Abstract
Environmental low frequency noise and vibration (or “hum”) is a growing annoyance and potential health hazard to many people, according to surveys conducted by the UK's Low Frequency Noise Sufferer's Association. This paper describes attempts to measure the “hum” using microseismic methods. Sensitive three-component seismometers and high resolution digital dataloggers were employed in the homes of “hum” sufferers, and three-dimensional vibrational data were recorded overnight. Frequency analyses were then performed on the time series data using Fast Fourier Transform methods.
In one case study, a clear signal was observed corresponding to a fundamental vibrational frequency peak of 10 Hz. At least one harmonic frequency peak (30 Hz) was also apparent. It is suggested that local industry of some kind (with machinery running overnight at an operating frequency of 10 Hz) may be responsible for this ground-borne disturbance.
In another house occupied by “hum” sufferers, no notable ground velocities were recorded overnight with the seismometer mounted on ground floor concrete foundations. Significant levels of vibration were only observed in an upstairs bedroom, by placing the instrument on floorboards which appear to be excited by acoustic waves in the room. It is inferred that in this case the “hum” is predominantly air-borne; again, local industry is a likely source.
Low frequency “hum”, both acoustic and ground-borne, is a very real problem which causes sufferers great distress. It is possible to measure the “hum” and determine its frequency characteristics using microseismic techniques. Urgent revision of current legislation is needed to limit industrial output levels of low frequency noise/vibration, especially at night time.