What the Devil Does in His Spare Time
First, he invents the leafblower. Then he hires crews to blow things all around his back yard in Hell, at times when he is not around to hear them himself but the rest of the neighborhood is.
But let’s look on the positive side. A reader named Dag, in Norway, sends this old YouTube video of someone who has put a leafblower to relatively constructive use.
Also on the positive side, for the first minute of the video the blower that is pushing this child on his swing is running at low RPMs, rather than the highest speeds with their disproportionate peak of noise. You can start to hear that peak in the final part of the video.
If you’re looking for a technical explanation of why the leafblower sound is disproportionately brain-wave-disrupting, please check this analysis, by Ted Mitchell, with excerpts after the jump.
Meanwhile, this next video shows how I would prefer the Devil to spend his time. This whole thing is enjoyable, but the real fun starts about 55 seconds in. If they’re ever up for a remake, I volunteer.
For a collection of past meditations on this modern misuse of technology, please see this. For other heartening videos, go here (which includes the second video, above).
Here’s an excerpt from the Ted Mitchell analysis:
The blades are oriented perpendicular to the outlet and generate noise by a rapid change in air pressure. This generates something approximating a square wave, which is one type of spectral character (timbre is the musical term, which seems inappropriate to describe this kind of noise!).
The fundamental frequency is determined by RPM / 60 times the number of blades, for example in the electric blower above, 1800 rpm / 60 seconds per minute x 13 blades = 390 Hz.
A sine wave generates a pleasant, gentle tone. A square wave of the same amplitude generates sound perceived as relatively loud and harsh. This is due to multiple harmonics above the fundamental frequency. In the above example, f = 390 Hz, f2 = 780 Hz, f3 = 1170 Hz, f4 = 1560 Hz, and so on.
Add to this the sound from a two stroke engine, where exhaust gas is rapidly released through ports with a tiny muffler and you get a similarly percussive sound of rough waveform, but at a lower frequency. The fundamental frequency is RPM / 60, for example 6000 RPM / 60 = f = 100 Hz, f2 = 200 Hz, f3 = 300 Hz.
Adding the complex harmonics from these two waveforms is what results in a noise that is like the bastard offspring of bagpipes and an air raid siren.
Followed by this chart, which shows that the leafblower noise signature is different from the seemingly similar snowblower, in a way that magnifies its impact:
See if you can guess why this has been on my mind this past weekend.