how amplifying or cushioning a sound source falls more under air magic than it does the ability to manipulate sound itself. o_O

As for the rest of your post though, I get my powers' boundaries now. However, have you played the game Skyrim? If not, the main character has this thing called "Shouts": if s/he shouts a certain word or groups of words, it can create various effects such as breathing out fire or an icy blast. I was wondering if that would be out of the realm of my character, to bellow a powerful sound blast, low in frequency. Of course, this would have drawbacks to him as well, as he can become disorientated after using it because of his sensitivity to sound. He also cannot use in closed spaces, as that actually guarantees disorientation and possibly, massive headaches.