Source: https://jmrplens.github.io/phonometry/guides/sections/materials-surfaces/ Every room prediction and many an insulation model end up consuming a coefficient that describes what a material or a surface does to sound. This section covers where those coefficients come from: the laboratory instruments that measure them, the single-number ratings that summarise them, and the in-situ methods that recover them outside the laboratory. [Acoustic Materials](/phonometry/guides/materials/) covers the sample-scale instruments. The **reverberation room** yields random-incidence absorption coefficients that ISO 11654 collapses into the weighted rating α_w with its letter class, the figure absorber datasheets quote. The **flow rig** measures airflow resistance and resistivity per ISO 9053-1/-2, the parameter that governs a porous absorber's low-frequency behaviour and anchors most material models. The **impedance tube** recovers, at normal incidence, the complex surface impedance, reflection factor and absorption coefficient of a small sample (ISO 10534-1/-2) and, with four microphones, its transmission loss (ASTM E2611). [Porous and Multilayer Absorbers](/phonometry/guides/porous-absorbers/) turns the measured flow resistivity into *predictions*: the Delany-Bazley, Miki and Johnson-Champoux-Allard equivalent-fluid models give a porous material's characteristic impedance and wavenumber, and a transfer-matrix stack of porous, air, perforated, microperforated (Maa) and membrane layers predicts the absorption of a whole construction, at any incidence angle and in a diffuse field, before anything is built. [Surface Scattering, Diffusion and In-situ Absorption](/phonometry/guides/surface-scattering/) moves from samples to *surfaces*, asking not how much energy a surface absorbs but where it sends what it reflects. The random-incidence **scattering coefficient** (ISO 17497-1) quantifies how much energy leaves the specular direction; the **diffusion coefficient** (ISO 17497-2) quantifies how uniformly the reflected energy spreads; and the ISO 13472 methods measure the absorption of a road surface in situ, by the extended-surface subtraction technique (Part 1) or the spot tube (Part 2). The consumers of these numbers are spread across the site: absorption coefficients feed the reverberation predictions in [Room acoustics](/phonometry/guides/sections/room-acoustics/), dynamic stiffness (measured by a related load-plate method) feeds the floating-floor model in [Sound insulation](/phonometry/guides/sections/sound-insulation/), and the road-surface methods connect to the outdoor-noise interest of the [Environment and transport](/phonometry/guides/sections/environment-transport/) section. ## Pages in this section - [Acoustic Materials](/phonometry/guides/materials/): the ISO 11654 weighted absorption rating and class, ISO 9053-1/-2 airflow resistance, and impedance-tube absorption, impedance and transmission loss. - [Porous and Multilayer Absorbers](/phonometry/guides/porous-absorbers/): the Delany-Bazley, Miki and JCA porous models, the transfer-matrix multilayer solver with perforated, microperforated and membrane layers, and the random-incidence Paris integral. - [Surface Scattering, Diffusion and In-situ Absorption](/phonometry/guides/surface-scattering/): ISO 17497-1/2 scattering and diffusion coefficients, and ISO 13472-1/-2 in-situ road-surface absorption.