[Effects of the body in personal sampling of noise]

In acoustic free fields the human body changes the energy distribution surrounding it, mainly under narrow band or pure tone noise conditions. Hence, sound levels measured close to the body should be intrinsically incorrect if performed via personal sampling. An experiment was carried out to verify whether this statement is still valid in a diffuse field, such as occurs in industrial workplaces. Noise measurements were made in diffuse field laboratory conditions without the presence of a person (steady state) and were repeated close to the ear of a person (perturbed state). The measurements were carried out with integrating precision sound level meters and also with personal noise dose meters. The trials were repeated in an industrial environment. The states 1/3 octave band levels were matched, as also were the equivalent continuous levels. These findings show that in diffuse fields the human body does not significantly affect equivalent continuous level measurements performed near the body. The mean differences between equivalent continuous levels measured by sound level meter were less than 0.3 dBA, and ranged from -0.6 to 0 dBA between levels measured by sound level meter and by personal noise dose meter. The results of the trial performed in the plant showed closer differences between steady and perturbed states and between sound level meter and personal noise dose meter measurements.