Sabine measured sound absorption by comparing a material to a fully open window.

Evidence

In real rooms, we must also allow for the presence of a variety of different materials, as well as accounting for their variation of absorption as a function of frequency. This is complicated by the fact that there will be different areas of material with different absorption coefficients, and these will have to be combined in a way that accurately reflects their relative contribution. For example, a large area of a material with a low value of absorption coefficient may well have more influence than a small area of material with more absorption. In the Sabine equation, this is easily done by multiplying the absorption coefficient of the material by its total area and then adding up the contributions from all the surfaces in the room. This resulted in a figure Sabine called the “equivalent open window area,” as he assumed and experimentally verified that the absorption coefficient of an open window was equal to 1. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 2845

Categorization

• DEFINE: Defines ‘equivalent open window area’ as the unit Sabine used to quantify material absorption.
• CANDY: The idea that an open window itself served as the yardstick of sound absorption is a neat, tweetable nugget.