Contact mics
Capturing the sounds from within
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Show Sonic Journal, Ep #01 Contact Mics - Jan 13, 2023
The requirement for contact mic use came about from the opportunity to record the fermentation of cider and perry in oak barrels (see The sound of cider posts for more info on this). While i have been aware of and have used contact mics, mostly in live music settings, the opportunity had never arisen to creatively use such a method of capturing sound, until now. Which makes this very new experimental territory for me (and of course, quite an exciting prospect!).
My aim was to record the bubbling of air created as a result of wild yeast fermentation in fruit juices. This process can get quite wild, and is audible, although the sound is subtle to the ear. My thinking was that a contact mic attached to some part of the barrel, or air trap, would result in a strong, clear capture of the bubbling. But to get to the point of testing whether this would work, i would first need to source some contact mics, and after some research it became apparent that the DIY build option was to be the best way forward for my needs.
The mic build: components, processes, trial and test
Setting resin around the element to protect and hold in place [mic #1]
Setting resin around the element - to protect and hold in place [mic #2]
Plasticote spraying of the contact elements [Mic #2+3]
Contact mic preamp buffer circuit board - DIY build. This was seriously tiny and so needed magnification to see the components and accurately solder everything in place. Two of these were built to enable the contact mics to operate properly and capture the full frequency spectrum. They work a treat!
Testing Mic #2 with neodynium magnet - taped to the mic with PV tape. This was very useful for attaching the mic element to metal objects such as machines, creating a firm attachment and good clear sound pickup.
Testing Mic #2 taped to a wheelbarrow
Combination of contact and acoustic mic methods (isolated close up vs sound in space) . More on this in a dedicated write up all about capturing the sound of the barrel rooms.
Thoughts on future use
I built three contact mic pickups and two mic buffer preamps in the end, all of which worked very well in initial tests. I look forward to putting the units fully to the test in long form barrel room recordings, which i will write up in due course.