Finally - an update on our enclosures (from snack boxes)

Hello all you AudioMoth’ers,

So it turns out that the update to my previous post (https://www.openacousticdevices.info/support/enclosures/summary-of-enclosures-to-date ) has taken a little longer than I anticipated (TWO years!!... sorry!). But, maybe, better late than never? Anyway, it looks like enclosures have moved on in that time, with a quick skim through this forum showing 3D printed cases and the official AudioMoth IPX7 cases having risen in popularity/use. For what it is worth, here is what we settled on to use for frog calls in south-western Australia (with great success last season; April-June 2020).

We have adapted small lunch-box containers by adding a foam insert and a metal loop for cable-tie retention, and giving them a coat of paint to get this:

We’d done some rough field testing with a prototype or two and found that, much to our very pleasant surprise, we did not need to include a microphone ‘hole’ to successfully record the target frog calls (dominant around c.400 Hz). [This still seems to be the sticking point for most cases… letting the sound in but not the weather.] This surprised me greatly (I still don’t fully understand – I have a lot to learn!) but containers without a microphone hole in them performed as well, or better, than those with a hole covered with sticky tape (for weather proofing) at any distance up to 20m from the sound source. At distances over about 10-15m, they also performed almost as well as an AudioMoth with no case at all. So we decided on retaining the integrity of the containers (maximum weather-proof-ness) and not adding a microphone hole.

Step by step, here’s how we made them (photos of various materials at the end of the post).

(1) Bought the containers: 200 mL rectangle KLIP IT containers made by sistema (https://sistemaplastics.com/products/klip-it-rectangular/200ml-rectangle) and purchased from our local supermarket.

(2) Attached the metal loop: we used a plastic-specific superglue (local hardware store) to attach metal picture frame hangers (also from the hardware) to the lid of the container.

(3) Painted the container: the secret to success here (learnt from early failures, where the paint flaked off) was to give them a couple of coats of a spray-on plastic primer first. Then we just used the cheapest enamel spray paint we could find. A couple of base coats of black followed by a top coat of ‘mocha’ (interestingly, this light colour was subsequently really important in the camouflaging). Then a partial squirt (using artistic licence) of dark green and brown to complete the camouflage look.

(4) Made the foam insert: we used 10mm thick expansion joint filler as the foam (bought from local hardware store) and cut this to shape with scissors and glued it together with a hot glue gun. We had a base layer (full container size) and then a half-length layer on top which meant the AudioMoth unit sat nice and snug at one end of the container, with its microphone pressed against the lid (when closed). There was also room for a little bag of silica gel (as a desiccant, just in case) in there as well.

Then we inserted a flashed, configured and switched on AudioMoth, ready for deployment.

The KLIP IT containers have a recess in the lid so we mounted the units (using a cable tie) on angled tree branches so any rainfall ran off (but not vertical to avoid moisture getting in under the lid).

They performed great though the austral autumn and winter (we brought most of them back in by spring). There was no water ingress into any unit, as far as we could tell. One unit from last year was collected today – 280 days since it was first placed out! It was incredible how well this had survived the Australian summer (direct sunlight, heat and strong winds etc.). The only two minor issues we had were (i) the unsticking of a couple of the metal hangers (when the unit was removed, this fell off) and (ii) we had made such lovely enclosures that a family of ants decided to set up their home in the container-hinges of one unit.

We’re not sound engineers (or high-level analysts like many of you reading this) but the recordings were well and truly good enough to identify our target species by human ear (the next challenge is getting a computer to do this for us – an entirely other topic).

So you’re probably wanting to know how much we spent? For each case the materials (container, foam, hanger, super glue, paint primer and spray paints) would cost us today c. $4.39 (AUD). That’s about $3.34 (USD), €2.85 (EUR) or £2.41 (GBP). Plus sundries like the hot glue gun, silica gel and cable ties would still land us below $5 AUD a case (with, obviously, time not factored in). We were very happy with that.

All the best with your endeavours in the AudioMoth case/housing/enclosure realm,

wes