I assume that Tuba is a fairly air intensive instrument, in that it takes a lot of air to get that big fat deep sound out of the thing. I wouldn't know, I'm a sax player.
Anyhow, a friend of mine recently switched from Euph to Tuba, and seeing as the Tuba is almost as big as she is, you can imagine that she would have some volume issues.
Do you tuba players have any advice on breathing exercises to raise lung capacity? I fear that if I ask her to "breathe deeply!" one more time, she'll pass out on me!