How Do Different Noise Cancelling Headphones Work?
| Reuben Howe
Noise Cancelling Headphones and Earbuds have been around the block a few times now, and over the years the technology has branched in to separate, entirely different types of Noise Cancellation!
Learn the 3 types of noise cancellation, what they do, and how they work all in one place before exploring the best noise cancellation options for your personal use.
What are Noise Cancelling Headphones?
Most simply noise cancellation is technology that reduces or stops noises from being heard. Now, this has some caveats. For example, noise cancellation will target audio of specific characteristics. You can filter certain frequencies or volumes electronically, or reduce all outside noise physically via engineering. No matter how they achieve it, noise cancelling headphones always reduce or remove background noises from either yourself as the wearer or in some cases the recipient of phone calls from the headset.
Noise cancelling reduces or removes certain frequencies and amplitude from the sound waves around you. This is actually far simpler than it sounds! Removing sound waves of certain frequencies is the same as removing sounds based on their pitch. For example, removing high-pitched whining or low, thrumming droning noises.
Removing or reducing sound waves of certain amplitudes is the same as lowering their volume. For example, removing low-level chatter or traffic noise below a certain volume.
The Types of Noise Reduction
There are many different ways in which headphones and earphones can go about achieving that same goal of noise reduction. Some ways use the idea of frequencies and amplitudes to create a digital or electronic solution while others are more tangible and simpler. The three types of noise reduction are:
Passive Noise Reduction from Headphones and Earphones
The most basic way to reduce and cancel noise is Passive Noise Reduction. This describes the passive (Ongoing) noise reduction that happens naturally as a consequence of wearing the devices in the first place!
It makes sense that covering your ears makes the sound around you quieter and less likely to be heard, and that’s exactly why headphones and earphones have Passive Noise Reduction.
Headphones have a high degree of passive noise reduction through the soft, thickly padded earpads. This padding is for comfort, but also much harder for sound waves to propagate (Move) through than air. Essentially, the padding stops outside noises from reaching you, or at least exhausts the waves of energy which lowers the amplitude / volume.
Earphones perform similarly, but generally with less dramatic results. While the silicone tips of earbuds do block the ear well, reducing the chance of any sound waves reaching your oscillatory bones, a headphone earpad has much more space to work with and so passive noise reduction tends to be higher in headphones.
Passive Noise Reduction can be amplified by smart physical design and engineering, like using very sound-resistant materials for the earpads or using silicone tips that entirely fit the ear. No electronics of software is at play, the reduction is purely physical.
How Do Active Noise Cancelling Headphones Work?
No that we understand simple Passive noise reduction, what about Active noise reduction? As the name implies, Active noise reduction / cancellation takes a much more hands-on approach than simply blocking sound from getting in your ear.
Active Noise Cancellation (Often just called ANC) uses microphones built in to the headset to “hear” the sounds around you. After the sound is “heard”, the headset can produce a counter-tone which exactly cancels-out the original noise! Let’s break that down a little:
You wear your ANC headphones, with ANC mode on. Power is provided to one or more microphones inside the headset.
You are working near a busy road and there’s traffic droning. This noise is filling the air around you and reaching your ears. But, because you have ANC on, the microphones are also picking up that noise.
The microphones take the frequency (pitch) and match it. They take the amplitude of the wave and reverse it!
This new sound, created using the background noise, is played through your headphones alongside the music.
The new sound wave perfectly counters the background noise heard by the microphone. The waves line up (From having the same frequency) but cancel out (From having opposite amplitude) so in the best-case scenario will leave no sound wave left!
The only sound wave remaining to reach your ears is your music, call, audiobook etc!
Active noise cancelling runs this process constantly while enabled, meaning background noises like walking near traffic, airplane engine thrumming or even sitting in front of a desk fan in this heat will all be picked up in real time. The ANC is reactive and electronic so doesn’t require manual calibration.
How Does DSP Noise and Echo Reduction Work?
We have seen Passive and Active noise reduction, which are dedicated to making your listening experience as a wearer as pure as possible. However, people make phone calls and attend meetings with these headphones and earphones! So, there is an off-shoot of noise reduction dedicated to making calls crisp and clear: DSP Echo and Noise Reduction.
DSP Noise and Echo reduction works using the same principle as ANC, explained above. However, DSP is entirely “digital” and works within the closed audio system itself.
To understand this, look at the journey the sound wave took:
Passive Noise Reduction interrupted the wave in the air around you.
Active Noise Reduction interrupted the wave between your headset and your ear itself.
DSP Noise and Echo Reduction interrupts the waves once they’re already digitised!
You can see how each stage aims for the same goal, just at different times. So, DSP takes the signal sent across your microphone wire or wireless connection and prunes the unwanted frequencies by inversing them just like ANC. The resulting audio has only the clear voice capture and none of the background noise which has been cancelled out in transit!
Choosing the Best Noise Cancellation for You
Understanding these three types of noise reduction and how they work can help make the best decision about your headphones.
The Best Budget Noise Cancellation is Passive Noise Cancellation.
The cancellation is a product of the device construction and requires no extra power or electronics so remains the cheapest option as seen in these budget headphones with extra over-ear padding.
The Best Travel Noise Cancellation is Active Noise Cancellation.
This provides the best moment-to-moment noise reduction for constant noises like airplane engines (Make sure you have an airplane headphone adapter!).
The Best Phone Call Noise Cancellation is DSP Noise and Echo Reduction.
Because this reduction operates digitally in transit from your microphone to the recipient, it is the only way to make the other member of the call benefit from your noise cancellation. The best Bluetooth Earbuds for Calls with always use DSP or other digital noise pruning.