Optimized directionality in acoustically coupled, dual motor, uniphase, moving coil microphones

Abstract

In uniphase, moving coil microphones, pneumatic vibration cancellation is an effective means to minimize structural excitation. However, pneumatic vibration cancellation requires precise control of the transfer function between the capsule and the microphone body, and the internal volumes are large. Therefore, the uniphase, moving coil capsule with pneumatic vibration cancellation is not well suited as a portable platform in applications that require a compact size. The addition of a secondary transduction mechanism is commonly used to mitigate a variety of unwanted signal sources in microphones, and is an effective alternative to the pneumatic vibration cancellation. Because the secondary transduction mechanism is integral to the capsule, precise control of the capsule/body transfer function is not needed, resulting in a more portable solution. However, the current strategy for vibration cancellation is to isolate the secondary transduction mechanism from the acoustical excitation, which does not minimize the internal volume and is not compact. A new strategy proposes an alternative architecture where the two transduction mechanisms share an internal volume. When certain constraints are met, acoustically coupling the motors results both a minimized internal volume and an optimized microphone directionality at low frequencies. Simulated and measured results are shown to illustrate the implementation.