Ongoing research at Neolithic sites around the UK has revealed striking similarities in their acoustical properties. Key examples, both in Ireland, are the huge passage tomb of Newgrange and the burial mound known as Cairn L at Loughcrew. These sites contain passageways leading to large circular chambers, and have a resonant frequency (at which sounds naturally echo and reverberate) of about 110hz - the frequency of the male baritone, the second lowest singing voice. Standing waves, whereby sounds are reflected off walls and superimposed on to one another, and other acoustic curiosities, have been observed in these and other sites. Stone circles including Avebury and Stonehenge also appear to reflect sound in distinctive ways.
     Archaeologists have suggested that chanting, singing and drumming at these sites would have produced reverberating echoes that might have been interpreted as voices of spirits or gods; they may also have induced physiological and psychological changes in people, adding to their potency as sites of spiritual importance. These acoustic discoveries may also shed light on some of the visual motifs etched into the walls of many ancient sites. Experiments in a replica of the Newgrange passage, at Princeton University, showed that if a site was smoky or misty, standing sound waves would become visible as they vibrated particles in the air. Could this visualising effect account for the zigzag and concentric ring markings on the chamber walls?
     Acoustic archaeology is a young field finally gaining academic respectability. New discoveries are made constantly, so next time you're at an ancient site, sing, clap your hands - and listen carefully.

Source: The Guardian (6 November 2003)