Index of content:
Volume 52, Issue 3A, September 1972
52(1972); http://dx.doi.org/10.1121/1.1913165View Description Hide Description
The nonlinear equations for the static deflections of the moving electrode due to the electrical fields between the electrodes in capacitancemicrophones are presented. These equations are valid for the historic method of constant bias voltage and the more recently developed polymerelectret biasing. The equations were solved numerically for boundary conditions of circular and annular membranes. Because of the nonlinearity of the electrical attraction forces, certain values of the microphone parameters exist for which the deflections can become unstable. The results compare closely with past solutions and experimental deflection data obtained on constant bias voltage microphones using a laser interferometer.
52(1972); http://dx.doi.org/10.1121/1.1913166View Description Hide Description
Few methods are available for converting sound power levels to a single rating number. In this study, the relationships between sound level A, the Air‐Conditioning and Refrigeration Institute (ARI), sound rating number (SRN), and perceived noise level (PNL) are explored. If the ARI rating method is modified slightly, a direct correspondence can be established between the sound rating number of a band power spectrum and the perceived noise level of a band‐pressure spectrum whose band levels are 20 dB lower in value. To differentiate between a rating based on sound power and a rating based on sound pressure, a single number called the power level rating (L PR) expressed in units of PRdB is proposed.
52(1972); http://dx.doi.org/10.1121/1.1913167View Description Hide Description
This paper presents the result of an experimental investigation designed to study the effect of high‐intensity sound on muffler element performance. Five prototype mufflers were built and tested over a wide range of frequency and intensity. The mufflers were chosen as being representative of basic single‐element and combination reactive mufflers. The apparatus consisted of an acoustic transmission line driven by an electromagnetic sound source and terminated anechiocally. Attenuation data are presented superimposed on curves derived from linear‐acoustic theory. Conclusions are stated for expansion chamber mufflers at higher sound pressure levels (SPLs) than could be produced by the test equipment by using constriction tube data and acoustic similarity between these elements. It is shown that the expansion chamber muffler will operate as a linear element when subject to incident SPLs of 165–180 dB depending on muffler attenuation. Mufflers containing resonator elements show no deviation from a linear theory when subject to SPLs of the order of 160 dB except at points near a resonant frequency
52(1972); http://dx.doi.org/10.1121/1.1913168View Description Hide Description
Generalized curves and a simple equation are developed by which it is possible to relate the sound‐power level of a plane array of equal, incoherent, simple sources to the sound‐pressure level at any distance. The array may have the form of a circular disk or a rectangle.