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Archaeoacoustical analysis of Cividale del Friuli Hypogeum using a shamanic drum

TAG: archaeo-acoustics, archaeoacoustics , hypogeum , Cividale del Friuli, resonance, ultrasound, infrasound, shamanic drum, SBRG, SB Research Group

On 21th of February 2014 we revisited Cividale del Friuli Hypogeum (Italy) to stimulate the resonance phenomenon in those chambers whose structure has been unaltered.

In particular, we wanted to test the resonance of one of the Hypogeum deeper chambers in which the effect appears to be more intense (chamber D on the map), this chamber is oriented within a few degrees of south.

Fig. 1 – Above: the map of the Hypogeum of Cividale del Friuli. Below: the entrance to the deeper chamber (marked D on the map)


This room is tuned to a frequency of around 101- 103Hz (102Hz on average), it is sensitive to songs and prayers (mantras) sung at this frequency by a male voice. The female voice, which does not have this range, is unable to stress the structure.

SB research group began to study this underground structure not based on the commonly held hypothesis that the Celts used it as a burial place, or it was used as a prison by the ancient Romans and Longobards. Our study was based on the hypothesis suggested by the independent researcher V. Maestra who suggested it is much older. He considered this structure to be a temple dedicated to the Mother Goddess. In fact this temple has sound resonance characteristics that would suggest it was geared for sacred rituals and not as a burial place.

During our study we found only two chambers (C and D of the map) to be sensitive to the resonance phenomenon. These are most likely the only rooms which have retained the original features and have not been modified in later times for a different use.

Our earlier research has been published in the international literature in the United States (here).

If we consider the Hypogeum of  Cividale to be a temple of Mother Earth whose date has been lost in time, we must consider that this cult was usually conducted by priestesses. For this reason we have compared it to the more well-known underground Hypogeum of Hal Saflieni in Malta notoriously dedicated to Mother Goddess.

But if priestesses conducted the religious rites in this structure, it seems counterintuitive that the only way to stimulate the resonance effect, which creates a strong emotion in those present in the rituals, was only through a male voice. Surely if our hypothesis is correct, there must be other ways to activate this process.

After taking this into consideration, we decided to use an easy to play acoustic instrument which would have been available in the historical period corresponding to the construction of a temple dedicated to the Mother Goddess.

We discarded wind instruments as the tone was too high or other methods such as glass goblets. Instead we looked at the kind of percussion instrument that is known as a "shamanic drum" still commonly used today in Celtic music performed in Northern Europe and also shamanic rituals.

This ancient instrument is found in virtually all cultures of the world and are still made today. It is a drum with one head, built on a circle in solid wood on which is stretched an animal skin, typically goat or deer, but skins can also be derived from different animals, depending on the area and culture.

These skins are stretched on the wooden circle still wet with ropes to reach the right amount of tension when drying.

Typically they range in diameter from 30 to 50 cm, and usually on the back side the shamanic drum is a handle. This can be made from ropes or parts of skins cut into strips and then tied, or with a wooden cross that allows it to be grabbed firmly with one hand while the other hand remains free to strike him with a wooden beater that can be made
of leather or other materials.

There are still a large number of craftsmen who can make such drums in many versions, and different patterns present on the skin can make a drum have a unique sound.

The sound is deep, but if the skin is damp from moisture, the tone changes as it vibrates less. The skin needs to be dry to produce the correct sound.

So the sound can change very quickly and is conditioned by the environment, if this is humid then the skin needs to be heated over a fire in order to obtain a more pure sound.

For our research we used a shamanic drum with a diameter of 50 cm made from goat skin. On the skin is a symbol of the Thunder Bird with two heads from Native American mythology, created by the craftsman who produced it. This design does not change the sound characteristics of the instrument, but it is purely for decoration.


Fig. 2 – The shamanic drum used during the experiment seen from the front


This drum has an average resonance frequency of around 55Hz when beaten at the center. As previously mentioned, the sound characteristics of this instrument can be undermined after a prolonged stay in the moist environment such as that found in Cividale Hypogeum.   This meant that at the start of the experiment the drums were working more efficiently than after prolonged exposure to the moist environment. The tone of the sound can also change depending upon where the beater strikes the skin, for example at the periphery the tone rises, but there is also a decrease in sound pressure that can be exerted.

The drum used in our experiment was placed at the end of the chamber D. As expected, the greatest effect was achieved by placing the drum in the sound node previously found. The term "node" refers to the point in the interior space of the chamber where the greatest effect acoustic resonance effect is felt. In this case about half meter from the bottom of the chamber and one meter in height. The resonance effect decreased dramatically the further away we moved from this point.


Fig. 3 – The drum has been used in different parts of chamber D, but the best configuration occurred in node sound (image below)



The frequency response of the structure was amazing, even though the drum had a frequency extension of i around 55Hz, the room responded at 103Hz, the frequency for which it is tuned. It is conceivable that the high sound pressure exerted by the drum or one of its harmonic vibrations put the chamber into this resonant vibration.

This effect amazed us, however graphical analysis of the recorded files has shown there are two very distinct peaks, the first from the shamanic drum, the second from the chamber.

If we look at the logarithmic plot of the recordings made during our  sound tests, we notice the presence of two peaks of greater intensity. If we put the cursor on the second peak in the graphic program, we can verify that the response of the chamber is tuned on 103Hz. This graphic
behaviour is the same one that is obtained by the male voice tuned to the same frequency of the chamber. If you point the cursor to the first peak it reads 55Hz, which is the average frequency of emission of the shamanic drum. As you can see, the sound response of the chamber in volume is equal to the sound pressure exerted by the drum. There are also higher harmonics of a smaller volume.


 Fig. 4 – The logarithmic graph that come out from the analysis of the recordings : two peaks of the same volume are evident, one determined by the sound of the drum (first from left ) and one from the chamber


By drumming at a certain rate, the chamber almost continuously vibrates. These vibrations, that are composed of frequencies in which we are investigating in another area of research using EEG, are capable of interfering with brain activity, and can create a state of ecstasy.

What seems clear at this point is that if this was originally an underground temple of Mother Earth, it was not necessary that a man was present to use his voice to generate the resonance response, rather it was sufficient that the Mother Earth priestess used a drum during a ceremony, beating at the right pace and in the right position (acoustic node). While it is conceivable that the onlookers were sitting on the seats carved into the rock in several places close to the celebrant.  We have verified that sound easily travels within the Hypogeum.


Fig. 5 – The digital recording equipment (Tascam DR -680) and Sennheiser mics (MHK3020), as from our standard SBSA protocol


On one of the recorded files after the beat of the drum it is possible to hear distinctly the response of the chamber that creates saturation within the microphones (here). To listen to this file you need to use a good pair of stereo headphones with a large bass component. If you use standard computer speakers you may run the risk of not hearing anything.


We had heard about the risk of remaining too long in the hypogeum due to Radon gas emissions from below, we wanted to measure the radioactivity using a Geiger counter (GAMMA - SCOUT model w/ALERT).

The environment was free from any radioactivity, we measured a maximum of 0.08 to 0.09 mSv/h. There is therefore no danger in this environment. It should be remembered that in the underground Ravne tunels in Bosnia, we measured a maximum radioactivity of 0.20 mSv/h. We have to recall too that the alarm threshold is set at 0.4 mSv/h, while values
greater than 0.60 mSv/h reveal the presence of a radioactive source.



Fig. 6 – The Geiger counter demonstrates a very low radioactivity levels because the underground structure is protected from the action of cosmic rays  and there is no presence of Radon gas


All recordings were performed according to the Standard SBSA protocol.

Paolo Debertolis - January 24, 2014


A sincere thank you from the SBRG research group to the owner of Cividale del Friuli Hypogeum, Mr. Gaetano Bront for his helpfulness and kindness in allowing us to enter even at night his ancient monument for our experiments. Heartfelt thanks also to Mr. Federico Morandini, who patiently gave us the keys of the hypogeum to conduct our research at all hours of the day and night. Thanks also to our new collaborator, Mrs. Dolores Dreosti, for her support in Cividale del Friuli researches.



Translated by Nina Earl


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