Noise cancellation

Engineering Silence: Active Noise Cancellation

Michael Benoit Christopher Camastra [e-mail] [e-mail] Kimberly Li [e-mail] Richard Romanowski [e-mail]

Melissa Kenny [e-mail] Kevin Shannon [e-mail]

Abstract
In order to create active noise canceling headphones, a pair of Sennheiser HD 202 headphones was modified with microphones and a series of op-amp circuits. Attenuation of low frequency ambient noise was successfully observed.

Introduction
Noise cancellation technology is aimed at reducing unwanted ambient sound, and is implemented through two different methods. The first of these is passive noise cancellation: an approach that focuses on preventing sound waves from reaching the eardrum, and includes devices such as circumaural headphones or earbuds [3]. The other technique used to achieve the same – and often better – result is active noise cancellation, which uses aural overlap and destructive interference to target and attenuate background noise. While passive and active noise cancellation may be applied separately, they are often combined to attain maximum effectiveness in noise cancellation.

Although active noise canceling devices are still being integrated commercially, the concept has existed since the beginning of the 20th century. In 1933, a German patent was issued to a Paul Lueg for the concept of active noise cancellation; he was the first to realize the possibility of attenuating background noise by superimposing a phase flipped wave [5]. In the 1950s, Olsen successfully demonstrated Lueg’s concept in rooms, ducts, and headsets [5]. Research and development of active noise reduction (ANR) headphones truly began in 1978 after Dr. Amar Bose felt the need to develop headphones that masked the low rumbling of plane engines and other cabin noises [6]. With the invention of integrated circuits – opamp circuits – and miniature microphones, the existence of ANR headsets