Why noise reduction coefficients aren’t enough

Abstract

Noise reduction coefficients have been around for decades. The use, and misuse, of the data supplied by these tests has been well-documented over that time. The desire by some to bring changes to standards like ASTM C423 and ISO 354 have been met with tremendous resistance by both manufacturers, laboratories and others over the years. This paper will discuss the use of these standards, what they tell us about sound and where they fall short in the assessment of the quality and assessment of sound absorption. Discussion of inappropriate use of standards in testing materials will also be presented. A discussion on the subject of timbre and how different materials may sound different while having similar NRC ratings will also be presented. The need for different test data and higher standards in the industry of acoustics will also be discussed. A presentation of the use of a free-field test method for assessing the quantity and quality of absorption will be presented along with test data from this method.