Acoustic tiles and boards: materials, values, selection

Acoustically, tiles work by two principles. Porous boards (mineral wool, PET felt, wood wool) let sound enter the material and convert it into heat through friction; their effect grows with thickness and air gap. Perforated boards (gypsum, wood, metal) act as perforated absorbers: the holes form a resonating air system with the cavity behind, and the absorption maximum can be tuned via open area and cavity depth.

In practice: porous boards are more broadband and hard to beat in the mid/high range; perforated boards, with the right cavity, also reach mid and lower frequencies while offering a closed, robust surface. Many systems combine both, for example perforated boards with an acoustic fleece and mineral wool in the cavity.

Tiles only become comparable with four pieces of data: the weighted absorption coefficient αw with its class from an ISO 354 reverberation-room measurement, the mounting used in the test (direct or with a defined cavity; for ceilings type E with a millimetre figure, e.g. E-200), the absorption values per frequency band, and the fire class per EN 13501-1. An αw without the mounting is worth little, because the same build-up can measure completely differently mounted directly versus suspended.

Watch out for two patterns: NRC values from the US run systematically somewhat higher than αw and are not directly comparable. And absorption coefficients above 1.0 as a product promise are unserious; ISO 11654 caps αw at 1.0, and raw αs values exceed 1 only due to edge diffraction in the test.

The chart at the top of this page shows median absorption curves of the board materials from the Acoustic Index catalogue, computed from the stored ISO 354 measurements of the listed products. The typical pattern becomes visible: mineral wool reaches high values early and holds them across the spectrum, wood wool and gypsum join later and stay below depending on the build-up.

The median is a deliberate choice: it is robust against outliers and shows what a typical product of the family delivers. For designing an actual room, the measurement of the actual product in its actual mounting still decides; exactly those are stored per product in the catalogue.

Most acoustic tiles end up on the ceiling, as lay-in tiles in a grid or glued/suspended over the full area. That is usually right, because the ceiling is the largest free surface. Wall mounting pays off additionally against flutter echoes between parallel hard walls and in rooms whose ceiling is unavailable, for example with concrete-core activation.

Design is a further reason for the wall: PET felt and printable boards turn the absorber area into a design element. Mechanically stressed areas (sports halls, corridors, parking) are the home of the wood wool board, the only family regularly available impact-resistant.

For specification, the values belong in the text per build-up: board type and thickness, mounting including cavity, required absorber class or αw per octave band, fire class, plus impact resistance or humidity suitability where relevant. Proof runs through the reverberation-room test report; serious manufacturers provide it on request or link it directly.

In the Acoustic Index catalogue, measurement data is stored and filterable per product and build-up, including fire class and EPD availability. A board shortlist can be narrowed to the requirement in minutes and checked directly against the room's target in the reverberation calculator.