A Virtual Design Studio for Low-Frequency Sound from Walking in Lightweight Buildings

Doctoral thesis, 2019

In recent years there has been a growing interest for building lightweight multistorey wooden residential buildings in countries like Sweden with large and renewable forests. While positive aspects of these buildings, such as sustainability, ease of construction and lightness, motivate building more in wood, poor acoustic performance is a risk which concerns the wooden-building industry.
Low-frequency impact sound from walking of the neighbors upstairs is the main source of complaints about the acoustic performance of these buildings. The disturbance caused by walking sounds, transmitted through lightweight wooden floors, results in acoustic discomfort and impairs the perceived quality of the building; sometimes even when the building has fulfilled an acoustic class higher than minimum requirement, according to the national standard on sound classification and its single number ratings. The standard methods for objective evaluation of impact sound insulation of floors cannot predict, at a satisfactory level, the walking sound annoyance that the inhabitants of wooden buildings experience. This causes an uncertainty about the resulting perceived quality of these buildings, which greatly concerns the building manufacturers and demotivates them from choosing lightweight wooden elements over heavyweight building materials such as concrete. This uncertainty can be overcome by evaluating the perceived acoustic quality of the building prior to its construction.

One solution is to build test houses where the subjective acoustic performance of floor samples can be evaluated in advance to the building construction. However, building a test house is expensive; besides, for evaluating the effect of every design modification on the experienced acoustic comfort of the building, a real floor sample has to be built and installed in the house, which would be time-consuming and costly. An alternative solution is to use virtual acoustic test facilities.

In this thesis a virtual design studio for impact sound is developed. It is a tool that facilitates creating and listening to the acoustic field generated by impact forces such as footsteps on lightweight floors. It also provides the possibility to evaluate the acoustic performance of floor elements in an early design phase, and to investigate the correlation between design parameters and the perceived impact sound insulation of the floor. The tool is demonstrated and a very first listening test shows that one can obtain results which are in good agreement with the results in literature. Loudness, reverberation and thumping are shown to influence the annoyance. It is also shown that there is a difference in judgement of walking sounds by persons who have experience with lightweight floors at home and by those who do not have that experience.