Question: How do different active noise-cancelling headphones work?

Answer: Have you looked at noise-cancelling headphones and wondered how they differ? There are many terms used to describe these headphones, such as “passive noise-cancelling” vs. “active noise-cancelling” or “feedforward” vs. “feedback.” Audio-Technica engineers use different techniques to achieve reduction of unwanted sounds and noises.

Let’s look at some of these terms in detail.

Passive noise cancellation is nothing more than material between the outside sound and your ears. Having a tight seal and dense materials between the two reduces the level (volume) of the outside noises. Passive noise-cancelling devices are worn for hearing protection in loud environments.

On the other hand, active noise cancellation uses electronics and acoustic technology with the specific intent of reducing unwanted sound. We previously addressed how active noise-cancelling headphones work, however here is a brief overview. Noise is captured by microphones in the headphones where a DSP (digital signal processor) chipset reverses the polarity of the sound wave 180 degrees. This out-of-phase, noise-cancelling signal is produced by the driver along with the music or other audio you want to hear. To our ears, noise or unwanted sounds are greatly diminished using this active noise-cancelling technique.

The graphic below visually demonstrates how the unwanted noise (red) is captured and how the opposite blueprint of the noise (green) is injected into the audio signal. The result is the summing of the two (red and green together make a lime green color), which to our ear is no noise, (aka: noise cancellation). Let’s consider this concept using simple math. If noise is +1 and we add it to the reverse or negative of the noise (-1), we get zero noise.

There are three different types of active noise-cancelling headphones that are regularly used today. They are “feedforward,” “feedback,” and a combination of the two referred as “hybrid.” The difference between them is where the microphone is used in the signal chain. Feedforward technology uses an external microphone, which is typically on the outer casing of the headphones or sometimes, with wired models, on the cable. The unwanted noise is captured externally, processed in the DSP chipset, and finally the headphone driver (speaker) outputs the corrected audio. If you are playing music through the headphones as well as cancelling noise, the level of your desired audio does not need to be as loud to overcome unwanted noise. This is the simplest form of active noise cancellation.

Alternatively, feedback active noise-cancelling headphones place the feedback microphone in front of the driver, which changes the way the unwanted sound is processed. If the internal microphone picks up any noise that is not coming out of the driver, the DSP chipset identifies it as unwanted noise and creates a cancelled waveform, which is sent back out the speaker to your ears. This technique requires more processing power as the DSP is constantly adapting to changes in sound.

The “best of both worlds” comes in the form of hybrid active noise-cancelling headphones, which use both feedforward and feedback techniques. The DSP uses two (or more) microphones to identify unwanted noises and generates the highest level of noise cancellation.

Audio-Technica continues to develop products that enhance your listening experience. If you have further questions about active noise-cancelling headphones, you may contact the Audio Solutions Department.