I was messing about with this new Google program that searches all of their scanned library for word usage - the results for tuba,Sousaphone are rather dramatic! http://ngrams.googlelabs.com/graph?cont ... moothing=3
You also do have to figure the sample - Google is not inputting Band Director Magazine (is there such a thing?) or Modern Sousaphonist - they are doing books of general and technical interest, some in public domain, some not. Does "Tuba" show up in "The Great Gatsby?" - not sure, but I don't think so... neither does Sousaphone AFAIK