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I recently purchased some Audiomoths with their waterproof cases for terrestrial recordings. I did run some test in the lab recording my simple voice without and with the case. I payed attention to have the microphone in front of the acoustic vent of the case. I can see a high difference in the recordings with a huge attenuation of the sound when the recorder is in its case. What do I do wrong ? Here a spectrogram of the three scenarios: 1) without protection, 2) in a plastic bag 3) in its protection box.Here a spectrogram of the three scenarios: 1) without protection, 2) in a plastic bag 3) in its protection box.

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    $\begingroup$ That's some serious attenuation of intensities happening there. I am assuming that you are using the IPX7 Waterproof case and not the Underwater Case? If it was the latter, I can completely understand why this would attenuate the intensities of given frequencies since it is specifically designed for underwater environments. $\endgroup$ Aug 26 at 4:59
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    $\begingroup$ I did the same test with the terrestrial casing (not the underwater one) and get the same huge attenuation $\endgroup$
    – lframond
    Aug 26 at 14:09
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    $\begingroup$ @Iframond here is something I read on a website: "The case requires 40 minutes for the air pressure to equalize after the clasp is sealed." Did you try recording after 40 minutes? $\endgroup$
    – Amandine Gasc
    Aug 26 at 18:00
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    $\begingroup$ @AmandineGasc Could you post this as an answer as it seemed to do the job. Thanks $\endgroup$
    – Rasmus
    Sep 1 at 15:32
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    $\begingroup$ @lframond could you post your results from testing after waiting 40 mins as an answer? Comments can get hidden or even deleted over time so posting as an answer will ensure others see it in the future. Thanks! $\endgroup$
    – selene
    Sep 21 at 20:02

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To adress @Selene's comment, here is the result of my (quick and dirty) experiment. I have broadcasted white noise to an Audiomoth in the case and one outside of the case for 40 minutes from the moment I closed the case (thanks @Amandine Gasc for the info). If you wait a little bit, the amplitude of the recording comes back to normal (it was already fine 10 minutes after I closed the case). Here is the graph of the difference between the amplitude at the end of the experiment (40 minutes after closing the case) and the amplitude at each time point:

enter image description here

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