A sharp sound inside Pirunkirkko can leave a ringing tone behind. At the back of this narrow cave in Finland’s Koli landscape, researchers recorded a physical resonance whose pitch falls around 219–232 Hz. The finding offers a concrete contribution to a place long associated with spirits and ritual specialists. It does not establish that every story about the cave arose from sound, or that the people telling those stories understood resonance in the same terms.
Riitta Rainio and Elina Hytönen-Ng brought acoustic measurements, published archival material and ethnographic observation together in their 2023 study. Its interest lies in the distinction between what instruments detected and what visitors experienced. The cave can measurably respond to a voice or an impulse, while the cultural meaning of that response remains open to interpretation.
One Devil’s Church among many
Pirunkirkko means Devil’s Church, but the name alone is a poor way to identify a site. The study found many Finnish places bearing it, and even the Koli area has another similarly named cave on Hattusaari. The investigated location is the crevice at Kirkkokallio in the southern part of the Koli mountain range. Its geometry, rather than a general reputation shared by every similarly named rock, is essential to the findings.
The authors describe a roughly 34-metre passage arranged in three sections like a letter Z. Some parts are open above; other sections have high walls and a covering of cliff or wedged boulders. The especially narrow inner corridor has smooth, nearly parallel walls. Those surfaces provide conditions that can select and prolong particular frequencies from a passing sound.
A cave can therefore behave differently from one corner to the next. The authors did not report the same strong ringing in the middle corridor or in the neighbouring caves they checked. Calling the whole landscape acoustically unusual would flatten that distinction. The measured effect belongs to particular spaces within the studied cave.
Traditions of sages and a church inside the mountain
The historical material describes Koli as a place of spirits and powerful ritual practitioners. Some stories identify the accessible cave as only a vestibule, with a more remarkable church beyond the back of the mountain. A sage called Kinolainen is connected with the place. The authors discuss the possibility of a historical basis for that name, while observing that several of the tales also occur elsewhere.
That warning prevents a familiar folkloric pattern from becoming an individually verified biography. A tale associated with a real family or locality may retain widely travelled motifs. In the study, archival references identify where accounts were collected; they do not certify the supernatural actions within them. This article uses the researchers’ published transcriptions and analysis, rather than claiming independent access to the underlying folklore manuscripts.
The authors also distinguish historical Finnish–Karelian sages from contemporary practitioners. The older descriptions emphasise shouting, striking, stamping and other forceful sounds. They do not justify a simple claim that modern drumming at the cave continues an unbroken, identically performed ancient ceremony. The study itself discusses a break in transmission.
How the acoustic tests worked
Acoustic fieldwork took place in September 2019 and July 2020. Rainio’s team recorded impulse responses at the entrance, in the middle corridor and at several positions in the inner corridor. A sudden, broad-spectrum sound supplies many frequencies at once. Recording what follows reveals which parts fade rapidly and which the surrounding space reinforces.
The team used balloon pops for a reasonably repeatable excitation. Handclaps, percussion and voices served as demonstrations, but were less suitable as standardised measurement signals. An intended loudspeaker method had an important practical limitation: the large loudspeaker would not fit into the most interesting rear part of the cave. Its results could not simply be treated as equivalent measurements across every location.
The study combines these recordings with a measured floor plan and spectral analysis. Spectrograms show frequency and time together, allowing a lingering narrow band to be distinguished from a broad initial noise. The article reports the equipment and recording arrangements so that its explanation is more than a claim that the cave sounded strange to the investigators.
The ringing left after an impulse
At the entrance, the response resembled an outdoor soundscape with many overlapping reflections. In the middle corridor, early reflections increased the initial sound but faded relatively quickly. In the inner corridor, distinct frequencies remained for roughly three-quarters of a second to almost a second after the initial impulse. Their strength increased towards the rear positions.
The lowest reported ringing band was 219–232 Hz. Higher bands lay approximately at integer multiples of that frequency, producing a harmonic series heard as a musical tone. The researchers relate this pattern to a standing wave between the walls. Sound energy travels repeatedly between the surfaces, and frequencies fitting the space are reinforced and decay more slowly.
This is an ordinary physical process in an unusual natural setting. It does not require an external unseen speaker to continue producing a tone after a clap. Nor is resonance a claim that the rock generates energy without an input. The sound put into the space and the geometry of the space interact. That physical account is the strongest directly tested part of the case.
A ritual recorded in the same space
Hytönen-Ng separately accompanied a contemporary practitioner into the cave on 13 March 2020. The published paper describes drumming and singing performed near the back, followed by an interview about the place’s meaning. The practitioner knew the activities were being recorded and consented to the research. The article reports experience and interpretation alongside acoustic analysis of the recorded performance.
In that performance the drum’s own lingering tones overlapped with the cave’s response, making their contributions harder to separate by ear. One sung pitch was close to the cave’s resonant frequency. The authors found an associated increase in level of about five decibels compared with other sung pitches, repeated within the analysed passage. They interpret this as the cave reinforcing a tone used during the ritual.
Neither the practitioner nor the local folklore quoted in the paper explicitly describes the measured ringing as resonance. The authors suggest that cultural expectations help shape what listeners attend to and how they describe it. That is a reason to consider perception carefully, rather than a demonstration that every reference to spiritual experience can be translated into a particular frequency.
What remains an interpretation
The measured response supports a physical explanation for a distinctive part of the cave’s sound. Its role in earlier rituals is a historical argument: the researchers compare the noises described in tradition with the effect those noises can produce in the present space. There is no recording of the historical sages against which to test that reconstruction directly.
The authors’ acoustic data are not wholly open, and the sensitive interview material is expressly unavailable publicly. No private dataset or interview was requested or accessed for this article. The account rests on the methods, selected original results, discussion and conclusions published in the paper, not an independent reanalysis of recordings or a claim to have heard the sound samples.
The cave’s reputation is undated and cumulative. Fieldwork years and the paper’s 2023 publication are kept separate from an incident date, so no incident-year filter value is assigned. The useful outcome is a documented natural resonance and a carefully limited proposal about how a physical environment may contribute to a meaningful place.
Location and source trail
The map is an approximate cave-area reference for the Kirkkokallio Pirunkirkko in Koli National Park, rounded from the Koli–Lieksa visitor listing. It is not a microphone position, a surveyed corridor plan, a different Pirunkirkko elsewhere in Finland or a statement of current access conditions.
The main source is Rainio and Hytönen-Ng’s “Ringing Tone and Drumming Sages in the Crevice Cave of Pirunkirkko, Koli, Finland”, Open Archaeology 9 (2023), article 20220328. The source is published under Creative Commons Attribution 4.0; the discussion here is an original, attributed summary of the research. The University of Eastern Finland’s report provides institutional context. The artwork above is a modern illustration and supplies no additional observational evidence.