Theory of Office Screens below a Sound Absorbing Ceiling

摘要

The intention with office screens in large rooms is to produce working areas with an acoustic privacy. Therefore, the office screens are sound absorbing and sound insulating and their principal acoustic quality is the sound level reduction behind the screen. This reduction normally is limited by the sound being scattered around the upper edge of the screen which lets an open area towards the - mostly absorbing - ceiling of the room. A theory, suitable for numerical computations, is derived, which develops the sound fields in the room into silencer duct modes, because these are orthogonal over the height of the room, if the ceiling can be (approximately) assumed to be locally reacting. A principle of superposition is applied for screens which are symmetrical with respect to their central plane; this principle helps to reduce the amount of computation. For non-symmetrical screens or rooms, the procedure of computation is presented without the principle of superposition. Variants of the theory apply to either locally or bulk reacting screens, to either sound transmitting or non-transmitting screens, to screens with or without a gap between screen and floor. Numerical examples are presented.