How 'loud' is underwater noise compared with air noise?

摘要

This article is based on a presentation made at the IOA 40th Anniversary Conference held in Birmingham in October 2014, but now with much additional material contributed by Magnus Wahlberg. The concept of "loudness" involves psychoacoustic questions, which need to be answered by the creature involved. Most creatures including humans are ill equipped to compare noise underwater with that in air, but evolutionary forces will have optimised the performance of amphibians in both media. What does the seal feel? These issues are now of increasing interest to the general public, but in the absence of guidance, comparisons are made using sound pressure levels of sources often at unspecified distances. "A dolphin is as loud as a jet engine" we are told, with no indication that this may be contentious.