Earlier this year I started listening to sounds from the ground, and used AKG and PIEZZO microphones attached to metal sheets and shoved into our allotment clay soil to pick up and listen to what sounds  I could.

The results were intriguing, and question arose about the behavior of the microphones and what I was exactly hearing.

What was the sound source, and what was the low frequency white noise I was picking up?

Questions came up like -Do totally submerged microphones pick this white noise up, and what were the sound frequencies from the local traffic and what was from sources further away?

Here’s the spot near the Clifton Suspension Bridge where I put in the metal plate, and below  an AKG pick up microphone on a rock face not far from the road by the bridge.

As I did more tests, it became clearer to ask testable questions  – using comparisons. So comparing different sized metal plates, burying them differently in the ground, setting them out at different distances from the road, told me a bit more about the sound.

Questions started forming like: what sound came from above ground and what from underneath, which settings on the equipment should I adjust? In fact how did the different equipment compare?

I did distrust my equipment somewhat and I looked for other microphones I had heard of. My quest to look into equipment had begun.