Porous facing

It is common to have a porous cloth covering over acoustic materials. This can have an influence on the absorption coefficient particularly where a perforated or slotted panel is placed in close contact with the cloth.

The flow resistance of the cloth ( in Rayls) can be entered into the appropriate box.

Fabric properties

The flow resistance must usually be measured directly for the cloth concerned as it is a function of the closeness of the weave of the fabric and is difficult to predict from looking at the fabric