Acoustics and rock art sites, an enigma to be resolved

9 Nov 2021

By Lidia Alvarez Morales

There are always a many uncertainties when analysing human interaction with sacred places, since a wide variety of physical, social and cultural factors needs to be considered at the same time. Such uncertainties are even more difficult to elucidate when prehistoric societies and rock art landscapes are involved. How did these people interpret the sonic environment of the sites? Did their aural experience influence how they used the sites and the paintings and carvings they made? Did they actually consider the acoustics as an important element when selecting a place? In truth it is extremely complicated to find a correct answer to any of these questions, and they are just examples of the many in this area that remain a mystery to us. Nevertheless, what cannot be doubted is the fact that the acoustics of any place influences how we as humans perceive that space and interact with it, even when we are not aware we are doing so. Under this premise, the ERC Artsoundscapes project gathered a multidisciplinary team with the aim of approaching this research from different angles and considering all the variables involved: five research lines studied together to find a plausible explanation in support of the hypotheses on which the project is built.

To continue delving into these questions, the team working on Research Line 1, Physical Acoustics, spent the past summer gathering acoustic data in several rock art landscapes on the Iberian Peninsula. We followed a specially created methodology, i.e. a measurement protocol adapted to cover some of the technical needs arising from the research work undertaken so far in the project and the exceptional accessibility requirements of the new surveyed sites. This refined methodology is based on that initially designed to capture high-quality spatial responses, as described in the blog entry How we take acoustical measurements in the Artsoundscapes project. It was successfully applied during the fieldwork carried out in the rock art landscapes of Altai (Russia) and Catalonia in 2019 and 2020. In 2021 the adaptations of the measurement protocol involved the acquisition of additional hardware and software to be introduced into the measurement chain. This was not only to facilitate access to those remote places where the portability and autonomy of the equipment is crucial, but also to allow on-site monitoring of the gathered acoustic responses, which is essential to ensure the validity of data while it is being collecting.

One of the key updates in hardware was the purchase of a smaller, lighter omnidirectional loudspeaker almost half the size and weight of the previous one. The new loudspeaker easily fits into a standard rucksack, making it much more portable. This is a key issue when we are talking about sites that are difficult to access, including those that require walking through dense undergrowth (even thorny brambles!) and/or across steep terrain.

This smaller dodecahedral loudspeaker was carefully tested and calibrated in an anechoic (reflection-free) chamber prior to the fieldwork and gave excellent results. With this new acquisition, the project now has two high-quality dodecahedron loudspeakers with different features, so that the research team can choose the measurement protocol that best suits its needs according to the requirements of the site and/or the type of acoustic analysis to be performed.

Interdisciplinary meeting at the BrainLab

Figure 1. Picture of the two dodecahedral loudspeakers to scale: the innovative directivity-variant MIMO loudspeaker array on the left, and the new ultralight omnidirectional mini sound source, IAG DD4, on the right.

Figure 2. Pictures taken during the acoustic test performed on the new equipment in the CETIC-UGR anechoic chamber on 25th-26th May 2021.

In terms of software, EASERA, a new commercial solution for measuring and analysing the acoustic response of the rock art sites, was purchased and included in the new measurement protocol to measure (up to this moment) the monaural (1-channel) omnidirectional (sound reflections coming from everywhere) impulse responses. This simplifies the measurement protocol in several ways, including by reducing data post-processing and, more importantly, allowing researchers to monitor the impulse responses in situ.

The 12-channel loudspeaker

Figure 3. Screenshot of an impulse response measured with the EASERA software.

The protocol established to take the measurements with the EASERA software is complementary to the previous protocol set up to register the spatial responses, which are still collected by using the Zylia microphone array (3rd order Ambisonics) as in previous campaigns. Here is a time-lapse video showing the measurement process.

The 12-channel loudspeaker

Time-lapse video: spatial acoustic measurements taken with the Zylia microphone array for the Artsoundscapes project (2021); Jesús Galdón site Valencia Community (Spain). Video filmed by team member Laura Fernández Macías.

Once the new measurement protocol had been set, two important fieldwork campaigns in Spain were successfully completed: the first in Cádiz (southern Spain) in June 2021 and the second in Valencia (eastern Spain) in July-August 2021.
In Cadiz, an area where three different rock art styles are found – open-air Palaeolithic art, Laguna de la Janda and schematic rock art traditions – the new equipment and measurement protocol were put to the test. Thanks to Artsoundscapes’ collaborator, the University of Cádiz professor Dr Maria Lazarich, a selection of rock art sites representing the three styles was chosen. The geological nature of these sites was diverse. Palomas I, for example, is a semi-enclosed space in which Palaeolithic and schematic rock art paintings can still be seen despite the significant bee-panel-shaped erosion suffered by the sandstone typical of the area (due to the strong wind). Mujeres I, is a shelter formed by two cavities and an wide platform, where the deliberate arrangement of stones in a line suggest it could once have been a suitable place for gathering a large group of people. These two sites contrast with Bacinete which is, once again, a very different type of site. It consists of several shelters of different sizes and shapes, which in some areas of the site brings to mind the configuration of a contemporary «theatre», although formed naturally. Finally, Tajo de las Figuras, with its impressive Laguna de la Janda rock art motifs is, in contrast to the previous sites, small in size and very difficult to access, to the extent that, for safety reasons, climbing equipment and specialist assistance is currently required.

Figure 4. Pictures taken by Lidia Alvarez Morales during the fieldwork in Cadiz: a) the team at Palomas I, from left to right, Lidia Alvarez Morales, Laura Fernandez, Paco Torres, Neemias Santos da Rosa and Margarita Diaz-Andreu; b) the equipment used for measuring the spatial IR at Palomas I; c) general view of Mujeres I; d) the equipment used for measuring the spatial IR at Bacinete Principal; e) the omnidirectional ultralight mini sound source, IAG DD4, at Tajo de las Figuras; and f) the equipment used for recording the monaural IR at Tajo de las Figuras.

The extreme heat typical of the Mediterranean summer in the Valencia region did not prevent our team from performing acoustic measurements at 18 rock art sites in the areas of Caroig Massif and Millares-Dos Aguas. We were assisted in the selection of the sites by our project collaborator, Dr Ximo Martorell . The selected rock art sites offered a uniform typology, allowing comparisons between them. They differ mainly in terms of the landscape in which they are located, the number of motifs in each shelter, and the possible uses of each space. There are also three different styles in this area: Levantine, Early Schematic and Schematic. Acoustic tests were undertaken at the splendid Cueva de la Araña, in which a widely publicised honey-gathering scene can be observed, along with many other beautiful hunting and animal scenes. Another site evaluated was Cinto de las Letras, which is full of figures representative of the schematic and Levantine styles; and the fantastic Abrigo de Voro, with its exceptionally well-preserved figures in Levantine rock art style, including a group of dancers and several figures depicting women, among many other scenes studied in Ximo Martorell’s doctoral thesis.

Figure 5. Pictures taken by Neemias Santos da Rosa during the fieldwork in Valencia (except the one he is in): a) equipment used for measuring the monaural IR at Cueva de la Araña; b) the team at Cinto de las Letras: from left to right, Laura Fernandez, Margarita Diaz-Andreu and Neemias Santos da Rosa (Ximo Martorell behind the camera); and c) the equipment used for measuring the monaural IR at Abrigo de Voro.

Yes, we have been busy during the last few months and now we can’t wait to finish analysing all the data we gathered to try and shed some light on all these unknowns, which could be summed up in a «simple» question: what could have been the role of acoustics in the relationship between prehistoric societies and rock art sites?

Figure 6. The acoustic team in action! With our main collaborators during these campaigns: Maria Lazarich and Ximo Martorell.