Weighting noise with the hearing curve of animals can have a large impact on regulation

What is it about?

Some types of underwater noise are so loud that it is important to protect wildlife from harm by mitigation measures, such as air bubble curtains. As these bubble curtains are not equally effective at all frequencies, but most often attenuate high frequencies more than low frequencies, it is important whether one factors the hearing of the animals in, when evaluating the effectivity of the bubble curtains. This is illustrated with noise from pile driving, where most of the energy is a low frequencies, well outside the best hearing of for example small dolphins and porpoises. This means that bubble curtains will lower the overall (broadband) noise level only little, but if focus is on the range of best hearing, the bubble curtain is much more effective.

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Why is it important?

In regulation of underwater noise from for example pile driving it is often desired to have maximum allowable exposure levels. However, as illustrated with the bubble curtain example, it is essential to specify whether these levels are weighted or unweighted, as this could mean the difference between complying with regulation and not complying.

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