5 Sound and hearing

The substance that a wave travels through is known as the medium, so for a sound wave in air the air is the medium. The frequency of a sound affects how far it can travel through different media. In general, longer wavelength (low frequency) waves travel further than shorter wavelength (high frequency) waves because there is less energy transferred to the medium at these frequencies. For example, a frequency of 10 kHz could travel a few km in seawater but very low frequencies can travel for thousands of km – interestingly, lower frequencies are the ones that the large species whales use to communicate.

The song of a humpback whale (Megaptera novaeangliae) consists of waves of many different frequencies – if you listen carefully to Audio 1.1 (Humpback Whales Songs Sounds Vocalizations, 2008) you may be able to hear the lowest frequency, which will travel the furthest underwater.

Marine mammals such as the bottlenose dolphin generate higher frequency waves for another purpose – echolocation – as explained in the next section.