The importance of sound to science
Sound can be produced by biological and non-biological sources (Natural Sounds, 2023). And how sound is perceived by the senses of a living thing, helps it to gather information, communicate and survive within its environment. Even when there are no living things present, sounds are still produced.
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The science of sound
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The field of science that specializes in sound is called acoustics, and an acoustician (a researcher who specializes in sound) studies mechanical waves, which refers to an oscillation of matter in a medium, such as, solids, liquids, and gases (Sound, 2023).
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Sound studies
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Scientists use sound to study the environment and there are two separate fields of acoustic ecology: ecoaccoustics studies sounds the environment produces while, bioacoustics, focuses on the calls of specific wildlife species (Acoustic Ecology, 2023). There are three categories in ecoaccoustics: anthropophony (noise made by human activity), biophony (wildlife calls), and geophony (surf, wind, fire, and rain) (Acoustic Ecology, 2023, Soundscape Ecology, 2023).
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How does sound travel?
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Sound energy is produced, when a force or pressure, causes a substance or an object to vibrate. The molecules in the media – gas, solid or liquid – don’t move, instead a molecule starts to vibrate, and the energy from its vibrations will cause the next molecule to vibrate, and so on. Sound waves can travel over long distances (Britannica, 2023) but if there is nothing for the molecules to vibrate in, then sound energy cannot travel (Sound, 2023). The speed of sound depends on the type of media (gas, solid or liquid) and the temperature (NASA, 2023, Speed Of Sound, 2023).
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When you listen to a chorus of birds in the morning or late afternoon, this is how bird song reaches your ears. The bird produces sound when air flows into its syrinx, or vocal cords, and the membrane of the syrinx starts to vibrate. Muscles in the bird’s throat control the tension of the membrane and openings in the bronchi, which work to modulate the sound the bird produces (Syrinx, Bird Anatomy, 2023). The sound wave travels from the bird through the air molecules to your ears, where the energy from the wave vibrates your ear drum or tympanic membrane (Syrinx, Bird Anatomy, 2023). The vibration is processed by the middle ear, and cochlea, and converted into an electric signal that is carried by the auditory nerve to the brain, where it is translated into a sound we understand (NIDCH, 2023).
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Hearing ranges
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The range of hearing possessed by living organisms varies. Humans can hear within the range of 20 – 20,000 hertz (Hz), cats can hear frequencies from 55 Hz up to 79 kHz, while some bat species have acute hearing of up to 200 kHz. (NASA, 2023). Sounds are important to ecologists who use it to assess the health of the environment or wildlife communities, for example, migratory patterns of whales, a community of fish in a coral reef habitat, or how manmade sounds might impact wildlife behavior, for example, infrastructure development or highway traffic noise (Acoustic Ecology, 2023).
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Soundscapes
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Scientists use a mathematical formula to convert sound waves into a spectrogram, a visual reference made up of spectral indices that represent acoustic energy recorded in a study area, also referred to as a soundscape (Towsey et al., 2018). The calls of frogs, insects, and birds are sound marks or acoustic signatures and used like landmarks to ‘navigate’ through the soundscape to find answers to specific ecological questions (Ecologists Wild on Sound, 2018). For example, using a spectrogram, an acoustician can uncover the sounds of cryptic species by locating the calls made by an animal that shares a mutual relationship with it (Ecologists Wild on Sound, 2018). Another advantage to using spectrograms is researchers save time in listening to recordings of a particular bird call or frog chirping. In addition, some wildlife calls occur at a frequency that is not within human hearing range, so by referring to a spectrogram, the scientist doesn’t miss any information and can locate the wildlife call visually.
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Can sound travel in space?
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There are sounds in space, but they are electromagnetic waves. Unlike sound waves, which are mechanical, they don’t need a medium to travel in (Britannica, 2023). At the National Aeronautics and Space Administration (NASA) scientists have developed technology that records the electromagnetic vibrations planets produce, including Earth, and have translated these recordings into audible sounds humans can hear (Wisdom Land, 2023). For example, sounds from Jupiter, interstellar space (Wisdom Land, 2023), or the storms lashing the surface of the planet Mars (Science ABC, 2023).
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Conclusion
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Through the study of soundscapes, scientists are learning more about ecosystem interactions and human activity, data that is informing projects aimed at conserving and improving the health of the planet Earth for the future (Soundscape Ecology, 2023). Learn more about how researchers use sound to study the environment in Ecologists Wild On Sound or understand the evolution of sounds produced by a fish species trapped in a dark, subterranean environment in The Sounds Cavefish Make.
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Written by Gabrielle Ahern,
