I have been contacted by my previous employer, which has led me to remember the various works I used to do. One of which was measuring and evaluating noise. That has meant that I was making and interpreting pictures like this.
Of course, this was only done with my phone, whereas at the laboratory I had various kinds of fancy equipment and software available. But back then I did in fact check whether this phone app measures reasonably accurately, and it does.
At the very top, you can see that grinding handles is a very noisy work indeed. When the equipment runs idle, it emits over 78 dB, which is very near to a level when the noise becomes truly dangerous (80 dB). And during work, it exceeds 89 dB. So I am indeed diligent about wearing hearing protection since that noise level would damage my hearing pretty damn fast.
Whoever knows how to interpret the above picture, can tell that when the grinder runs idly (those parts with green at the top), most of the noise – and indeed the loudest noise – is below 500 Hz. And whenever the wood touches the belt, another very loud component is added, between 5 and
80 18kHz (those parts with red-magenta stripes at the top). There is nothing I can do about the noise that is emitted during the grinding, but I could if I were inclined to spend my time on it, try and identify the spots where the loudest frequencies are during idling and try to do something about that. For example, I suspect that a significant source of the low-frequency loud noise is the tensioning wheel.
However, as much fun as it might be, I do not think I will spend a lot of time over this anytime soon. It would be fun though. I liked my previous job, the work was not the reason why I quit.