SUPPLIER COMMENT | GYPROC
Sound-off with Gyproc In the last article to look at acoustics ‘Sound-off with Gyproc – Part 1’, Gyproc’s Technical Development Manager, Jason Hird talked about ‘noise’ and some of the science behind it, for example the difference between sound insulation and sound absorption and what is airborne and impact sound. This time we shall look at why lightweight partitions work so well and how to maintain that performance when built on site. Sound insulation performance of lightweight partitions
The mass law tells us that sound insulation performance is governed by mass – This is certainly true of solid masonry partitions, where a doubling of the mass (or thickness) will increase performance by around 5dB. However, using lightweight systems, it is possible to consistently exceed the performance predicted by the mass law. A simple Gyproc metal stud partition, for instance, can provide an Rw rating around 6dB better than predicted by the mass law. Different configurations of stud can result in even better levels of insulation, and adding an additional layer of Gyproc plasterboard to one or both sides of the partition will increase sound insulation performance by around 6dB or 10dB respectively. Further improvements can be obtained if the plasterboard lining to one side is partially decoupled from the lining. The best results, however, can be obtained using two completely independent metal stud frames separated by an air space such as GypWall audio. Using the so called ‘mass spring - mass’ principle, the air space between the two frames acts as a damper to reduce sound passing between the two independent linings, minimising sound transmission. The principle demonstrates a much more effective and efficient way of achieving sound insulation in comparison to traditional solutions. Lightweight gypsum partitions designed and built correctly consistently outperform equivalent masonry construction. Typically you can achieve the same acoustic performance as a blockwork wall in only half the thickness with a Gyproc partition.
Performance on site
The sound performance values of systems quoted in literature are measured in the laboratory under ideal conditions and are unlikely to be achieved on site due to flanking transmission – sound leakage through indirect paths such as, windows, doors, external walls, corridors penetrations and services etc. The measurements used to determine the
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Flanking transmission
Flanking transmission is defined as any sound from the source room that is not transmitted directly via the separating element. It is transmitted indirectly via doors or other breaks in the dividing element, as well as via small openings, such as gaps, cracks and holes in the adjoining structure. Deflection heads in partitions are also a common source of flanking sound transmission, typically accounting for a loss of around 4-5dB due to air leakage, in addition to any flanking loss, if not adequately detailed and sealed.
Designing for effective insulation ABOVE: Jason Hird
“Deflection heads in partitions are also a common source of flanking sound transmission, typically accounting for a loss of around 4-5dB” acoustic insulation of a partition, lining or ceiling system are referred to as DnTw or FSTC (Field Sound Transmission Class). These take into account background noise levels and reverberation times in the receiver room and are affected by not only the performance of the separating element itself (partition, ceiling etc), but the performance of the surrounding structure, any penetrations and junction details. When planning for sound insulation, Gyproc therefore recommends a margin of safety of 7dB over the laboratory test results - Rw or STC in order to compensate for flanking transmission on site.
Once a building has been completed it can be expensive and inconvenient to address sound problems; it is therefore prudent to ensure appropriate sound insulation measures and detailing are incorporated at the design stage. Both internal and external sound transmission should be considered and the requirements for each individual space taken into account when planning the building design. Sensible measures, such as separating quiet and noisy activities and the careful specification of doors, windows and ductwork systems, will help to reduce the demands on insulation, whilst continuing partitions to the underside of the structural soffit and the use of Gyproc plasterboard suspended ceilings to both sides of the partition reduce flanking transmission. For separating wall and floor constructions, special care must be taken to ensure correct detailing at all junctions between the separating element and adjoining elements, such as external walls, other separating elements and penetrations or door openings etc. As any acoustic system is only as effective as its weakest component, failure to include effective detailing will seriously limit overall acoustic performance. Air tightness is essential and whilst most junctions will be sealed using standard jointing techniques any gaps or other small airpaths should be sealed using a proprietary sealant.