Short review on in situ measurement techniques of impedance or absorption

Abstract

The paper will present a short historical review on the development of in situ measurement techniques of sound absorption or the acoustic surface impedance. One of the earliest setups to measure the absorption of a material in situ has been proposed in 1933. In 1934 a method applying short tones to separate the reflected signal from the incident signal in front of a reflecting surface has been proposed. Many more methods have been described over the years. Applications of modern MLS-based measurement equipment to deduce the absorption coefficient in situ were brought up in the early 1990s. An MLS-based procedure similar to an early method has been introduced as subtraction technique and is the basis of European standard ENV 1793, part 5. Most of these methods are based on the assumption of plane wave propagation. Other methods relying on spherical wave propagation approach are being reviewed. Measurement examples and applications in room acoustics will be shown for some of the methods presented and compared to each other.