The Little Vulgar Book of Mechanics (v0.8.0) - Sound I - Frequency I

Last updated: February 21st 2022

Just updated this section of the book: Sound I - Frequency I

Sound I - Frequency I #

A thunder in the distance.

A bird's whistle.

The former is a low frequency. The latter is a high frequency.

Grab a piece of metal. I don't mean like a part of a Cannibal Corpse song, I mean an object. A metallic bar. And hit it. I assume you're not in Space, so you're in a vibrating system. Ideally, the thing you're hitting is a tuning fork. That's a metal tine that goes "diiiing!" when you hit it, generating a simple vibration, which we perceive as a simple sound. The rate at which it vibrates, we call frequency. The unit is hertz (Hz). E.g. If it vibrates 440 vibrations per second, we say it's a frequency of 440 Hz.

Why did I specifically say "simple" vibration, "perceived" as a "simple sound"?

Because, in real life, when you hit something, it will not vibrate in one single back and forth motion. We could more accurately say that, when you hit the tine, 440 Hz is the frequency of the main, or "most prominent," or fundamental, vibration, among other "secondary" ones. But we'll delve into that complexity later. For now, let's say this: Theoretically, the simplest sound, in terms of frequency, is a "sine wave," which corresponds to a "pure tone," acoustically. Hitting a tuning fork gets close to that.

OK, so hitting a tuning fork causes a simple, "periodic back and forth" type of vibration, which translates to a "pure"-ish tone acoustically. Got it.

How can we cause a complex vibration, then? Try grabbing a drum stick and hitting a crash cymbal (preferrably as your drummer is playing, to annoy him.) See how the cymbal is vibrating chaotically? That complex and chaotic collection of vibrations gives it its noise-like, waterfall-like, quality.

Go back to the tuning fork. It's called a "diapasón" in Spanish. I will refer to it in both ways, to keep you on your toes. In the past, musicians used this thing as a referece to tune their instruments to. Nowadays we use better technologies. But we all should have one, if only for experiments and teaching. Also, tuning fork-type devices are still used as part of some musical instruments. I'll give an example of that in the next section.

We'll delve into hearing later, in "Sound I - Anatomy I," but let's ask this question already: Can our ears sense all frequencies?

No. The range of frequencies our ears perceive as sound is limited. E.g. we can't hear some frequencies that other animals can. Also, this range shrinks as we grow older, not so much due to age, but rather due to living in noisy cities, listening to loud shit on headphones, going to wars, dating militant feminists, etc. I.e. We put our ears through constant torture.

But, injuries and mutations aside, humans can hear in the frequency range from 17 Hz to about 17,000 Hz.

Stop hitting the diapasón. I have a history question:

How are these two things related?

  1. World War II aircraft.
  2. A certain classic, mellow 1970s piano sound.

The next section has the answer to this thrilling mystery!

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