Explanation:

Noise cancellation is accomplished acoustically. Imagine a drum. If you hit one side, you get a sound. If you hit both sides of a drum simultaneously you do not get a sound.

A noise canceling transmitter is ported with two openings. Noise goes into both holes, strikes both sides and gets cancelled. Whereas, your voice only goes into one side and does not get cancelled. This noise reduction greatly improves telephone conversation in loud or crowded environments. Noise cancellation is great for offices, garages, warehouses, and trading floors for example.