Noise Calculation Method for Industrial Premises with Bulky Equipment at Mirror-diffuse Sound Reflection

The paper presents a method of sound energy characteristics calculation in premises with bulky equipment at mirror-diffuse character of sound reflection from enclosures. At such character of reflection a part of sound energy falling on an enclosure is reflected specularly, and the other part is dissipated under the Lamberts law. Sound pressure levels in reference points of a premise are determined by the sum of direct sound energy emitted by sound sources and energy of mirror and diffuse components of reflected sound field. The numerical method is proposed for calculation of sound energy density and the subsequent determination of sound pressure levels. The method is developed on the basis of the combined design model in which the mirror component of the reflected sound energy is determined by ray-tracing method and the diffuse energy component is calculated by numerical statistical energy method. The equations for determination of density of the direct, mirror-reflected and diffused sound energy are provided and technique of realization of the design model is given. The proposed method takes into account space-planning features of premises, presence of bulky equipment, sound absorption characteristics of enclosures and the nature of sound reflection from surfaces, and provide an opportunity to solve problems of estimating noise in industrial premises. The comparison of the calculated and experimental data obtained for rooms of different sizes and shapes in the absence and presence of bulky equipment confirmed the adequacy of the proposed calculation model for the description of noise field formation in such conditions. It is shown that divergences of calculation and experimental data do not exceed ±2÷3 dB in octave bands with central frequencies equal or more than 250 Hz.