  Micro-electro-mechanical system (MEMS) microphones (mics) with two acoustic
ports are currently receiving considerable interest, with the promise of
achieving higher directional sensitivity compared to traditional one-port
architectures. However, measuring pressure differences in two-port microphones
typically commands sensing elements that are softer than in one-port mics, and
are therefore presumably more prone to interference from external vibration.
Here we derive a universal expression for microphone sensitivity to vibration
and we experimentally demonstrate its validity for several emerging two-port
microphone technologies. We also perform vibration measurements on a one-port
mic, thus providing a one-stop direct comparison between one-port and two-port
sensing approaches. We find that the acoustically-referred vibration
sensitivity of two-port MEMS mics, in units of measured acoustic pressure per
external acceleration (i.e., Pascals per g), does not depend on the sensing
element stiffness nor on its natural frequency. We also show that this
vibration sensitivity in two-port mics is inversely proportional to frequency
as opposed to the frequency independent behavior observed in one-port mics.
This is confirmed experimentally for several types of microphone packages.
