ABSTRACT
Noise in the 10–40 kHz frequency range emitted by ultrasonic devices is numbered among work environment acoustic factors harmful to workers. The most effective way to reduce the noise (apart from intervention in the device structure) is providing noise sources with sound-insulating enclosures. This chapter presents a noise source emission measurement method adapted specifically to the 10–40 kHz range. The point of departure were methods recommended in EN ISO 3744:2010 and EN ISO 3746:2010 for frequencies below 10 kHz and in EN ISO 9295:2015 for frequencies below 20 kHz. A method is proposed for measurement of enclosure-insulating performance in the frequency range 10–40 kHz expressed in terms of the sound power insulation of the enclosure, based on the method set out in EN ISO 11546-2:2009 for frequencies up to 10 kHz. Further, a measuring setup developed in the Central Institute for Labor Protection—National Research Institute for the purpose of application of this method is described and example results of enclosure sound power insulation measurements are quoted. Results of a study on the effect of enclosure wall thickness and application of sound-absorbing materials inside the enclosure wall on the sound power insulation properties are presented for a demonstration enclosure.
