Method of Testing of Sound Absorption Properties of Materials Intended for Ultrasonic Noise Protection

Abstract

Efficient ultrasonic noise reduction by using enclosures requires the knowledge of absorbing properties of materials in the frequency range above 4 kHz. However, standardized methods enable determination of absorption coefficients of materials in the frequency range up to 4 kHz. For this reason, it is proposed to carry out measurements of the sound absorption properties of materials in the free field by means of a tone-burst technique in the frequency range from 4 kHz to 40 kHz at angles of incidence varying from 0• to 60• . The absorption coefficient of a material is calculated from the reflection coefficient obtained by reflecting a tone-burst from both a perfectly reflecting panel and a combination of this panel and the sample of the tested material. The tests results show that mineral wool and polyurethane open-cell foam possess very good absorbing properties in this frequency range.

Narażenie na hałas o częstotliwości 10 ÷ 40 kHz na stanowiskach pracy zgrzewarek ultradźwiękowych – techniczne sposoby ograniczenia narażenia

“…obudowy i ekrany wyposażone niekiedy w materiały dźwiękochłonno-izolacyjne (Dobrucki i in. 2010;Pleban 2013;Smagowska 2012;2014). W przypadku stanowisk pracy zgrzewarek ultradźwiękowych do zgrzewania przewodów elektrycznych (zgrzewarki nr 8 i nr 11) zastosowano obudowę wykonaną z tworzyw sztucznych (zgrzewarka nr 11) oraz uszczelniono istniejącą obudowę (zgrzewarka nr 8).…”

Reducing the harmful effects of noise on the human environment. Sound insulation of industrial skeleton enclosures in the 10–40 kHz frequency range

“…In Poland, when harmful and uncomfortable factors in the human work environment depending on frequency of involved sound vibrations are considered, the noise is categorised into three ranges, of which the first is called the infrasonic noise (the frequency range 1-20 Hz), the second is referred to as the audible noise (the frequency range 20-20,000 Hz), and the third is named the ultrasonic noise (the frequency range of about 10,000-40,000 Hz) [2,3,[6][7][8][9][10]. In Poland, the latter noise category encompasses all 1/3 octave frequency bands with mid-band frequencies falling into the range of 10-40 kHz [2,3,[6][7][8][9][10][11][12][13][14]. In other countries, the 10-20 kHz range is called the very high frequency range whereas the bracket of higher frequencies is referred to as the ultrasonic range [3][4][5].…”

“…Some of these devices can be operated in sealed (fully closed) sound-insulating enclosures [11] and then ultrasonic noise outside such enclosure is, in the majority of cases, very small and negligible from the point of view of its harmful effect on humans [4,5]. Therefore, fully sealed enclosures (especially those provided with an inner lining of sound absorbing material) turn out to be a very effective measure of ultrasonic sound reduction [11][12][13][14][15][16][17][18][19][20][21][22]. The parameter characterising acoustic effectiveness of an enclosure in scope of its ability to attenuate the sound penetrating through it is called "the sound insulation of acoustic enclosure" (or "the sound insulation of enclosure") in applicable standards and literature of the subject [11,[15][16][17][18][19][20][21].…”

Methods of Testing of Sound Insulation Properties of Barriers Intended for High Frequency Noise and Ultrasonic Noise Protection

“…Due to the specificity of ultrasonic noise (short ultrasound waves) consisting in the occurrence of exposures mainly in the direct neigh borhood of noise sources, the most efficient protective means will be enclosures and acoustic screens which limit noise on its way of propagation. Efficient noise reduction using the above-mentioned technical methods requires, among others, the knowledge of acoustic properties of materials (including the values of sound absorption coefficients for the materials [8,9,10,11,12] and the knowledge of insulating properties of barriers in the frequency range above 5 kHz. Standardized methods [13,14,15,16,17] enable the determination of sound insulation of boards, barriers and construction elements in the frequency range up to 5 kHz.…”