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Wind Sounds: Power Structure In Utah

09 Mar 2023

The first stop in my “mid career break” was Salt Lake City, Utah. I found out on the first afternoon that the snow was deep anywhere past about 500ft above the city, which meant I was on the hunt for flat runs in the lower elevations.

One of these was the Westline Powerline Trail. There were a few flat sections with strings of powerline structures, and I noticed that if the wind was just right, they’d sing a single pure note as I ran by. There’s a lot of wind noise, but you can hear an example in the video below at around 00:26 and again at 00:41 (not the periodic metalic squeak, or the rustling jacket!).

This is awesome! It’s an example of aerodynamic flutter, and there’s a ton of fun analysis that can be done around it. The first is just to figure out what frequency the structure sings at. I wrote a script that loads the video, pulls out the audio, does a fourier transform on a number of segments, and then plots the frequency spectrum of each segment.1 If you do this with a singing segment, you get a clear peak at 758-760 Hz (call it 759 Hz).

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You can play this frequency using an online tool, or just by using python to create a tone for you:1

Kool! Moving beyond this first step, something more would be to use a sense of scale, like me standing next to the base, and some assumptions about materials and joints, to figure out which part is resonating at the singing frequency.

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That’s up next.

  1. You can find the code for this on github in wind-sounds 2