And there is an MEMS mic called ICS-40800 from TDK with a front and back hole.?
Regarding this Figure-8 mic, it has an undamped membrane, meaning the frequency response has a +6dB/decade slope. The datasheet is a bit misleading, showing a "Typical Omnidirectional Frequency Response", i.e. with the back port covered. With the back port uncovered, it has this slope, which can be seen in Figure 16 of
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The application note proposes compensating with an electronic filter.
