The state of the art in the measurement of acoustical coefficients

For over 100 years, the acoustical industry has measured and characterized sound absorption. And yet, standard measurements of the random incidence absorption coefficient, according to ISO 354 and ASTM C423-09, are still inaccurate and lack reproducibility among labs. Research is underway to improve accuracy by replacing traditional hanging diffusors with boundary mounted diffusors, to allow proper determination of the rev room's surface area and volume, evaluating edge diffraction, replacing Sabine with Eyring, etc. Calibration methods using an absorptive or reflective reference are also being evaluated to improve reproducibility. The field of measuring and characterizing scattered sound is in its infancy by comparison, yet in the past three decades much progress has been made. Two standards have emerged for measuring scattering (ISO 17497-1) and diffusion (ISO-17497-2) and the current state of the art for both will be reviewed. This paper is intended to be a tutorial on the evolution and current state o...