The relationship between sound‐power level and sound‐pressure level in dwellings and offices

Abstract

In 1985, Ted Schultz undertook a research project for the American Society of Heating, Refrigerating and Air‐Conditioning Engineers (ASHRAE) to investigate the relationship between the sound‐power level of a source and the sound‐pressure level produced in “real” rooms typical of dwellings and offices. For many years, the use of the diffuse field theory of sound propagation had been suspect as not being applicable in normally furnished spaces to the prediction of sound‐pressure level resulting from a known introduction of sound‐power level. Ted's research confirmed that the use of this latter theory led to significant errors that both overestimated and underestimated true conditions depending upon the distance between the source and observer. Recognizing the complexity of developing a rigorous theoretical solution within the time frame of the project, he undertook an empirical approach and reviewed a large body of his own and others' reliable test data to develop an equation that predicted with considerable accuracy the measured results in rooms ranging from bathrooms and kitchens to plush furnished offices, conference rooms, and living spaces. In summarizing the conclusions of this study, Ted made several cogent observations, typical of the subtle Schultz style: “Since the room absorption, A, does not appear explicitly in the formula, the customary normalization with 10 log (A/A0) in transmission loss and impact noise tests is probably incorrect. In addition, since no uniform reverberant sound field occurs in normally furnished spaces, it is not clear what one ought to measure for the receiving‐room sound pressure level in tests of transmission loss, noise reduction, and impact noise.” He was pursuing these concerns at the time of his death.