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Assessment of airborne ultrasound noise


Noise by airborne ultrasound is increasingly polluting our daily environment and can be a risk to our health. There is a growing need for an understanding of the perception and the influence of ultrasound and for establishing consistent regulations. The EARS project has brought researchers of several disciplines together and combined neuroimaging and audiological measurements to create a basis for the assessment of ultrasound noise...

Our daily environment at home, at work and at public places is polluted by airborne ultrasound noise caused intentionally or as a by-product of their operation by a growing percentage of technical equipment. There are numerous indicators that sound in the ultrasound frequency range can be perceived by humans and that this noise has influence on human health. The amount of knowledge about the perception and the risks of the ultrasonic noise is still small. This leads to the fact that even the small number of existing guidelines on measurement and assessment of airborne ultrasound are inconsistent with one another. There is a growing interest of users, manufacturers and occupational health and safety agencies in consistent and rationally underpinned regulations.

This was the impetus for fundamental studies within the EARS project [1] which was funded by the European Union via the “European Metrology Research Programme” (EMRP). A group of otologically normal test persons passed through a set of hearing tests covering the high-frequency and ultrasound frequency ranges. The hearing tests were performed as classical audiological tests as well as brain imaging studies using magnetoencephalography (MEG) and functional magnetic resonance imaging (fMRI) facilities. This specific concept combined the advantages of both methods and allowed studying brain responses with test persons whose individual hearing sensitivity was known based on sound pressure levels. A first proposal for future limits for the exposure to airborne ultrasound could be derived from the results.

Figure 1: Audiologically measured hearing threshold at high audible and at ultrasonic frequencies, given as the median values (solid line), maxima and minima values (dotted lines) and literature data (red and blue lines). For comparison, measured noise levels of ultrasonic machines are plotted.

The findings of the study suggest that there is more likely a health risk – at least in the case of the ultrasound pressure levels investigated – due to annoyance oo disturbance, and also agitation than to physical damage to the inner ear. This lead to a proposal of the following strategy for the assessment of ultrasonic noise: Prevent any annoyance as fundamental impact on humans by avoiding even the perception of airborne ultrasound. The basis for this strategy is the measured hearing threshold data. At frequencies between 10 kHz and 20 kHz they are more individual and diversified than at conventional audible frequencies. Additionally, the age-related effect of younger adults and children perceiving frequencies between 10 kHz and 20 kHz at lower levels than older adults do, is also much more pronounced in comparison to conventional audible frequencies. For ultrasound above 18 kHz, this effect decreases, but there the thresholds are very near to loudness levels that cause annoyance. To account for this, the 1 % percentile or the minimum threshold of an appropriate data set should be used as an exposure limit. Extra margins for groups of individuals with specific ultrasound hearing sensitivity can be provided; this must still be a subject of discussion in the future.

All conclusions drawn are a first attempt to improve the rational underpinning of noise assessment in the frequency range of airborne ultrasound. New data from greater cohorts and from age-specific groups are necessary to further investigate this serious matter.



[1] Website EARS project: Opens external link in new windowwww. Opens external link in new windowears-project.eu


Contact person:

Christoph Kling, FB 1.6, AG 1.63, E-Mail: Opens window for sending emailchristoph.kling(at)ptb.de