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Improved ear defenders enable selective hearing

Improved ear defenders enable selective hearing
NPL's acoustic and materials experts were involved in a large European project to design novel ear-defender technology to prevent noise-induced hearing loss. The project known as Piezoselex ('Piezo Pair Materials for the Selective Exclusion of Workplace Noise') was funded by Europe's Framework 7 programme.

The challenge

Many people will be familiar with the 'ringing' in one's ears after leaving a noisy environment such as a factory, nightclub, or concert. Where people are exposed to noise levels in excess of 80 dB, many experience noise-induced hearing loss (NIHL).

There are various ways of protecting your ears (e.g. various in-ear plugs, or external ear defenders), but many of them involved cutting down all sound frequencies before they reach your ear drum. This becomes a problem when, for example, a fire alarm goes off - if you are wearing traditional ear plugs/defenders you may not hear the alarm over the ambient noise. The same is true of other 'helpful' sounds, such as speech. So the first challenge was to design technology that would block harmful noise, but allow helpful sounds through.

The second challenge in this project was to make the device small and comfortable to wear, as one of the main hurdles to protecting people's hearing is persuading them to wear protection in the first place. That is, despite EU legislation that requires employers to provide ear protection for their staff, many people choose not to use them - believing them to be inconvenient, bulky, and ineffective.

The solution

The Piezoselex project aimed to design a new battery-less ear defender device no bigger than a standard in-ear plug, that would block out the noisy din that damages your hearing whilst still allowing you to hear certain frequencies of sound (such as alarms and speech).

How does it work?

The prototype ear defender uses piezoelectric material to cut down the noise level reaching your ear drum to a safe level (under 75 dB).

Piezoelectric materials are simply materials that take a vibration, in this case vibration due to sound, and convert it into an electric signal. This type of material was chosen for this project for two reasons:

1. It enables the ear defenders to power themselves, and therefore require no batteries.
2. It allows 'signal processing' of the incoming noise, and therefore filtering of helpful sound frequencies (e.g. speech, alarms).

NPL's main role in this project was the initial design, systems modelling, and selection of the most appropriate piezoelectric material. NPL also established the method that would ultimately allow the device to be tuned so that speech and alarms could be heard.

The impact

The device is at prototype stage, but once it reaches the market as a finished product it is expected that it could have the following impact:
  • Increased productivity due to easier communication between staff
  • Reduction in the risk of NIHL
  • Contribute to a more comfortable work environment
  • Reduction in employee absenteeism due to increased wearer comfort and a reduction in NIHL
  • Create a safer working environment as warning signals will be easier to hear




Provided by National Physical Laboratory