The German authorities are now clear in that there is a very real issue with low frequency sound and recognise that they both need to update their regulations and complete more research.

http://www.umweltbundesamt.de/sites/default/files/medien/378/publikationen

/texte_40_2014_machbarkeitsstudie_zu_wirkungen_von_infraschall.pdf

Abstract

This feasibility study evaluated the state of knowledge about the effects of infrasound on human beings, the identification of infrasound sources and the potential concernments in Germany due to infrasound. Furthermore, a study design was developed for a noise impact study concerning infrasound immissions. Based on these findings, recommendations for the further development of regulations on immission control were made. The study led to the following conclusions:

•   The literature review does not present a coherent picture about the determination and assessment of low frequency sounds. Especially in Germany, there are just a few studies that deal with infrasound. A database was created for further research projects.
•  Survey tools that allow for an initial acoustic description and classification were developed for the acoustic identification and assessment of potential infrasound sources. 
•  The surveys of the immission control authorities of the Länder (German states) and the evaluation of Internet communication on infrasound show a somewhat higher level of noise pollution in Southern Germany. Above all, noise pollution from air-conditioning systems and biogas facilities were mentioned. In the official practice, the Technical Instructions on Noise Abatement and DIN 45680 generally apply in cases of conflicts concerning infrasound. 
• A study design was developed for an interdisciplinary field study and the essential survey contents and sources were defined. 
• The DIN 45680 Measurement and Assessment of Low Frequency Noise Immissions in the Neighbourhood can be used for the assessment of low frequency noise (<100 Hz). The international standard ISO 7196 Acoustics – Frequency-Weighting Characteristic for Infrasound Measurements was especially created for the measurement of infrasound immissions (<20 Hz). The research findings indicate that these standards have deficits with regards to the assessment of infrasound and should be further developed. The current revision of DIN 45680 shows a path for how inconsistencies in the area of low frequency sounds can be rectified.

On page 15 of the document, which is about the state of knowledge about the effects of infrasound on people, we get a really important conclusion:

 

• Wind energy plants are a frequently studied source of noise in connection with infrasound. The publications show that the measurement of emission and propagation of noise from wind energy plants is plagued by uncertainties that complicate a substantiated noise forecast. With an increasing height of the wind energy plants, the rotor blades cut through an even more varied wind profile. It is therefore questionable whether the emission and propagation models of smaller wind energy plants can be applied to more modern and larger wind farms. This is very unlikely given the theoretical observations of aeroacoustic scientists. Deeper knowledge of the above-mentioned processes would not only be a prerequisite of better immission forecasting, but the acquired knowledge could also provide information for an improved noise reduction of wind energy plants.

On Page 55 we have another important statement:

• The A-evaluation method is seen many times in the literature as unsuitable, in order to correctly assess the the impacts of low frequency sounds. 

The next page (P 56) states how with wind energy there are frequent discrepancies between measured results and those predicted by the models. This is also followed by a section, which explains as to why wind turbines have a more pronounced impact at night, due to the meteorological conditions. Page 110 talks about the harmonics in wind turbine noise found in the range 1 Hz to 8 Hz.

There seems to be quite a bit in this document, maybe one could criticise it for being a bit of a literature review rather than a new study. However, the main thing is that the German authorities are now clear in that there is a very real issue with low frequency sound and recognise that they both need to update their regulations and complete more research. On the other hand here in Scotland and the UK we are in absolute denial that there is a problem with such low frequency noise.