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. With this background, a joint research project started in 2012 which is funded by the European Metrology Research Programme (EMRP) 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.
One of the main issues is the development and standardisation of measurement methods and calibration techniques for airborne ultrasound to provide traceability for noise measurement in this high-frequency range. The talk will present a first preliminary set-up to determine emission of typical air-borne ultrasound sources. The sound pressure is measured using a quarter-inch microphone with a wide-band acoustic analyzer and the dependence of the results on spatial sound field distribution is analyzed. First proposals of data analysis for an assessment of air-borne ultrasound were presented. Moreover, the metrological basis will be delivered for a proper traceability of microphones in the ultrasound frequency range.
The measurement results can be used for a risk assessment of noise emission at working places comprising industrial ultrasonic devices. No international standard exists to date for this topic. A first step is a new regulation in Germany which for the first time defines milestones for measurement procedures for the determination of airborne ultrasound at working places. In the talk the relevance of these procedures will discussed taking in account the experience from the measurement results obtained for practical sources. These are first steps for establishing a rationale for the assessment of the hazard for hearing by non-audible sound.