In 2011, over 520 thousand persons worked in hazardous conditions (according to the GUS). Among hazardous factors related to working environment noise was found to be the most common one, threatening 199,6 thousand people (52.9% threats-per-persons related to working environment). The prevalence of workplace noise and increasing awareness of effects of its impact on the human body causes increase of the demand for knowledge of the methods of noise reduction. Due to the lack of knowledge concerning the proper use of hearing protectors, effective noise exposure in the real world may be about a dozen dB higher than the declared assumed protection value. For this reason, in Central Institute for Labour Protection - NRI “The interactive system for learning the correct use of hearing protectors” has been developed. The system includes a multimedia guide on hearing protectors supplemented by video tutorials, training materials with training hearing protectors, and software for evaluation of the activities of the trainee.
Additional sound sources are used as actuators in the vast majority of active noise reduction systems. One of the possible opportunities to extend the field of applications of active noise reduction systems is using active structures of variable sound insulation. The paper presents an analysis of ways of reducing noise with a structure of variable sound insulation consisting of a metal plate, active elements (Macro Fiber Composite), and a control system. The paper presents results of acoustic radiation simulations and measurements of sound intensity generated by the structure under the influence of stimulation by an acoustic wave. Simulations of mechanical vibrations and acoustic radiation for the plate were performed with the finite element method and ANSYS software. Simulation results made it possible to select locations for gluing the active elements and sensors. Analyses of the sound pressure level in the space to which the plate is radiating made it possible to determine dominant frequencies in the characteristics and, as a result, indicate vibration modes that can be reduced. Sound intensity measurements were performed with a three-way probe of USP mini Microflown. Results of simulations and measurements show that it is possible to achieve an improvement of the insulating power of a metal plate by approx. 10 dB.
Application of active noise reduction (ANR) systems in hearing protectors requires the use of control algorithms to ensure stability of the ANR system and at the same time highly effective active noise reduction. A control algorithm based on NOTCH filters is an example of solutions that meet these criteria. Their disadvantage is operation over a narrow frequency band and a need for prior determination of frequencies to be reduced. This paper presents a solution of the ANR system for hearing protectors which is controlled with the use of modified NOTCH filters with parameters determined by a genetic algorithm. Application of a genetic algorithm allows to change the NOTCH filter reference signal frequency, and thus, adapt the filter to the reduced signal frequency.