Noise-cancelling headphones come in either active or passive types. BT Waves Blurtooth headphones use active noise cancelling technology that adds an extra level of noise reduction by actively erasing lower-frequency sound waves. The headphones actually create their own sound waves that mimic the incoming noise in every respect except one: the headphone’s sound waves are 180 degrees out of phase with the intruding noise waves.
The sound wave coming from BT Waves noise-cancelling headphones and the one associated with the ambient noise have the same amplitude and frequency, but their crests and troughs (compressions and rarefactions) are arranged so that the crests (compressions) of one wave line up with the troughs (rarefactions) of the other wave and vice versa. In essence, the two waves cancel each other out. The result: the listener can focus on the sound coming from the headphones.