Sound: 13.7 billion years ago

Sound has its origin far back in time, not long after the disappointingly silent Big Bang. In fact, sound waves formed as soon as there was a medium for them, which was 300,000 years after the beginning of everything, and thirteen billion years before there was anyone to listen.

The primordial sound was of a very low frequency, but powerful and omnipresent, and it formed when the plasma of the newborn universe arranged itself in pseudo-regular patterns through space. Galaxies eventually formed in the denser regions, including the progenitor of the world we live on and the sun we orbit.

Moving on a few billion years to the first days of Earth (about4.6 billion years ago), there were sounds aplenty, passing through the solid planet’s crust and its subsurface liquid areas, and bouncing and bending through its atmosphere. Eventually, the hot land cooled, rains fell, and oceans formed—oceans full of sound. So, the environment in which the first living things evolved was an acoustically rich one, which profoundly affected the forms, habits, and destinies of those creatures.

Hearing: 500 million years ago

For us, there is a clear distinction between hearing and feeling, but it’s a very different matter for undersea creatures: sounds pass as easily through their bodies as vibrations do through ours, and, in fish, are detected by structures called neuromats, which are distributed over their body surface (fish have several other hearing structures too).

Neuromats contain hair cells similar to those in our ears and provide their owner with information about the strengths and directions of local sounds. They evolved perhaps 500 million years ago. To detect airborne sound, eardrums and cochleae are essential, and hence evolved once amphibians began to colonize the land, around 400 million years ago. Communication was probably the main spur to the evolution of hearing, since sounds have overwhelming advantages over visual signals: while the ability to make lights and change colours exists in some marine organisms, putting on a light show is far more challenging and narrower in range than making noise. Noises are made easily—as easily as breathing. In humans, breath-made sounds (precisely controlled by our big brains) gave us the power of speech.

Music: 40,000 years ago

The appreciation of music is a mysterious pleasure and an ancient one too: over 40,000 years ago Neanderthals probably had flutes and, by the time Homo sapiens emerged, no well-appointed cave dwelling was complete without a rock gong. It may be that the first humans sang; perhaps even before speech evolved. But why? Enjoying music has no obvious evolutionary advantage. Darwin himself was baffled, but suggested that a taste for music might arise through sounds made in mating rituals, and many echo this view today. Others, however, prefer the suggestion of evolutionary psychologist Steven Pinker that music is an auditory equivalent of cheesecake, which we enjoy not because that preference assisted our ancestors in surviving, but because many of the sensations cheesecake elicits are of evolutionary value in themselves: the sweetness of fruit announces its ripeness and creamy flavours suggest energy-rich fats. Or perhaps music reminds us of birdsong—the presence of which indicates that no large predators are around.

Harmony: 2,500 years ago

Today, sound plays a huge variety of roles in our lives. Many of our inventions are dedicated to its creation, transmission, storage, modification, or reproduction. But the conquest of sound is by no means a recent development: some of the most ancient artefacts we know are musical instruments, and acoustics was one of the first sciences; in 500 bce or so, Pythagoras discovered that the sound made by a strummed string mingles pleasantly with one made when the string’s length is halved. The ‘distance’ between the two sounds is an octave, by definition and by universal agreement the most harmonious of all pairs of different notes. Sounds almost as harmonious result if the string lengths bear other simple numerical ratios: if one string is one-and-a-half times the other, a fifth is produced, for example.

According to legend, Pythagoras made this discovery when he heard tuneful hammer sounds emerging from a forge where a number of blacksmiths were at work. When (being a budding scientist) he weighed the hammers they were using, he found that those pairs which made a pleasant sound had weights which were simple multiples of each other. The fact that this story is told to this day is surprising given that the frequency at which a hammer sounds is not fixed by its weight. Whatever actually piqued his interest, the instrument Pythagoras used to study harmony was the monochord—a device with a single string whose length can be set by a moveable bridge.

To Pythagoras, the fact that the pleasantness of sounds was defined through whole-number ratios suggested that numbers were the key to the universe. ‘All’, so he is supposed to have said, ‘is number’. Today’s scientists would agree, and, in its impact on scientific method, mathematics, music making, and acoustics, his discovery may be one of the greatest breakthroughs of all.

Although anyone who makes or plays a stringed instrument knows that tension, as well as length, affects the note a string makes (otherwise turning pegs to tune stringed instruments wouldn’t work), this was not quantified until the 16th century by Vincenzo Galileo, father of the scientist, who showed that pitch increases with the square root of the tension. We now know that it also depends on the string’s thickness and density.

The Greeks were interested in the practicalities of sound, thanks to their keen interest in making their voices heard: plays, orations, declamations, debates, songs, chants, and proclamations abounded. Perhaps their greatest acoustic structure is the theatre of Epidaurus, built in the 4th century bce. The distance from stage centre to the back row is about 60 metres, yet actors can be heard clearly from any of the 1,400 seats: fifty-five rows in total. It is in these seats that the theatre’s acoustic secret lies: the limestone of which they are made, their corrugated surfaces, and the spaces between them all contribute to absorbing sub-500 Hz frequencies and reflecting higher ones, quietening crowd murmur and enhancing performances respectively.

But there are disadvantages to open air speech, even in Epidaurus. With no ceiling to contain the sound, speakers must be very loud indeed, which is not only tiring but also tends to rob the voice of its subtlety. (Despite legends to the contrary, the Greeks lacked megaphones, which were not invented until the 1670s—simultaneously by Athanasius Kircher in Germany and Samuel Morland in England.) Background noise becomes far more intrusive too, though in the Greek theatres performance days would have been quiet, since the majority of the local population would be in the theatre.

Indoor public spaces solved these problems but introduced new ones: echo and reverberation. For an echo to be an echo, it must be heard more than about 1/20 of a second after the sound itself. If heard before that, the ear responds as if to a single, louder, sound. Thus 1/20 second is the auditory equivalent to the 1/5 of a second that our eyes need to see a changing thing as two separate images. (Hence, when camera frames move faster than this, we obtain the illusion of flowing movement. This ‘persistence of vision’ is what makes us see the rapid sequence of still images that make up a cinema film as a smoothly changing image.)

Since airborne sounds travel about 10 metres in 1/20 second, rooms larger than this (in any dimension) are echo chambers waiting to happen. Luckily echo can be reduced by covering hard surfaces with soft, fabric-covered objects, such as audience members.

There is of course more to sound than science or entertainment. Even wordless sounds come freighted with meaning, much of which was attached in prehistoric times. The lonely howl of the wind, a shocking scream of pain, the joyous songs of birds, the happiness of children’s laughter: in these and many other cases, evolution has forged unbreakable links between sound and emotion. These emotional attachments have been exploited by us since ancient times: war cries, for example, have long been produced both to chill the blood of the enemy and to unite and rouse the courage of the attackers.

The modern world: acoustics and more

Following the work of the ancient Greeks, little research on the nature of sound was carried out until the 17th century, when Robert Hooke proved by simple demonstrations that frequency and pitch are linked. Although Isaac Newton suggested an equation for the velocity of sound, it was incorrect, and an accurate version was only derived by Pierre Simon Laplace in

1816. Laplace showed that, to an excellent approximation, the velocity of sound depends only on the density and the elasticity of the medium through which it passes (Box 1).

Box 1

The invention of the first electroacoustic devices in the mid-19th century led to revolutions in both the understanding and the control of sound: the microphone, telephone, and loudspeaker appeared in quick succession, spurring rapid developments in research, commerce, and the arts.

The 20th century and electronic engineering began together, with the inventions of the diode (the first rectifier, used initially for detecting radio signals) in 1903 and the triode (the first amplifier) in 1906. The development of electronics was greatly accelerated by the World Wars, which also led to the birth of underwater acoustics research through interest in submarine warfare and ship detection.

While the existence of sounds with frequencies too high to hear had occasionally been discussed in the 19th century, they were only investigated in the context of the upper frequency limit of human hearing. Even though such sounds could be made easily by sparks, whistles, air jets, or piezoelectric crystals, they remained of little interest until World War I, when it was realized that they might be pressed into service as part of what we would now call sonar systems. Soon after the war, further investigations revealed that such sounds had a range of unique properties, not all of which could be explained: they could kill living things, cause chemical changes, generate light and heat, and make wood explode in showers of sparks. It may be that they were called supersounds in part because of their strange powers. Although far less famous than X-rays and radium emanations, supersounds soon gained a similar reputation as secret forces wrested from nature by the tools of science, but still retaining a glamour of almost supernatural mystery and power.

It was the middle of the 20th century before the power of ultrasound was properly understood and exploited. By then,the use of amplifiable electroacoustic technology had truly transformed the world. Public speakers, formerly limited to audiences of a couple of thousand at the very most by the sounds of their voices and the sizes of their venues, could now talk to people in their millions, thousands of miles away—either instantaneously or a day or a century later. Life could be captured, recorded, and analysed as never before.

There were whole new fields too, including sound art; an ill-defined discipline with origins in the futurist movement of the 1900s to 1930s, and in the development of electronic music and good recording technology. Luigi Russolo’s Gran Concerto Futuristico (1917) is an important early example, and a recent one is Lowlands by Susan Philipsz, a set of variations on a lament played over one another, which won the Turner Prize in 2010.A related area is ambient music (often called muzak by its detractors), which is designed to provide an appropriate background to public spaces. Brian Eno’s Ambient 1: Music for Airports (1978) is a good example, and saccharine carols looped endlessly in supermarkets (accompanied by gloomy employees forced to dress as elves) is a bad one.

Ambient music is an example of an artificial soundscape, a concept popularized by Murray Schafer, who helped set up the World Soundscape Project in Vancouver in the late 1960s. The project led in turn to the formation of the World Forum for Acoustic Ecology in 1993. Schafer has been highly influential, in part through his galvanizing claim that acoustic environments can not only reveal the social conditions of those who inhabit them, but even predict how that society will evolve.

Applying Schafer’s approach, economist and polymath Jacques Attali argues that changes in musical convention prefigure wider changes in society. Some have gone much farther than this; historian Alain Corbin argues that village bell ringing in 18th- and 19th-century French villages moulded social and economic relations there, and artist and writer Brandon Labelle says that ‘my feeling is that an entire history and culture can be found within a single sound’.

More generally, the concept of the soundscape has enjoyed great popularity in a range of disciplines, though Schafer’s definition of the term has been extended to take account of the relative and dynamic nature of an acoustic environment: technology historian Emily Thompson points out that it is ‘simultaneously a physical environment and a way of perceiving that environment’.

In film, the construction of artificial soundscapes is achieved partly through sound effects. These have also been a mainstay of radio drama since its inception and, in the form of artificial thunder for example, have been heard in theatres since ancient Greece. In films, the craft of designing, producing, and synchronizing sound effects with events on screen is known as Foley.

No longer dependent on our ears to detect sounds or on voices and mechanical devices to make them, we can study and use sounds too low pitched, high pitched, or quiet to hear, and we can generate and direct acoustic beams with enormous power and precision, leading to applications in medicine, defence, mapping, and many other fields. Since World War II, serious attempts have been made to develop sound-based weapons, mainly by producing and directing extremely high-intensity beams. Perhaps the best-known example in current use is the Long Range Acoustic Device (LRAD), which projects either commands or unpleasant sounds. It has been used against humans and wildlife in several countries.

Alongside the deliberate and controlled development of sound, noise pollution has also spread through much of the world. The highly sensitive hearing systems that served our ancestors so well, and still allow our pleasure in music and our facility in speech, are now the conduits of annoyance, stress, and damage.

So while we have gained mastery of the production of sound, we are far from being able to control it. In order to have any chance of doing so, we need to understand its nature.