- Understanding aviation noise
- Noise concepts
Acoustics is a scientific discipline, which combines the physical aspects for describing sound phenomena and the physiological aspects for characterising the auditory sensation. Physical sciences and neurosciences are, therefore, inseparable for understanding and for interpreting the auditory perception induced by sound and, finally, for evaluating the human response (e.g. annoyance). To deal with this last aspect, which goes beyond physics, it is necessary to understand other sciences – human, psychological and sociological.
Over the past 50 years and more, the main drivers for action to limit, minimise, and reduce aircraft noise have been noise complaints and reported noise annoyance. Actual aircraft sound exposure can, and does, vary over a vast range of different situations and contexts, often leading to considerable differences in subjective outcomes; this can be difficult to represent by the use of just one specific metric. There is an underlying tension between the need to develop simple single number numeric metrics based on overall average quantities and the need to properly reflect the full range of input variables (e.g. the timing, duration and noisiness of single events), which may need to be taken into account to reflect key input variables in specific situations properly.
Such varied use of metrics has the potential to compromise the practicality of any regulatory application. On the other hand, this use of a variety of metrics can provide for a more detailed representation of a given situation, which can significantly enhance the public’s understanding when used in communication and consultation.
The main dimensions over which sound can vary are:
- Instantaneous sound quality, represented by the short-time varying frequency spectrum;
- Longer time temporal distribution, represented by the sound level time history; and
- Spatial distribution, which can only be represented by the use of multiple measurement positions.