Friday, June 5, 2020

Trying to quiet down my T-post driver

One of the first apps I loaded on my smart-phone was a spectrum analyzer for sound.

I will be playing with it over the next few days as I find ways to make a cheap T-post driver quieter.

If you ever spent much time operating one of these beauties (T post drivers) then you know they can leave your ears ringing if you don't wear hearing protection, especially if the ground is dry or rocky.

The protocol is simple. Suspend the driver horizontally but running strings through the handle. Tap the end of the driver where the T posts impact. For convenience, I am tapping the outside of the surface rather than the inside, a difference of a 1/4 inch or so.

Preliminary results
Log scale along horizontal axis.
Many peaks with two tall ones at 3400 Hz and 3900 Hz. Also, a broad band with many peaks between 1000 Hz and 2500 Hz. The tallest peaks are 40 dB taller than the baseline you see at approximately -70 dBa level in the 5000-to-10,000 Hz region.

I do not know if the instrument is reporting pressure or energy. An increase in 10 dBa indicates a ten-fold increase. A 40 dBa increase is a relative increase of 10,000.

A scientific study would use an instrumented and calibrated hammer to measure the inputs to the system.

This chart is poorly labeled. The numbers along the left side refer to the COLOR. The chart itself scrolls or cascades from the bottom upward and the height of the peaks refers to how long they rang in the time-domain. The tall peaks at 3400 Hz and 3900 Hz damped out quickly but the broad band rang for a long time.

The plan
Various modifications will be made to the T-post driver and I will re-test. Our metric will be the height of the 1000-to-2500 Hz region and 3400 Hz relative to the heights of the 5000-to-10,000 Hz region.

Secondarily, to see who quickly we can damp down or dissipate the duration of the noise levels.

10 comments:

  1. Weld cap with steel shot at the top. Improves efficiency of driving a d quiets things a LOT.

    Seriously

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  2. 1/2 in thick hickory round inserted into the driver would take most of the sound out. Might not last too long under use though.

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  3. Noise cancelling ear protection :)

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  4. Not to rain on the parade and scientific research project, but would not a good pair of earplugs do the trick AND be useful for other loud tools? Maybe it's my old German grandfather coming to the fore, but the shortest distance between two points...

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  5. The tube is a bell or resonator. Wrap the tube with a self adhering sheet of rubber or other durable rubber material to dampen the echoes. The echoes of the impact are the tone you are hearing. If you stop the tube from resonating by absorbing the initial impact as a wave on the outside it will stop the repeats or attenuate them substantially.

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  6. I used mine a lot for decades and just ignore the noise. Just part of putting in posts. Kinda like the smell with a fart. But maybe that's why I can't hear very well.---ken

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  7. Buy the stick-on dampeners used on recurve bows. Stick them to the top and sides and then see what....

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  8. Strips of commercial sound deadener.

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  9. Maybe try wrapping that sucker in a couple layers of old inner tube.
    My plan for a post driver is to fabricate a dead blow T post driver. Two different sizes of pipe. There's gotta be two short scraps of steel pipe somewhere around this farm. Some scrap flat stock for the anvil and between pipes. A couple of pieces of stout round bar for the handles. Probably wind up using rebar. And 3 pounds of pea gravel.
    But I've got to build a driveway first.

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  10. Fred: Pea gravel doesn't last long.

    I learned this the hard way. Lead shot is good but eventually can stick together unless oil is added before closing the container....Steel shot lasts longer. Rocks turn to dust fairly quickly.

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