0845 680 0312
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0845 680 0312
Email
0845 680 0312
Email
These calculators estimate the sound level at the ear when wearing hearing protection. The noise must be measured using a suitable sound level meter and the details of the hearing protectors in questions must be available too. Our calculators support four methods.
Check with your noise regulations to see which methods can be used. The HML and Octave Band methods are the most accurate, but also the most time consuming. For very high noise levels we recommend the Octave Band method.
NRR Method - You need an "A" or "C" weighted sound level meter and the protector's NRR figure.
SNR Method - You need a "C" weighted sound level meter and the protector's SNR figure.
HML Method - You need the "A" and "C" weighted sound level and the protector's HML figures.
Octave Band Method - You need a meter with Octave Band Filters and the hearing protector's APV values.
The NRR (Noise Reduction Rating) method is the easiest way to assess a hearing protector's performance. It isn't as accurate as the HML or Octave Band methods, but easier to use. You need to measure the "A" or "C" weighted sound level and you need to know the NRR figure for the hearing protector in question.
This NRR calculator follows the US OSHA method.
To calculate the level at the ear, first measure the worker's noise exposure, either in dB(A) or dB(C). This level can be entered into the calculator along with the NRR figure, which is usually displayed on the protector's box.
The OSHA NRR method is as follows:
| Weighting | Calculation |
| A | Lprot = L - (NRR -7) / 2 |
| C | Lprod = L - NRR / 2 |
Where:
L is the measured level or TWA.
NRR is the Noise Reduction Rating provided by the hearing protector manufacturer.
Lprot is the estimated sound level at the ear when wearing the hearing protection.
The SNR method is very simple, as long as you can measure the "C" weighted sound level. The HML and Octave Band methods are more accurate and recommended if the noise levels are high.
This calculator provides the assumed level at the ear to ISO 4869-2:1995.
To calculate the level at the ear, enter the measured C weighted sound level along with the protector's SNR value, which should be marked on the protector packaging or associated paperwork.
Some regulations, such as those used in the UK and some other parts of the EU, recommend adding 4dB to the calculated level to take account of real-world issues, such as poor hearing protector fitting.
This is one of the more accurate methods, and recommended if you have A and C weighted sound level along with the protector's H, M and L figures. It takes into account some of the frequency content of the noise as the H, M and L figures are related to the High, Medium and Low frequencies.
The HML figures should be available on the hearing protector's packaging or associated paperwork.
Some regulations, such as those used in the UK and some other parts of the EU, recommend adding 4dB to the calculated level to take account of real-world issues, such as poor hearing protector fitting.
This is the most accurate of the hearing protector assessment methods. To use it you need a sound level meter capable of measuring in the octave bands, in this case 63 Hz to 8 kHz as the lower and higher bands that are often available are not used. You also need the octave band assumed protection values for the hearing protector. This will usually be on the packaging or associated paperwork.
Octave Band Hearing Protector Method
First measure the noise close to where the person is working using the meter's octave band filters. There should be no additional filtering, as the calculator takes into account the A weighting curve.
After entering each octave band measurement and the hearing protector's assumed protection values you should see the calculated level at the ear in dB.
Some regulations, such as those used in the UK and some other parts of the EU, recommend adding 4dB to the calculated level to take account of real-world issues, such as poor hearing protector fitting.
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