Posted by: recordingsofnature | November 22, 2014

Tree-Ears microphone setup

This is a demonstration of an another variant of the binaural microphone setup presented in the last post. This concept could well be called something like a tree-ears microphone setup. I think it can be useful for many types of nature recordings including for remote unattended recording stations. Furthermore, It should have potential for good sound capturing, being easy to install and stay relatively compact and unnoticed.

Tree ears setup

Basically, the mechanical parts of this prototype are just the same as used in the previous post. Only now, the two sides are strapped on to a suitable sized tree trunk. Clearly, there is no room for the Earthworks microphones, so I’m using a smaller custom made microphone setup based on the Primo 172 capsules.

Below is a test recording with the setup, directly connected to the microphone inputs of the Microtrack II recorder. It is captured in Ballerup, Denmark November 5th 2014 at sunset – same location as previous post,  just 10 minutes after.

Being the first raw take with the setup, only post processed with a low frequency (<30Hz) rumble filter, I think the sound is surprisingly good and with a low noise floor (apart from wind noise). This is also surprising taking into account that this is a set of low cost of the microphones which can be bought for ~£25.

Details about the setup are in the following.

Details of the setup
The microphone construction is basically two 3d printed ears glued to two sheets of cardboard.

prototype of the forest recording microphones

Ear design

Art of illusion ear model

The ear geometry was modelled in Art of Illusion (free, open source 3D software) and is actually supposed to be a model of my own ear. It was printed in PLA plastic with a  Wanhao Duplicator 4 3D printer. The 3D drawing and stl-file can be downloaded here.

Below is how the ear looks straight out of the 3D printer, where the  support material is still present. It would also have been possible to print it out by use of 3d printing services all around the world. The microphone capsule is inserted just at the entrance to the ear canal.

3d printed ear just out of the printerWind shielding was done by attaching a little sock of nylon stocking. The recording indicates that the wind shield needs to be improved, e.g by adding extra layers.

Electrical circuit

The microphones are built using a pair of small Electret omni capsules, Primo 172.

primo 172 capsules

These electret microphone capsules need about 5V power in line voltage in order to operate. To supply that, I have implemented the following electrical circuit using the guide lines from  epanorama.net.

circuit_m

The components used were R1=3.3 kOhm and C=10 uF capacitor and a power supply of 3 x AAA 1.5V alkaline batteries.

Initially there was a problem with hum and noise, and the circuit seemed very sensitive to EM noise. To prevent that, I have tried to wrap everything in aluminum foil which is connected to ground (-). So far this solution seems to work.

The images below show the implementation of the microphone electronics on the backside of the ears. The brown wrap is the is the alu foil+tape. The microphone capsules are inside the green fittings.

IMG_3323 back side of forest microphones the micriphones power in line supply primo 172 microphone power supply

Next steps

This is clearly a prototype which needs improvements in order to survive in the wild. I need to find some better, weather proof materials and camouflaged colors. I also think the hard surfaces needs be improved to better imitate human skin. For that I need to start applying some rubber sheets do some experiments with latex rubber milk.

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Responses

  1. […] The final setup (Tree Ears setup) uses the same ear models as the binaural setup (with no ear canals) but now using the Primo 172 microphone capsules instead of the Earthworks microphones. This setup is also described here. […]

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