Akustik

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Evaluation of outdoor environment in Swedish preschools using the soundscape approach

29 januari 2021

This year I published my thesis titled Evaluation of outdoor environment in preschools using the soundscape approach, as the final project for my master’s degree at Lunds Tekniska Högskola.

A lot of education in Swedish preschools occurs outdoors, which means that a good sound environment is important for both children and teachers alike. The denser the city, the more difficult it might become to build preschools with good outdoor sound environments. Therefore, it might be reasonable to look for other less conventional solutions. One such option is a methodology known as soundscaping. Soundscaping is an approach which relies on perception of the sound environment from human experience.

During the last couple of years, research regarding soundscaping has increased significantly. With information from new research and the new ISO standards (12913), the soundscape method could prove to be a good complement to the current standardized approach.

How to perform a soundscape assessment

Until recently there was no definitive method for performing soundscape assessments. However in recent years a number of ISO standards (ISO 12913-1:2015, 12913-2:2018 and 12913-3:2019) have outlined how to gather and analyze the data. In the ISO standards there are three methods mentioned called Method A, B and C.

There are some differences between these methods when it comes to data gathering (and thus also analysis), but there are also some similarities. One similarity is the requirement of having participants with good knowledge on the area of interest. These participants are referred to as local experts. Other similarities are connected to using binaural (or ambisonic) recordings and combining the subjective experience of the local experts with data gathered from the recordings. The benefit in using binaural recordings, compared to normal microphone recordings, is that binaural recording can closer resemble the human hearing system, which would give a more authentic human hearing experience.

Figure 1. Illustration of a binaural recording using an artificial head.

Assessed methodology and conclusion

As part of my master thesis I used Method A, where I asked the participants (which in my case were the preschool educators) to answer a standardized questionnaire. Due to not having access to binaural recording hardware I chose to use three Norsonic 140 for my measurements. The measurements were performed in preschool yards.

Figure 2. Norsonic 140 on tripod.

The data analysis usually consists of calculating the sound pressure level but is also combined with several other parameters sometimes referred to as sound quality metrics. The sound quality metrics consist of; Loudness, Sharpness, Roughness, Fluctuation strength and Psychoacoustic tonality. The expertise of participants is also required, as they must answer some questions. The questions depend on what type of Soundscape method has been chosen.

The parameter values are usually used in reference to questionnaire answers in the hope of finding a statistical correlation. If or when a strong correlation is found, a prediction model can be created. In my study the statistical analysis showed little correlation. The highest correlation was found for the parameter called max loudness Nmax and the perception of natural sounds. This correlation was used to create a regression model to help predict what levels of Nmax in sones would be needed to generate higher score in natural sounds.

Figure 3 Regression model of max loudness versus existing natural sounds.

The purpose of such a model is to use it to assess what level of max loudness is needed to obtain a preferred value for the natural sound.

Is soundscape a good compliment to the traditional methods of sound predictions used today?

I think that the ability to use prediction models to distinguish good (i.e. bird songs) and bad sounds (i.e. traffic) could be very useful. So, by predicting for instance what loudness or other parameter is needed for the listener to shift focus for instance to natural sound such as previously mentioned bird songs could be an interesting means of improving the perception of a particular sound environment.

However, soundscaping methodology is still relatively new, especially in terms of standardization and is still being improved upon. There are several aspects that are yet to be standardized such as some parameters including for example no standardized calculation for roughness. But of course, if we don’t use it, we won’t see any improvement in this methodology. My hope for the future is that city planners take a more holistic view of the sound environment and try to accentuate the positive potential of soundscaping to improve the general health and wellbeing of city dwellers.

If you want to read my whole thesis. It can be found here:

http://www.akustik.lth.se/fileadmin/tekniskakustik/publications/tvba5000/webTVBA5062.pdf

If you are interested in projects where soundscape was used in some extend there a homepage made by Gunnar Cerwén:

https://ljudplanering.se/category/projekt/

Written by Semir Caban

Saga Hävermark
Författare
Saga Hävermark är akustiker på Sweco sedan 2019. Hon har en civilingenjörsexamen inom miljö- och vattenteknik från UU och fastnade under utbildningen extra för akustik. Hon har tidigare arbetat kommunalt med bullerfrågor rörande dels åtgärder i befintlig miljö, dels buller i stadsplanering. Saga brinner extra för samhällsbuller och ser det som en självklar hållbarhetsfråga. Att hon gillar akustik är ingen överdrift; när hon inte jobbar sitter hon oftast bakom sitt trumset och skapar musik eller är ute med hunden Buller.

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