Mike Lotinga, October 2017 . Thanks to Dan Pope for helpful comments.

The ancient Celtic pagan festival of Samhain was a time in which the doorways between the spirit-world and ours were thought to be traversed by dead souls, invited to enjoy hospitality in the homes of Gaelic folk, some dressed in costumes representing the spirits and receiving offerings for them.

This mystical celebration, later combined with the Christian tradition of All Saints Day, has become the modern-day descendant we now know as Halloween, when the dark and spooky side of life (and death) are celebrated, also signifying the annual descent towards the bleak winter months.

Our sense of things that feel creepy is intimately connected with sound – our hearing is fine-tuned from birth to pick up the tiniest sounds of things sneaking up behind us, and can often be the first sense to indicate alarm or discomfort with our surroundings. As a child I remember occasions lying awake at night, unable to believe the tiny high-frequency rustles and creaks I could hear were not the sounds of unimaginable horrors clambering or slithering into my bedroom (not a problem anymore, thanks to presbycusis).

According to a YouGov poll in 2014, nearly 30% of UK adults believe that ghosts or supernatural beings probably or definitely exist (N = 1629), with almost as many claiming to have actually seen or felt the presence of a supernatural being[1].

One well-documented case of ghostly activity was investigated by two lecturers at Coventry University: odd occurrences and a night-time visual apparition led one of the engineering-inclined authors to conduct an experiment into his own perceived paranormal experience. This led to two papers published in the Journal of the Society for Psychical Research, which linked the events with the apparent presence of a low frequency standing wave, the culprit of which was found to be a recently-installed ventilation unit; this was thought to be exciting an acoustic mode in the room at a frequency estimated at 19 Hz[2]. In the second paper, the same frequency was again linked with a modern account of a tourist struck by a chill and physical but unexplained presence while visiting the cellar of a 14th century house, also in Coventry. The investigator used an impulsive source and an infrasonic/low frequency measurement setup to estimate the cellar’s frequency response; two particular peaks were noted – one at 19 Hz and another at 23 Hz, which were connected with modes expected from the geometrical dimensions[3]. These works may have led to popular media descriptions of the so-called ‘fear frequency’, which is said to instil a sense of dread and terror in unfortunate victims, although other researchers have been openly sceptical of the findings, citing methodological inadequacies[4].

The appropriately-titled ‘Haunt’ project conducted at Goldsmiths College attempted to investigate this link between acoustics and paranormal experiences further: the researchers set up a chamber designed to expose occupants to closely-controlled infrasonic and electromagnetic fields (EMFs), and asked the subjects to record their perceptive experiences in the room over a period of 50 minutes. Responses were quantified using paranormality measures such as the Australian Sheep-Goat Scale, and the results statistically analysed. The findings suggested that although participants reported experiencing unusual sensations (eg ‘feeling detached from their bodies’), this was linked primarily to their degree of suggestibility, rather than exposure to infrasound (or EMF)[5]. However, this study has also been subsequently criticised for lack of rigour in determining infrasound levels, combined with further empirical evidence for the 19Hz ‘fear frequency’ gathered during ghost walks in Edinburgh[6]. These experiments were designed by self-styled ‘ghost hunter’ and ‘ghostology’ educator Steven T Parsons – also co-editor of a book examining the link between sound and the paranormal[7], which previously featured in an IOA Acoustics Bulletin review.

Other acoustical studies of the paranormal have considered such questions as ‘what does a poltergeist sound like’, but one that occurred to me while writing this was: why do ghosts go “WOOOO”? Fortunately, with the internet being what it is, it didn’t take long to find someone else asking the same question – with an intriguing suggestion that it may have something to do with early movies and the use of spooky sounds such as generated from the theremin. Another interesting mention refers to the ancient Roman ghost story of Pliny the Younger, which describes, before any other frightening sensation, the sound of a haunting: ‘in the dead of night, a noise…’, ‘…which, if you listened more attentively, sounded like the rattling of chains, distant at first, but approaching nearer by degrees. Immediately afterwards, a spectre appeared in the form of an old man…’ – surely the source of inspiration for Dickens’ ghost of Marley!

Whether you believe in the supernatural or not, there’s no denying the incredible power of sound to induce feelings and emotions, including fear and terror.

And how can you be so sure, …I mean, really confident, that something sinister isn’t occurring…when things go bump in the night…?