Noise measurements for engineering purposes

The 2 principles of noise measurement, namely, the subjective and objective principles, are discussed in this paper with special reference to electrical plant. Two forms of measurement embodying the subjective principle are considered: One is the proposed primary standard method, which is essentially a laboratory method; the other is the noise audiometer, which enables the subjective principle to be applied directly to the study of engineering noise problems. A form of audiometer and technique, together with their practical advantages, are described. The objective method of measurement is particularly needed for commercial acceptance tests. The evidence shows that the objective type of instrument now available evaluates the noise of many types of plant correctly, but that with noises predominantly harmonic in tone structure, the principle of the method is inapplicable. It is concluded that the audiometer provides the only practicable means at present available for measuring transformer noise and that no satisfactory solution for the commercial testing of such apparatus has yet been reached.