How does the headset know which noise is your voice and what noise to cancel? To answer that, try this: Plug your ears with your fingers so that you can't hear the noise around you. Now talk. You can still hear yourself, right? Your voice sounds different from the way it sounds when your ears are unblocked, but you can definitely have a conversation with yourself in your head. Whether that's a good or bad thing is up to you.
How is this possible? Thank your jaw bone. When you speak, you create vibrations that travel through the ear and reach another person's ear. Regular phones use air conduction hearing, which uses the outer ear to catch sound waves. The sound waves are then transported through the middle and processed in the inner ear. Noise-canceling headsets combine this air technology with bone conduction hearing [source: Anjanappa et al]. The bone conduction method transmits sound vibrations directly to the inner ear along the bone itself. For more on hearing, see How Hearing Works.
The mouthpiece on a noise-canceling headset is actually two microphones -- one for air conduction and the other for bone conduction -- combined into one. This is called a bi-directional microphone. The microphone sends the signal to a sound processor. The processor then sends the signal across the airwaves so the person on the other end of the call hears your voice. This is similar to the process of voice transmission featured in hearing aids.
Because the sound hasn't passed through your entire mouth (since your lips also help with speech) when it hits the jaw, bone conduction is slightly lower in sound quality, so the air conduction method of transmission is needed to make your voice clear. The noise-canceling headset uses the bone conduction method only to discern the correct noise to recognize, thus filtering out surrounding noise. This active noise control can be controlled by an on/off switch on headsets [source: Aliph Jawbone].
Noise-canceling headsets help you hear yourself clearly despite the noise around you, but how do you hear who you're talking to? Read on to find out.