However, ceiling tiles do not provide a uniform surface e.g. joints between tiles, and also there are light fittings either recessed or suspended. Sometimes suspended ceiling baffles in a checkerboard pattern are used. These are usually the next most important surface. Their importance increases as room size decreases. Typically walls have very poor sound absorbing qualities and this is often made worse by putting sound reflectors against the walls e.g. filing cabinets.
Windows are also problematic here.
Floor - Carpeting the floor will increase the NRC, but only up to about 0.3. Furniture - Most furniture is designed to be functional or aesthetically pleasing rather than to be a good sound absorber. In many types of offices, screening has been purchased in an effort to improve visual and acoustic privacy. To have any impact at all the screening needs to be at least 5 feet high and one needs solid mass in this screening to block sound energy. When steps have been taken to reduce the signal strength, then measures to increase noise can be adopted.