As to how a talk box works, basically it is a tweeter horn driver hooked up to your amp instead of the normal speakers. The guitar sound is sent up to your mouth thru the tube. Then you can alter the sound be "mouthing" words this sound is then picked up over a microphone and this sound is sent thru a PA system. This is how the original HEIL talk box worked. It had problems though because the ohm load on the amp was sometimes not sufficient and could blow up the amp :eek: You often needed two amps with this design.
There are newer designs which eliminate this but I can't think of the names.
Hope this helps