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What is noise isolation?

Why is acoustic isolation so important to your listening experience?

Published onFebruary 2, 2024

Growing up, I was the kid who always had headphones on. Riding the bus, studying, working out: if it wasn’t absolutely necessary for me to be talking to other people, I was listening to music on my giant Koss headphones. My parents rolled their eyes and tried to get me to wear smaller, more “fashionable” models, but those just ended up on my shelf because they never sounded as good. It was hard to describe why I loved large headphones so much then, but I know now the reason is that better noise isolation most often means better-sounding music.

Editor’s note: this article was updated on February 26, 2024, to update information surrounding hearing loss.

What are decibels?

When we talk about sound levels, we talk in terms of decibels (dB). Like our hearing, the dB scale is logarithmic, so every increase of 10dB represents an increase in sound pressure by a power of 10 and an increase of perceived loudness by roughly a factor of two. For example, 70dB is ten times as powerful as 60dB but roughly twice as “loud.” Similarly, a decrease of 10dB is a halving of loudness; a reduction of 20dB will mean the sound is only one-quarter as loud, and so on.

A digital drawing of how noise-induced hearing loss impacts the ears. The one on the left shows how sound travels into the ear and the right is a close-up fo the middle and inner ears.
Noise-induced hearing loss is usually a result of damage to the stereocilia, which are located in the organ of the Corti. This organ rests inside the cochlea.

Even when connected to your smartphone, some headphones can output sound levels of over 115dB(SPL), so it’s important to limit the volume to avoid hearing loss. But what level is considered safe changes depending on how long you expose your ears to a certain sound pressure. If you listen to music eight hours a day, NIOSH recommends keeping your levels below 85dB(SPL). However, casual listeners who only listen for 45 minutes or less can feel free to crank their tunes a bit louder.

Your inner ear is a lot more delicate than you might realize: it is extremely easy to damage your hearing with loud music. Our ears are made up of a lot of parts, but we have an exceptionally weak link in the chain: teeny-tiny hairs inside our cochleas. If those tiny hairs bend, break, or fall out, our ears can’t send signals to our brains to interpret as sound. While they do that anyway, they don’t grow back as we age. Ever. Once the damage is done, it’s done.

How do you limit noise exposure and keep the volume down?

Electra volume limiting headphones on a wooden desktop
Some headsets come with a built-in volume limiter, but it doesn’t always work with cheaper headsets.

So, if you’re trying to limit your exposure to high levels of noise, there are a few strategies you can employ:

  1. Avoid noise: This sounds a little navel-gazey, but if you can avoid loud noises, you should do so. A study in 2012 concluded that you should listen to your music below 50% of your smartphone or MP3 player’s volume slider, and that’s a fairly good benchmark. Beyond that, you tend to stray into territory where your tunes might be a little too loud with typical headphones. If you need to crank your tunes up past that, it’s a good idea to figure out what needs to change—unless the problem is a lack of output power.
  2. Block out noise: This is the preferred solution because it directly addresses the problem of being in the presence of noise. By physically blocking out sound, you make every other strategy you use to dispel noise much more effective. This is the main strategy employed in many workplaces with noisy environments.
  3. Cancel noise: Noise-isolating headphones are fairly bad at blocking out low-end sounds like rumbles and hums, but active noise canceling headsets can kill constant tones with destructive interference, something called anti-noise. Active noise canceling (ANC) uses sound to effectively cancel out loud, droning sounds extremely well.

But even if you’re not worried about noise-induced hearing loss (you should be), there’s another reason you should care about noise isolation: outside noise impacts the audio quality of the sound that reaches your ear.

Why is noise isolation the most important factor for music quality?

Our biology is complex, but we don’t have microphones for ears or a computer for the brain. Instead, we have meat, bones, and nerve tissue that are very imperfect.

While that’s not necessarily a problem, it does mean that we, as humans, have a few shortcomings that we can’t overcome. Namely, we experience a phenomenon called auditory masking. Exactly how this works in totality is quite complex, but the long and short of it is: if there is a loud sound present (a “masker”), weaker sounds similar in frequency will be “masked” out. Ever struggle to hear someone over a vacuum cleaner or have to yell over music at a party? The same factors are at play there.

This has strange but predictable consequences for your music. Outside noise tends to mask out some notes but not others, and subtle sounds, like string attacks and whispers, will not be audible in the presence of louder sounds. Additionally, many more sounds will be quieter than you’re expecting. It’s something that is happening all the time, whether or not you’re aware of it, because our brains and biology simply can’t work in a way that would avoid it. Heck, that’s even how MP3 compression works: an algorithm deletes all the sound that the music itself would mask, and nearly every listener is none the wiser.

A chart demonstrating auditory masking.
Wikipedia If your music’s notes are quieter than the masking threshold of outside noise, they’ll be near-inaudible.

So, how do we fight this? Increasing the volume to an unsafe level to mask the offending noise will lead to hearing loss, so that’s not an option. If you listen to music on a commute or in a noisy area, isolation is the most important factor for music quality because of how much of your music will be masked by noise otherwise. All the high bitrates, accurate headphones, or enhancements in the world can’t overcome your biology (yet), so ridding ourselves of outside noise is the most effective way to improve your audio quality in those places.

But now that you know what the problem is, you can address it! There is no need to destroy your hearing with constant exposure to dangerous levels: we’re here to help.

How do we measure attenuation?

A hand holds one of the Apple AirPods (3rd generation) to the ear of a head simulator.
We use a Bruel & Kjaer 5128 to perform noise isolation and frequency response tests, as seen with the Apple AirPods (3rd generation).

Acoustic isolation can also be considered a measurement of how well the headphone attenuates (the opposite of amplifies) the ambient noise around you. It’s hard to determine how well a given set of headphones blocks out noise because most product specifications are vague. You may find that the headphones you’re looking at offer a “30dB noise reduction,” but that number doesn’t tell the whole story. While it implies that a set of headphones reduces all outside noise by that level, that’s not the case: headphones don’t attenuate all noise frequencies equally because their acoustic isolation properties will be frequency dependent.

To demonstrate, we rigged up a dummy head to get some measurement data. By recording a noise test signal played over a speaker (once with headphones off the head, once with headphones on), we can get an idea of what sounds are blocked and which aren’t.

Like so:

While we cover the more in-depth strokes in the open vs closed-back headphones article, it’s pretty clear to see with these charts just how much better closed-back headphones are at blocking noise. Adding noise canceling on top of that can also attenuate a huge amount of unwanted noise from the outside world, and the difference is extremely noticeable.

The reason is that active noise canceling works best on constant, easily processed sounds by pumping out what’s called anti-noise or destructive interference. Essentially, using the inverse of the sound’s pressure wave to destroy the noise’s amplitude. That doesn’t mean it can’t attenuate incidental noise or irregular sounds, but it’s possible that those may still get through depending on a few common issues that can’t always be controlled.

For example, are the ear pads sealed adequately to your head? What materials are used? Are the headphones fully enclosed? For best results, combining passive isolation and active noise cancellation will stop the most noise.

Which headphones offer the best noise isolation?

A picture of the Etymotic ER3XR in-ear studio monitors on a notebook.
In-ears like the Etymotic ER3XR are extremely good at blocking outside noise.

If you’re in the market for headphones to use in noisy places, you’ll want to find a set that blocks out a bunch of noise through isolation, for starters. If you want to throw in ANC on top of that, even better: the more noise you get rid of, the less it will affect your listening, and the lower your volume needs to be when you rock out. This means that open-back headphones shouldn’t even be considered for places like an airplane: you only want closed-back cans if you’re looking at over-ears.

Earphones are the best at blocking out noise

Great in-ears are the best isolators on the market because they seal your ear canal… when they fit correctly. Getting a proper fit can take a bit of finagling, and because everyone has a differently-shaped ear canal. We always recommend using memory foam ear-tips for in-ear. Not only will they always fit, but they’ll block out a bit more noise than the silicon tips (except Etymotic’s Christmas tree tips). If your in-ears don’t come with them in the box, you can grab some tips from a company called Comply that will fit your in-ears for only a few bucks. Just be sure to use its sizing chart first so you don’t get the wrong ones.

On-ear headphones aren’t great at isolating you from the environment

A man wears the AKG N60NC on-ear noise canceling headphones outside.
The AKG N60NC is one of few good on-ear ANC headsets, but it’s not widely available anymore.

On-ear headphones are out because they don’t seal your entire ear: by resting on your pinna, sound can still get past the headphones fairly easily—either through the gap between the speaker and your ear or through your ear’s cartilage into your middle/inner ear. Over ears go completely around your ear, meaning that more noise is blocked depending on the headphones you get. But because no headphones will fit everyone the same way, we always suggest going out to brick-and-mortar stores so you can try them out for yourself. The better the fit, the better they’ll isolate.

Over-ears are also great with ANC

Because over-ears have a lot more room to play with when cramming in microphones and processors, they often have very good ANC performance if they have it. Not only is it easier to get more electronics into a large casing, but it’s also generally easier to provide more power to the ANC unit when your headphones are rocking a giant battery in comparison to those dinky little true wireless ones that fit in your ear. Many of the top-flight ANC headphones out there have cellphone-sized batteries, a couple of orders of magnitude more powerful than those found in in-ears.

What are the best headphones for kids?

For kids, you’re going to want to check out our guide to headphones designed for young ears. Because hearing damage is permanent and young kiddos are super sensitive to sound, listening to music at high volumes can have seriously negative consequences. If your children want headphones, please take the time to talk to them about safe listening habits so they don’t have to suffer from tinnitus.

Can you block out too much noise?

A growing worry about noise isolation and its impacts on hearing health has emerged in the last ten years, and it’s worth paying attention to. Though short-term wearing of hearing protection is beneficial, constant, interminable use of hearing protection has been observed to cause tinnitus.

The primary mechanism of this tinnitus is caused by your brain trying to hear the sounds that your headphones are blocking out. Essentially, it overcompensates by attempting to be more sensitive to the sounds, which then leads to the perception of tinnitus. Because headphones and earplugs mainly block out noise above 1kHz, that is the range you have to worry about.

If you’re worried about this phenomenon, don’t: it’s very easy to avoid:

  1. Don’t wear headphones or earplugs for extreme amounts of time without music playing
  2. Don’t fall asleep with earplugs in unless you’re in the presence of noise
  3. Don’t work in an anechoic chamber for long periods of time

See? Not so tough.

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