Monday, November 17, 2008

Infrasonics Wrap-Up

Finally, we get to our original problem with the poor guy and the 5 km farm power line. Turns out this is a simple problem of bell ringing resonance. The line is too tight, and ringing like a bell. You only need a transformer on the line, and the 12 Hz harmonics will do the work.

Solving this might be expensive. Most transmission tower lines now dispense with the Stockbridge damper, by slacking the line a bit. However, the new multi-line arrangement now needs torsional dampers! This farmer could isolate the house from the tight line by putting in a pole to take the tension. Then a loose line to the house would not transmit the infrasonics. It all depends on how much you want to pay.


Anonymous said...

For isolation, is only the short, 1m., loop needed?

You actually going in the inside again?

I like the tethered accelerometer.
Could it be calibrated?
I don't think it could sweep frequencies. DSP maybe?

Ever hear of that doe-oit reflection I was describing, bouncing off the long corogated concrete wall?

Harold Asmis said...

This is my old hydro friend with the humming power line.

Corrugated concrete walls would do some bizarre things to echos. I would think the wall would trap sound waves that are some harmonic of the height of the corrugation.

Before you break up your line, you've got to have some fun experiments with the accelerometer! Bash a pole in different directions with the backhoe, and record the waves! Don't break the pole!

You have to guy the last pole to take the tension, just like a corner fence pole. then the last bit of line is loose. You don't want that last pole too close to the house, or the infrasonics will transmit through the ground.

And lastly, I'm not really going inside. I'm doing CSA standards, but they are paid by the old boys.

Anonymous said...

I will get one of the small out-board tethered USB babies, and try not to topple the line. hehe

I will need to measure the vibrations at distances. The vibrations could be linked between the proximal poles thru the ground!

Corrugated wall:
Clearly the reflection is skewed from bouncing off the multiple surfaces. Why the freq rise at the tail? Intuitively, (what ever that is), it feels like a compression/doppler action. I'm baffled/dampened.
We need more Harolds on this planet!
Thanks Peter

Have you ever used

Harold Asmis said...

Have fun. As soon as I get my money, I'm getting a usb accelerometer as well! It'll be important for the Seismic@Home experiment.