The goal is to interpret and calculate the "niche effect" for the airborne sound transmission through a specimen mounted inside an aperture in the wall between the source and receiving reverberation rooms. The low-frequency sound insulation is known to be worse for the specimen placed at the center than for the specimen mounted at either edge of the aperture. As shown, the aperture with a tested specimen can be simulated at low frequencies as a triple partition where the middle element is the specimen and the role of the edge leaves is played by the air masses entrained at the aperture edges. With a centrally located specimen, such a triple system is symmetric and has two main natural frequencies close together. In this case, the resonant transmission is higher than for the edge arrangement simulated as a double system with one natural frequency. Analogous resonant phenomena are known to reduce the low-frequency transmission loss for symmetric triple windows or solid walls with identical air gaps and lightweight boards on both sides. The theoretical results obtained for the mechanical and acoustical models are in a good agreement with the experimental data.
This paper presents several analytical solutions for the conventional electrostatic parallel-plate model and explains the effect of the quality factor decrease with the voltage applied. Such a model is of importance in the development of electrostatic (capacitive) sensors and actuators including acoustical transducers and loudspeakers, and micro/nanoelectromechanical systems (MEMS/NEMS). It serves to reveal and interpret the basic phenomena (in particular, the “pull-in” instability and “negative spring” effect) but there is still some room for new effects and analytical results, although the model is nonlinear and provides rather computational than comprehensible close-form relationships as “negative quality factor effect” described in this paper. The new results obtained can be supportive to analyze, test, and design electrostatic sensors and actuators.
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