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Preliminary results of our research in archaeoacoustics in Cividale del Friuli hypogeum, Italy


TAG: archaeoacoustics, hypogeum, Cividale, resonance, ultrasounds, infrasounds, SBRG, SB Research Group, Paolo Debertolis, Valter Maestra

After careful analysis on the recordings made in the last months, some members of SBRG have started a new season of acoustic analysis of the Cividale del Friuli hypogeum.

This consists of various underground spaces below the surface, carved out of the conglomerate with different levels and branches. Its shape looks very rough to a careless eye, but in reality despite the alterations over the centuries, the builders made full use of the shape of the rooms to take advantage of the resonance phenomenon, obtained during prayers mystic songs.


Fig. 1 - Map of the hypogeum of Cividale del Friuli


The underground could have been derived from a natural cavity along  the right rocky riverbank of the Natisone river. Aside from the fanciful interpretations mixed with legends, it was hypothesized that during the Celtic age, the Hypogeum was used as a depository for funerary urns, however other researchers believed it was used as a prison during the Roman or Lombard period.

On the other hand, there are three big and disturbing masks carved on its walls in the style of the Celtic tradition, similar to the remains of sculptures found in Celtic graves in France known as têtes coupées. So the niches carved out by other hands along the route are perfectly dry, possibly used at a later date as a mortuary. In respect of the other chambers they are wet so would have been unsuitable for use as a mortuary.

It is assumed that even some of the hypogeum rooms functioned as tanks with water and rites of uncertain origin. However, the true function and origin of this underground structure, which is unique in Friuli, remains a historic mystery. We can be certain that the underground had been remodeled in successive periods, however all the other hypotheses have not been supported by evidence.

The structure is represented by a central higher chamber, which is reached from the surface through a steep ladder that descends in depth. At the beginning of this ladder, you can find the only window that gives you the access to the riverbank of the  Natisone, the rest of the structure is totally underground. Three corridors depart from the central chamber, with niches and seats of various heights. Many niches appear to have been dug with a pick and refer to later periods.


Fig. 2 - The stairs leading to the central room (chamber A of the map)


The focus of our research group on this archaeological site was drawn from the theories about the function of this place by Valter Maestra, an independent researcher and historian of ancient civilizations. He drew a parallel with similar existing caves found in Peru, which were used to officiate rites of prayer to Mother Earth. According to this hypothesis, the hypogeum would have the same function as the caves found in Peru, with the aim of contacting the esoteric underworld.

The assumption seemed to us undoubtedly striking and, in parallel with research in archaeo-acoustics recently conducted in the South of England from SBRG. We are aware the resonance phenomenon has been detected in the Maltese underground temples by other researchers, so we wanted to test in the same way this structure.


Fig. 3 - Chamber B of Cividale del Friuli hypogeum has a different shape than C and D chambers. Therefore it is likely it was adjusted in subsequent periods or had another purpose


A few months after the beginning of the research, we have been able to detect the presence of the resonance effect in two chambers C and D (see map), these maintain the original form retaining an arched shape along the top. There is also a small truss on the end wall which seems to have been specially built to tune up the room for a male voice singing or praying.


Fig. 4 - The entrance to chamber C which seems to have retained the original shape and has demonstrated the presence of a conspicuous effect of resonance


Fig. 5 - The logarithmic plot of the effect of resonance in C chamber. The hump between 30KHz and 90KHz is due to increased sensitivity of the Sennheiser microphones at these frequencies, but there is not anomaly in this. No ultrasounds have been found in the Cividale hypogeum so far


The male voice is absolutely necessary to stimulate the resonance phenomenon as the two chambers are tuned to 94 and 102Hz. On several occasions we used a female voice, including a female mezzo-soprano voice however the resonance effect was not reached because below 150Hz it is wholly insufficient to stimulate the structure.


Fig. 6 - The recording devices placed at the entrance of the room C


Fig. 7 - The unilluminated bottom of  D chamber with highlighted in red microphones positioned for recording


Fig. 8 - Our collaborator, Dolores Dreosti, who sung using her mezzo-soprano voice for sound analysis of D chamber


The recordings were made with the usual archaeo-acoustics technical protocol of SBRG. Digital Recorder Tascam DR-680 programmed for a 192kHz sampling rate and Sennheiser MKH 3020 microphones, equipped with shielded cables Mogami Gold Edition XLR and gold-plated connectors.


 Fig. 9 - The extremely flat response of Sennheiser MKH 3020 microphones with a greater sensitivity in the field of ultrasounds


The experiment took place on various days over the last months and different singers were used to search for the right frequencies for the resonance phenomena. The tracks were examined with two programs for sound analysis: Praat program version 4.2.1 from the University of Toronto and Audacity open-source program version 2.0.2, both for Windows PC.


Fig. 10 - Top: the harmonious appearance of the graph from chamber D, with a male voice stimulating the resonance at 102Hz. Bottom: the detectable graph of D chamber when the voice is female. The dominant feature is around 198Hz, the hole in the low frequency range between 20Hz up to 200Hz is clearly shown in the graph


The resonance sound response is a range of sound that starts from infrasonic up to the frequency of 102Hz for D chamber or 94Hz for C chamber (the tuning by a male voice to create the resonant effect). This is particularly evident when comparing this graph with the graph of the female voice in which a hole appears in the same range of audible frequencies.


Fig. 11 - Chamber E located below the access ladder, had no resonant effect. It is possible this was dug in a later period as its shape is completely different from the other rooms


Fig. 12 - The researchers who participated in the experiment of May 14, 2013


We will publish as soon as possible the final results in an international scientific journal.

Paolo DebertolisMay 19, 2013


This is an original studio file collected in the hypogeum on 13th of May, 2013. It is recommended to listen ONLY through high-fidelity stereo headphones with a wide range of low frequencies, otherwise you can not hear just a little the resonance phenomenon. The file is not altered, but only compressed into .mp3 format because the original file in .wav format with 192kHz sampling rate has more than 200 Megabytes. This file takes about 2 minutes to listen in silence. To download the file (for personal use only and not for distribution) please click here.

A sincere thank you from the SBRG research group to the owners of Cividale del Friuli hypogeum for their helpfulness and kindness in yielding even at night their ancient  monument for our experiments. Heartfelt thanks also to Mr. Federico, who patiently gave us the keys of the hypogeum to our researches at all hours of the day.


Translated by Nina Earl



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