Sounding off! Overcoming barriers to timber use in mid-rise construction by solving a decades-old puzzle

However, research has highlighted that inter-tenancy acoustic isolation across timber systems is one of the major barriers to the construction industry’s uptake of timber framing into this new market. 

For instance, transmission of 20–120 Hz structure-borne sound through a timber floor system in a multi-storey timber building does not fall within NCC requirements and causes significant discomfort for occupants, particularly in buildings with multiple dwellings. 

Existing approaches to mitigating this problem - namely increased mass and stiffness, and viscoelastic vibration isolation - are impractical due to the very long wavelengths that result from the low frequency structure-borne sounds that are transmitted through multi-storey buildings with timber systems.

CAMP.H is now developing acoustic metamaterials (engineered materials with special properties not found in naturally occurring materials) to reduce low-frequency structure-borne sound, and enhance the acoustic performance of timber building systems.

The research team consist of Bernard Gibson, PhD student at The University of Melbourne (UoM), Dr Tuan Nguyen, Research Fellow at UoM, Prof Tuan Ngo of UoM, and Prof Priyan Mendis, Professor and Director of CAMP.H at UoM. The team is proposing this new approach, which involves employing distributions of small, independently resonating metamaterial masses within timber floors to lessen the low-frequency sounds.

The system is currently modelled with small-scale prototypes and advanced simulation software. The models are being used to undertake a parametric design study to identify an optimal configuration for the design, construction and testing of a physical prototype. 

The recent experimental program and advanced computer simulation results concluded that the new metamaterial system dramatically decreased low-frequency propagation across wide frequency ranges. 

Further to this, the research team will extend its work by incorporating an inertial amplification-based metamaterial approach into the design of a cost-effective, practically manufacture-able system that limits the spread of 20–120Hz structure-borne frequencies between tenancies in multi-storey timber buildings.

By offering a solution to the poor, low-frequency acoustic performance of multi-storey timber buildings, the industry will solve a significant issue that has been recognised for more than forty years. 

“Acoustic metamaterial approaches offer real potential for the development of a practical and cost-effective solution for prefabricated floor system, and solve one of the major barriers to construction industry uptake of timber building systems,” said Gibson.