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This didn't help: Why do power lines buzz?, as what I'm hearing is not a buzz like a transformer.

Observations:

  • It occurs on both calm days and windy days.
  • It does not always occur. I suspect it's partly a function of current.
  • The pitch is not the same from one section of line to the next, even when the poles are very regularly spaced. (wooden poles)
  • Pitch is not close to 60 or 120 hz, but is at least an octave higher.
  • Our local distribution network runs at ~about 12,000 V on wooden poles.
  • The timbre (music term) is not the same from one segment to the next.
  • Even through a camera's zoom lens there is no apparent vibration either of the wire, or of the pole.
  • While often louder at the pole, it's still very audible in the middle of a segment (A segment is typically about 300-400 feet.)

EDIT 1:

  • Looking up vortex shedding, some preliminary calcs show that a 1 cm cylinder in a light breeze has a vortex cycle of about 5 cps, about 2 octaves below most people's hearing. The frequencies I hear are much higher than that.
  • The transverse vibrations, same type as a plucked guitar string) seen in high winds are even slower, with the fundamental being over a second in length.
  • That there are days when the wind blows but there is no sound, and calm days when there is sound suggests that this is an electromagnetic effect.

/EDIT

My working hypothesis is that it's some form of resonance effect. The different pitches due to slightly different lengths and tensions between segments. The different timbres being due to that wire's resonance not favoring some overtones.

However, I can't come up with a plausible mechanism to convert this into an audible sound.

I will try to get both decibel readings and recordings of this.

Sherwood Botsford
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1 Answers1

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The popular explanation is as follows.

when wind blows across a stretched wire, the wire sheds vortices which impose a cyclic force on the wire with each shedding. the cyclic forces can and will excite resonances in the stretched wire that are unrelated to the line frequency. the stretched length of the wire then "twangs" or "sings" loud enough to be audible when you press your ear against the nearest power pole to which the wire is attached. this happens in cities too but the singing is too faint to be audible above the background noise there. In the quiet countryside, though, you can hear this.

the singing vibrations on the wire have such a small amplitude and high frequency that from the ground they are not visible.

the vortex shedding frequency depends on the velocity of the wind and the diameter of the wire and was first studied by von Karman after WWII.

As a boy in rural Denmark in 1960 I would entertain myself by listening to the wires sing at every wooden pole I passed on a windy day. the waveforms were quite complex.

niels nielsen
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