Low Frequency Noise from Aircraft Factsheet

What is low frequency noise?

This is noise below 200 Hz (range 20-200 Hz). A good example is a big sound-system. If you stand beside a sound system in a club you not only hear very loud music you can feel the vibrations in your body. This also illustrates how noise affects your whole body, not just your ears.

Is low-frequency noise a problem? It can be. Not when you are in the club where you usually come for the ‘experience’. But low frequency noise can be very disturbing. The reason it is used to torture prisoners. The World Health Organisation has found that, while not conventionally loud, wind turbine noise, including low-frequency noise and amplitude modulation (a “swishing” sound), causes higher levels of annoyance than other noise sources at similar decibel levels.

Is low-frequency noise a problem with aircraft?

It is. Aircraft noise has always contained a high amount of low-frequency noise. But modern jet aircraft, e.g. B737 MAX, A321neo, with high-bypass jet engines emit a greater proportion of their noise energy in the low frequency range (<200 Hz) than earlier generations of commercial aircraft. This is especially so during take-off and climb-out phases of the Landing and Take Off (LTO) cycle when engines are operating at near maximum thrust and aircraft are below 3,000 ft (914 m)

Does the way aircraft noise is measured capture the problem?

Many noise experts argue it does not. Noise is measured in decibels (dB) and given a “weighting” (e.g., A-weighted, dBA) to adjust raw measurements, so as to better reflect how the human ear perceives sound. But ‘A’ weighting almost completely misses low frequency noise. The 1999 World Health Organization (WHO) Guidelines for Community Noise recommend that when noise includes a large proportion of low-frequency components, A-weighted measurements will not adequately characterize the noise. It recommends C-weighting for noise with a large proportion of low-frequency sound, usually applied when there is a difference of 10–15 dB between C-weighted and A-weighted levels. An even more accurate measurement is the Zero-weighted (dBZ) scale that captures the whole noise spectrum (1 Hz to 16 kHz).

Does low frequency noise cause health problems?

There is a lot of evidence low frequency aircraft noise disrupts effective functioning of human vascular and lymphatic systems (Munzel et al, and others) through disrupting the innermost lining of blood and lymph vessles, increasing the risk of cardiovascular diseases (e.g. heart attacks), diabetes and other life-threatening ailments. Nighttime aircraft noise increases this by about 50% over daytime aircraft noise. Walls and even big buildings, e.g. hospitals, do not reduce the intensity of low frequency noise.

Conclusion

There is a lot of evidence that low frequency noise, which can be more annoying and damaging to health, is not accurately captured by the way aircraft noise is currently measured.