If you’re a commuter or want to listen to music in public, noise cancelling headphones are the best update you can make. Many people feel that spending more money would bring them greater sound quality, but this is only half true: noise that could dominate your music must also be prevented from reaching your ears.
Many firms have tried their hand at active noise cancelling (ANC) headphones, and a handful have gotten so excellent at it that it’s one of their wireless headphones‘ key selling points. However, how do noise-cancelling headphones function? What’s the deal with it being so cool?
Active noise cancellation’s physics
Active noise reduction technology works by utilising a physics phenomenon known as phase cancellation. Sound travels in waves, which move the air molecules, as you surely know. These waves pass through the air and into your ear canal, causing your eardrum to vibrate. When a sound wave hits another sound wave with the same frequency but opposite amplitude, the two sound waves substantially cancel each other out.
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Consider the air molecules to represent a string between two places. If someone pressed down on the string directly in the middle, the string would be disturbed, generating a ripple. If you pressed on one side of the string while someone else pressed on the opposite side of the string in the exact same area with the exact same force, the string would scarcely move. Although this image may not accurately depict how sound waves work, it does help you see how a wave is effectively cancelled out when it is matched in phase with its opposite.
Active noise-cancelling headphones process sound directed at your ears using tiny microphones on the inside (and sometimes outside) of the earcups and immediately play the opposite phase of that sound through the headphone drivers. The opposing forces successfully decrease the movement of air molecules, resulting in a reduction in audible sound. Again, this is a simplified explanation, but it is the underlying notion that all modern ANC headphone designs are based on.
This sort of active noise cancellation is particularly effective at lower frequencies of sound, between 50 Hz and 1 kHz, in general. (If you want to hear what 1 kHz sounds like, check out this video.) This is partly due to the fact that lower frequencies produce longer waveforms that are easier to align. You’re also more likely to get feedback at higher frequencies if the waveforms don’t line up perfectly. As a result, most active noise-cancelling headphones experience a considerable drop in usefulness around 1 kHz.
This is why ANC headphones are better suited for minimising low, continuous sounds like motors and jet engines, but they can’t filter out crying children. (Researchers have told us that there are ANC concepts in the works that would do a better job with higher frequencies, but that technology is still a few years away.)
How do your headphones block out noise from the outer world?
Outside noise is blocked by your headphones thanks to a physics trick known as “anti-phase.” The notion is simple but extremely tough to master.
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When two similar waves are stacked on top of each other, their peaks and troughs line up, the two waves are said to be “in-phase,” resulting in a larger wave (louder sound). What if you delay one of the waves by exactly one-half wavelength, aligning the troughs with the peaks of the other, as shown in the diagram below?
As the positive pressures of one wave act against the negative pressures of the other, the two waves are said to be “out of phase” and subtract from one another. Consider it as though you were trying to add and remove one. You’re left with nothing. This is the fundamental mechanics of active noise cancellation.
Let’s see what your noise-cancelling headphones can do?
You might have pondered noise-canceling headphones to put an end to the never-ending conflict between your headphones and outside noises. They assist protect your hearing by blocking out background noise and allowing you to lower the level of your music or podcast. However, they aren’t always the best option; read on to find out why.
Noise-canceling headphones come in two varieties that can protect your hearing in two different ways.
Passive noise-canceling (PNC) headphones are soundproofing headphones with a heavy-duty design that isolates your ears from outside noise. PNC headphones are often tight-fitting and heavy, but they are good at drowning out sound, especially explosive transient sounds like gunshots and firecrackers, as well as high-frequency sounds like a baby crying or a dog howling.
To “eliminate” external sounds, active noise-canceling (ANC) headphones use sound-matching technology. They work by detecting the pitch of adjacent ambient sound, such as the whir of a jet engine or the collective hum of a crowded coffee shop; they work best in environments where the overall sound and level remain consistent.
ANC headphones require some “settling” time to measure sound waves before producing 180-degree out-of-phase neutralising sound waves.
Is it true that noise-canceling headphones protect your hearing?
Yes, noise-canceling headphones do, for the most part, protect your ears from both active and passive noise.
PNC headphones preserve your hearing by isolating your ears from harsh external sounds, especially transitory sounds like gunshots or explosions. People who work in noisy environments but need to communicate, such as pilots or construction workers running heavy machinery, can benefit from PNC headphones.
Because they limit the volume at which you listen to music through headphones, ANC headphones preserve your hearing to some extent. The cells of small sensory hairs in your inner ear, which assist send auditory information to your brain, are damaged by loud music. The lower the volume, the less likely those cells will be damaged.
However, because ANC headphones rely only on the ANC function and do not provide the protective sealing that PNC headphones do, they will not shield you from sudden, explosive sounds. In all cases, a pair of headphones with a PNC structure and ANC technology would provide the best protection.
It’s time to see what your noise-cancelling headphones can’t do?
Headphones with Noise Cancellation don’t block voices.
No matter which noise-cancelling headphones you buy – from the costliest to the cheapest – they won’t totally eliminate some noises. Voices, for example. Try them on and turn on the noise-cancellation without turning on the music if you know someone who has a pair. You’ll examine that you can still hear everything that’s going on around you. Those haphazard noises could even seem exaggerated.
It’s understandable that you’d be perplexed as to why you’d pay for noise-cancelling headphones if they don’t block out conversations. Unfortunately, no technology exists at this time that can block out random sound waves, such as those generated by a close conversation or a crying infant.
Why can you hear voices even if you’re wearing noise-cancelling headphones? It’s simply that simple. When frequencies are below 500Hz, the technique performs admirably. For sounds up to 1000Hz, it is reasonably (but not completely) effective. The sounds of engines and the rumbling of the bus or subway train during your commute are usually below 500Hz (save for the random honking of horns). This is why active noise-cancelling headphones can effectively eliminate or considerably reduce them to the point where you won’t notice them at all.
Conversations, on the other hand, begin at roughly 500Hz. It all relies on how close someone is talking to you, how loud they are speaking, the pitch of their voice, and a variety of other factors. As a result, the frequency of a conversation could range from 500Hz to 4000Hz. Active noise cancellation technology can’t help you with noises that are higher than 1000Hz. Even with the best, top-of-the-line brands, this is true.
Perhaps this might change in the near future, but for now, no technology can stop you from hearing Janice’s hyena-laugh from across the office.
You can see the difference in Hz between noise cancellation and passive isolation if you look at a graph that compares the two. When using active noise cancellation at 1000 Hz, you may notice that you can hear the annoying sound whether you have it turned on or not. It could be even worse.
The good news is that you can get noise-cancelling headphones that include ANC (active noise cancellation) and noise-isolation technology, which will definitely help you block out Janice’s cackles. It may undoubtedly assist you in finding serenity in any noisy area, toning it down so you can effectively tune it out, with ear cups closing and isolating your ears.
Active noise-cancelling headphones with passive sound isolation are your best bet for blocking out conversations (and cackles). Perhaps this has nothing to do with the electronics in these headphones, but it will serve as an additional layer to drown out unpleasant background noise.