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What is isolation?

Why is acoustic isolation so important to your listening experience?
By
November 4, 2020

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 acoustic isolation most often means better-sounding music.

Editor’s note: this article was updated on November 4, 2021, for changes to wording and to add a contents menu.

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. As an example, 70dB is 10 times as powerful as 60dB, but roughly twice as “loud.” Similarly, a decrease of 10dB is a halving of loudness, a decrease 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’re listening to music eight hours a day, NIOSH recommends you keep 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 as we age, they don’t grow back. 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:

  • 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.

  • Block out noise

This is the preferred solution because there’s no amount of noise reduction that is ever really “too much.” 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.

  • Cancel noise

Noise-isolating headphones are fairly bad at blocking out low-end sounds like rumbles and hums, but active noise cancelling headsets can kill constant tones with destructive interference, something called anti-noise. While it doesn’t work as well on transient, incidental noises, active noise cancelling (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 isolation: outside noise impacts the audio quality of the sound that reaches your ear.

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

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

An illustration of the human cochlea.
This is your cochlea, responsible for determining what sounds you hear.

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.

Related: Why do your headphones sound bad?

This has strange, but predictable consequences for your music. Outside noise has the tendency to mask out some notes but not others, and subtle sounds like string attack 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 would be masked by the music itself, 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 to fight this? Because increasing the volume to an unsafe level in order to mask out the offending noise will lead to hearing loss, that’s not an option. If you’re going to 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! 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 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 find out how well a given set of headphones blocks out noise, because most product specifications are somewhat 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 dependant.

To demonstrate, we rigged up a dummy head to get the 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. Note: noise cancellation and isolation aren’t the same thing—and it’s important to know the difference.

The reason is that active noise cancelling works best on constant, easily processed sounds by pumping out what’s called anti-noise. For incidental noise like a crash, footsteps, or car horn, acoustic isolation provides attenuation—incidental noise is blocked out just the same as constant sounds.

See: Why you should buy noise cancelling headphones

However, isolation is hard to achieve because of so many different factors. Are the ear pads properly sealed to your head? What materials are used? Are the headphones fully enclosed? Even if everything is perfect, sometimes ANC can be far more effective. 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-ears. Not only will they always fit, but they’ll block out a bit more noise than the silicon tips (excepting 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 cancelling headphones outside.
The AKG N60NC is one of few good on-ear ANC headsets, but it’s not widely available anymore.

On-ears 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.

What are the best headphones for kids?

For kids, you’re going to want to check out our list of 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.

Next: The best noise cancelling earbuds