Straw as an acoustic material

The use of straw bales in construction is not as old as one may suppose. The first straw bale houses date back to the invention of the baling machine at the end of the 19th century and were built in Nebraska. After a long period of abandon, this construction technique was rediscovered in the 70s and since then it has significantly evolved, gaining attention among both self-builders and professionals. The huge amount of straw available worldwide can turn this material into a very interesting resource for the building sector. Nevertheless the absence of certified or reliable technical data discourages engineers and architects to use it. This paper aims at investigating the acoustic properties of straw bale constructions. The first section reports a brief summary about straw bale constructions and their energy and environmental performance. Then the state of the art of the acoustic properties is presented in more detail. Normal incidence sound absorption coefficient of loose straw is measured using a two microphone incidence tube in accordance with ISO 10534-2. Five and seven centimetres thick samples with different water contents were investigated. A limited variation of sound absorption with water content was noticed. Lastly the results of a fa?ade sound insulation test on a real straw bale wall are reported. The tested wall resulted to be a poor sound insulator, especially at low frequencies, because of the low mass of the structure.