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Commentary on the paper by Jahn, Robert G., et al; "Acoustical Resonances of Assorted Ancient Structures," Technical Report PEAR 95002, Princeton University, March 1995

A consortium called The PEAR Proposition: Princeton Engineering Anomalies Research are pioneers in the field of archaeo-acoustics, merging archaeology and sound science. Directed by Physicist Dr. Robert Jahn, the PEAR group set out in 1994 to test acoustic behavior in megalithic sites such as Newgrange and Wayland's Smithy in the UK. They found that the ancient chambers all sustained a strong resonance at a sound frequency between 95 and 120 hertz: well within the range of a low male voice.

In subsequent OTSF testing, stone rooms in ancient temples in Malta were found to match the same pattern of resonance, registering at the frequency of 110 or 111 hz. This turns out to be a significant level for the human brain. Whether it was deliberate or not, the people who spent time in such an environment were exposing themselves to vibrations that impacted their minds.  Sound scientist, Prof. Daniel Talma of the University of Malta explains:

"At certain frequencies you have standing waves that emphasize each and other waves that de-emphasize each other. The idea that it was used thousands of years ago to create a certain trance -- that's what fascinates me."

Dr. Ian A. Cook of UCLA and colleagues published findings in 2008 of an experiment in which regional brain activity in a number of healthy volunteers was monitored by EEG through different resonance frequencies.

Findings indicated that at 110 hz the patterns of activity over the prefrontal cortex abruptly shifted, resulting in a relative deactivation of the language center and a temporary switching from left to right-sided dominance related to emotional processing. People regularly exposed to resonant sound in the frequency of 110 or 111 hz would have been "turning on" an area of the brain that bio-behavioral scientists believe relates to mood, empathy and social behavior.

Although archaeologists had not found an explanation for such sophisticated engineering suddenly blossoming nearly six thousand years ago, Prof. Richard England, a Fellow of the American Institute of Architects, sees an evolution:

". . . a gradual growth, from the cave to the tomb. The idea of continuity comes from an underground architecture. Gradually from these ovular rock-hewn spaces, man moved above ground, and above ground he fashioned an architecture of the living which followed the form of an architecture for the dead."

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; others were rectangular, beehive, and petal-shaped. 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 been intentionally positioned to enhance the chamber's acoustical properties.

Why 110 Hz?

Many archaeo-acoustic investigations of prehistoric, megalithic structures have identified acoustic resonances at frequencies of 95-120 Hz, particularly near 110-12 Hz, all representing pitches in the human vocal range. These chambers may have served as centers for social or spiritual events, and the resonances of the chamber cavities might have been intended to support human ritual chanting.

A recent study evaluated the possibility that tones at these frequencies might specifically affect regional brain activity. In a pilot project, 30 healthy adults listened to tones at 90, 100, 110, 120, and 130 Hz while brain activity was monitored with electroencephalography (EEG). Activity in the left temporal region was found to be significantly lower at 110 Hz than at other frequencies. Additionally, the pattern of asymmetric activity over the prefrontal cortex shifted from one of higher activity on the left at most frequencies to rightsided dominance at 110 Hz.

These findings are compatible with relative deactivation of language centers and a shift in prefrontal activity that may be related to emotional processing. These intriguing pilot findings suggest that the acoustic properties of ancient structures may influence human brain function, and suggest that chanting might have been used to enhance right brain activities.