Sound solutions

Ian Usher, technical and marketing manager at Knauf AMF Ceilings discusses the benefits of installing suspended ceilings to create a good acoustic environment

The Whispering Gallery in St Paul’s Cathedral attracts around 50,000 tourists a year, many of whom visit to hear their hushed voices travel from one side of the 111m high dome to be heard clearly around the other side. This acoustic effect was an unintentional feature of the dome’s design but has become an entertaining tourist attraction.

But not all acoustic effects in buildings are entertaining. In office buildings background noise can have a negative impact on staff performance. In schools the situation is even more critical, where poor acoustics can have a detrimental effect on student concentration, behaviour and academic achievement. So how do you control unwanted noise and effects of sound when designing a new building or refurbishing an existing space?

When endeavoring to design a good acoustic environment there are two main factors to be aware of: the ambient noise within the room and the reverberation time of the space.

Ambient noise can come from a number of sources including sound transferring from adjacent rooms or corridors, speech, mechanical equipment inside the space and noises coming in from outside. Sound insulation or attenuation prevents noise from outside disturbing those inside the building and is measured as a decibel (dB) value. The Bel is a unit of sound pressure – named after Alexander Bell. A decibel is 1/10 of a Bel. The highest performance dB rating a suspended ceiling alone would provide is in the region of 45dB. The dB rating is actually a minus figure; generally speaking, if the sound source measures 100dB in a room, by installing a 40dB ceiling tile, the sound heard in the adjacent room is 60dB.

Reverberation is the time, in seconds, required for reverberant sound in an enclosed space to reduce by 60dB of its original level after the source of the sound has ceased. Reverberation times can vary from half a second to up to eight seconds in a large room with hard walls, floors and ceiling surfaces. Acoustic absorption within a room is important if you want to reduce the reverberation time, which can help improve speech intelligibility and clarity.

By installing sound absorption and insulation materials architects are able to control and alter the reverberation time in a space. Sound absorption is measured as an Alpha W (?W) value. The degree of sound absorption depends on the performance level of the material, which can vary from 0 per cent to 100 per cent absorption but for ease of reference it’s divided into classes A to E, where A offers the highest protection. A plasterboard ceiling provides less than ?W 0.1 sound absorption whereas a high performing acoustic ceiling can offer up to ?W 1.0 or 100 per cent sound absorption. This high sound absorption is achieved because of the lightweight porous materials the ceilings are made from which is why suspended ceilings are an extremely cost-effective solution for controlling ambient noise and reverberation.

Suspended ceilings offer a number of options to choose from in terms of appearance and performance. A wide selection of face patterns, sizes and shapes are available to suit any interior design, offering everything from enhanced sound absorption for areas such as atriums and halls, to higher sound attenuation for corridors and circulation zones adjacent to teaching or office spaces.

There is a growing trend in modern architecture towards the use of hard reflective materials such as concrete, steel and glass in large areas like atriums in office buildings. These areas are prone to high levels of reverberation with reflected sound bouncing off the many surfaces. A derelict building, recently renovated into a retail bank with a stunning central atrium, was installed with high sound absorbent panels to provide excellent acoustic control for the large open-plan area. The ceiling panels are made from perforated mineral board with an acoustic fleece facing providing up to 44dB attenuation to reduce unwanted noise and make for a more comfortable internal environment.

In older buildings, a suspended ceiling is not always viable because of architectural features or a low ceiling height. In these situations, ceiling rafts or baffles are a good option to provide the necessary acoustic control. Rafts offer flexible and stylish solutions in a wide range of shapes and colours. They allow the creation of elegant designs and produce a contemporary look; their bright and colourful appearance is particularly appealing to young children.

Staff at a primary school in a Victorian building were struggling with high noise levels in their classrooms. The problem of noise was getting so great, staff were leaving work with headaches and suffering with sore throats from having to shout to be heard. The installation of ceiling tiles and rafts with high sound absorption has made a dramatic difference to the staff and pupils at the school. The classrooms are now calm learning environments.

Wall absorbers can be used, either in conjunction with an acoustic ceiling or independently, to improve room acoustics and many offer higher impact resistance to cope with tough daily use in leisure centres or educational environments. Wall absorbers manufactured from mineral wool panels offer superior sound absorption and can make eye-catching decorative wall coverings.

Although St Paul’s Cathedral is the masterpiece of architect Sir Christopher Wren, building acoustically compliant buildings can be achieved by ensuring the design of the building is fit for purpose and specifying construction materials with excellent acoustic properties to create a good acoustic environment.