What do the measurement parameters of a noise meter (sound level meter) mean?
A-weighted sound level can better reflect the human ear's subjective perception of the intensity and frequency of noise, so it is a better evaluation method for a continuous steady state noise, but for an undulating or discontinuous noise, A-weighted sound level is not suitable. For example, traffic noise varies with the flow and type of vehicles; another example is that a machine works at a stable sound level, but because it works intermittently, it does not have the same effect on people as another machine that has the same sound level but works continuously. Therefore, a time-averaged method of evaluating the effect of noise on human beings is proposed, i.e., the equivalent continuous sound level, symbolised as "Leq" or "Laeq-T". It is to use a continuous and stable A sound level with equal sound energy in the same period of time to express the size of the noise in that period of time. For example, there are two machines with a sound level of 85dB, ** one works continuously for 8 hours, and the other works intermittently, and the sum of its effective working time is 4 hours.
Obviously the average energy acting on the operating workers is twice as large as the latter, i.e., 3 dB. Therefore, the equivalent continuous sound level reflects the size of the noise energy actually received by a person in the case of an unstable sound level, and it is an equivalent quantity used to express the variation of noise over time.
Laeq-T≈L50+d2/60, d=L10-L90 where L10, L50, L90 are the cumulative percent sound levels, which are defined as:
L10 - the noise level exceeded 10% of the time during the measurement time, which corresponds to the average peak of the noise.
L50 - the noise level that is exceeded 50% of the time during the measurement time, which corresponds to the average value of the noise.
L90 - The noise level that is exceeded 90% of the time during the measurement time, which corresponds to the background value of the noise.
Cumulative per cent sound level L10, L50 and L90 calculation method has two kinds: one is in the normal probability of the paper drawn on the cumulative distribution curve, and then from the figure; another simple method is to measure a set of data (such as 100), from big to small arrangement, the 10th data that is L10, the 50th data for the L50, the 90th data that is L90.
