Experience The Difference
The principle of Active Noise Reduction (ANR) has been known for a long time, but its application to real situations is often complex and raises numerous difficulties. It consists of cancelling an undesirable noise by superposing an inverse noise, which results in the destructive interference of the pressure waves. Sound is driven by the propagation of a pressure wave. It is possible to cancel this wave by adding its opposite.

First of all, the creation of an opposite sound requires the use of at least one noise source (loud-speaker). Sensors (microphones) are also needed to gather information about the acoustic field. The characteristics of the sources and sensors are closely related to the application concerned. Finally, the heart of noise control is an electronic system (analogue or digital), which generates the cancelling noise, which will interfere with the undesirable noise. With ANR headsets this process takes place either within an enclosed eardefender or under a more open type foam pad of a lightweight headset. Both these environments have a major effect on the ANR and its performance. With open types the ANR will only offer a small reduction in noise as it can only cancel the noise in its immediate environment above the ear which is surrounded by high ambient noise. A lightweight ANR headset does offer some noise reduction (see manufacturer’s claims) but this is unlikely to amount to the reduction offered by a good passive ear defender headset but may be more comfortable for prolonged use.

ANR eardefender headsets have the advantage of first reducing the ambient noise by approximately 20dB and then operating in the stable conditions within the earshell to often add another 10dB of attenuation.

Please be careful - the human ear is not good at measuring sound levels - an ANR headset with a poor eardefender will sound like it is working well (we call it ‘’the wow factor’’) when it is turned on as there is lots of noise getting through the eardefender for it to cancel. But if measured the resulting actual noise level at the ear is still noisier than a good passive eardefender. An ANR in a good passive shell may not sound so dramatic when turned on but if measured will be making a significant reduction in addition to the reduction of the passive shell resulting in a much lower noise level at the ear.

In our experience it is almost always better to buy a good quality ANR headset from a quality manufacturer, as they will have spent a lot of time and money setting up the ANR to provide optimum attenuation. We really would not recommend the ‘’do it your self to your own headset’’ ANR kits as although the ANR may work perfectly well, its installation into a standard headset as a front baffle often loses most of the passive attenuation of the original headset. The result we have often measured in our workshop is that the modified headset with the ANR on is noisier than the original headset with no ANR fitted!