Ljudalstingsmekanismer och beräkning av ljudtrycksnivå i fläktrum

Sammanfattning: When a fan room is to be built, it is important to have knowledge about the magnitude of the sound pressure level in the fan room since it will be used to dimension the surrounding structures. To be able to pre-calculate this sound pressure must assumptions about the characteristics of the room, the fan and the duct system be made. From the fan it is known which sound effect that will be generated and the magnitude that will be radiated directly to the environment or to the connected channels. This means that factors such as the channel geometry, channel length, muffler and channel bends will have some impact on the resulting sound pressure and those effects have to be predicted. From the fan room, factors like geometry and absorption will have an affect on the sound pressure level. From the calculated sound pressure level, walls, floors and ceilings in the fan room can be designed to ensure that the requirements in adjoining areas will be met. It is therefore important that a calculation method gives reliable results and above all, do not underestimate the resulting sound levels since it can result in undersized structures. This is true especially at low frequencies which in many cases will be the levels of design. Existing models and standard values are discussed and reviewed to find a computational model that can predict the sound pressure in the fan room in the best way possible. The interesting frequency range for this work is the octave bands between 63 Hz and 4000 Hz. Above all factors for absorption in the fan room and channel reduction is analyzed, but also the installation effects and gap correction factors studied.