The noisy reef – key terms
Travel under the waves to the reefs of New Zealand to explore sound and noise – what sound is, how it travels, what changes under water and how animals use it.
This resource provides explanations of the key concepts encountered when exploring the noisy reef – the ‘basics’ that every student should understand.
Sound
Sound is a pressure wave that can travel through air, water or a solid. It requires a source, a medium and a receiver. The loudness of sound is measured in decibels (dB) while the pitch is measured in hertz (Hz). Sound travels faster and further through water than it does in air.
Hearing
Hearing is the process of detecting sound. Humans hear frequencies between 20 Hz and 20 kHz. Sound below this range is called infrasound and sound above this range is called ultrasound. Animals are able to detect sound at a range of frequencies both above and below the limits of human hearing.
Helmholtz resonator
Named after a German scientist, a Helmholtz resonator is a structure with a small neck or opening that is filled with fluid or air. Pressure fluctuations over the opening causes the fluid or air inside the structure to resonate, forming an audible sound, for example, blowing across the top of a bottle. Kina act as Helmholtz resonators. The shell of the kina acts as an amplifier of the sound that it makes while feeding.
Metamorphosis
Some animal species develop through several different larval body forms before reaching adulthood. Each transformation from one body form to another is referred to as metamorphosis. Crabs metamorphose through five different body forms before adopting the adult body shape.
Noise
Noise can refer to any unwanted or distracting sounds, for example, from a motor mower or jet aircraft. We talk of ‘road noise’ and often tell children not to be noisy. However, in science, the term ‘noise’ is used to describe sound that isn’t pure or melodic. Randomly combined sounds from many different sources are less pleasant to listen to. ‘White noise’ is a special kind of noise made up equally from every frequency in the audible hearing range and is heard as a sustained hissing sound. In terms of listening under water, what we mainly hear is noise – a jumbled mess of sounds with no repeating pattern or clear pure notes.
Reef
A reef is a strip of sand, rock or coral that lies just under the surface of the water. As light is able to reach this area, a reef often supports rich biodiversity. Reefs in New Zealand are home to many numbers of species, from fish to shellfish to seaweeds.
