Table 16.1 - Main descriptors for the assessment of environmental noise

Source: Based on von Meier, 1993

Descriptor Symbol Definition Field of application
Maximum sound pressure level Lmax The maximum sound pressure level occurring during a certain period of time or during a single noise event. To characterise noises of short duration. Mostly used with regard to sleep disturbances.
Equivalent sound pressure level Leq The level of the average sound intensity taken over a certain period of time eg, 24 hours, daytime, night-time. To measure average environmental noise levels to which people are exposed.
Day/night sound pressure level Ldn Equivalent sound pressure level over a 24-hour period with all sounds occurring between 22.00 and 06.00 raised by 10 dB(A). To describe average environmental noise exposure by taking into account the increased sensitivity of humans during night-time.
Sound exposure level SEL Level of the sound intensity summed up over the period of time of a noise event related to 1 second. To describe the noise of a specific, usually short, noise event.
Statistical sound pressure level Ln The sound pressure level of a time-varying noise that is exceeded during a certain N per cent of the time during the period measured. To describe time-related properties of the noise eg, the background sound level L95 is the level which is exceeded during 95% of the time. Used to describe the acoustical quality of a residential area.