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By Julian Nettlefold, Editor BATTLESPACE

In 1993 an EU (European Union) proposal for a Physical Agents Directive was made, which looked to establish a framework for the regulation of physical agents at work applying initially to noise, vibration, optical radiation and non-optical electromagnetic fields. This Directive has particular relevance to Defence Ministries world-wide, given the high level of noise from armoured vehicles and artillery in particular. Given the methodology of waging war, a time reduction for exposure to high levels of noise is of course impossible; thus companies like Racal Acoustics and SELEX communications, Davies Communications Division in the UK, ELNO in France and Bose in the USA are working on new Active Noise Reduction Headset systems. In addition these headsets are now being developed with digital rather than conventional analogue technology, a technology leap that has proved to be a challenge. BATTLESPACE Editor, Julian Nettlefold visited Racal Acoustics at its London site to find out about this new technology.

After political agreement on the Vibration Directive in November 2000, the Swedish Presidency introduced a proposal for a Noise Directive in January 2001. This would repeal the existing 1986 Noise Directive (86/188/EEC) which was implemented in the UK by the Noise at Work Regulations 1989 and in the other European Union Countries around the same time.

What will the changes be?

A quick summary of the changes are:
The 1st and 2nd Action Levels will be reduced by 5dB(A) to 80dB(A) and 85dB(A) respectively.
The Peak Action Level of 140dB(C) will be replaced with 1st and 2nd Peak Action Levels of 135dB(C) and 137dB(C) Peak respectively.
A Maximum Exposure Level Limit of 87dB(A) and 140dB(C) Peak at the ear will be introduced which includes any hearing protection.

The Directive was formally adopted in November 2002 which will allow members of the European Union three years to bring in the new Directive as Legislation. When the new regulations are introduced in 2005, they will repeal any existing Noise at Work Regulations. This means that current regulations can continue until November or December 2005.

The new regulations will affect all countries that are members of the
European Union in November 2002. All member states will have 3 years to implement the new regulations. New members of the European Union will be required to implement the regulations as soon as possible after they become full members. The European Directive can be used as a minimum requirement and member countries may implement different regulations as long as the minimum requirements are met.

Active Noise Reduction Headphone Systems

Noise cancellation headphones (NCHs) supplement the acoustic isolation characteristic of headphones with active noise reduction. By their nature, headphones block out some degree of external noise because the earcups absorb it, but NCHs go a step further and diminish the noise that manages to get through. In industrial settings, NCHs protect the hearing of workers exposed to deafening levels of sound on a daily basis. In the field of communications, they can enhance the intelligibility of speech. NCHs come in a variety of styles: circumaural, supra-aural and in-ear. In principle, all NCHs counteract noise by generating “anti-noise” to nullify it. However, noise cancellation technologies vary in sophistication.

Noise reduction devices that are more advanced than simple earmuffs or earplugs go back many decades to the first half of the 20th century. The use of headphones in combination with electronic methods to handle noise emerged in the 1960s and 1970s. They first appeared as noise filtering headphones (figure 1), in which the electronics are bandpass filters and audio limiters that reduce noise by stripping the high and low frequencies in the audio

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