My team is using AudioMoths for large-scale, multi-species avian monitoring in California, but we have had moisture damage issues with many of our devices enclosed only in ziploc bags, despite being in a relatively precipitation-scarce environment during our field deployments. We wanted to use the official AudioMoth cases but I saw on this forum that another researcher had issues with the cases affecting detectability of lower-frequency sounds like owl calls. So, we ran our own very quick and dirty tests by playing various bird sounds to two AudioMoths, one version 1.1.0 the other 1.2.0, first with a ziploc bag enclosure and then with the official case. Disclaimer: this is of course not an actual study, but I thought whatever we found, however anecdotal, may have value to others so I wanted to share the results for anyone to see, for whatever they're worth. In a nutshell here's what I reported to my team:
"I just finished inspecting some results after playing bird sounds to 2 AudioMoths first with ziplocs then with the official cases (and waited about 3 days, since some people say the sound quality improves a bit after the case has been closed a while).
For one device (version 1.2.0), the case made everything MUCH quieter: for spotted owls and yellow-billed cuckoos the case made them 3 - 4 x quieter, with the lower-pitch/quieter sounds totally eliminated.
For the other device (version 1.1.0), the case seemed to reduce the volume of the lower-pitched species much less. For some higher-frequency sounds the volume was actually amplified. I don't understand why but I'm not sure that the different version is actually the cause. Even if it is, and we used all version 1.1.0 for birds, it seems like we'd still lose a number of owls and other low-frequency spp. And eventually v1.1.0 will be obsolete anyway."
Here is a table showing results as visually inspected using Raven Lite 2. I am not totally clear on units, I did this a while ago but my notes say this is "estimated volume to nearest kilo-unit."
Sorry this is a bit messy, I can try to provide more details if anyone is interested, but this is all I have time to produce right now. For now our team is opting to just use thicker ziplocs, bigger desiccant packs, and more protective tape around them this coming field season.
Good luck to everyone!
One thing to be aware of it that closing the case causes a slight overpressure which inflates the vent and reduces its sound transmission. The performance improved again (not to extent of no case for low frequencies) if given a few hours to equalise.