That is a Leslie speaker. They are used for Hammond type organs, etc.
The spinning aspect of it allows the organ player to get that wild
whirling organ sound. I'm not sure about this but I think that Charlie
Hunter uses a leslie as well. . . which probably allows him to get that
somewhat pseudo organ sound out of his guitar. Not to bust on Charlie
he's a great musician and I dig his stuff. It's just that when he goes
for the organ sound it tends to wear thin on my ears after a while.
Hope that helps.
bye
brian
p.s. ViperHouse has the great pleasure of opening up for the JTQ on
November 5th here in Burlington, VT. I'm glad that we're doing this
since it is probably the only way a poor musician like myself could
afford to get into the show. Ha. :)