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# Examples

## Highest Sound Level in Air under Normal Circumstances

What is the highest sound level value that one might theoretically encounter in air? Let’s first go back to the definition of a sound level. It is clear that to find the maximum sound pressure level value, one has to find out what the highest variation of sound pressure might be. This variation occurs around the mean atmospheric pressure (1.01325 x 105 Pa) and cannot be negative, so we have &pmax = 1.0 1 325 x 105 Pa, which corresponds to Lpmax = 194 dB.

Let’s first consider two pieces of equipment, with each of them singly generating 50 dB(A) at a workstation. When both are operating simultaneously, the resulting sound level value will be 53 dB(A).

Let’s now consider two pieces of equipment with the noisier one generating 70 dB(A) at a workstation and the other one 50 dB(A). When both are operating simultaneously, the resulting sound level value is 70 dB(A).

Note: This has a consequence when attempting noise reduction. If you do not work on the highest contributing noise source, you will have trouble making any progress.

Let’s complicate things a bit further by considering 400 pieces of equipment, with each of them singly generating 50 dB(A) at a workstation, and a larger one generating 70 dB(A) at the same workstation. When all of them are operating simultaneously, the resulting sound level value will be 77 dB(A). If the major contributor is heavily treated to the extent it is no longer significant (meaning at least a 30 dB reduction, which will sure be costly!), the resulting sound level will still be 76 dB(A).

Note: This also has a consequence when attempting noise reduction. If you do not work out all the contributions from noise sources, you will have trouble making any progress. In this particular case, most people will acknowledge the highest contributor as 20 dB over the other noise sources will be easily noticed. However, when eventually adding all the smaller contributions, they turn out to be overwhelming to such an extent that treating the noisiest piece of equipment will not bring any significant numeric improvement.

## Equivalent Sound Level

Let’s consider a situation where a piece of equipment is generating noise. There are three phases of operation with respective durations of 5, 10, and 45 min and corresponding sound level values of 90, 80, and 70 dB(A). The equivalent sound level over 1 h will be 80 dB(A).

Let’s now consider a situation where several pieces of equipment are generating noise at a given workstation. There are two phases of operation with respective durations of 5 and 15 min and corresponding sound level values of 100 and 80 dB(A). The equivalent sound level over 1 h will be 94 dB(A). Let’s now suppose that due to noise control reduction measures, the 80 dB(A) value over 15 min has now been reduced to 50 dB(A) over 15 min. The equivalent sound level over 1 h will still be 94 dB(A).

Note: This has a consequence when attempting noise reduction. There will not be any improvement as long as the noisiest contributor has not been properly treated.

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