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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. 

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.

Acoustics may well have been part of a widespread religious tradition.

A fascinating, though seldom discussed, mystery at Chichen Itza concerns the strange acoustic anomalies observable at the great ball court and the temple of Kukulkan. Words softly whispered at one end of the great ball court (measuring 545 feet long by 225 feet wide) are clearly audible all the way at the other end and a single clap or shout sounded in the center of the ball court will produce nine distinct echoes.

Visitors have also commented on a curious acoustic phenomenon at the pyramid of Kukulkan where the sound of a hand clap is echoed back as the chirping sound of the Quetzal bird, the sacred bird associated with both the name of the pyramid and its deity Kukulkan/Quetzalcoatl.

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.