Archived report · 2 min read · Set in Dunmore Row ·
The Sprung Floor at Dunmore Row
A structural survey of the sprung dance floor in the Dunmore Row assembly hall records a steady beat coming up through the boards, and a stop in the rhythm whenever someone stands on the centre spot.
- filed: Filed after the complaint from the Thursday class
- reference: DRA/SF/11
Subject: sprung hardwood floor, main hall, Dunmore Row Assembly Rooms.
1. The floor was laid in 1936 on rubber pads over a timber sub-frame. Its spring characteristics were tested in 1952 and found to meet the standard for ballroom use. It is maintained by the borough and was last surveyed in 2016.
2. The Thursday evening dance class reported that the floor was moving unevenly during sessions, and that the movement was not caused by dancers. The survey was carried out during an empty afternoon.
3. Accelerometers were placed at four points on the floor and recorded continuously for six hours. The unoccupied floor showed a regular oscillation at 2.2 hertz, matching a tempo of approximately 132 beats per minute. The amplitude was low, below the threshold of perception, but it was present across the entire floor and did not decay.
4. The sub-frame was inspected by lifting two boards in the centre. Beneath the boards, the joists and pads were in good condition. No loose fixings were found. The rhythm was still present when the boards were replaced.
5. The beat was recorded through the pads of the floor at each of the four sensor points, with a phase difference between them consistent with a source travelling slowly from the north wall toward the centre.
6. When a surveyor stood on the centre spot, the oscillation stopped for the duration of his presence. It resumed within one second of his stepping off. This was observed on three separate occasions by two surveyors and was recorded on the sensors.
7. The surveyors recommend that the hall be closed for a period of structural monitoring. The Thursday class has been moved to the church rooms.
8. Observation not explained by the survey: the sensors recorded, during the centre-spot pause, a second rhythm faintly under the first, at exactly half the tempo, which sounds, on playback, like a single word being counted in a voice that is not hurrying.