Information about music and culture informed what sounds we should expect to find at Stonehenge. We could expect music that is part of a ritual activity and addresses the supernatural; is integrated into its social context; is combined with dance; is designed to lead to the achievement of altered states of consciousness or trance; or that changes the ambience of a gathering. It may be used both to bond the community and to establish one’s position within the community. It may involve communication with gods and the ancestors, may be part of rites of passage from birth to death and may be used as part of healing of some sort.

Hardy had noticed a sense of enclosure and envelopment in the space, a reverberant acoustic, echoes when entering the Sarsen circle, interesting sound at the centre, and a low booming hum that was caused by the wind. Watson’s pilot study had shown that sound would be contained within the stone circle, creating a sense of envelopment within the space and a change in sound when approaching and entering from the Avenue. Theoretical analysis had indicated the presence of resonance (agreeing with Watson), as well as a low hum, echoes, reverberation, and particular effects at the centre (agreeing with Hardy). It indicated that echoes and resonance at the centre of the circle may be at be heard as semi-quavers at 156bpm (equivalent to 10.4Hz) or as semi-quavers (at 5.2Hz) at the edge.

Acoustic analysis of the Maryhill Monument concrete replica of Stonehenge, using it in order to provide a full size model, gave indications of the acoustic behaviour of Stonehenge. It indicated reverberation time of 1.5s (T30) and 0.8s (EDT). The site was able to resonate at a number of frequencies as a response either to generation of specific frequencies, or to simple rhythmic musical sequences at tempi equivalent to ‘infrasonic’ modal low frequencies of vibration. A focus of acoustic effects was observed along what appeared to be the main acoustic axis of the space, leading from the Heel Stone through the ‘entrance’ from the Avenue in the north-east, to the centre, Altar Stone and largest trilithon. There were also acoustic effects along an axis across the circle at 90 degress to this central axis.

The outer stone circle created a sonic threshold, with an unusual acoustic effect under the circle of stone lintels, and a marked difference in acoustic inside and outside of the stone circle, enhancing the moment of entering the stone circle. There were acoustic effects at the edge of the circle, where sound was louder. There was a sense of acoustic enclosure and envelopment within the circle. The acoustics seemed to focus on the central space bounded by the trilithons and entrance. There was considerable variation of acoustic within the space, with odd effects at specific positions, and a ‘backstage’ area behind the trilithons. There were echoes evident only along the main acoustic axis. Speech intelligibility, clarity and definition were subjectively assessed as good within the space, which was suitable for music or speech. Results from Hardy, Watson and theoretical work were supported.

Analysis of a digital model of Stonehenge using Odeon acoustic measurement software showed that standing at the exact centre of the stone circle one would experience boosted low frequencies, very high listener envelopment, reverberation and unusual acoustic effects including echoes. Being at the centre would stop one from hearing the speech of other people in the circle in a clear, intelligible fashion, it seems that other people would listen to this person, but the person would not listen to them. However, words spoken at the centre would be intelligible, clear and well defined to others, especially within the central area of the stone circle, and in particular next to the Heel Stone. Sounds from the centre would be amplified, and would have acoustic effects that would change their tone without destroying speech intelligibility. Standing at a specific sweet spot in the centre would have meant that acoustic effects would be more powerful than elsewhere. This sweet spot would have been small, suited to only a single person. Singing (or musical instruments played) at the centre would sound better when heard outside the stone circle, especially next to the Heel Stone, where there would be long reverberation and echoes. This implies that there would be people singing (or playing instruments) in the stone circle, and that there would be people listening outside it, but within the encircling bank. Rhythmic music made in the centre would sound better within the stone circle and worse (confused, lacking coherence, definition and clarity) outside.

There is an extremely high measure of perceived listener envelopment inside the stone circle. This falls away between the stone circle and the encircling bank to give comparable figures to seats increasingly far away at a concert hall. There was still a sense of envelopment and inclusion outside the stone circle but within the bank, but with clear delineation of the centre as the most high status space.

Standard measures of acoustics such as envelopment, clarity and definition, as well as speech intelligibility, are in some positions at Stonehenge better than the equivalent values for the Vienna Concert Hall, and Stonehenge had acoustic properties that seem too carefully controlled and close to ideal values in many cases to be anything other than at least partially intentional. Sound would be transmitted with very high levels of perceived clarity, out of the space along specific straight lines aiming towards the Cursus, Durrington Walls and the Heel Stone’s now lost partner. Within the stone circle there would have been a strong sense of acoustic envelopment and enclosure, far more powerful than that usually felt in a concert hall. This would still be present (at concert hall equivalent levels) within the bank around the stone circle, the sense of envelopment diminishing the further one was away.

The whole of the space inside the stone circle was a place where people would have found listening an involving process. This implies that people would have been present inside the space during ritual activity. Being ‘backstage’ behind the trilithons would have protected listeners to some extent from acoustic effects, and made them perceive themselves as separated them from central activity. At the edge of the circle next to the sarsen stones, low frequencies were boosted powerfully and had a long reverberation time T30 of 3.2s at 125Hz.
Standing at the Heel Stone there would not have been as strong a sense of envelopment, although sound made at the Heel Stone would have created a sense of envelopment when listening in the centre, much more so than sound made at other positions outside the circle. In this way the Heel Stone position would have been connected to the inside of the circle in a way that the rest of the surrounding space was not. Speech from the centre would have been very clear, intelligible and well defined immediately next to the Heel Stone, and much less so as little as a metre away in front of the Heel Stone itself. Musical sound made in the centre would have been enhanced by reverberation at the latter position. Small changes in the position of a person speaking at the centre could have reversed these conditions. If there were two people, one standing in front of the Heel Stone and one next to it, someone in the centre could have spoken clearly to one or the other by moving only a little to one side, using sight lines as a guide. The acoustics imply that someone at or near the Heel Stone may have spoken to those in the centre of the space, taking advantage of the particularly clear acoustic path between the two positions.

Echoes and other acoustic effects would have been heard at the Heel Stone. The acoustic significance of the Slaughter Stone, Portal Stones and Station Stones warrant further investigation, but it seems that their placement may have had particular and specific acoustic effects. These stones may have been placed to interact in particular with the modal resonances in the space.

Hardy’s description of echoes, reverberation, low frequency resonance and acoustic focus at the centre, as well as Watson’s observations of envelopment and the importance of changes in acoustic along the ceremonial approach to Stonehenge, are all backed up by theoretical analysis, field tests at Maryhill and digital acoustic modelling. There were clearly acoustic effects present that were powerful and dramatic, which were so strong that they could not have gone unnoticed. The results from the different stages of the project, even at this initial stage, support each other strongly.

One can never prove absolutely to a sceptic that acoustic design was intentional, but this level of acoustic interest and detail seems to make it highly likely that the acoustic properties of the space were a consideration in the development of Stonehenge. We acknowledge that the builders of Stonehenge could construct the site in a way that created visual and physical patterns that were able to map astronomical progress, why would we think it unlikely that they could also consider sonic construction? One no more needs an understanding of acoustics to create acoustic affects than one needs an understanding of the theoretical mathematics of force and energy, or architectural training, to raise a stone lintel on two uprights. When developing the site, the builders would have noticed the way the sound changed, and thus come to understand how placing stones changed the acoustics of the site. Over hundreds of years, trial and error could be a powerful method of learning. We believe the site was designed in a visual sense, not the result of random placement of stones, it now seems very likely the site was designed acoustically as well as visually.

However, intentionality is perhaps an irrelevant consideration. Whether the acoustics were intentional or a remarkable, and surely more unlikely, happy accident, the acoustic effects would have been obvious to anyone in the space, especially considering earlier comments about the importance of sound in oral cultures. It was likely acoustic effects would have affected, and been integrated into, ritual activity in the space. Just as one might be tempted to shout at an echoing mountain or in a tunnel, the echoes in the space would have been intriguing. Just as the reverberance of a cathedral makes one quiet because speech and footsteps are amplified, transmitted around the space and sustained, being within the Stonehenge circle or at the Heel Stone would have imposed a sense of awe upon the listener, a sense of being in a special place. It is clear that the acoustics of Stonehenge and its environment are significant and worth consideration.

This has implications upon the management and preservation of the site. The acoustic present of Stonehenge is destroyed by the proximity of the roads to the site, and vehicle noise is such that this significant feature of the monument is distorted. In particular it is impossible to appreciate the sound at the Heel Stone much of the time, or to explore the acoustic effects of approaching the site along the Avenue and experiencing the changes in sound. These acoustic elements are as much a part of Stonehenge and its landscape as the stones themselves, and as more is discovered about the acoustic significance of the site, the acoustic ecology of the site must become a consideration in plans to rearrange the site and this will surely add weight to the voices of those who wish nearby roads to be rerouted.

There were the prehistoric equivalent of cheap and expensive concert hall seats at Stonehenge, high and low status positions, with measurements of envelopment telling us that being inside the circle indicated clearly a separate level of status. This echoes the present situation, with archaeologists, and those who book specially, allowed within the circle while the mass of daily visitors follow a path around the outside. It may be that further research into the acoustics of the space will help us to understand why Stonehenge remained a focus of musical activity through the festivals of the 1970s, why there were those willing to fight to hold musical events in the space in the 1980s, and why the Salisbury Festival will use the space as a concert venue in 2009. The sense of envelopment within the space alone provides a sense of involvement that augments the power of communal musical experiences to bond individuals together. It does seem that those who met every year in the 1970s to celebrate the summer solstice with music and dancing were echoing the behaviour of their prehistoric ancestors to some extent.

This video shows a number of solstice celebrations at Stonehenge, note music is usually present. 

One important research question within this project was to suggest possible descriptions of ritual activities in prehistory. Our experiments showed that circular modes of vibration could be stimulated by a loud drum sound, creating low bass sounds, like a throbbing synthesizer bass or humming sound. But could this kind of loud bass effect been created in prehistory? There were few low bass sounds in prehistory except perhaps thunder, earthquakes and the sonic booms of meteorite strikes, and low frequency sounds would have been very unusual and noticeable. In order for these loud sounds to be generated, a large group of people would have to have played at the frequency or tempo associated with that resonance. Echoes in the space may have provided a kind of metronome to keep this rhythmic playing in time. In order to make the infrasonic frequencies audible the sounds would have to be loud, above 96dB. This is unlikely using human voices alone. However, percussion sounds can achieve this volume, especially considering the loudness of the space caused by its acoustics. It is possible that those with hearing unusually able to hear lower than usual (perception of low sounds varies form person to person), would have heard the low resonances in the space more clearly. Older people can also hear these sounds more clearly, so it may have been the wisdom of the old rather than the strength of the young that characterised participants. Singing a quaver rhythmic chant at the equivalent tempo to 5.2Hz, 156bpm, or singing long notes with a vibrato in time to the drumming, would help to entrain the brainwaves of participants to the music, and allow them to fall into a deep trance, eyes closed as their brain slowed to alpha rhythm and then theta.

We know that some of the working of stones at Stonehenge was done at the site, numerous stone chippings have been found, so we know that people were hitting stones, and making percussive sounds. We also know that in many cultures work music and ritual music are often linked. If one plays in time with the echoes in the space that come from the Heel Stone and other stones outside the stone circle, because of their positioning, the echoes would set a tempo like a metronome. Playing in time to the echoes would be what one would expect, playing against the echo patterns would result in a cacophonous sound. Hitting stones in time with the echoes would have helped to synchronise the work. Rhythmic music in the space would have to play in time with the echoes, otherwise it would also become a mess of echoes, whereas playing in time would build up the rhythm, help sound makers to synchronise and play in time together. In addition it would build these powerful bass modal resonances, the space could have started to resonate with modal vibration. The tempo required would be about 156 beats per minute, slower in the winter due to atmospherically driven changes in the speed of sound in air, with quavers played by the music makers, and echoes providing a galloping semi-quaver, fast, pounding beat in the centre. We have seen that that the acoustics of the space would have been encouraging to rhythmic rather than harmonic music. Dancing to music at this speed would raise the heartbeat and may have created a possession trance effect, overloading the brain’s input, enhanced by the high volume of the space, and by the effects of the infrasonic low frequencies present.

These low frequencies are very similar to the brainwave frequencies of alpha and beta types of activity. It is possible that those around the edge of the stone circle would have chanted at the speed of the percussive sounds, or sung long notes with a vibrato wobbling at 5.2Hz, in time with the music, in order to entrain their brainwaves to the music, to make the dominant frequency of their brain activity slow to a theta pattern, typical of deep meditation, hypnosis or trance. This is a similar state to the hypnogogic or twilight state between waking and sleeping, and the eyes would be shut for this practice. In the centre a different frequency could have been produced by modal vibration and echoes, one of 10.4Hz, still associated with closed eyes and meditation, and to some with healing. 10.4Hz is associated with alpha wave brain activity, a more active state. It may be that at the centre, a leader was able to stay alert because of this alpha state, continuing to drive a rhythm along and communicate with those at the edge of the stone circle, as they gradually became lost in a deep reverie. The leader could also communicate with those outside the circle. Turow makes a convincing argument that this kind of auditory driving of the brain’s frequencies is possible, and provides evidence from many traditional religious practices.

More generally, several cognitive psychologists hold that perception, attention, and expectation are all rhythmic processes subject to entrainment (Large and Jones 1999; see also Ward 2002, 2003). In other words, even when a person is only listening to speech or music, their perceptions and expectations will be coordinated by their entrainment to what they hear. Entrainment is fundamental then, not just to coordinate with others, but even to perceive, react to, and enjoy music. Music, as an external oscillator entraining our internal oscillators, has the potential to affect not only our sense of time but also our sense of being in the world.

More information (including a range of scientific and clinical studies) is available on the website of The Stanford Institute for Creativity and the Arts, Center for Arts, Science and Technology 2nd Symposium on Music, Rhythm and the Brain. This is a contentious theory. Brain entrainment is used in various therapies for healing of different types, by therapists as far ranging as hospitals and new age shamans. This subject is complex and warrants further study.

Flashing lights are often used alongside this auditory driving, in combination with pulsing sounds in medical audio-visual entrainment machines. Many people are familiar with the effect of flickering lights to cause epileptic fits. Epileptic fits can be caused by visual stimuli repeating at 5 or 10Hz, although it is more likely at higher frequencies. It is possible that flickering flames at Stonehenge may have been placed at night on posts outside the circle, or on top of stones inside, perhaps inside beakers that that enhanced audio resonances, or could have been present as part of cremations. Certainly flames may have been present if ritual events had been at night. The varying pressure of sound waves can make flames flicker with the same frequency as a sound resonance, appearing to dance and change shape in time with music. In a recording studio I astonished to find I was able to make a candle flame jump up and down in time to a 10.4Hz 156bpm rhythm, also growing and shrinking rhythmically, even at low volumes. A flame in a resonant space can also appear to make musical sound, as well as dancing in time to the music. Flame usually flickers at between 1 and 20Hz, (this fact is often used in infrared fire detectors), and when sound is close in frequency to a flame’s flicker frequency the two can become synchronised. In addition the powerful waves of changing pressure in infrasonic modal sound, may have made smoke from fires blow out of the circle, perhaps creating patterns of circles, or shapes out of the stone rings. Perhaps Woodhenge could have made a series of concentric smoke rings rise into the sky. My initial research into this indicates perhaps that Helmholtz resonances in chamber tombs may have had a similar effect, and this may link in with patterns in rock art. This is also an area in which my comments are somewhat speculative, and more research is needed. We can say with confidence that any flames present would have moved to some extent in time with any low frequency sound vibrations present. One can only imagine the effect on those present of seeing flames dance in time to music or smoke patterns rising into the sky, illuminated by the strobe-like lights of flames.

Bringing together a number of conclusions, as well as knowledge about trance practices from other sources, we can try to imagine what a ritual event at Stonehenge might perhaps have sounded like.

Perhaps a priestly cast of elder leaders, samans or shamans would have arrived first on the winter solstice, approaching along the avenue, the wind howling through the spaces between the outer sarsen stone uprights and making the stone circle ring with a low hum which rises and falls in pitch and level as the wind rises and falls. These would be experienced ritual leaders, perhaps with hearing that was unusually able to hear low frequencies. As they pass the under the sarsen lintels of the ring of stone, the change of acoustic marks their passage into this sacred space. They may have discussed various matters together first, using the good clarity, definition, intelligibility and amplification of speech in the central area of the space. As the sun began to set people are standing at the edge of the circle right against the sarsen stones, especially at the left and right of the altar stone. Flames are lit in beakers on the stones, and set on the posts outside the circle. In the centre the high priest / music director / ritual leader closes his eyes, and makes a percussion sound by hitting two flints /sticks / stones together or by beating the altar stone, or a drum consisting of the bottom of, or a skin stretched across the top of, a beaker or pot, perhaps using an antler drumstick.

Back to the leader at the centre comes an echo, a response from the ancestral spirits, the sacred beat that makes the stones sing. He plays more percussion sounds in time to the echoes, until from the centre is coming a 156 beat per minute quaver rhythm , made into a galloping semi-quaver rhythm by the responses of the stones, the sounds of the hooves of the horses pulling the chariot of the Thunder God, the rumbling of the wheels appearing to come from all around, enveloping and enclosing the participants in the ritual within the symbolic horseshoes of stones. The other elders standing in front of the sarsen or bluestones close their eyes and join in, playing in time to the rhythm from the centre until the space begins to rumble, hum, throb and thunder with the infrasonic 3 and 10Hz vibrations, a little slower than the summer rituals as the cold changes the speed of sound. They feel themselves relax, their brains becoming still as they slow to alpha wave patterns. The leader at the centre begins to chant in time to the music, a rhythmic syllable on every quaver beat. The others join in, their voices blending with and supporting the low frequency resonances, the rhythms helping to slow their thoughts further as they drift into a deep trance, halfway between wakefulness and sleep, visions starting to come into their heads enhanced in some by the effects of the magical plants they consumed and the scents of the herbs and oils burning around them.

As the low resonance builds, the flames start to dance with the music, most dramatic in the centre. The beginnings of the rhythms soften and throb, the attacks of the sounds slowing from sharp clicks to softer sounds. The drumming hooves start to turn into a rumbling thunder, taking the elders deeper into trance, watched by the leader in the middle. He seems less affected than the others, his voice and drumming staying steady and leading the group. The flashing flames produce flashing through the eyelids of some, others open their eyes and watch the pulsing light. The elders gradually lose their sense of self as they dissolve into the group, becoming one with the music and light, their brains and bodies entrained, synchronised with each other and united with the space, the bonds between them becoming stronger and stronger.

As the sun begins to set, a group of people approach along the avenue, having travelled from Durrington Walls when they first heard the booming music coming from the sacred grove of the dead, and saw the smoke patterns lit by the strange flickering light. They stop at the Heel Stone and its pair, listening to the strange low thundering sounds coming from inside, and the strange inhuman voice chanting seemingly melted into the music. One person asks for permission for the group to enter. They file in, this group of initiates, leaders in their own right, but not at the level of the great elders in the centre. Spreading out around the stone circle, they each find a position where the sound is at its most intense. Some dance, beginning to move in time to the rhythm, heads moving backwards and forwards, bodies pounding up and down into the ground. As their heads move the sound changes, getting louder and softer. The group of dancers start to slip into mild trance, losing themselves in the music and the dance. Some begin to react to the flickering light and throbbing sound, some beginning to fit, their bodies jerking.

Inside the stone circle and outside, people begin to feel themselves going past their initial feeling of nervousness. In the centre of the stone circle, the increased volume and strange sound effects inspire the dancer to let go completely, and an ancestral spirit comes and takes possession of his body. As his rhythm falters, one of the others comes to stand next to him and sustain the rhythm. Meanwhile others have arrived at the Heel Stone. Some are there to ask for the wisdom of the spirits, some to ask to come inside the great earth banks to be healed of an illness, released from a curse or protected from a spirit. The leader at the centre speaks inviting one through the earthwork, advising another, sending a third away unanswered. Those around him, and at the Heel Stone, hear the words of the ancestors as if by magic, above the pounding rhythms.

At the Heel Stone the others hear the voice twisted by the strange sound of the ancestors. Here they feel connected to those in the stone circle, to the otherworld of the ancestors and the gods. Outside the stone circle the strange sounds of the ancestors change and shift as people move from one place to another.
Obviously this is just a possibility, but just as postholes in the ground and wall markings are used by artists at archaeological sites to extrapolate an imagined drawing of what a site might look like, it is interesting to do something similar with sound and ritual. Some of this is speculation, some is based on the acoustic evidence and other research. Perhaps this was more like a shamanic rather than a possession trance tradition, where only one person at the centre would go into a trance-like state to meet the ancestors. Perhaps one person at a time was allowed to consult those in the centre, perhaps no one would have been between the bank and stone circle, but the unusual acoustic effects in this space make it seem likely.

At the very least, the evidence implies that sound and music were involved in ritual activity in the space; that it was fast and rhythmic, possibly at 156bpm with a semi-quaver pulse; that there may have been rhythmic chanting in time to the music; that flames may have flickered and smoke moved in time to the music; that one person in the centre had the most important position and the highest status when there; that there were participants inside the circle, who became to some extent entranced; that there were others around the edge of the stone circle(s) making rhythmic sounds; that a low booming sound would arise made by pounding rhythms made in time with the echoes in the space; that those near the very centre would hear a semi-quaver rhythm, and those around the edge would hear a slower quaver pulse. Those in the very centre may have found their brainwaves becoming slowed to an alpha rate of around 10Hz, relaxed but alert. Around the outside of the circle the slower rhythm would entrain their brains to be synchronised at around 5Hz to a theta wave state, becoming deeply entranced. Some may have had epileptic fits triggered. The extended periods of time in alpha or beta wave brain states may have had physical effects, aided concentration, changed mood, induced visions, and may have been as healing activities.

Measurements of envelopment, and levels of other acoustic effects, tell us that the centre of the circle was the most important position at Stonehenge, as one might expect, and shows a hierarchy of participation, with being within the stone circle the next level of significance, and within the bank a significant step less important. It will be interesting to see if earlier phases have less stratification. The Heel Stone seemed to be a significant position for people to stand. The level of envelopment made participants feel very much involved and helped participants bond and achieve altered perceived states of consciousness. The Stonehenge circle was an ‘other’ acoustic space, different to other natural or man-made spaces, the acoustic adding to its special status. The acoustics tell us it is likely that it was a place that would have had people in it participating in inclusive ritual activities, a place perhaps for spending time with the ancestors and gods, rather than for them to rest undisturbed. The Slaughter, Station, Altar, Portal and Heel stones seemed to cause echoes in the space., and this may be part of the reason for their exact placement.

More research is needed to further establish details of acoustics in the space. This may involve further analysis of digital models, for example investigating the Altar Stone upright or not and adding a partner for the Heel Stone. It will involve studying further the differences of acoustics in various phases of the monument’s development to understand what we can learn from how the acoustics of the space changed over time. The acoustics of the wooden circles at Durrington Walls and Woodhenge can be compared with those at Stonehenge, as can similarities with and differences to other Stone Circles. The results of this study need to be discussed in detail with archaeologists, ethnomusicologists and others. Eventually it is hoped to create an interactive digital 3D model of the site that would feature sound that would change as one navigated around it, perhaps also allowing one to travel through time to hear how the site develops. Meanwhile, more detailed information about the acoustic properties of sarsen and blue stones, improved accuracy of the digital model analysed by Odeon and other work should improve the certainty, specificity and reliability of results. It is hoped at some point to carry out acoustic field tests at Stonehenge to look for evidence remaining today that will help to confirm some of these ideas.

I have deliberately reached out beyond absolute proof, into the world of possibility, particularly when describing possible musically based rituals, in a way that some will find is extrapolating too much from the evidence, and perhaps this is a little provocative. I hope that it will encourage others to consider how much of what I suggest is likely to be correct, and what other corroborating evidence there might be. It is perhaps a useful process for the creation of a hypothesis that can be explored through further study.

This project in no way claims to have decoded Stonehenge or explained its meaning and purpose, it does not suggest that Stonehenge was created as an outdoor concert or dance hall, music venue or amplifier. It does suggest that music may, alongside other visual, astrological, ritual or cultural elements, have had a part to play, and that this is worthy of investigation. It hopes to show that music, sounds and acoustics were likely to have been an important part of this iconic site. By doing so it demonstrates the kind of information that it may be possible to discover about archaeological sites by a careful and detailed study of their acoustics, using a methodology that includes contextualisation, background research, theoretical analysis and the use of digital and scale (or full size) models.

The songs of the stones at Stonehenge have been heard in prehistory, in the era of Thomas Hardy, at the rock concerts of the 1970s, and can still be heard today. Perhaps as well as looking around when visitors enter the Stonehenge site, they wil be encouraged by this work to begin to listen as well as look, and thus more fully understand one of the most mysterious archaeological sites in Britain.