The conceptual foundation for active noise control was established in the late 1930s. The first patent for such a system, U.S. patent 2,043,416, was granted to inventor Paul Lueg in 1936. Lueg’s work described methods for canceling sinusoidal tones within ducts by phase-advancing waves and canceling sounds around a loudspeaker by inverting polarity.
Developmental work continued in the 1950s, notably by Lawrence J. Fogel, who patented systems designed to cancel noise within airplane and helicopter cockpits. In 1957, Willard Meeker developed a functional model of active noise control applied to a circumaural earmuff. This early headset achieved a maximum attenuation of approximately 20 dB within a bandwidth of 50–500 Hz.
The transition from experimental models to commercial applications occurred in the late 1980s with the release of the first active noise reduction headsets. These units were powered either by the aircraft's internal power system or by NiCad batteries.
The technology relies on the physical principle that sound is a pressure wave consisting of alternating periods of compression and rarefaction. To cancel an unwanted sound, a speaker emits a wave with the same amplitude but an inverted phase, known as antiphase. When these waves combine, they undergo destructive interference, effectively canceling each other out and reducing the perceivable volume.
Modern active noise control is implemented through analog circuits or digital signal processing. Adaptive algorithms analyze the waveform of background noise and generate a signal that either inverts the polarity or shifts the phase of the original signal. This signal is amplified, and a transducer creates a sound wave proportional to the original amplitude to facilitate destructive interference.
The technology is categorized into 1-dimensional and 3-dimensional applications:
1-Dimensional: This involves a simple relationship between the speaker and the listener, such as in headphones or air conditioning ducts. In headphones, a built-in microphone measures ambient noise, calculates the component reaching the ear via an acoustic transfer function, and generates an opposing signal.
3-Dimensional: Protecting a 3-dimensional zone, such as a car interior or aircraft cabin, is more complex and requires multiple microphones and speakers. This is most effective for periodic sounds, as the cyclic nature of engines, propellers, or rotors makes the noise easier to analyze and cancel.
The effectiveness of active noise cancellation is limited by the frequency and direction of the sound. High-frequency waves (above 1000 Hz) are difficult to manage in three dimensions because their short wavelengths lead to unpredictable patterns of reinforcement and cancellation. For example, a sound at 800 Hz coming from the side may be canceled at one ear but reinforced at the other, making the noise louder for the listener.
In road vehicles, global noise reduction in the passenger compartment is achieved by measuring the modal responses of the enclosure and using multiple speakers and feedback microphones. In mobile telephony, a multi-microphone design is used where the microphone furthest from the mouth captures the noise signal, which is then processed and canceled from the desired speech signal captured by the primary microphone.
Active noise control is distinguished from passive noise control by its use of a power source. Passive methods rely on noise-isolating materials such as sound-absorbing tiles, insulation, or traditional mufflers. While active cancellation is best suited for low frequencies, passive treatments become more effective at higher frequencies, where the spacing requirements and the number of nodes in active systems become unmanageable.
The first functional active earmuff in 1957 demonstrated the potential of the technology with a 20 dB reduction in noise. Modern applications have expanded this to include active vibration control, which addresses noise produced when the vibration of a physical structure couples with surrounding air or water. The technology remains a primary solution for repetitive, low-frequency environmental noise in aviation and automotive contexts.