This paper develops a theory for the sound absorption and scattering of perforated slit absorbers. A rigid plane, perforated periodically in one dimension with absorbing slits, scatters incoming sound waves as discrete wave components in different directions. The absorbing slits are assumed to be line-like in the sense that their width is much shorter than the wavelengths. The equation for the sound field is solved in the wavenumber domain. The slits are described with an impedance description, assuming local reaction of the slits (typically a Helmholtz resonator). The solution is found by means of an inverse transform, back to the spatial domain. This results in an explicit formulation of the sound field, including a sum consisting of components that either radiate energy in discrete directions or are surface waves. A similar sum is also included in a term that can be interpreted as radiation impedance. The explicit expressions for the absorption and scattering coefficients are found with the aid of the radiating part of the scattered and reflected field. Numerical results of the absorption and scattering coefficients are presented. The result is verified with finite element method and compared with the result from an alternative general formulation of the problem.

The LIFE + project NOISUN, concluded in February 2016, had as main objective to demonstrate an innovative noise barrier that produces solar energy for distribution to local district heating systems. Specially adapted solar collectors were installed at a major transport thoroughfare for both road (the E20 motorway) and railway traffic in the Swedish municipality of Lerum, and the effect of the intervention was evaluated in several ways. In the beginning of the project, calculations of expected noise mitigation were performed. Before and after the noise barrier was erected two actions were performed: Questionnaires were sent out to concerned households, and sound level measurements were performed in combination with recordings of noise events. The insertion loss of the noise barrier showed to be very close to the estimations. The noise reduction was most pronounced for loud train pass-bys but not as much for road traffic noise from the E20 motorway (also, contributions from other streets made the room for road traffic noise improvement smaller). The questionnaire results are presented and discussed in relation to the measurement results. The analysis shows a clear improvement of the perceived noise situation, but also points to some of the problems inherent in field projects analyses.

Fires are a major hazard resulting in high monetary costs, personal suffering, and irreplaceable losses. The consequences of a fire can be mitigated by early detection systems which increase the potential for successful intervention. The number of false alarms in current systems can for some applications be very high, but could be reduced by increasing the reliability of the detection system by using complementary signals from multiple sensors. The current study investigates the novel use of machine learning for fire event detection based on acoustic sensor measurements. Many materials exposed to heat give rise to acoustic emissions during heating, pyrolysis and burning phases. Further, sound is generated by the heat flow associated with the flame itself. The acoustic data collected in this study is used to define an acoustic sound event detection task, and the proposed machine learning method is trained to detect the presence of a fire event based on the emitted acoustic signal. The method is able to detect the presence of fire events from the examined material types with an overall F-score of 98.4%. The method has been developed using laboratory scale tests as a proof of concept and needs further development using realistic scenarios in the future.

The low-frequency properties of a room (where statistical methods in the standards cannot be applied directly) are often hard to estimate due to strong modal behaviour. The situation gets complicated by the fact that variations in the furnishing can have an impact on the modal patterns and therefore can also influence the results of measurements at certain points, in spite of the room properties being the same. The latter can hinder the achievement of acoustic comfort in dwellings, even if they comply with the current regulations, especially due to the fact that low-frequency noise is left outside the scope, since the standards currently in force do not require measurements below 100 Hz (albeit Sweden set 50 Hz as lower limit). This article aims to study variations of the sound field that results of varying the position of three moderately absorbing boards, which emulate how very sparse furniture can impact the sound field when relocated in the room. Furthermore, the potential of numerical models as prediction tools for such problems is pointed out.