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By Paul Power, Canford Technical Support Engineer

Our hearing is precious and very sensitive, we can hear very low level sounds to very high level sounds for example the dripping of a tap to the take-off of an aircraft. However, listening to loud music or being indirectly exposed to loud sounds for prolonged periods can damage your hearing and this can lead to permanent hearing damage.

Many people are now listening to music over headphones and a large amount of employees spend their working day either monitoring audio or taking calls utilising headphones and as a result can be spending large amounts of time unwittingly being exposed to high sound levels. In these circumstances users have to be conscious of the time period and sound level to avoid permanent hearing damage, although this can sometimes be difficult as there is no easy way to tell accurately how loud the audio is. Utilising a headphone limiter can be one way that the users can take measures to protect hearing and a way employers can ensure they are taking the management steps to protect workers from hearing damage.

In the UK the HSE provide guidelines which employers must follow to protect workers hearing, this can be found on their website along with tools and information about taking the necessary precautions to protect hearing. In short, the guidelines detail the upper and lower exposure levels, which include peak values and daily exposure levels. As an example a mobile phone used as a personal audio player is capable of delivering around 103dB to the ear drum at full volume, as a result after approximately seven minutes may cause irreversible hearing damage. Generally the daily threshold should not exceed 85dB for an eight hour continuous period, but exceeding this threshold will be dependent on several factors, most notably the time period of exposure and sound level.

At Canford we provide a unique headphone limiting service, this is an exacting service which requires specialist equipment in order to tailor the limiter to the headphone. There are retro fit limiters available on the market which can be added to headphones, however these have not been calibrated to work with a specific headphone, therefore there is no way of being certain that the limiter is working at the correct level. This is due to the fact that every headphone varies in electrical characteristics, as a result it is necessary to assess the headphone to determine if the limiting level required can be achieved. In short, this process involves fitting the limiter to the headphone then utilising specialist equipment that include an ear and cheek simulator which basically utilises a synthetic ear which mimics the shape and contour of the ear canal and pinna. The ear and cheek simulator is connected to a sound level meter and then using a test signal and application of correcting coefficients we are able to then tune the limiter and calibrate it to the limit level required.

Not all headphone models requested by the customer have to go through the initial assessment stage since we have a vast headphone database of previous headphones that we have assessed, this includes a large variety headphones from in ear headphones to headphones for audio monitoring and communication systems, although the limiter still has to be properly calibrated to the specified level. The limiter circuits used are passive and do not require batteries to work, therefore you can always be certain that they are engaged, in addition the only time they will affect the audio is when they are in limit.

Utilising headphones fitted with properly calibrated limiters ensures that users are taking the steps to protect their hearing from damaging sound levels and from an employer’s perspective that they are taking the necessary precautions to manage and ensure the health and safety of their employees and comply with legislation.

Find more detail on Level Limited Headphone here.

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