Malta’s Hypogeum of Ħal-Saflieni

The UNESCO World Heritage Site at Paola, Malta has special significance due to its remarkable acoustic properties. The Hypogeum of Ħal-Saflieni is an underground cave system covering around 500m² on 3 levels, with various inter-connecting corridors and passageways that lead to a number of small chambers, built between 3000-2500BC. The cave system was re-discovered in 1902 and since then there has been particular interest in one of the rooms, named the “Oracle Chamber”. The space is said to amplify voices dramatically, with certain frequencies resonating enough to be felt through the body.

The Oracle Chamber

The Oracle Chamber

As knowledge of this phenomenon has spread, many investigations have been carried out into its acoustic properties as well as other similarly designed spaces across the world. Research has shown that a number of these locations (such as that at Newgrange, Ireland) have very similar acoustic features, specifically resonating at 110Hz. Ritual chanting along with simple instruments (drums played by hand for example) may have been able to excite the resonances around the 110Hz area of the frequency spectrum that would have created some odd acoustics effects.

FFT of male voices showing 110Hz resonance.

FFT of male voices showing 110Hz resonance.

It is still not known whether the space was specifically designed to produce these resonances (which would indicate a very early understanding of acoustics and sound) or if it was simply a lucky coincidence with those particular room dimensions and rock type. The use of the space is also unknown, was it a ritual site where chanting and singing were common, or maybe a temple for prayer?

Research carried out in February 2014 by Dr. Paolo Debertolis, Department of Medical Sciences, University of Trieste, Italy and Linda C. Eneix, Mediterranean Institute of Ancient Civilizations, may shed some light on the use of the space by investigating the type of noise sources that are capable of exciting the resonances of the space.

Their studies investigated the effects of the space on male and female voices, conch shells, cow horns and basic percussion. FFT’s recorded in the space show that there is one main resonance (at 110Hz) as well as a secondary lower frequnecy of around 70Hz. This indicates that low frequency elements of male voices (shown in FFT above) as well as that of drums would be capable of exciting it. When played softly a drum does not excite the resonance sufficiently enough to be audible, however when played forcefully the resonance is loud enough that it sounds like a male “ooooh”. Listen here.

FFT Drum

FFT of forceful drum hit showing 114Hz and 70Hz resonance

Further recordings of chanting in the space give an idea of how this may have sounded thousands of years ago.

In future, more investigations into the acoustics of this remarkable place will likely reveal what rituals and events went on there thousands of years ago, and maybe one day we will be able to explain the design and construction that has lead to such an interesting acoustic space.

Comments (7):

  1. Erny Dedmon

    3 May 2014 at 2:10 am

    It is a shame they talked throughout the recording, do not let any reverberation go to the end, and uploaded the mess in a lossy format. This made it far from scientific and not useful as an impulse response. I find it hard to believe that archeoacoustic scientists are this sloppy. I could have done better with a cheap digital recorder and a balloon.

    • Lawrence Yule

      3 May 2014 at 8:54 am

      Unfortunately for us I am under the impression that the researchers in this case were not pure acousticians but archeologists with an interest in the obscure sound of the space. However, due to the amount of interest in this phenomenon in Malta, as well as at other sites around the world, there is almost certainly more detailed acoustical information available.

    • Paolo Debertolis

      31 August 2014 at 6:14 am

      Instead I think your thoughts are totally wrong and your comments are a simple example of a lack of knowledge in archaeoacoustic research.
      You cannot upload on Internet all our records taken at 192KHz of sampling rate (24 bits) in Hal Saflieni Hypogeum. They are too heavy for Internet. It is clear if you say “lossy” is because probably you never researched in this field and you cannot understand these little problems for spreading our results to the public.
      Second: my research group is working on several sites in Europe for archaeoacoustics from 2010 and we always let the reverberation going to the end for analyzing better this phenomenon. You did not listen all other recordings.

  2. Lee Davison

    3 September 2014 at 9:46 am

    Hi Dr. Debertolls, Thanks for dropping by to our blog! If you have other recordings available we would love to hear them. Is there a place they have been made available?
    I’m afraid Erny is quite correct when he states that a lossless format might have been better. SoundButt I believe allows you to upload in lossy format for re-download by your listeners, while the streamed version is compressed via lossy. Otherwise it would be relevant to re-sample it to 44.1, because it will retain all the frequency information you need.

    Either way the data is good to analyse. If you could provide us with an impulse response or a sweep, that would be excellent!


Leave a Reply

Your email address will not be published. Required fields are marked *