I read this about subharmonics in the New Scientist -
"Mari Kimura, a New York-based violinist, can go even lower without retuning her instrument. From the violin's bottom G string she can produce sounds a whole octave lower - a G with a pitch of 98 Hz - as well as everything between that and 196 Hz. It is the sort of note that you can normally only hear on a cello or a double bass."
She has a web page here - http://homepages.nyu.edu/~mk4/subharmonics.html
I thought it was fascinating. I've never heard of this before.