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MEMS beam configurable boundary microphone

Question asked by naimark on Aug 27, 2013
Latest reply on Aug 28, 2013 by naimark

HI,

 

For my project – “beam configurable boundary microphone” I using 2 MEMS ADMP521ACEZ mics with ADAU1761 DSP. The project is almost complete, but I was curious about low frequency respond difference between data from “ Beamforming calculator” and DSP equalization settings. For example, for edndfire array configuration and 21mm spacing I need to boost 100 Hz frequency up to 20db to achieve 0db out as 1KHz, based on calculator data. But actual DSP setting for 100HZ is +10db. I think may be PCB surface acts like a low frequency booster. When I closed acoustical ports with 2mm thick tape, I got approximately 7db attenuation. See attached graphs for open and closed audio ports. My question is: is it PCB or something else boosting low frequencies. Also is there is any formula or calculator for acoustical port opening, based on board thickness and how it’s correlated to frequency respond.

 

Thank you.

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