Volume 119, Issue 5, May 2006
Index of content:
- TRANSDUCTION 
119(2006); http://dx.doi.org/10.1121/1.2188367View Description Hide Description
This paper provides evidence for electrical noise as the dominant source of excess noise in piezoresistivemicroelectromechanical systems(MEMS)microphones. In piezoresistors, the fundamental noise sources may be divided into frequency independent thermal noise and frequency dependent excess noise dominating at low frequencies. Noise power spectra are presented for both commercial and research-prototype MEMSpiezoresistivemicrophones as a function of applied voltage bias for both free and blocked membranes. The contributions of various mechanical and electrical noise sources are compared using a lumped noise equivalent circuit of the piezoresistivemicrophone. The bias dependence and membrane independence of the output noise indicate that the primary source of the excess noise is electrical in origin.
Adaptive wave field synthesis with independent radiation mode control for active sound field reproduction: Theorya)119(2006); http://dx.doi.org/10.1121/1.2186514View Description Hide Description
Sound field reproduction finds applications in music or audio reproduction and experimental acoustics. For audio applications, sound field reproduction can be used to artificially reproduce the spatial character of natural hearing. The general objective is then to reproduce a sound field in a real reproduction environment. Wave field synthesis (WFS) is a known open-loop technology which assumes that the reproduction environment is anechoic. For classical WFS, the room response thus reduces the quality of the physical sound field reproduction. In this paper, adaptive wave field synthesis (AWFS) is analytically investigated as an adaptive sound field reproduction system combining WFS and active control with a limited number of reproduction error sensors to compensate the response of the listening environment. The primary point of this paper is the definition of AWFS. Therefore, the fundamental behavior of AWFS is illustrated by analytical considerations and simple free-field simulation results. As demonstrated, AWFS is fundamentally related to WFS and “Ambisonics.” The paper introduces independent adaptive control of sound field reproduction on the basis of radiation modes, via the singular value decomposition of the transfer impedance matrix. Possible practical independent control of radiation modes for AWFS is discussed.