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Title Modelling distortion in condenser microphones
Author Dessein, Arnaud
Supervisor Jacobsen, Finn (Acoustic Technology, Department of Electrical Engineering, Technical University of Denmark, DTU, DK-2800 Kgs. Lyngby, Denmark)
Agerkvist, Finn T. (Acoustic Technology, Department of Electrical Engineering, Technical University of Denmark, DTU, DK-2800 Kgs. Lyngby, Denmark)
Olsen, Erling Sanderrmann (Brüel & Kjær)
Eriksen, Anders (Brüel & Kjær)
Institution Technical University of Denmark, DTU, DK-2800 Kgs. Lyngby, Denmark
Thesis level Master's thesis
Year 2009
Abstract Distortion in condenser microphones has dierent origins : electrical, acoustical and mechanical. According to the preliminar litterature study, the electrical distortion is found dominant compared to the acoustical and mechanical distortions. The electrical distortion is produced by two phenomenon. First, the presence of passive capacitances in parallel to the active capacitance (which varies with the acoustic signal) introduces nonlinearity in the transduction principle. Then, the curved de ection prole of the diaphragm is responsible for an inhomogeneous repartition of the active capacitance. Many papers have already been written about the eect of stray (passive) capacitance but the in uence of the de ection shape has not been studied into details yet. A better prediction of the membrane de ection prole is made possible by a new model developped during this study. This model takes the variations of the electrostatic force along the membrane into account. When the movement of the membrane is large (high sound pressure levels or soft diaphragm microphones), these variations become an important factor in the detrmination of the de ection shape and thus in the microphone distortion. The in uence of the membrane de ection shape is then simulated using dierent models of membrane de ection. It is found that the in uence of the curved de ection shape on the distortion is about 6 dB (re fundamental) for a normal measuring microphone and about 7 dB for a low-noise microphone (soft diaphragm). Optimum backplate radius and reduction of the distortion by means of a curved backplate are investigated. A reduction of approximately 5 dB is found possible by using a curved backplate with an optimised radius of curvature.
Imprint Technical University of Denmark (DTU) : Kgs. Lyngby, Denmark
Pages 92
Fulltext
Original PDF Arnaud_DESSEIN.pdf (0.95 MB)
Admin Creation date: 2009-09-01    Update date: 2009-11-04    Source: dtu    ID: 249608    Original MXD