The Sound Book: The Science of the Sonic Wonders of the World

by Trevor Cox

  When you come out to a place like this, where it is very quiet and you can hear the echo and imagine what the ancient people were thinking, there is something hypnotic about it, and it really reaches into certain areas of the brain and the soul, and you hear these ancient voices.38

  This is Steven Waller describing the experience of visiting outdoor ancient rock art. Waller believes that many people miss a trick when visiting prehistoric sites. Not only should we test the sound close to the paintings by clapping, yelling, or singing, but we also need to step back to search for acoustic effects. Stand back from examples in Australia, for instance, and the effect is “almost spooky,” he says. “Where they’ve drawn a person, and you yell at it, it’s like the person is speaking to you.”39 A similar effect is heard at Indian Hill, near San Diego, where sound repeatedly echoes from a cave entrance “as if the rock is calling out . . . and spirits were speaking back, right from the place where they chose to decorate.”40 To get these effects, the sound reflecting from the wall or cave must be heard separately from the sound going directly from your throat to your ear. And this happens only if you stand back from the surface so that the reflections are delayed. “Unfortunately, most people walk right up to a painting and study it from inches away, talking in hushed voices,” says Waller. “They never step back and see, or hear, the forest for the trees.”41

  I’ve found rock art difficult to explore as a sonic tourist because many sites have restrictive access to preserve the paintings and some sites have been altered. I was hoping to see if there was an echo at L’Abri du Cap Blanc in France, which is a stunning frieze of prehistoric sculptures carved into a rock shelter. But I was dismayed to have my sonic explorations thwarted by the building that had been constructed to protect the frieze from the elements.42 One thing that can endanger sonic wonders is well-meaning conservation that considers only the visual to be important.

  Waller carried out statistical analysis of Horseshoe Canyon in Utah and Hieroglyphic Canyon in Arizona. The latter is in the Superstition Mountains on the edge of Phoenix, and when I was in the US for the Great Stalacpipe Organ, I took the opportunity to visit it. I set off at sunrise to avoid the worst heat of the day (it peaked at 41°C, 106°F, that day) and admired the stately saguaro cacti dotted over the hillside as I hiked up the 2.4-kilometer (1.5-mile) trail to the Native American rock engravings. The petroglyphs are in a canyon, etched into rocks just above where a stream normally flows (it had dried up when I was there in June). Thousand-year-old geometric shapes—lines of sheep and deer drawn by the ancient Hohokam people—intermingle with more recent graffiti etched by vandals.43

  Not long after I arrived, I was joined by a large, friendly family whose parents had somehow managed to get their children out of bed very early. Unable to make any acoustic measurements, I sat back and listened to the family playing and exploring the space. As the children yelled, a distinct echo reflecting from the U-shaped mountains could be heard. As they ran about the canyon close to the engravings, their footsteps and high-pitched voices were colored by the reflections from the semi-enclosed rocks. But these effects were not just restricted to the area around the engravings; plenty of unadorned spots had a similar acoustic.

  The heat was debilitating, even in the shade. I could not help thinking that however interesting the acoustics are in the canyon, the presence of water must have made this place significant to the Hohokam. The only archaeological study into the canyon that I’ve been able to find says the spring was a natural place for the artwork because that is where sheep would have gathered to drink.44

  At Horseshoe Canyon in Utah, the Great Gallery contains particularly fine, often ghostly figures, some of which are even life-sized. These were described by Polly Schaafsma as “dark, tapering, immobile anthropomorphic form[s], painted in dark red pigment . . . hovering in rows against a sandstone backdrop within arched alcoves and rock-shelter.”45 Along the canyon, the four sites where the echoes are strongest are those where the paintings are found; Waller’s statistical analysis shows that the probability that this co-occurrence arose by chance is one in 10,000.46 Places with no echoes and good rocks to paint on are not decorated.

  Ninety percent of drawings in the Horseshoe Canyon include hoofed animals such as bison or buffalo. Waller has suggested that the percussive echoes mimic the sound of the animals moving and stampeding. Slow-motion footage of horses reveals that two of their feet land on the ground almost, but not quite, at the same time, giving a double “clop.” Stand a few tens of yards from a large, flat surface and clap with a steady rhythm, and you can mimic this sound. But you could also produce the rhythm without the echo. When a hoofed animal walks or gallops, there is a distinct jaunty rhythm to the hooves hitting the ground—something I remember simulating with two halves of a coconut when I was a child.

  Such theories in archaeoacoustics are necessarily speculative. Some mainstream archaeologists initially doubted David Lubman and his ideas about echoes from Mayan pyramids. As he explained to me, “I thought the archaeologists would be jubilant that somebody has discovered something that they had understandably overlooked, but instead they are angry with me.”47

  The pyramid of Kukulkan, a Mayan feathered serpent deity, at Chichén Itzá in Mexico was built between the eleventh and thirteenth centuries. It is the height of a six-story building, with a square base that is about the size of half a soccer field.48 On every side it has a staircase running up the middle that contains ninety-one steps, and at the top there is a square temple. Visit the site, and guides will delight in clapping and producing a chirping sound. Stand in the right place, about 10 meters (30 feet) from the bottom of one of the staircases, and reflections from the stairs create a squawking echo with a distinctive descending pitch. David Lubman claims that this echo mimics the call of the scared and venerated quetzal bird.

  Imagine an ancient Mayan priest presiding over a ceremony and, with great theatricality, summoning the sound of the quetzal bird by clapping his hands. Did this happen? And is there an even greater story to tell, about how the Mayans built their pyramids with specific acoustics in mind? Is this perhaps another example of their legendary technological talents, now lost?

  I will return to the physics of the sound effect in Chapter 4, but for now it is important to know that many staircases can be made to chirp. The Mayan pyramids are not particularly unusual. Rupert Till, a musicologist from the University of Huddersfield, demonstrated this fact while waiting for his X Factor audition at the Old Trafford soccer stadium, the home of Manchester United. Till’s studies of ancient acoustics made him curious about whether the steps between the terraces in the stadium would behave like a Mayan pyramid. Sure enough, when he clapped his hands, a distinctive chirp could be heard.49 Now, no sane person would suggest that the stadium steps were deliberately designed to chirp, so why should anyone assume that the echo from the Mayan pyramid is anything but an acoustic accident, or that it was used during ceremonies?

  David Lubman, however, says it’s “hard to believe it wasn’t intentional, hard to believe it wasn’t noticed.”50 And he goes further, explaining that the acoustic phenomenon is connected to the light shadows that are cast on particular days. At the equinoxes, a zigzag shape appears down the side of the staircase—a distinctive shadow forming a tail for the serpent statues at the bottom of the stairs. His explanation is that around the spring equinox, the quetzal bird undertakes a spectacular diving display, and it looks like a flying serpent. At the bottom of the staircase is the head of the serpent, at the exact point you need to clap to make a chirp. So the echo helps explain the visual display.

  I think there are three possible scenarios. First, the Mayans deliberately built their pyramids to make serpent shadows and chirping staircases. Second, it was not deliberate design, but the Mayans noticed that their pyramids chirped and then incorporated the sound into ceremonies. Third, and least romantic, modern guides noticed the chirp and made up this tall tale to entertain tourists.

  Unpa
cking which of the three scenarios is correct is difficult. It is like examining the orientation of ancient structures to the stars and sun. It is easy to prove that places are astronomically aligned in an interesting way, but proving that such alignment was deliberate is impossible.51 We can learn from modern examples where documents exist to resolve arguments. There are whispering galleries in the US, Europe, and Asia where you can hear ghostly voices apparently emerging from within the walls (more on this in Chapter 5). With so many places built that have this acoustic effect, it is tempting to assume deliberate sonic design. But most are accidents of design, and none appear to have been exploited for rituals and ceremonies—even the ones within cathedrals.

  I find it hard to believe that Mayan pyramids were deliberately designed to chirp, but I am open to the idea that the sound might have been exploited in ceremonies. Whichever account of events you believe, an important thing to try at Chichén Itzá is to test the chirp and wonder whether, a thousand years ago, Mayan priests did the same, summoning the quetzal bird, a messenger from the gods.

  The wind, playing upon the edifice, produced a booming tune, like the note of some gigantic one-stringed harp. No other sound came from it . . . overhead something made the black sky blacker, which had the semblance of a vast architrave uniting the pillars horizontally. They carefully entered beneath and between; the surfaces echoed their soft rustle; but they seemed to be still out of doors. The place was roofless . . . “What can it be?”52

  This dramatic description of Stonehenge comes toward the tragic end of Thomas Hardy’s Tess of the d’Urbervilles, where Hardy refers to that famous ring of stones as “a very temple of the winds.” Disappointingly, the wind-driven drone has fallen silent, probably because many stones were removed and rearranged in the twentieth century. But even without the “booming tune,” the sound of stone circles can surprise because, as Hardy observes, they can have an unexpected indoor quality.

  Stonehenge is one of the most iconic prehistoric sites in the world, so naturally it has attracted curious acoustic archaeologists. There have been many suggestions for why ancient denizens built Stonehenge. Ignoring the ridiculous speculation that it might be a UFO landing site, most sensible ideas involve rituals.53 Across cultures, human rituals involve sound, whether for celebration or for mourning, so it is probably safe to assume that speech, music, and other sounds were played within stone circles.

  My colleague Bruno Fazenda and musicologist Rupert Till went through a standard acoustician’s ritual of bursting balloons one morning at Stonehenge just after sunrise. Bruno told me that the sunlight catching the mist and clouds cutting through the circle of stones stunned him with its beauty. But he was less impressed by the sound. When he stood in the middle and clapped his hands or burst a balloon, he could hear only a faint echo from the partial remains of the sarsen circle (the iconic uprights that are capped with horizontal stones). Unfortunately, modern-day Stonehenge is very different from its ancient counterpart, and not just because of the polluting noise from the nearby road. With many stones removed or rearranged, the modern acoustic is a poor imitation of any past sonic glories.

  To go back in time to hear the past acoustic, Bruno and Rupert decided to travel nearly 8,000 kilometers (5,000 miles) because, extraordinarily, there is a full-scale replica of Stonehenge in Maryhill, Washington. Constructed by a wealthy American named Sam Hill to honor his fallen companions in World War I, the monument was completed when the altar stone was dedicated on July 4, 1918. On a trip to England, Hill had been told about possible human sacrifices at Stonehenge and had decided that a copy of the prehistoric monument would be a fitting tribute to the suffering and loss of servicemen from Klickitat County.54

  Bruno and Rupert made detailed field measurements at the Maryhill monument one hot and dusty summer, annoying dog walkers and tourists with loud drumming and chirps as they tried to capture and understand the acoustic. They rose early in the morning so that they could get going before the winds had a chance to pick up and create too much buffeting noise on the microphones. Fortunately, the monument was carefully constructed as a faithful replication of one of the old layouts of Stonehenge. Still, some differences between the monument and the original Stonehenge remain: the concrete blocks at Maryhill are too perfectly square and have a finish reminiscent of a 1970s textured ceiling, whereas each Stonehenge stone has individual character from the way the stones were shaped. From my knowledge of designing acoustic reflectors for concert halls, however, I would doubt this made a vast difference to the sound within the circle.

  “Maryhill is quite awesome, a beautiful architectural place on the banks of the Columbia River. It is also a valuable archaeological model, a window into the past, giving you a sense of what it would have been like standing in the original Stonehenge,” Bruno explained to me.55 He also described how his footfall on the gravel changed as he entered the circle, giving a striking, unexpected sense of being inside a room. Exactly the same feeling described by Hardy in Tess of the d’Urbervilles.

  At first the results of the acoustic measurements surprised me. Burst a balloon at Maryhill, and the sound will ring and reverberate for over a second, a decay time more in common with a school hall than an outdoor space. Given that there is no roof and there are spaces between the stones, I naturally assumed sound would rapidly disappear up to the heavens, but actually, some sound stays bouncing around horizontally among the stones. However, the acoustic is subtler than that of a booming school hall because the reflections are quieter; you have to listen carefully to notice the difference. Nevertheless, these reflections would have been helpful during rituals. As Bruno explained, “It is a surprisingly good place for speech, because reflections reinforce your voice and you can talk to people even from behind some of the inner stones.”56

  Whereas the insides of the stones at Stonehenge have been carefully and meticulously worked to make a smoother, more concave shape, the outsides are often quite rough. Pioneering acoustic archaeologists Aaron Watson and David Keating have suggested that the purpose of smoothing the stone interiors might have been to focus the sound.57 However, Bruno heard no distinct echo caused by focusing from the rings of rocks in the Maryhill monument. The outer sarsen stones might have produced a focused echo on their own, but reflections from the inner ring of stones hid whatever echo there might have been. The ear combines reflections that arrive at roughly the same time. At Maryhill, the sounds bouncing off the inner and outer stones arrive too close together to be perceived separately, rendering inaudible any possible echo.58 Bruno and Rupert had hoped to hear a whispering-gallery effect around the circle of stones, but the gaps between the stones ruin this effect. Neither did they hear bass drones or Hardy’s “temple of the winds”—even when a gale was blowing through the stones in the afternoon.

  The chance to experience an ancient resonance like the one that eluded Bruno Fazenda at Stonehenge is what drew me to the Neolithic burial mound at Wayland’s Smithy. I also had a less noble motivation: a curiosity to sample a chamber that featured in an infamous academic publication. In 1994, Robert Jahn and collaborators carried out what they described as “rudimentary acoustical measurements” inside six ancient structures.59 What they found was that the chambers contained acoustic resonances.

  Just like a Roman wine jug, a beer bottle contains air with a particular resonant frequency, which is why you can make a flutelike hooting sound when you blow across the top of one. More specifically, when you blow across the mouth of a bottle, a small plug of air in the neck begins vibrating back and forth against an air spring created by the rest of the vessel. Blowing across the mouth of another bottle, identical except for an elongated neck, sounds a lower-frequency note. The elongated neck means that a longer plug of air is oscillating, and because this greater quantity of air is heavier, the resonant frequency is lower.

  Paul Devereux, one of Jahn’s collaborators, claimed in a 2001 book that the ancient structures had specific resonant frequencies that enhanced the human v
oice in an intentional way.60 This assertion irked acoustic scientist and mathematician Matthew Wright, who noted that all enclosed spaces, such as bathrooms or burial chambers, have resonances—rarely as dramatic or obvious as that emanating from an empty beer bottle, but still powerful enough to fool you into thinking you are a great singer while showering. Wright composed a conference paper entitled “Is a Neolithic Burial Chamber Different from My Bathroom, Acoustically Speaking?”61

  I decided to put Wright’s research to the test by analyzing the balloon bursts from Wayland’s Smithy and measurements I made in my bathroom (Figure 2.3). Both plots are jagged lines, with distinct peaks and troughs. The peaks represent the frequencies where there are resonances. Any singer will find notes at these frequencies sounding richer and fuller than normal. If you were to sing a note a little above 100 hertz in one of these places, you would excite a resonance that would reinforce and enrich the sound. Move up to about 150 hertz (a musical interval of a perfect fifth, the leap between the first two notes of the Star Wars theme), and the valleys in the graphs at that frequency show that there is no prominent resonance to reinforce your voice, so it would sound thinner. The 100-hertz resonance is conveniently located toward the bottom of my vocal range, ideally suited for impersonating Barry White singing “Can’t Get Enough of Your Love, Babe” (a song slightly more appropriate in a bathroom than in a burial mound).