Noise reduction of an acoustical enclosure --- Mechanisms and prediction accuracy
Noise reduction (NR) of an acoustical enclosure with flexible boundary walls has been predicted using t he Statistical Energy Analysis (SEA) method by several authors. Although it is useful for a rough NR estimation, a lar ge discrepancy often exists between the predicted and measured NR levels. Moreover, some physical mechanisms which may affect NR prediction were not addressed in the e xisting SEA models. The sources of the discrepancy were identified by investigating the limitation of SEA f or system energy transfer in the entire frequency r ange of noise transmission, and the effect of enclosure wall coup ling and sound-structural coupling on the NR and its prediction accuracy. This paper presents a modified SEA model, which includes the non-resonant response and more accurate transmission coefficient of finite panels, and comp ares the model prediction with experimental results . A reasonable agreement between the prediction and experiment was observed.
Study on Noise Prediction and Reduction in Coupled Workshops Using SEA Method
A theoretical model for predicting noise reduction in coupled workshops is presented by using statistical energy analysis (SEA) method. An opening between the coupled workshops is considered into the theoretical model properly. The leakage issue is dealt with in the process of SEA modeling. An experiment is also carried out. A reasonable agreement between the prediction of noise reduction and the experimental data is observed. Moreover, it is concluded from the simulations that the sound energy transmit through the opening was the most important way to affect the noise reduction and the leakage is a significant element to influence the effect of noise treatment.
Thermal Circuit Approach to Vibrations in Coupled Systems and the Noise Reduction of a Rectangular Box
Stationary, wide‐band vibrations of complex dynamic systems are treated in terms of energy quantities, neglecting details of structure and excitation. Approximate relations between the average energies in loosely and conservatively coupled systems are obtained in terms of modal densities, internal losses, and coupling losses. It is shown that the products of modal density and coupling‐loss factor are equal within each pair of subsystems. The general theory is applied to study the noise reduction of a rectangular box, and experimental results are compared with theoretical predictions with generally good agreement. The transmission behavior of a box at a given frequency is shown to depend on the relation of this frequency to the lowest mechanical‐ and acoustic‐resonance frequencies and the critical frequency of the walls. Theory and experiment show that near the lowest mechanical resonances the pressure in the box may considerably exceed that in the incident sound field.