(ollie @ Jan 16 2006, 04:28 PM)
It is called a talk box
a small audio speaker or high end driver is enclosed, air tight, into a metal box with a hole in the top where a tube comes out. The guitar is plugged into an amp, but the speaker output is routed through the TalkBox. Then the signal is routed back from the box into the amp again. So, the sound from the guitar is sent through the box, up the tube to a waiting mouth, where the sounds are manipulated, before being picked up by the microphone! So by this method you can mouth the words while the sound of the guitar replaces the human voice box....hence the name Talk box
also popularised by joe walsh and in recent times by richie sambora, bon jovi "livin on a prayer" all in all a bit of a gimmick really there's (got to be carefull or the apostrophe police will get me) no real substitute for harmonic knowlege.
cheers Ollie.