This definitive guide covers the design and application of absorbers and diffusers in acoustics. Surface diffusion is a relatively young subject area, and diffuser design, application and characterisation are often not well understood. Although there is greater knowledge of absorption, it is also informed by new research. As two of the main design tools for altering the acoustic conditions of rooms, the correct use of absorbers and diffusers is important to the creation of quality acoustics. This text details the evolution and the current state of the art in diffuser and absorber research and application. It covers a range of practical and theoretical aspects, with extensive examples of installations and case studies to cater to practitioners working in the measurement, modelling and design of rooms, semi-enclosed spaces as well as in noise control. It is also invaluable for students and researchers wanting a grounding in acoustic treatment, as well as understanding the latest developments. All chapters have been revised and brought up to date in this new edition, with new applications, absorbers and diffusers featured. Sustainability, portable vocal booths, and fast time domain models for diffusers are just a few of the new sections. Improved techniques for measurement and prediction are included, as well as bringing old methods up-to-date with the latest refinements from standards and research. Most of the prediction methods in the book are now linked to open source implementations and downloadable MATLAB scripts, enabling readers to exploit the knowledge in this book more readily in design and research.