Guide to Predictive Modelling for Environmental Noise Assessment
Glossary
A-Weighted Noise Level:
A measured noise level which has been weighed by filters to produce a reading that corresponds approximately to what we hear.
Acoustic Wave Equation:
An equation which describes the propagation of a sound wave through a specified medium.
Ambient Sound:
The totally encompassing sound in a given situation at a given time usually being composed of sound from many sources near and far.
Assessment:
Any decision making process that uses objective evaluations of environmental noise fields.
Background Noise Level:
The underlying level of residual noise remaining when specific noises have been removed. The background noise level is often quantified by using the LA90 sound level. This is the A-weighted sound pressure level that is exceeded for 90% of a given time interval, T, measured using time weighting, F.
Derived Value:
A derived value is the assessment parameter that must determined from a set of measured sound levels in order to provide a basis for decision-making.
Eikonal Equation:
An equation which specifies travel times to points on an acoustic wavefront. It can thus be used to represent the development of a wavefront over time.
Receiver Site:
The place for which a noise assessment is required.
Risk:
The likelihood of an incorrect assessment outcome resulting from uncertainty. Note, however, that uncertainty does not automatically imply risk.
Sound and Noise:
Sound is pressure fluctuations in the air, or other supporting medium, that can be detected by the ear or by a microphone. Noise is sound which is loud or perceived to be unpleasant in a given situation and thus causes disturbance.
Specific Noise:
A component of the ambient noise that can be attributed to a specific source.
Variability:
The inherent changes in environmental noise levels that occur with changing location and time period. Unidentified or misunderstood variability is the prime source of measurement uncertainty and risk in practical environmental noise assessment.
User:
Any person or body having an interest in the prescription, commissioning, execution, or use of environmental noise measurements.