Eloise Barber gives an overview of advances in the science of acoustics, from the seventeenth century to the present day.
Sound surrounds us, shaping our experiences, our playlists, and even our physical spaces. But have you ever wondered how our understanding of the nature of sound has developed?
Significant advances in acoustics were made in the seventeenth century, during the Scientific Revolution. One of the pivotal figures in this period was Robert Boyle, a Founder Fellow of the Royal Society, whose New experiments physico-mechanicall (1660) included a variety of experiments on pressure, magnetism, and – in ‘Experiment 27’ – the behaviour of sound in a vacuum.
Boyle suspended a watch by a piece of thread in the glass dome of his air pump (above), and then lowered the air pressure. He found that when the pressure was reduced, the sound of the ticking disappeared – one of the first recorded experiments on sound propagation.
Robert Hooke FRS, who assisted Boyle on his air pump experiments, carried out his own research into the nature of sound. He explored the behaviour of vibrating strings, demonstrating how changes in tension and length affect pitch. For example, he examined the vibrations of a violin string, noting that as the tension increased, the pitch rose, providing an early understanding of the relationship between tension, length, and frequency in stringed instruments. In a Royal Society meeting in 1681, Hooke demonstrated the sound made by a piece of card held to the edge of a rotating toothed wheel. As the speed of the cog increased, so did the pitch of the sound, demonstrating how pitch relates to frequency.
Hooke's work also foreshadowed later explorations in cymatics, the study of visible sound and vibration, where patterns emerge in granular materials or liquids when subjected to sound waves. His 1680 experiment, in which he ran a violin bow along the edge of glass plates covered in flour and the vibration caused the flour to move into different shapes, illustrated how sound and vibration can manifest visually. This in turn influenced the work of Ernst Chladni (sometimes called the ‘father of acoustics’) and his creation of that well-known phenomenon, Chladni figures:
Daniel Bernoulli FRS contributed to our understanding of sound with his research on fluid dynamics. In Hydrodynamica (1738), Bernoulli introduced the concept that sound waves are similar to waves in water, and outlined his famous principle stating that an increase in the speed of a fluid occurs simultaneously with a decrease in pressure. This principle can be seen in the production of sound in musical instruments like the flute, where air blown across the opening increases in speed, causing the pressure to drop and a sound wave to be produced.
The nineteenth century saw further advances, including the discoveries of John William Strutt, 3rd Baron Rayleigh FRS, whose Theory of sound (1877) is regarded as one of the most significant contributions to acoustics. In this comprehensive work, he explored sound waves in detail, including their reflection, refraction, and diffraction. For example, Rayleigh conducted experiments on resonance using tuning forks, demonstrating how they vibrate in harmony when placed at specific distances apart, producing louder sounds. This concept of resonance is essential in various fields, from engineering to music, influencing the design of concert halls and musical instruments to enhance sound quality.
Internet Archive Book Images, No restrictions, via Wikimedia Commons
In the twentieth century, the pioneering ultrasound work of Paul Langevin ForMemRS marked a significant leap in the application of sound science. Inspired by the need to detect underwater objects during World War I, Langevin developed a practical ultrasonic transducer by 1917. Using piezoelectric quartz crystals, he was able to generate high-frequency sound waves, beyond the range of human hearing, and study their propagation through different media.
Paul Langevin by Henri Manuel, CC BY 4.0, via Wikimedia Commons
Langevin’s experiments demonstrated how these ultrasonic waves could travel long distances underwater and reflect off solid objects, paving the way for sonar technology. This breakthrough revolutionised naval navigation and submarine detection and laid the groundwork for the later development of modern applications such as medical ultrasound imaging.
Today, the science of sound continues to evolve, fed by technological advances and interdisciplinary research. Modern studies encompass a wide range of topics, from psychoacoustics – how humans perceive sound – to medical diagnostics. From the foundational theories of sound propagation to contemporary applications in technology and medicine, the study of sound exemplifies the interconnectedness of science, engineering, and the arts, and continues to shape our cultural experiences.
Headline image: front cover of Wonders in acoustics; or, The phenomena of sound by Rodolphe Radau (1878 edition). RS.11832
