Low frequency noise

We can generally sense sounds at frequencies between 20 and 20,000 cycles per second, or hertz (Hz), although this range shrinks as a person ages. Prolonged exposure to loud noises within the audible range have long been known to cause hearing loss over time, but establishing the effect of sounds with frequencies under about 250 Hz has been harder. Even though they're above the lower limit of 20 Hz, these low frequency sounds tend to be either inaudible or barely audible and people don't always know when they're exposed to them.

The effect of low frequency noise (LFN), however, is often not recognised as a nuisance, even though it may have a profound effect on the psychological and physiological wellbeing of some people. These complaints are very difficult for Environmental Protection to investigate, as the levels of noise are often barely audible and the source direction is unclear. It's hard for us to know exactly how much of a serious nuisance low frequency noise is, but it is often a source of irritation. It's also difficult for us to assess the level of nuisance caused by low frequency noise. Ordinary sound level meters may not be able to detect LFN on the decibel scale as its decibel level is often lower than background noise.

The following may all be sources of LFN:

• Amplified music
• Pumps
• Fans
• Boilers
• Ventilation plants
• Utilities eg - water or electricity

LFN can be more noticeable indoors, which is why it is often associated with disturbed sleep. In the open air other noises such as traffic may mask the annoying low frequencies. Indoors, middle and high frequency noise from outside is reduced because the insulating effect of the building increases with sound frequency. Noises from the lower frequency bands, may remain the same or even increase, hence rattling windows etc. Another problem is that LFN travels further than higher frequencies, so the source is often difficult to trace. Sleep may be disturbed by the hum of a distant boiler, or the rattle of a window caused by passing traffic.

Throughout the country there are cases of people who can hear 'hums'. These sounds have no obvious source, but in some areas small groups of people apparently complain about noise from the same, unidentified source. These have been blamed on industrial sources and on gas pipelines. In some areas they have been investigated extensively, but their actual sources remain unconfirmed.

If you wish to make a formal complaint, please follow this link & complete our online complaint of nuisance form.