Wiring for stereo mic using MAX9814

The cause of the "problem" is really simple, and there's not much you can do about it.

If you have two of these things together in any normal sized room, they will both "hear" the same sounds.

The output of both microphones will look similar because they are picking up the same sounds.

With the automatic gain control (AGC) that the MAX 9814 has, even the output levels will be similar.

There's nothing wrong with your modules, and you are almost certainly not getting noticeable crosstalk electronically.

---

The 9814 may not be the best choice for sound localization.

The AGC may distort the signals in ways that interfere with the correlation methods normally used for localization.

The AGC will certainly interfere if you try to do localization based on the sound volume.

You ought to understand how the chip works as a preamp. It has variable gain with AGC and attack/decay rates.

https://datasheets.maximintegrated.com/en/ds/MAX9814.pdf

I suggest you should be using STP cable with a grounded shield.

The microphone isolation is more about acoustic pressure isolation and focus than electrical connections.

If the mikes have passive rear cancellation for far field, you will have problems in phasor acoustic measurements even with equalization.