Acoustic strategies

The acoustic response of a cladding system will depend on its mechanical properties. A good rule of thumb is that the stiffer the panel, the more sound it will transmit. A profiled steel sheet of a given thickness can produce the same structural strength as a flat panel of substantially greater weight and thickness.

The acoustic response of a cladding system willdepend on its mechanical properties. A good rule ofthumb is that the stiffer the panel, the more sound it will transmit. A profiled steel sheet of a given thickness can produce the same structural strength as a flat panel of substantially greater weight and thickness. That isbecause a profiled panel will have a higher bending stiffness than a flat one. Indeed, profiling the claddingsheets will impart stiffness and structural strength to arelatively thin and flexible sheet of metal. For this reason, a single profiled sheet will transmit more sound than a flat sheet of the same weight. Built-up composite and other multi-layered cladding systems can be used for better acoustic performance.

In designing an acoustic solution, there are three fundamental questions that should be asked at the outset:

• Is the requirements to keep sound in or out?
• Is it necessary to minimise internal acoustic reflections.
• That transmission loss is required (in dB).

By careful design of a profiled cladding system, a costeffective solution which combines structural strength,weight, durability, ease of manufacture and acousticperformance can be attained. Generally, to achieve ahigh value of transmission loss for a wall or roof, threethings are required: high surface weight, high internal damping and low bending stiffness.

A built-up steel cladding system comprises an external profiled sheet, a perforated or non-perforated internal liner sheet and an in-fill between the two sheets, such as mineral fibre. The transmission loss of such a system can be modified in a number of ways:

• The total mass can be increased by using a denser or thicker layer of in-fill.
• Better performance is possible through using dense, soft rolls of mineral fibre in-fills, rather than rigid ones.
• Transmission loss is also improved via an air-gap inside the outer face of the cladding as it minimises transmission of reverberations from the external sheets to the insulation.

If composite panels are specified for the cladding, other strategies can be used. For example, a soundabsorbing quilt can be applied inside the inner-face of the panel with either a steel or plasterboard lining.

If sound absorption in a room is important, then the internal sheet of the cladding system should be perforated to allow deadening by the insulation. However, this can also have a reverse effect on the transmission loss characteristics of a structure. If the particular application requires both efficient transmission loss and internal absorption, the absorbing in-fill must be of increased density and thickness to overcome the acoustical weakness of the perforated liner.

Manufacturers of cladding systems are able to give specific recommendations on the appropriate combination of the above strategies for achieving a system tailored to the specific requirements of an individual project, and should be consulted at an early stage of the design process.