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Noise Cancelling Headphones

I am regularly asked about whether noise cancelling headphones are necessary to help students with sensory processing difficulties concentrate more easily. My response is usually something along the lines of “probably not”. Let me explain…

Passive Noise Cancelling (Noise isolating)

Noise-cancelling headphones come in either active or passive types. Passive types are sometimes called ‘noise-isolating’ headphones. All headphones can provide some noise reduction because headphones cover or fit in ears and block out some sound waves, especially those at higher frequencies. The best passive noise-cancelling headphones either fit firmly within the ear canal or are packed with layers of sound-absorbing material and fit snugly all the way around the ears.

Active Noise Cancelling

Active noise-cancelling headphones add an extra level of noise reduction by actively erasing lower-frequency sound waves. They do this by creating their own sound waves that mimic the incoming noise in every respect except one: the headphone's sound waves are 180 degrees out of phase with the intruding waves.

This illustration shows how this works: The two waves have the same amplitude and frequency, but their crests and troughs are arranged so that the crests of one wave line up with the troughs of the other wave and vice versa. These two waves cancel each other out, a phenomenon known as destructive interference.

Several components are required to achieve this effect:

  • Microphone - this "listens" to external sounds
  • Noise-cancelling circuitry – Electronics sense the input from the microphone and generate a "fingerprint" of the noise. Then, they create a new wave that is 180 degrees out of phase with this noise.
  • Speaker - The "anti-sound" created by the noise-cancelling circuitry is fed into the headphones' speakers along with the normal audio to create the destructive interference.
  • Battery – to run the microphone, noise-cancelling circuitry and speaker (will require either charging or replacing)

The human factor

You might already have started to guess that all this means noise needs to be fairly predictable for the computer circuitry to produce the opposing sound wave. But there’s another complicating factor: current active noise cancelling technology works best for frequencies below 500 Hz and is somewhat effective only up to about 1000 Hz. Engine noise and traffic rumble are mostly below 500 Hz and so are greatly reduced or even completely eliminated through active noise cancelling. However, the important frequency range for understanding human speech only starts at around 500 Hz. The most important bands for speech intelligibility are 500 Hz, 1000 Hz, 2000 Hz, and 4000 Hz. Consequently, most active noise cancelling headphones do not block this noise at all and because the lower ambient noise is blocked, the voices can actually sound louder.

In the classroom

In classroom situations, active noise cancelling technology does not provide significant advantages and the costs are quite high (headphones start at around $250). Instead, consider looking for quality over-ear headphones with padding that will enable a comfortable snug fit around the ears. Also consider whether an in-line or boom microphone may be required.

Another option that could be considered is Bluetooth earmuffs. These will provide industrial level noise-isolation while still allowing the Bluetooth connected device to be heard. The downside is that these headphones are unlikely to have a microphone as well. Remember that Bluetooth devices need to be charged regularly (or have batteries replaced). They can also be quite a firm fit on the head and may not be sized for younger students.

As always, if you have any suggestions or questions, please don’t hesitate to get in touch.

Assistive Technology

Assistive Technology

Using technology to support students with disabilities and special learning needs.