The Little Vulgar Book of Mechanics (v0.17.2) - Sound I - Waves I

Last updated: February 20th 2023

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

Sound I - Waves I #

When I say "wave" in this section, try not to think of the rings that form when you throw a stone into calm water.

Instead, imagine a sphere made of many sub-spheres. I.e. Layers, or levels, like an onion. Think of each layer as either condensed, or rarefied air. Those are, respectively, the crests and troughs of a sound wave. Because when you disturb a particle in the air, it will disturb its neighbors above, below, etc. A spherical propagation of vibrations.

Say you're a metal singer, and you're thinking "I'm sending my powerful vox from my mouth to the mic!" while recording. No. This is what you must think instead:

I'm vibrating every bone in my skull and torso. Shaping my mouth to direct some of the energy. The vibrations are propagating spherically. This energy sphere is expanding and colliding with the walls, floor, and ceiling, etc. Now they are vibrating. Creating additional energy spheres, which overlap with my original sphere (which I'm still generating, as I sustain my scream). A sum of all this is being caught by the mic.

Your "voice" is the sum of the whole atmosphere vibrating, because of your whole body and the room's acoustic properties. This is why body posture, mic position, and room acoustics, all matter.

A powerful, monster, beast scream, is not something that sounds like it's right next to your ear. Any child can get up close and disturb your ears greatly. A fucking mosquito can make itself heard when near enough. (Clarification, though: The mosquito's sound is from its little wings flapping super fast. That's the buzzing sound.) A beast is a thing whose roars shake the whole fucking room. So room sound in metal vocals is often key.

However, too much reverberation makes things sound "distant," and a "beast in the distance" is usually less of a threat! Keep that in mind too.

So how do you make your metal (or video game, or movie) monster scream to sound threatening? Gotta find that sweet spot: Clear and dry enough for the brain to go "Oh shit, the beast is near me!" yet with a room sound (either real or manufactured in the mix) to make the brain go "Oh shit and this beast is powerful cos it's making the room vibrate."

Recording studio acoustics is not just about slapping some shit on the walls to "kill reflections" or "isolate." Proper room acoustics must take into account the artistic necessities of the types of instruments (including vocals) meant to be recorded in it.

Try setting up a mic on a snare. Place it near the snare, pointing at it. Record it. How does it sound? Like shit. Go back and tinker with the placement. It doesn't fucking matter: The close snare mic always sounds like shit, no matter what.

This is why room mics, overhead mics, "mic leak," and/or artificial reverberation, are always added to the close snare sound in the mix. To recreate the complex natural signal. So don't panic, recording engineer: Close snare mic sounds like shit. You always have to "fix it in the mix."

But I digress. Acoustics and sound engineering should be separate sections.

Enough about screaming monsters. Let's go back to the tuning fork.

Strike the tuning fork again. It's vibrating now, and you're in a sound-friendly medium, so the disturbed tine disturbs the particles in the medium (atmosphere in this case), and the medium lets particles disturb their neighbors. This "chain of disturbances" has a certain order, or pattern, that we call a "wave." Sound waves are compressional waves. They are made of compressions and decompressions of the medium.

How fast sound waves propagate depends on the medium where the propagation is taking place. In seawater, sound waves propagate at about 1500 meters per second. That's like 15 soccer fields end-to-end per second. In the air, sound propagates at about 340 meters per second, much slower.

Sound waves travel faster in water because water is denser than air, which means particles will more likely bump into one another. There are about 800 times more particles in a bottle of water than there are in the same bottle filled with air.

The first accurate experiments to measure the speed of sound were done by members of the French Academy in 1738. They fired cannons, and observed the retardation of the reports at different distances. Temperature and wind affect everything, but back then they nailed it down to 337 meters per second, for still, dry air at 0 degrees Celsius.

Walk into a cathedral. Snap your fingers. Or say "hello." You'll notice that the sound doesn't just cut off instantly. Even seconds after you stopped causing vibrations, you're still hearing the "tail" of the sound so to speak. That's what we call reveberation. But that's not what I wanna talk about. I wanna ask this question:

When does sound stop? Or, why do the spherically propagating vibrations ever stop?

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