The “talk box” is a unique effect that allows you to modify an audio signal — most commonly a guitar sound — using the player’s mouth as a filter to shape the sound. The talk box itself consists of a box, in which a speaker (often a compression driver) feeds into a plastic tube. The speaker connects to the speaker output on the instrument (guitar) amplifier, and reproduces the audio signal from the instrument.
The player places the other end of the tube in his or her mouth. Sound flows through the plastic tube and the player uses their mouth as a filter to shape the sound. Different vowel sounds can be produced with the guitar signal as the “carrier” or audible part of the signal, or complete words can be “sung” using the guitar signal. Words and sounds only need be formed with the mouth, they don’t need to be spoken aloud, in order to modify the sound from the speaker. Since the actual SPL of the sound out of the plastic tube is fairly low, a microphone is usually placed in front of the musician to capture the sound.
Popular songs using the talk box prominently include Joe Walsh’s “Rocky Mountain Way” and Peter Frampton’s “Do You Feel Like We Do.”