An Experimental Evaluation of Annoyance Due to Low Frequency Noise

Annoyance due to environmental noise from various sources constitutes an important public health problem. Extensive work has been performed to obtain a basis for dose response curves, which can later be used for regulation purposes. Using such data, limits for noise exposure have been suggested or enforced for noise from aircraft, trains and road traffic. The estimation of the noise exposure for environmental noise is usually performed using the dB(A) unit. This is based upon early experiments where equal loudness curves were constructed by exposing test subjects to mainly pure tones of various frequencies for short exposure periods (e.g. Fletcher and Munson 1933, Churcher et al1937, Robinson and Dadson 1956). Experience from practical public health work demonstrates that this concept for judging annoyance can be questioned. Complaints to Local Health Authorities are frequently raised concerning low frequency sounds, and annoyance is reported, although dB(A) levels fall well below current limits. Sources oflow frequency noise, such as heavy vehicles, ventilation installations and compressors have increased in number in urban areas. In Sweden a recent source of low frequency noise is the use of heat pumps which extract heat from the air. There has been a rapid rise in the number of heat pumps owing to their ability to reduce heating costs. The pumps and compressors used, radiate low frequency noise, usually dominated by frequencies in the range 63-125 Hz. This is not a high noise level according to current noise limits, seldom exceeding 40 dB(A) outdoors. Despite this, many heat pumps have been reported as sources of annoyance to people living in the vicinity as shown by complaints received by Local Health Authorities (Persson and Rylander 1986). To further study annoyance from low frequency noise, we have performed studies in a laboratory environment. Subjects were exposed to two different noises of the same dB(A) levelbut where one of the noises contained a higher proportion oflow frequencies. The annoyance experienced by the subjects was assessed after a 30 minute exposure.