An objective noise-meter for the measurement of moderate and loud, steady and impulsive noises

The present paper relates to an instrument of the microphone-amplifier-meter type, which has been adjusted for measuring the equivalent loudness of noise. Many noisemeters on these lines are available commercially, but the author has not met with any (other than those based on designs supplied to firms by, the National Physical Laboratory) which give results even approximately correct for a series of impulsive sounds. The essential feature of the work now described has been the adjustment of the circuits of the meter so that gives correct results for intermittent and impulsive noises, as well as for continuous tones. The paper describes the principles upon which an empirical adjustment was made, and produces evidence that the meter gives results in excellent agreement with average assessments, by the standard aural technique, of the equivalent loudness of a variety of moderate and loud noises. It is commented that meters which pass certain specification for sound-level meters which has been tentatively proposed recently may give results for impulsive sounds very much below the true values of their equivalent loudness. An important point revealed incidentally was that inconsistencies arise in aural measurements when the loudness of noise is compared. with that of a reference tone heard simultaneously. The difficulties are resolved by adopting technique in which the noise and the reference tone are heard alternately.