Sound insulation & noise flanking describes the reduction of sound that passes between two spaces separated by a dividing element, such as a wall or floor partition. The sound energy passes through the dividing element (direct transmission) and through the surrounding structure (indirect or flanking transmission). The noise reduction attributed to the sound insulation is realised via sound insulation testing.
When the building’s acoustic design is taken into consideration, it is important to consider both methods of transmission. The dividing walls or floors, which flank/abut the dividing element/s, usually constitute the main paths for flanking transmission, but this can also occur at ventilation ducts, doorways, windows etc. If windows are positioned very close to the dividing partition then noise flanking will usually occur around the main building envelope, thus rendering your ‘high spec’ acoustic solution useless.
It is extremely unlikely that figures quoted from ‘laboratory sample’ sound test conditions will be achieved on site, as the laboratory installation is described in detail and followed to the letter. However, due to time constraints etc. it is not always possible to replicate the same conditions on a construction site, which is the reason why a 5dB point difference is allowed between the laboratory and construction site sound insulation performance.
Noise Flanking Paths
Flanking sound is defined as sound from a source room that is not transmitted via the separating building element e.g. the wall or floor partition. The sound is transmitted indirectly via paths such as external walls, windows, doors and internal corridors.