Computerized Multi Microphone Test System

An acoustic testing approach based on the concept of a microphone sensor surrounding the product under test is proposed. Partial microphone signals are processed simultaneously by a test system computer, according to the objective of the test. The spatial and frequency domain selectivity features of this method are examined. Sound-spatial visualization algorithm is observed. A test system design based on the concept of a microphone surrounding the tested product has the potential to improve distortion measurement accuracy in a noisy ambience, to meet spatial resolution requirements for acoustic inspection. Introduction. Microphone arrays are used for acoustic wave source position localization (e.g. in seismology, hydro-acoustic systems). The spatial selectivity feature of acoustic array systems may help to suppress acoustic noise. This feature of microphone arrays finds its application in mobile voice communication. This article focuses on design issues of computerized testers used for automated testing of acoustic characteristic of production (e. g. in acoustic test of mobile communication devices like cell phones). The Product Under Test (PUT), which is mounted in a tester, should be configured and activated to output acoustic waves. In conventional testing, for example, a harmonic signal is applied to the PUT speaker, while the tester microphone transducer picks up signals produced by the acoustic wave. The electrical output signal of the microphone is analyzed to verify whether its parameters, as sound pressure level and distortion, are within specified limits. Accurate acoustic test measurements, especially distortion, (e.g. Total Harmonic Distortion (THD), should be performed in an acoustic chamber where extraneous acoustic waves are thoroughly suppressed on the fundamental frequency and its harmonics, as 2 well. The weakness in the traditional testing concept is a lack of robustness, especially if measurements are carried out without sufficient acoustic isolation from ambient noise. Concept. The acoustic testing concept considered in this article is based on employment of a microphone array. In accordance with the concept proposed here, the microphone array surrounds PUT; unlike in the classical concept, PUT is enclosed by the microphone sensor. This kind of sensor is termed here the Enclosing Microphone (EM). EM may be implemented practically, not only as an array of microphones, but also as a net structure membrane. The EM technique permits potential reduction of external acoustic noise, improved quality of acoustic product testing, and improved test robustness, without significant acoustic isolation. It has also some other useful features, such as spatial resolution. Spatial resolution is an inherent feature of the EM technique. A test system equipped with EM may provide additional diagnostic capabilities (e.g., monitoring of production quality, possible enhancement of PUT assembly failure detection) and more. This article is based on the author’s unpublished papers from the period 1992 to 2003. Analysis. It is assumed that a microphone array or net does not significantly deform acoustic waves. Figure 1 shows a simple EM configuration. Figure 1 comprises eight identical EM partial media pressure microphones, on a cube with vertexes M1... M8.