| Sine waves (in fact, anything that centers around a small frequency range in the mids and highs) is most damaging because it reaches the ear's receptor cells without interference and full power. In broadband noise all those frequencies come at once, so none is nearly as loud as when being heard seperately.
The ear also seems to be able to "learn" to accept more noise without getting permanent damage by being permanently exposed to moderately loud background noise over a longer period of time: In a recent study in China people living in urban areas proved to have siginificantly better hearing than country population. One explanation seemed to be the city's noise floor making people less vunarable to harmful firework noise on New Year's Eve, a protection the country people did not have. |