Various experiences related to research work, including the less successful ones, are all part of the research process. Awareness of their existence allows to draw conclusions from one’s mistakes and a more responsibly design of a research. This article aims to understand the traps a researcher, exploring intellectual disability, may fall into. As a result of search and reflection, three kinds of traps can be listed: resistance — submission, norm — pathology, correctness — negligence.
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.