N2 - The physical phenomena occurring in sound-absorbing and insulating enclosures are subject of the present paper. These phenomena are: absorption in air and by the sound-absorbing material covering the walls and the coincidence effect. The absorption in the air can be neglected in small size enclosures for low ultrasonic frequencies (20-30 kHz). The coincidence plays a role in decrease of the sound insulation, however the main role play the leaks. The boards made of ceramic fibers have been chosen as the optimal sound-absorbing material. They are dense and have deeply porous structures. The enclosure for insulation of 20-kHz noise produced by a welding machine has been designed and manufactured, and reductions of 25 dB of peak and Leq levels have been achieved. L1 - http://www.journals.pan.pl/Content/107541/PDF/71.pdf L2 - http://www.journals.pan.pl/Content/107541 PY - 2010 IS - No 2 EP - 164 DO - 10.2478/v10168-010-0014-4 KW - ultrasonic noise KW - sound absorbing and insulating enclosure KW - welder A1 - Dobrucki, Andrzej A1 - Żółtogórski, Bronisław A1 - Pruchnicki, Piotr A1 - Bolejko, Romuald PB - Polish Academy of Sciences, Institute of Fundamental Technological Research, Committee on Acoustics VL - vol. 35 DA - 2010 T1 - Sound-Absorbing and Insulating Enclosures for Ultrasonic Range SP - 157 UR - http://www.journals.pan.pl/dlibra/publication/edition/107541 T2 - Archives of Acoustics