Noise is an important enemy of concentration, both for learning and working. This new study shows the latter again.

From the press release:

Researchers at Chalmers’ Division of Applied Acoustics have conducted a laboratory study in which test subjects took concentration tests while being exposed to background traffic noise. The subjects were asked to look at a computer screen and react to certain letters, then to assess their perceived workload afterwards. The study shows that the subjects had significantly poorer results on the performance test, and also felt that the task was more difficult to carry out, with traffic noise in the background.

“What is unique about our study is that we were able to demonstrate a decline in performance at noise levels as low as 40 dB, which corresponds to the regular noise level in an office environment or a kitchen,” says Leon Müller, Doctoral student at the Division of Applied Acoustics in the Department of Architecture and Civil Engineering.

The background noise consisted of two audio sequences simulating trucks passing by at a distance of ten and fifty metres. Both sequences were normalised to the same total indoor level of 40 dB.

“The audio sequence simulating the closer passages, where the sound changes significantly as the vehicle passes by, was usually the one that bothered the test subjects the most,” Müller says. “This could be because traffic that is further away is perceived as a more constant drone.”

Housing is built closer to roads now

The new results emphasise an already problematic situation of negative impact on health and job performance due to traffic noise. In recent years, the distance between roads and newly built housing in Swedish cities has been allowed to shrink — a trend that can also be seen internationally.

Put somewhat simplistically, the Swedish regulations for where construction is permitted are based on the average outdoor noise level over a 24-hour period — meaning that they do not take individual pass-bys into account. In addition, current regulations do not cover the peaks of low-frequency noise indoors, which is difficult to avoid and is, according to research, more disruptive and therefore more impacting on human health.

In one study modelling low-frequency noise, Jens Forssén, Professor of applied acoustics at Chalmers, showed that such noise is primarily generated by heavy traffic at low speeds, and is difficult to shut out even with well-insulated windows and buildings that comply with all the construction norms and guidelines for sound insulation.

Reduced vehicle speed can increase the noise exposure indoors

“The calculations for different types of facades show that it is difficult to achieve ideal indoor sound environments near heavily trafficked roads,” Forssén says. “Reducing speeds is not a solution, as our calculations show that the indoor noise exposure can even increase at lower speeds.”

Further, Forssén says that noise and the sound environment are a factor that is often considered too late in the planning process, and that there are advantages that could be achieved if adjustments were made in order to better utilise the space in terms of noise pollution.

The researchers also agree that the most effective solution would be to avoid urban densification in areas where traffic noise would have too great an impact on health and wellbeing.

Abstract of the first study:

Urbanization leads to an increased demand for urban housing, which can be met by building dwellings closer to streets. Regulations often limit equivalent sound pressure levels which do not account for changes in time structure that occur when decreasing the road distance. This study investigates the effect of such temporal changes on subjective workload and cognitive performance. A group of 42 participants performed a continuous performance test as well as a NASA-TLX workload test under three different sound conditions, i.e., close traffic, far traffic, both with the same equivalent sound pressure level of LAeq≈40�Aeq≈40 dB, and silence. Additionally, participants answered a questionnaire regarding their preferred acoustic environment for concentrated working. Significant effects of the sound condition on the multivariate workload results as well as on the number of commission errors in the continuous performance test were found. Post hoc tests showed no significant differences between the two noise conditions, but there were significant differences between noise and silence. This indicates that moderate traffic noise levels can influence cognitive performance and perceived workload. If there is a difference in the human response to road traffic noise with constant LAeq�Aeq but different time structures, the used methods are not suitable to detect them.

Abstract of the second paper:

Indoor low-frequency noise levels due to road traffic has been modelled for facade examples consisting of a lightweight steel facade, a concrete facade and two types of windows. Possible audibility of heavy vehicles passing by has been investigated as well as the dependence of the exposure level on driving speed and distance to road. The results show that pass-by events may be audible at low frequencies for cases complying with building standards and noise guideline values exemplified by Swedish regulation. Moreover, the A-weighted levels may be dominated by low frequency noise, and the frequency of occurrence of pass-by traffic noise events may be sufficiently high to create disturbance for typical traffic situations. Furthermore, it is shown that the contribution of pass-by events to the equivalent level indoors may increase when the driving speed is lowered.