GENERAL KNOWLEDGE

Detailed explanation-1: -The L90(t) is a statistical descriptor of the sound level exceeded 90% of the time of the measurement period (t). This is considered to represent the background noise without the source in question.

Detailed explanation-2: -L90 is the level exceeded for 90% of the time. For 90% of the time, the noise level is above this level. It is generally considered to be representing the background or ambient level of a noise environment.

Detailed explanation-3: -L10-L90 is often used to give a quantitative measure as to the spread or “how choppy” the sound was. L10 is the noise level exceeded for 10% of the time of the measurement duration. This is often used to give an indication of the upper limit of fluctuating noise, such as that from road traffic.

Detailed explanation-4: -DNL (Ldn) stands for Day-Night Average Sound Level and is used to describe the cumulative noise exposure during an average annual day. Ldn does not represent the sound level heard at any particular time, but rather represents the total sound exposure.

Detailed explanation-5: -Background noise level LA90, T The ‘A’-weighted sound pressure of the residual noise at the assessment position that is exceeded for 90 per cent of a given time interval, T, measured using the time weighting, F, and quoted to the nearest whole number of decibels.