I was stood looking at Pillar Rock when I accidentally hit this old fence post with my walking pole. I got a nice note out of it. There was clearly a node at the bottom where it is fixed to the ground and cannot vibrate. There was another cross bracket attached about 80 cm up which would have acted as another fixed point or node. Two nodes with an anti-node between constitutes half a wavelength, so one whole wavelength would have been 1.6 metres. Using c = f x lambda, with speed of sound in air as 340 m/s then frequency f = 314/1.6 = 200 Hz to 1sf. That sounds about right as what I heard was nowhere near high enough to be 1000 Hz.
