be heard in loud surroundings.

A human is capable of hearing (and usefully discerning) anything from a quiet murmur in a soundproofed room to the loudest heavy metal concert. Such a difference can exceed 100 dB which represents a factor of 100,000 in amplitude and a factor of 10,000,000,000 in power. The dynamic range of human hearing is roughly 140 dB, varying with frequency,