a) at least twice the distance betw

a) at least twice the distance between the microphone position and the most remote point of the source under test;b) not smaller than 10 m.With more complex conditions for sound propagation, e.g. more reflecting surfaces or with microphone positions screened from the sound radiating part of the source under test and reflecting objects in the vicinity, accuracy grade 1 can only be claimed if it is proven by simulation techniques or with a reference sound source that the influence of all reflecting objects does not exceed 0,3 dB at any microphone position.NOTE The contributions of reflections can be calculated, e.g. by using the methods of ISO 9613-2111).The influence of meteorological conditions like temperature, ambient pressure and humidiy on sound propagation is negligible with a measuring distance of 1m.Measurements shall not be made during period of precipitation (e.g. rain, hail) or when wind speeds exceed 3 m/s.5.2.2 Accuracy grade 2 (engineering)5.2.2.1 IndoorsMeasurements with accuracy grade 2 may be made indoors in conformity with this International Standard provided that the environmental influence is negligible. This condition is met if both the following statements are true.The environmental correction, K2A, does not exceed 2 dB for the reference measurement surface onwhich the microphone positions are located.The radiation of the source is not directed mainly upwards or to opposite directions of the work station.