Brass instrument native to the Whovian people of Whoville, who live on a speck of dust. When their world is threatened, they use this instrument to make noise enough to be heard by larger creatures. From the 1954 children's picture book Horton Hears a Who! by Dr. Seuss.
"Oompah" is an onomatopoeic word, based on the sound of a tuba, and dates back to the late 1870s.
They blew on bazookas and blasted great toots
On clarinets, oom-pahs and boom-pahs and flutes!
Great gusts of loud racket rang high through the air.
They rattled and shook the whole sky!