Sat Apr 02 2022
How Does Noise Cancellation Work? Unveiling the Science Behind Silence
When some important audio sound appeals are getting lost, you’ve probably considered noise-canceling headphones. It cancels out the annoying sounds that surround you without diminishing the audio you want to hear. The result…a peaceful enclave to enjoy the important nodes of sound, music or movies of your choice. Noise-canceling devices save us from the madding hum of white noise. So, what is Noise Cancellation? How does it work? Why do use noise-canceling headphones, and how does it help to hear the audios clearly what you want to hear? In this article, we'll delve into the science behind this remarkable technology and explore the two primary methods it employs: passive and active noise cancellation.
What is Noise Cancellation?
Noise cancellation is also known as Active Noise Reduction (ANR) or Active Noise Control (ANC), is a method for reducing unwanted sound by the addition of a second sound specifically designed to cancel the first. The sound is a pressure wave, which consists of alternating periods of compression and rarefaction. A noise-cancellation speaker emits a sound wave with the same amplitude but with inverted phase to the original sound. The waves combine to form a new wave, in a process called interference and effectively cancel each other out - an effect which is called destructive interference.
Noise cancellation makes possibilities to listen to audio contents without raising the volume excessively. It can also help a passenger sleep in a noisy vehicle such as an airliner. In the aviation environment, noise-canceling headphones increase the signal-to-noise ratio significantly more than passive noise attenuating headphones or no headphones, making hearing important information easier such as safety announcements. Noise-canceling headphones can improve listening enough to completely offset the effect of a distracting concurrent activity.
How does Noise Canceling work?
In order to understand how noise canceling work, it’s imperative to first understand the basics of how sound waves function. In short, sound waves, which are longitudinal waves, have similar characteristics to the transverse waves such as those seen in shallow water. Transverse waves cause a disturbance in a medium perpendicular to the direction of the advancing wave. The crests and troughs in the wave reflect the wave’s amplitude, while the distance between two crests/troughs is indicative of the wavelength. Finally, the number of crests passing through a fixed point per second is known as the frequency of the wave.
And, longitudinal waves are the disturbance in a medium moving parallel to the direction of the wave; they are produced from the mechanical vibrations that originate from a series of compressions and rarefactions in that medium. Adaptive algorithms are designed to analyze the waveform of the background aural or non-aural noise, then based on the specific algorithm generate a signal that will either phase shift or invert the polarity of the original signal. This inverted signal is then amplified and a transducer creates a sound wave directly proportional to the amplitude of the original waveform, creating destructive interference. This effectively reduces the volume of the perceivable noise.
The microphone is placed inside the ear cup to detect whatever white noise makes its way past the passive canceling components. The special circuitry then senses the microphone’s input and generates a matching pattern of the noise from it. This pattern serves as a template for creating a new 180-degree reflection. The ensuing reverse-wave or anti-wave is fed through the headphone speaker simultaneous to the normal sound. The process of destructive interference is then initiated and the white noise is destroyed, leaving only the desired sound waves. Also worth mentioning is the fact that active-noise canceling headphones must rely on a rechargeable battery of some sort to power the ongoing operation.
To prevent higher-frequency noise from reaching the ear, most noise-canceling headphones depend on soundproofing. Higher-frequency sound has a shorter wavelength, and canceling this sound would require locating devices to detect and counteract it closer to the listener's eardrum than is currently technically feasible or would require digital algorithms that would complicate the headphone's electronics.
There are actually two types of noise-canceling headphones - Active and Passive.
Active Noise Cancellation (ANC)
Active noise cancellation is a sophisticated technology that can significantly reduce or eliminate unwanted external sounds. It involves the use of electronic components like microphones and speakers to counteract incoming noise. Here's how ANC works:
- Microphones: ANC headphones or earbuds are equipped with one or more built-in microphones. These microphones continuously pick up external sounds, including ambient noise and unwanted background chatter.
- Noise Analysis: The captured sound is then analyzed by an ANC circuit, which processes the incoming audio signals.
- Anti-Noise Generation: After analysis, the ANC circuit generates an "anti-noise" signal that is the exact opposite (inverted phase) of the incoming noise. This anti-noise signal is essentially a sound wave designed to cancel out the incoming noise.
- Speaker Playback: The anti-noise signal is played back through the headphones or earbuds' speakers, which are positioned close to the user's ears. As the anti-noise signal interacts with the incoming noise, they cancel each other out through a phenomenon called destructive interference.
- Result: The result is a quieter listening experience. The unwanted noise is effectively neutralized, providing the listener with a more peaceful and enjoyable environment.
Active Noise-Canceling Headphones
Active noise-canceling headphones are one step above the passive sort; they actively erase lower-frequency sound waves by creating their own sound waves to replicate the exact traits of incoming sound in all but one way, they are 180-degree reflections of intruding waves. This phenomenon, known as destructive interference, actually cancels out the incoming white noise and reduces sound by another 20 dB.
Destructive interference is accomplished by producing a wave with the same frequency and amplitude as the incoming wave, and arranging its crests and troughs, or compressions and rarefactions if you will, to mirror those of the incoming wave. This effectively cancels the white noise.
How do active Noise-Canceling headphones work?
Active noise-canceling refers to special circuitry inside headphones that tricks your ears into thinking there isn’t any sound around you.
Tiny microphones embedded within the headphones listen to ambient sounds in the outside world.
Electronics inside the headphones generate a sound wave that is 180° out of phase with the sounds around you, literally canceling them out. You enjoy an island of near silence, save for whatever music you decide to play through the headphones.
Passive Noise Cancellation
Passive noise cancellation, often referred to as noise isolation or noise reduction, doesn't involve any electronic components. Instead, it relies on the physical design and materials of the device to block or reduce external noise. Here are some common ways passive noise cancellation works:
- Earmuffs and Earplugs: These physical barriers create a seal around or in the ear canal, preventing external sounds from entering. They are simple but effective tools for reducing noise.
- Closed-Back Headphones: Closed-back headphones have sealed ear cups that enclose the ears, reducing the amount of sound that can pass through to the listener. This design provides a degree of passive noise cancellation.
- Soundproofing Materials: In architectural and industrial settings, soundproofing materials like dense walls, acoustic panels, and foam can absorb or deflect sound waves, reducing noise transmission.
While passive noise cancellation is valuable, it may not completely eliminate all unwanted sounds. For more robust noise reduction, active noise cancellation (ANC) technology comes into play.
Passive Noise-Canceling Headphones
Passive noise reduction initiates from the type of material used to construct the headphones and excels at dampening higher frequency sounds. Regardless, the majority of noise-canceling headphones provide passive reduction, as most are constructed with layers of sound-absorbing materials such as high-density foam. With that said, the most efficient passive noise-canceling headphones are circum-aural, or closed-back headphones that cup around the ear to form an airtight seal. Average noise reduction is about 15 to 20 decibels, significantly less than the 75 to 80 dB produced by a jet engine.
How do passive Noise-Canceling headphones work?
You won’t find any of the special electronics that live inside active noise-canceling headphones. Passive noise-canceling models are also called noise-isolating headphones. You’ll find these headphones as either - Closed-back, over-ear headphones that separate you from ambient noise, or in-ear headphones that form a tight seal to prevent sound from getting in and interrupting your music.
Benefits of Noise-Canceling Headphones
Noise-canceling headphones can not only enhance your listening experience in noisy environments such as offices, subway trains, or airplanes but also provide a silence devoid of noise altogether.
Noise-canceling headphones help create an environment that’s free from ambient noise and distractions - something that’s almost impossible to achieve under normal conditions.
High-quality noise-canceling headphones erase virtually all of disruptive noises. As a result, you can engage with your music and listening experience.
Noise-canceling headphones are perfect for anyone who wants to check out for a while and spend some quality alone time with their favorite tunes.
Challenges and Limitations
While active noise cancellation is highly effective, it does have limitations:
- Specific Frequencies: ANC works best for steady, repetitive noises like engine rumble or the hum of an air conditioner. It may be less effective against sudden, unpredictable sounds.
- Battery Usage: ANC devices require power to operate, which means they rely on batteries. Battery life can be a limiting factor, especially on wireless devices.
- Cost: Quality ANC technology can add to the cost of headphones or earbuds.
Noise cancellation, whether passive or active, has become a crucial tool in our quest for quiet in a noisy world. Passive methods rely on physical barriers, while active noise cancellation employs advanced technology to create a zone of tranquility amidst the chaos of noise pollution. As technology continues to advance, we can expect even more effective noise cancellation solutions that enhance our everyday experiences, from listening to music in peace to enjoying a quiet flight in a noisy world.