A global noise protective solution, based on the idea of virtual acoustic corridors, dedicated to industrial areas, is investigated. Research studies on decentralized ANC system with several secondary sources and error sensors are performed in the KOMAG Institute of Mining Technology. The models of the electro-acoustic paths are obtained through dynamical systems identification. Experimental results from the proposed active noise reduction system are presented, based on recorded noise signals from the Rybnik Power Plant. Finally, effectiveness and usefulness of hearing protection of such a global system are verified.
There are many industrial environments which are exposed to a high-level noise, sometimes much higher than the level of speech. Verbal communication is then practically unfeasible. In order to increase the speech intelligibility, appropriate speech enhancement algorithms can be used. It is impossible to filter off the noise completely from the acquired signal by using a conventional filter, because of two reasons. First, the speech and the noise frequency contents are overlapping. Second, the noise properties are subject to change. The adaptive realisation of the Wienerbased approach can be, however, applied. Two structures are possible. One is the line enhancer, where the predictive realisation of the Wiener approach is used. The benefit of using this structure it that it does not require additional apparatus. The second structure takes advantage of the high level of noise. Under such condition, placing another microphone, even close to the primary one, can provide a reference signal well correlated with the noise disturbing the speech and lacking the information about the speech. Then, the classical Wiener filter can be used, to produce an estimate of the noise based on the reference signal. That noise estimate can be then subtracted from the disturbed speech. Both algorithms are verified, based on the data obtained from the real industrial environment. For laboratory experiments the G.R.A.S. artificial head and two microphones, one at back side of an earplug and another at the mouth are used.
There are many industrial environments which are exposed to a high-level noise. It is necessary to protect people from the noise. Most of the time, the consumer requires a miniature version of a noise canceller to satisfy the internal working place requirements. Very important thing is to select the most appropriate personal hearing protection device, for example an earplug. It should guarantee high passive noise attenuation and allow for secondary sound generation in case of active control. In many cases the noise is nonstationary. For instance, some of the noisy devices are switched on and off, speed of some rotors or fans changes, etc. To avoid any severe transient acoustic effects due to potential convergence problems of adaptive systems, a fixed-parameter approach to control is appreciated. If the noise were stationary, it would be possible to design an optimal control filter minimising variance of the signal being the effect of the acoustic noise and the secondary sound interference. Because of noise nonstationarity for most applications, the idea of generalised disturbance defined by a frequency window of different types has been developed by the authors and announced in previous publications. The aim of this paper is to apply such an approach to different earplugs and verify its noise reduction properties. Simulation experiments are conducted based on real world measurements performed using the G.R.A.S. artificial head equipped with an artificial mechanical ear, and the noise recorded in a power plant.
For environments subject to high level acoustic noise communication between people is difficult. This bemuses workers, limits working efficiency, and may even lead to accidents. Additionally, prolonged exposure to such noise results in damage to the human hearing system. A better isolation of people from the noisy machines is frequently technologically unfeasible or very expensive. Communication headsets available on the market are not ergonomic. On the other hand, they are not accepted in warm and humid environments because wearing them may cause skin galls. Therefore, at some places in mines, power plants, car factories, assembly lines, etc., the workers use earplugs made from an elastic noise absorbing material, and communication between them is limited to a set of gestures only. The aim of the paper is to present NoiseCom -a complex ergonomic earplug-based communication-improvement solution, integrating high passive and active noise reduction, enhancement of speech intelligibility and wireless speech transmission for a group of workers. Developed algorithms are presented and obtained results are reported based on recordings in real industrial conditions.
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