Hearing Protection
EN 352 Part 1 Ear Muffs
EN 352 Part 2 Ear Plugs
EN 352 Part 3 Helmet mounted ear muffs
EN 352 Part 4 Level Dependent (amplitude sensitive) ear muffs
Noise is measured in decibels, this is abbreviated as db. Decibels are quoted in a logarithmic scale and an increase of 3 decibels is equivalent to doubling the level – 88 decibels is twice the level of 85, and 85 is twice 82.
Generally sound is measured using two scales: “loudness” is measured in decibels (Db) and the pitch or frequency is measured in Hertz (Hz). As humans we do not hear sound as it actually is. We amplify certain frequencies and attenuate others (a good example of this is a dog whistle, we cannot hear it but a dog can). Consequently a noise level is often denoted as dBA, ie. decibels as they are, then A weighted to reflect sound as humans perceive it.
The effectiveness of a hearing protector can be gauged at different frequencies by referring to the attenuation data for that product. This chart includes a range of frequencies. The average, or mean, attenuation is based on a sampling of people involved in the testing. The average is made up of both low and high (to recognise, and allow for, worst case scenarios The standard deviation is subtracted from the mean attenuation to give what is called the “assumed protection”. This is the level of protection that you can assume the hearing defender will offer when correctly fitted.
SNR (SINGLE NUMBER RATING)
SNR (Single Number Rating) is a European Union rating system. The test results serve as a guideline to indicate the amount of potential protection a hearing device can provide. It is only a general means of comparing different hearing protectors. Normally, the higher the SNR number the better the performance of the ear protector across a range of noise frequencies. For example, a SNR of 30 may not give a 30 decibel attenuation at all frequencies. The additional figures associated – H, M and L – indicate the level of protection within the range of High, Medium or Low frequency noise.
Examples: For the wearer of an ear muff where H=35, a high frequency noise of 100 decibels will drop to 65 decibels. Wearing the same ear muff, where M = 25, a medium frequency noise of 100 decibels will drop to 75 decibels.
For some applications, a more detailed breakdown of the character of the noise is needed in order to select the correct ear muff. For this purpose, attenuation tables are quoted alongside each of our ear protection products in our Head, Eye & Ear Safetywear catalogue.