Determination of Sound Power Levels of External Noise Sources. Part 1: Measurement Methods. Part 2: Some Measurements

摘要

A general frame standard for determining sound power levels of external noise sources by in situ measurements is proposed. Suitable ISO standards, a long distance method which permits directivity measurement and a short distance method are incorporated. Measurements can be made in front of walls and in corners. The short distance method uses a parallelepipedical measurement surface, omitting the top microphone position. Recommended measurement distance is or = 5 m. The microphone height h = (height of reference box) + d may be exchanged for height 10 m, giving highest sound pressure level whenever h 10 m. For very large sources, near field corrections are introduced to cancel the effect to sound energy not passing at right angles to the measurement surface. The long distance method uses a 1/2, 1/4 or 1/8 spherical measurement surface. When directivity measurements are made, the number of microphone positions are doubled relative to those of ISO 3746. The directivity index is then calculated as in ISO 3744. Measurements confirm the validity of the methods.