antinoise

Antinoise, or anti-noise, is a technology and concept in acoustic noise control that aims to reduce unwanted sound by producing a secondary sound field with opposite phase and similar amplitude. When anti-noise is combined with the original noise, destructive interference reduces the net sound energy in a local region. This approach underpins active noise control systems, particularly for low-frequency, tonal, or otherwise persistent noise.

Most antinoise systems use microphones to pick up noise (reference or error microphones), digital signal processing to compute an anti-noise signal, and loudspeakers to emit the corrective sound. Two principal configurations are used: feedforward systems, which anticipate noise using a reference sensor, and feedback systems, which react to residual noise in the environment. The effectiveness depends on the acoustic path from the speakers to the ear or target zone and can be limited by latency, model errors, and nonlinearities.

Applications include active noise canceling headphones and ear defenders, in-vehicle cabins, aircraft, HVAC ducts, and machinery enclosures. Antinoise is most effective at low frequencies (below about 1,000 Hz) where sound fields are more coherent; higher-frequency noise is more challenging due to rapid phase variations and diffraction.

Historically, the concept has roots in mid-20th-century research into active noise control, with practical consumer devices appearing in the late 20th century. Advances in digital signal processing, sensor technology, and adaptive algorithms have expanded the use of antinoise in industrial and consumer settings, though it remains a complement to passive noise control measures such as insulation and muffling.

Related topics include active noise control, noise reduction, and acoustic dampening.