A noise-cancellation speaker emits a sound wave with the same amplitude but with an inverted phase (also known as antiphase) to the original sound. The waves combine to form a new wave, in a process called interference and effectively cancel each other out – an effect which is called destructive interference.
Modern active noise control is generally achieved through the use of analog circuits or digital signal processing.
Adaptive algorithms are designed to analyze the waveform of the background aural or nonaural noise, then based on the specific algorithm generate a signal that will either phase shift or invert the polarity of the original signal. This inverted signal (in antiphase) is then amplified and a sound wave is created, which is directly proportional to the amplitude of the original waveform, creating destructive interference. This effectively reduces the volume of the perceivable noise. Active noise control is sound reduction using a power source.
