Why You Want Noise Cancelling
Sounds are vibrations that travel through the air in waves. When multiple sound waves overlap, they can obscure or amplify one another. It's called auditory masking, and it's why you might feel the urge to crank up the volume when you're listening to your favorite music in loud environments. That, friends, is bad for your ears.
One way to avoid blasting out your ears is to buy a pair of noise cancelling headphones. Since they can block much of the background noise that interferes with your music, show, or podcast, you'll be able to keep the volume at safer levels. Conventional wisdom is that it should stay at or below 70 decibels, or roughly the sound of a casual conversation. Noise cancelling headphones (NCHs) also help you hear the nuances of every note, making your favorite music sound the way it's meant to be heard.
Keeping your ears healthy and creating an ideal listening environment aren't the only benefits of noise cancelling technology. For people who are easily stressed out by noisy environments, like an airplane in flight, they can also offer a calming effect. Some workers find that noise cancelling headphones calm the mind and increase focus during and after the workday, as Digital Trends reports. (Many of our staffers heartily agree.) The article cites a 2016 study that NCHs can help autistic children deal with stressful sounds and another indicating that they reduce the pain and anxiety of patients undergoing a painful procedure.
In this article, we'll explain noise cancelling technology and help you understand the key factors to consider when choosing the right pair of earbuds or over-the-ear headphones for your needs.
How Sound Works
A waveform is a graph that charts time on the horizontal x-axis and amplitude on the vertical y-axis. Amplitude is measured in hertz (Hz), or the number of waves that pass each second. We use waveforms to visualize sound waves. The height (amplitude) and length (frequency) of those waves impact how our ears interpret them. Taller waves have more amplitude, or more space between the height of the peak and the trough, and sound louder. Longer waves have lower frequencies (i.e. they roll in less frequently) and register as bass notes. Short, high frequency waves, and register as high pitched treble notes.
When multiple sound waves share space, the sound you will hear depends on how the peaks and descents of each waveform align and combine — a process known as additive synthesis.
As we explained, each wave is made up of a peak and a trough, just like in the ocean. If the peaks of two sound waves align, they will combine and grow taller and louder. For example, if both peaks have an amplitude of 1 Hz, they will sound twice as loud. Sound waves that peak at the same time and have the same frequency have the same phase. If the peak of one wave aligns with the trough of another, they are out of phase by 180 degrees. In that case, the +1 of the peak and the -1 of the trough combine to equal zero.
How Noise Cancelling Works
Noise cancelling headphones and earbuds have microphones that record the ambient sounds around you, then an internal processor creates the inverse sound and plays it through the speakers, along with your music or show. Viola, the external noise is canceled, mostly. In reality, it's often just minimized. Here, we'll dive into the details so you can understand the subtleties to help you make decisions about the type of noise cancelling you need.
There are two elements that dampen external sounds when you're using headphones — active and passive noise cancellation. The process discussed above is active noise cancellation; passive noise cancellation means physically blocking sound waves. All headphones accomplish this to an extent simply because they create a barrier between your ear and the external world.
How well your headphones and earbuds create a good seal around or in your ear makes an enormous difference in how well they isolate sound. If your earbuds come with multiple silicone fittings, be sure to take the time to find a good fit. Try each one, asking if it's better or worse than the last. It shouldn't be so tight that it's uncomfortable or so loose that it feels insecure. Play your favorite song and turn on fan in the background, which fit softens the sound of the fan the best?
Passive noise isolation is best at blocking higher frequency or higher pitch sounds. Low, rumbling noises like a bus or airplane engine often make their way through. Luckily, those consistent, low-frequency sounds are the easiest for active noise cancelling technology to filter out.
What Creates the Best Noise Cancellation?
The best noise cancelling earbuds and headphones take advantage of both passive noise isolation and active noise cancelling. It also matters how they cancel noise, which is largely a factor of where the microphone that records ambient sounds is placed.
Some microphones are located outside of the ear cup. This is known as feedforward ANC. Since it captures sound before it's muffled by the headphones themselves, this method excels at blocking middle frequencies, like conversation and traffic, but struggles to mask noises like the wind.
In contrast, microphones placed inside the ear cup, known as feedback ANC, record ambient noise as you hear it, after it passes through the initial noise cancellation of the headphones themselves. This helps them improve noise cancellation accuracy, but they can still struggle to cancel out higher frequency noises.
The best noise cancelling headphones are hybrids of these two technologies, offering you the best of both worlds. The only downside is that hybrid ANC tends to be more expensive.
How Frequencies Factor Into ANC
To summarize, a solid seal around or in your ear will help your headphones or earbuds passively isolate your ear from high pitched noises. Active noise cancelling works best at lower frequencies, those below 2,000 Hz, though hybrid ANC technology can increase their optimal range.
The other factor to consider is how consistent or erratic surrounding sounds are. Steady sounds, like the drone of an airplane engine, are easier for ANC to mask. In contrast, sounds like people talking, office noise, or a piano playing change constantly, making it harder for noise cancelling headphones to create an inverse soundwave in real time. That's why it's important to have excellent passive isolation as well, to muffle those tones.
How We Calculate Noise Cancellation
We test earbuds for both the passive isolation and active noise cancelling capabilities of each set of headphones and earbuds we review. Both tests employ our Brüel & Kjaer Type 5128 Head Simulator, Darwin and it's connected SoundCheck software.
To test active noise cancellation, we play pink noise for Darwin. Pink noise is a type of static that plays all frequencies at a known volume. First, we play it without the earbuds or headphones to get baseline data. Then, we see how much the headphones or earbuds block passively before turning on the active noise cancelling mode for the models that offer it.
We repeat the same tests while playing cafe recordings, which include the hum of conversation and clatter of plates and silverware. The high-pitched clinging sounds are among the hardest background noises for the headphones and earbuds to filter out.
After all that, we chart the data that SoundCheck provides, as in the results of the tests shown below. The red line represents the control, with no noise cancellation. The blue line shows how much noise the active cancellation and passive isolation are able to block together.
In the noise cancelling graph below you can see that the red line sometimes overtakes the blue in the higher frequencies. That is where passive isolation is doing the heavy lifting. Some of the earbuds we test do not offer active noise cancelling. For these, we just test their passive isolation.
Listen to the video below to see just how difficult it is for ANC to block out higher frequencies.
Transparency and Background Modes
Some noise cancelling headphones let you turn off the active noise cancelling feature, allowing background sound to come through as it would with normal headphones. This is known as background mode. Some versions also include a transparency mode, which uses the headphone's microphones to pump outside noise into your ears through the speakers. This is useful to break through particularly impressive passive noise cancellation barriers.
Conclusion
Noise-cancelling headphones aren't without trade-offs. They're more expensive than traditional headphones, and noise-cancelling features also drain battery life. If you're worried about maintaining your battery, be sure to get a model that lets you turn off the ANC feature to preserve it.
Once you use a really good pair of active noise cancelling headphones though, it's hard to go back. We prefer even subpar versions to traditional options. By removing distractions, they can create incredibly immersive entertainment experiences. There is nothing quite like sitting down in the back of a plane and hitting play on your favorite movie as the engine roar fades away.
