Significant evidence exists for the importance of organised sound in prehistory. Research in this area has progressed for over 30 years, as within the International Council for Traditional Music (ICTM) and International Study Group for Music Archaeology (ISGMA).
     A number of archaeological finds that are thought to be musical instruments have been found in caves. Particularly well known are bone flutes. The discovery of a fairly advanced example of an aerophone dated to 40,000 BP emphasises the complex nature of such artefacts, even during the Palaeolithic period, yet surviving artefacts are not the sole method of examining prehistoric sounds.
     Discussions with researchers at the universities of Valladolid and Zaragoza in Spain led to a project exploring the relationships of Palaeolithic cave art with sound, music and acoustics. Dr Rupert Till (University of Huddersfield, UK) and Dr Bruno Fazenda (University of Salford, UK), who had together previously explored the acoustics of Stonehenge, visited caves in Asturias and Cantabria in the summer of 2012 to carry out a pilot study. Till, Fazenda, and Professor Chris Scarre (Durham University, UK) carried out a fully funded research project in 2013.  
     The acoustics within a cave are strikingly different from those outside. Many activities in the cave would have made sound, whether talking and moving, or grinding and preparing pigments for painting.
     A high quality digital record made between 2004 and 2007 of the imagery within Tito Bustillo cave (Spain) resulted in the discovery of unknown decorated spaces, and a pit in the Gallery of the Anthropomorphs which contained ochre and crushed bone, teeth and shell dated to around 33,000 years BP, suggesting a far greater age than previously thought for at least some of the imagery.
     The Songs of the Caves project thoroughly investigates the acoustic environment of the Asturian cave of Tito Bustillo, as well as four Cantabrian caves - La Garma, El Castillo, Las Chimeneas and La Pasiega - examining the hypothetical relationship between the acoustic environment and the placement of imagery in caves, and exploring such acoustics experimentally.  
     Experts from Spain and the UK used a range of devices including reconstructions of Palaeolithic bone flutes and bullroarers, as well as drums, bark rattles, cow horn trumpets, bones, wooden sticks and even river pebbles were used to excite the acoustic space. Additionally several voices were recorded. The level of background noise was as low as the equipment was capable of measuring - far lower than a quiet environment outside. This makes acoustical effects inside the cave particularly striking.
     Small, simple percussion instruments such as river stones and bones hit together were notably effective. Drums had powerful effects in all situations, as they produce lower frequencies loudly enough to stimulate effects not otherwise heard. Natural reverberations enhance the sounds of voices and bone flutes. The long reverberation times of the main open central space make speech difficult to understand, but support a wide range of musical sounds. When heard from a distance the effect of reverberation makes it difficult to locate the source of sounds, which within the cave could be heard from as far as 50 metres away.
     Scientists also found that sounds associated with the imagery were particularly effective - for example using a cow horn to play a single note in front of a bovine image, or simulating the bellow of a bull by vocalizing along with the pitched note of the horn.
     Marimba sticks were used to test the lithophone in Tito Bustillo, which produced a range of notes. Over 50 stalagmites - some near the lithophone - produced clear ringing notes. Some are over a meter tall and produce a powerful low note. As drops of water fall on stalagmites, notes ring out from time to time by themselves.
     Experts also investigated correlations between acoustics and archaeology, recording five characteristics related to paintings and motifs - type of decoration, colour, number of images, chronology, and depth within the cave. The team also tried to find positions at which to take measurements where there were no images, but imagery would have been possible - for example on flat, blank wall panels.
     With one exception, all comparisons of acoustical parameters between decorated and non-decorated caves are statistically significant, suggesting a different acoustic response where decorations are found. Tito Bustillo has reverberation in a main central space of up to 2.5 seconds, today considered an almost ideal value - quite high for a concert hall, low for a church and certainly lower than many cathedrals.
     The term 'live' is used for spaces with reverberation, and 'dead' for those without, and these are useful ways of thinking about how these spaces would have been perceived. The acoustics of a place could have influenced whether it was selected as the position of a painting or engraving.
     Caves such as these were the only places where Palaeolithic people would have encountered such acoustic effects. This project provides evidence of how sounds would have contributed to a sense that these were places of importance.
     Discover more about it on songsofthecaves.wordpress.com website.

Edited from Songs of the Caves: Sound and Prehistoric Art in Caves (2014)