A team of scientists lead by Dr. Bruno Fazenda of the University of Salford in the UK has reconstructed the soundscape of the Stonehenge circle. Using the practice of archaeoacoustics and state-of-the-art sound equipment at both the original cultic circle in England's Salisbury Plains and the reconstruction in the US state of Washington, the scientists behind a new study have resurrected a part of the structure's sonic awe.
Because the original Stonehenge is incomplete, with some of the stones toppled, and because electric generators are not permitted, as well as the relative nearness of a main highway, the study's authors decided to augment the measurements they took there with measurements from the World War I memorial Stonehenge replica at Maryhill Museum.
Fazenda explained what they were looking for.
"For both sites, the goal was to obtain impulse responses at specific source-receiver locations. Measured impulse responses contain all the acoustic information from a system comprised of the enclosure, the position of the source and the position of the microphone. From the impulse response it is possible to derive frequency response functions, determine the decay rate of energy, and plot energy time curves (ETC) at the measured positions. These acoustic descriptors of the space are used as an attempt to describe the acoustical behaviour of the space in objective and comparable terms. The measurements are presented in the results section."
Because electricity is not allowed in the original henge, Fazenda and his crew popped balloons to capture those responses with a battery-operated field recorder. In such a situation, said Fazenda, "only the first few milliseconds of energy decay are available for measurement and a full length T60 reverberation time has to be extrapolated from this."
With electricity available at Maryhill, the scientists were able to computerize the entire measurement process, using a soundcard fed through a 1000 watt amplifier and the responses captured "using the swept sine measurement method, with a length of 10 seconds... (exciting) the site at every frequency between 20Hz and 20kHz."
Although the original is stone, including the famous Welsh bluestone, and Maryhill is made of concrete, the audio difference from the two surfaces is negligible, in Fazenda's opinion. Probably in part due to the Maryhill designers' decision to texturize the concrete surfaces. Due to the regularity of the Maryhill structure it has more high-end diffusion than Stonehenge, though they are very close on the low end.
The study's conclusion is that Stonehenge was a reflective environment, in which any sound is made to reverberate due to the flat, hard surfaces.
"The existence of a 1 second Reverberation Time would certainly be noticeable to any person entering the circle. Interestingly, 1s is a typical, optimal RT for a large lecture hall, ensuring good speech intelligibility. Anecdotally, the space exhibited this feature, i.e. speech was clearly audible regardless of speaker and listener position, undoubtedly due to the large number of reflective surfaces surrounding them but also due to the high degree of scattering provided by the interspacing between the stones, preventing any strong reflections from becoming a nuisance when interacting with the direct sound from the speaker."
Scientists, whether acoustic scientists or archaeologists, are for good reason reticent to draw conclusions that are not based on provable, duplicable facts. But at least we can do this. Picture what such a structure, with such an acoustical profile, would have meant experientially to visitors. Quite aside from any overt religious message, cult activity, and astronomical import, anyone entering the site would have felt the sense of sound change. Sound echoed, but in a specific way, bouncing from the stones' surfaces, but being rescued from noise by the interstices between them.
Proclamations must have borrowed a sense of supernatural import, prayers a kind of aural fecundity they would have been denied outside the circle. The human imagination values form. The circular form of Stonehenge, and the relationship of points therein, must have been lent an otherworldly dynamic by the special character of its sound.
Judge for yourself. Here is a sound recording of the Maryhill structure, with an accompanying animation, recorded and created by the University of Salford's Professor Trevor Cox, for his Sonic Wonders site.