How to Specify the Noise Rating of Large Electric Rotating Machines

This paper presents a guide to predetermine the noise rating of an electric rotating machine which will satisfy the requirements of a certain psycho-acoustic criterion at any given point in the noise field of a machine or combination of machines where an operator habitually stands or where there is a stnrcture wbich houses people. The paper gives a simple method whereby one can proceed from the deafne Esrisk criterion, speech-communication criterion, or neighborhood-reaction criterion to the specification of the noise rating of a machine in terms of octave-band power levels. Because most users and manufacturers of large electric rotating machines are accustomed to the old specification of noise rating in terms of the average sound pressure level under essentially free field conditions, at a distance of 5 ft (feet) from the major surfaces of the machine, and at shaft centerline height, a simple relationship based on noise analysis tests on many machines is also presented to help correlate the new noise rating in terms of power level and the old noise rating in terms of pressure level.