So, Addi Somekh uses two balloons (he says 3, but I can't see where the other one goes) to make a 'Balloon Bass with a three octave range. The round balloon is the resonator, and the 'string' is a long thin 'modelling' balloon, not inflated. Yes, there are recordings and they sound pretty good, although the tuning is a little haphazard. (Thanks, JM)