ANC — Active Noise Cancellation

ANC — Active Noise Cancellation. The active noise cancellation (ANC) function operates on the principle of destructive interference of sound waves. This means that headphones generate sound waves with equal amplitude but opposite phase to the external noise waves. When these sound waves combine, they mutually cancel each other, thereby reducing the volume of the resulting sound signal. This effect is called phase cancellation — a phenomenon in which identical waves with opposite phases combine to reduce the amplitude of the resulting wave, in other words, the waves annihilate each other. As a result, external noise is reduced to a minimal level, allowing for clearer sound perception.

To determine which sounds to remove, headphones are equipped with microphones that detect the sound waves around the user. Then, the processor analyzes this data and generates audio to reduce noise. High-quality headphones are equipped with two pairs of detecting microphones: internal and external. External microphones perform the task described above, while internal ones analyze the result of the system's operation and provide signals for adjustment. This helps to avoid resonance (noise amplification) and parasitic feedback.

The active noise cancellation (ANC) function, unlike the Environmental Noise Cancellation (ENC) function, affects the sound reproduced by the headphones.

Main Active Noise Cancellation (ANC) Modes

There are four main types of noise cancellation that can be distinguished.

1. Feedback: The microphone is located inside the headphone cup in front of the speaker. This allows the headphones to respond to the sounds you hear and adjust noise cancellation accordingly. However, feedback is less effective at suppressing sounds in the 1–2 kHz range.

2. Feedforward: Microphones are located on the outside of the cups. They quickly react to external noises and create an opposite-phase signal for compensation.

3. Hybrid approach: This method combines feedback and feedforward. It uses two microphones — one on the outside of the cup and another in front of the speaker.

4. Adaptive approach: The hardware setup of adaptive noise cancellation is similar to the hybrid approach. However, here a software processor is added to automatically adjust the noise cancellation level depending on the environment and the headphone fit. This method was first developed by Qualcomm for TWS wireless headphones.

History of ANC Technology Development

In 1933, Paul Lueg (USA) developed the theory of noise cancellation and obtained a patent for applying interference principles to suppress sinusoidal and other (arbitrary) sound signals in the loudspeaker area by inverting polarity.

Then, in the 1950s, Lawrence J. Fogel created the first headphones with this technology. Fogel's systems were used to reduce noise in helicopter and airplane cabins.

In 1957, Willard Meeker created the first over-ear headphones with active noise cancellation, also used in aviation. Meeker's system was capable of suppressing noise in the 50–500 Hz range with attenuation of 20 dB.

In 1986, the first mass-produced headphones with active noise cancellation (ANC) appeared. The device was developed by Bose Corporation specialists Dick Rutan and Gina Eager. The technology was first implemented in the Series I aviation headset. Initially, ANC was used exclusively for professional purposes by pilots and other specialists working in high-noise environments. In 1989, another Bose Corporation employee — Dr. Amar Bose — adapted active noise cancellation for consumer use. Today, this technology is widely used in consumer headphones by BOSE, Philips, Sennheiser, Audio-Technica, SONY, JBL, including TWS earbuds.

Disadvantages of ANC Technology

Although noise cancellation technology has significantly advanced, it still cannot provide complete isolation from ambient noise, especially when music is not playing. Headphones with active noise cancellation additionally block up to 30 dB of low-frequency noise below 1 kHz. However, each system has its drawbacks, which should also be mentioned.

Active noise cancellation systems in headphones have the following significant disadvantages:

1. The need for an additional power source to operate noise cancellation.
2. The possibility of additional negative effects such as headaches and discomfort during listening.
3. Use in areas with heavy traffic may increase accident risk.

Since ANC relies on signal processing to function, DSP requires time to react to the ambient noise it attempts to suppress. For this reason, ANC works best at reducing monotonous repetitive sounds, such as the constant hum of an engine or transformer. Generally, white noise (rustling leaves, ocean waves, airplane roar) is suppressed more effectively. The system also suppresses low frequencies more efficiently than high ones. This has a side effect — speech, though muffled by active noise cancellation, becomes more intelligible because the monotone background noise disappears, making conversations easier to hear.

For safety purposes, some manufacturers produce headsets with active noise cancellation systems that specifically allow and emphasize sounds such as car horns, sirens, and a crying baby.

Are ANC Headphones Harmful to Health?

Among reviews of headphones with active noise cancellation, there are reports of various side effects after prolonged or even short use. These effects may include headaches, discomfort during listening, and psychological unease. It is known that approximately 5–7% of users who regularly use headphones experience intolerance to devices with active noise cancellation.

The reason is that over a lifetime, a person becomes accustomed to a certain level of background noise. Music generally differs from other auditory stimuli, and this difference forces the brain of some people to adapt again to a new, more monotonous background created by ANC headphones. In some cases, the operation of the active noise cancellation system may also be accompanied by its own high-frequency noise background, which can cause headaches and discomfort after prolonged exposure.