Concerns exist that non-audible sound outside of the hearing range presents a hazard to hearing or creates annoyance. Since the perception mechanism of non-audible sound is not well understood an urgent need for mitigating rationally underpinned safety criteria and a risk assessment protocol exists. New technologies and industrial processes emit infrasound or airborne ultrasound either intentionally or as a by-product of their operation. Producers of such machinery require noise emission regulations to be well founded and not unnecessarily restrictive, while those responsible for workplace safety also need reliable safety criteria and risk assessment processes. Only when the metrology infrastructure of primary standards and methods of calibrating measuring devices have been established can any damaging effect of airborne ultrasound and infrasound be quantified and legislation to limit exposure and protect the population be put in place.

Ear simulators are reference devices which underpin quantitative hearing assessment by enabling audiometric equipment to be calibrated. However established standards and practices currently relate primarily to pure tone audiometry for adults. As a result of initiatives to capitalise on the benefits of early diagnosis and treatment of hearing disorders in neonates and children, alternative objective audiometric methods using non-sinusoidal stimuli are now mainstream. The greater focus on testing neonates and children and the expanded range of methodologies used, has created new user requirements for ear simulators.

Aims of the project

The project aims to support preventative strategies to hearing conservation through two major interdisciplinary research and development activities. The first aims to establish new understanding of human perception of non-audible sound as well as the metrology infrastructure necessary to put in place effective safety criteria based on establishing perception thresholds. The second aims to improve the relevance of metrology in modern audiological practices, to bring about improved quality and reliability of results by development of a universal ear simulator.

Key project tasks

The project will develop new methods and technology for the determination of brain responses using magnetoencephalography (MEG) and functional magnetic resonance imaging (fMRI) to non-audible sound. New transducers appropriate for delivering and measuring the acoustic stimuli will also be developed. For metrological underpinning new measurement methods and calibration techniques for non-audible sound, including a new primary standard for airborne ultrasound need to be established. A new understanding of the perception mechanisms of non-audible sound will be generated by comparing brain response measurement and hearing thresholds which will underpin the determination of safe exposure limits. A new universal ear simulator will be designed, developed and manufactured for which new calibration methods will be developed and reference equivalent threshold sound pressure level values will be determined. A selection of clinical users will then be engaged to evaluate the new device in audiological practice and provide valuable feedback on usability, and the standardization process will be initiated.

Key results and expected impact

The main goal of the project is the improvement of quality of life by understanding and then controlling noise hazards and possible detrimental effects on hearing which is a task concerning the whole of European society. Key to addressing these concerns is developing the necessary knowledge and fundamental understating of human hearing, and the impact of noise and non-audible sound has on it. This will be achieved by developing a variety of innovative measurement techniques and instrumentation, establishing traceability where it does not yet exist, and using this to underpin new or improved measurement protocols for noise assessment, hearing assessment and conservation and regulations on health and safety.

The project will have impact on a wide range of stakeholders including health and safety bodies, equipment and plant manufactures, industrial workers, environmental pressure groups, audiologists, healthcare policy formulators, the general public and every newborn child. It will strongly influence standardisation in the areas of hearing thresholds and ear simulators (ISO TC43 WG1 and IEC TC29 WG21 respectively) and will produce new guidance leading to regulations on health hazards posed by non-audible sounds.