Author(s): Orlis Dimitris, Giouvanakis Marios, Sevastiadis Christos, Papanikolaou Georgios
Closed spaces present interesting characteristics in the low-frequency range in which the acoustic modes are intense and sound absorption is insufficient. Noise of low-frequency content can cause harmful effects to human health, especially in workplaces. Active noise control (ANC) techniques have been studied and implemented in order to counteract such issues.\nIn the present work, simulations of ANC to an orthogonal room model of a common workplace have been conducted. Focusing on the optimal placement of the secondary sources, the improvement offered by the specific ANC system configuration is studied. The Finite-Difference Time-Domain (FDTD) method is used to compute the acoustic field in the room before and after the control is applied. Considering the work activity, specific areas of interest are aimed to perform noise reduction. An adaptive feedforward FxLMS algorithm is implemented, using virtual microphones on fixed nodes of the grid. \nThe quality of the simulation model was assessed by comparing the resulting modal frequencies with the theoretical values, showing negligible differences. A low frequency tonal signal was used as primary source in a specific location. The criterion for the optimal placement of the secondary sources is the maximisation of the ANC system effect at the area of interest. It is shown that noise reduction can be achieved with a certain configuration of the secondary sources that is related to the modal stimulation of the room. Parts of the simulation data are stored, so that a time-wise evaluation of each configuration can be carried out at the post processing stage. Hence, critical metrics of an ANC system, e.g. noise reduction and convergence time, can be obtained.
Name: Mr Dimitris Orlis