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Journal of the Acoustical Society of America

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Jun 2009

Volume 125, Issue 6, pp. EL221-4109

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Electroacoustic analysis of an electret loudspeaker using combined finite-element and lumped-parameter models

Mingsian R. Bai, Rong-Liang Chen, and Chun-Jen Wang

J. Acoust. Soc. Am. Volume 125, Issue 6, pp. 3632-3640 (2009); (9 pages) | Cited 3 times

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An unconventional type of electrostatic loudspeaker is presented in this paper. The loudspeaker made of thin, light, and flexible electret material lends itself well to the space-concerned applications. Electrical impedance measurement reveals that the coupling between the electrical system and the mechanical system is weak, which renders conventional parameter identification based on electrical impedance measurement impractical. A different approach is thus employed to model the electret loudspeaker. To predict the loudspeaker’s dynamic response, finite-element analysis (FEA) is conducted on the basis of a simple model and a full model. In the simple model, FEA is applied to model the electret membrane, leaving the rest of system as rigid parts. In the full model, FEA is applied to model the entire membrane-spacer-back plate assembly. Velocity response of the membrane subject to a uniformly distributed force is calculated using FEA harmonic analysis. Mechanical impedance is then calculated with the velocity response. The acoustical impedance due to the back cavity, pores, and the radiation loading at the front side is calculated by theoretical formulas. The volume velocity of the membrane and the resulting on-axis sound pressure level are predicted with electrical-mechanical-acoustical analogous circuits. The response data predicted by the simulation compare very well with experimental measurements.
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43.38.Bs Electrostatic transducers
43.38.Ja Loudspeakers and horns, practical sound sources
43.40.Dx Vibrations of membranes and plates

Design optimization of condenser microphone: A design of experiment perspective

Chee Wee Tan and Jianmin Miao

J. Acoust. Soc. Am. Volume 125, Issue 6, pp. 3641-3649 (2009); (9 pages)

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A well-designed condenser microphone backplate is very important in the attainment of good frequency response characteristics—high sensitivity and wide bandwidth with flat response—and low mechanical-thermal noise. To study the design optimization of the backplate, a 26 factorial design with a single replicate, which consists of six backplate parameters and four responses, has been undertaken on a comprehensive condenser microphone model developed by Zuckerwar. Through the elimination of insignificant parameters via normal probability plots of the effect estimates, the projection of an unreplicated factorial design into a replicated one can be performed to carry out an analysis of variance on the factorial design. The air gap and slot have significant effects on the sensitivity, mechanical-thermal noise, and bandwidth while the slot/hole location interaction has major influence over the latter two responses. An organized and systematic approach of designing the backplate is summarized.
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43.38.Kb Microphones and their calibration
43.38.Bs Electrostatic transducers
43.38.Ar Transducing principles, materials, and structures: general
43.58.Ta Computers and computer programs in acoustics
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