The Newgrange chamber, with acoustical nodes and antinodes. Antinode occur at the chamber's stone walls.
R.G. Jahn et al have taken sound generators and meters into the chambers of six ancient structures and measured their acoustical properties. The sites selected were: Wayland's Smithy, Chun Quoit, and Cairn Euny, all in the U.K.; Newgrange, and Cairns L and I, Carbane West, all in Ireland. All of these sites date back to about 3,500 BC. The chambers were all bounded by roughly hewn stones, but they had very different configurations. Newgrange was cruciform (see sketch); others were rectangular, beehive, and petalshaped. Quoting the abstract from the Princeton report, here is what the acoustical surveys found:
"Rudimentary acoustical measurements performed inside six diverse Neolithic and Iron Age structures revealed that each sustained a strong resonance at a frequency between 95 and 120 Hz (wavelength about 3m). Despite major differences in chamber shapes and sizes, the resonant modal patterns all featured strong antinodes at the outer walls, with appropriately configured nodes and antinodes interspersed toward the central source. In some cases, internal and exterior rock drawings resembled these acoustical patterns. Since the resonant frequencies are well within the adult male voice range, one may speculate that some forms of human chanting, enhanced by the cavity resonance, were invoked for ritual purpose."
In a few cases, it appeared that some of the standing
stones had beeen intentionally positioned to enhance the chamber's acoustical
properties. (Jahn, Robert G., et al; "Acoustical Resonances of Assorted
Ancient Structures," Technical Report PEAR 95002, Princeton University,
March 1995. Devereux, Paul, et al; "Acoustical Properties of Ancient Ceremonial
Journal of Scientific Exploration, 9:438, 1995.)