Sound-off with Gyproc - Part 1

As noise becomes ever more intrusive in our lives from traffic, noisy neighbours, modern stereo equipment and tv’s etc, our health & safety and comfort expectations rise and as such, controlling noise in buildings has become one of the biggest challenges to face today’s building designers. Gyproc’s Technical Development Manager, Jason Hird, looks at how noise is transmitted within buildings and how we can control it through careful planning and design.

Noise is often referred to as unwanted sound. It is intrusive on our daily activities. It affects our ability to concentrate, to hear and to be heard. Continuous exposure to high levels of noise can temporarily impair our hearing and lead to long term hearing loss, and may even cause psychological and physical health damage to humans.

The ability to control noise levels in buildings is therefore fundamentally important to ensure that the building, and its individual parts, are suitable for the purpose for which they are intended. The level of acceptable noise in a particular building or room will obviously depend on its use, with areas such as gyms and playrooms able to tolerate higher noise levels than quiet areas, such as bedrooms and libraries.

The science of controlling noise
Building acoustics is the science of controlling noise in buildings and includes not only the transmission of noise from one space to another – referred to as sound insulation, but the control of noise levels and characteristics within each individual space – referred to as sound absorption.

Sound levels are measured in decibels (dB), with the generally accepted range of human hearing being between 10dB (quiet) and 120dB (painful to the human ear). The dB scale is logarithmic, with each 10dB rise equating to a doubling of the sound level – thus a sound measured at 40dB is effectively double the intensity of a sound measured at 30dB, and half of that measured at 50dB.

Sound insulation
When addressing sound issues, sound insulation is the first thing that comes to mind for most of us, as this relates directly to the design of the structure (walls, ceiling, and floor). It describes the reduction in sound as it passes between two spaces separated by a dividing element and is affected both by the performance of the dividing element itself (direct transmission) and that of the surrounding structure (flanking transmission). When considering sound insulation, it is important to recognise how the sound is propagated, as this will affect the way it is addressed. There are two types of sound transmission:

• Airborne sound - as the name suggests, this is sound transmitted through air. The source of the noise is easy to identify and transmission is propagated directly via air to the receiver. Examples include the sounds of speech and office equipment which are produced in one room and heard in another. It is rated using ‘Rw’ (Weighted Sound Reduction Index). An alternative and similar rating would be ‘STC’ (Sound Transmission Class) both of which provide a single number rating to describe the overall sound performance of a construction system when tested in a laboratory.
• Impact sound - this is produced as a result of impact or shock to the building structure that produces vibrations transmitted via the building elements. Typical examples of this type of noise are vibrations produced by footsteps or vibrations from operating machinery, which are transmitted through their structural supports. Impact sound is rated using ‘Lnw’ (Normalised Weighted Impact Sound Index), and is normally addressed by introducing separating elements into the structure which isolate the impacted element from the main building structure, for example vibration dampers or a floating floor system using resilient layers.

Sound Absorption 
Whilst effective sound insulation will minimise the transmission of sound between spaces, it is also important to consider how best to control the sound generated within a particular area – this involves the use of sound absorption techniques. Sound absorption is particularly important in large open areas, such as receptions, lobbies, restaurants etc to control the level of sound reverberation from hard surrounding surfaces; in schools to create an improved learning environment and in music halls, cinemas etc to improve the acoustics for better audience enjoyment.

Sound absorption is achieved using special wall and ceiling linings, such as Gyptone tiles and boards which combine patterns of full depth perforations with an acoustic fleece backing to provide absorption across the full spectrum of sound frequencies.

Sound absorption performance is measured using either ‘alpha w’ (Weighted sound absorption coefficient) which measures the sound absorption coefficient at standard frequencies and compares them with a reference curve to give a single figure rating, or ‘NRC’ (Noise reduction coefficient) which is a mathematical average of the measured sound absorption coefficients across a range of frequencies.

For quick comparison of the absorption performance of different materials, international standard ISO 11654 describes five different absorption classes, A to E, where A is the best performer and E the worst. Most Gyproc Gyptone boards and tiles fall within the C to B bands and are therefore very effective for use in corridors, lobbies, auditoria etc to control unwanted reverberation.

Next time we will look at the performance of lightweight partition systems compared to traditional masonry / blockwork equivalents, along with some practical solutions in design and ways of maintaining their performance on site.