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Roger: Sound is a continuing compression wave in the air, like the old rock in the pond. If there's one wave produced by an instrument every second, that's "one hertz". If there are twenty thousand little waves produced every second then that's "twenty thousand hertz".
Roger: Simple enough.
Dave: Sound travels at a speed of 340.29 meters per second, varying a bit according to temperate and elevation, etc. The lowest notes our voices produce and that we can hear are around 20 per second, or 20 hertz, as an engineer would say it. That means each individual wave is about 16 meters long. The highest notes, or waves, which come 20,000 times per second, are only about 20 centimeters long. And we can hear higher and lower notes, unconsciously. But that's another story. The high notes aren't a big problem, but the lower, longe notes are.
Dave: From noise?
Roger: To some extent: motor noise tends to be in the low frequencies. If you ever spend a lot of time with ranchers and farmers, you'll notice there's a massive difference between the voices of ranchers, versus the voices of farmers.
Dave: Haven't been to a lot of agriculture fairs recently.
Roger: Well, if you do go, you'll notice that the farmers' voices are a lot higher pitched than ranchers. They're used to speaking over tractor noise, combine noise, and truck noise. A hell of a lot of noise, and a hell of a lot of low frequency noise. So they don't even bother with a lot of heavy chest resonance. Their voices are further up in their chest and throat because they've gotten used to having any bass notes they produce be swallowed up in machinery noise.
Dave: And ranchers?
Roger: Are somewhat the opposite. They need to communicate over longer distances than a salesclerk, and they talk outdoors a lot.
Dave: That makes a difference? From the fresh air?
Roger: From the acoustical environment. Ranchers tend to have great, rich voices with plentiful chest resonance. A joy to listen to, really. And very natural. Native people, particularly in their first language, and soldiers' voices can be similar. There's a video from the Canadian Film Board of a confrontation between Mohawk warriors and the Canadian army in the seventies, in the woods of Ontario. The soldiers have great rich voices, very natural, but the native voices are even richer.
Dave: Chest resonance produces the lower notes.
Roger: Right. But the thing to remember here is that the ranchers have great, natural voices because they don't sit around talking in small, square rooms. We just figured out that the longest sound waves we can hear are bigger than a regular room, from crest to crest. That means that some of the low notes that aren't quite that low, and exactly match the size of the rooms we're in, so they can really resonate, really have some punch.
Dave: Yeah, I've been in some small rooms with terrible acoustics.
Roger: And we tend to compensate by clenching muscles in the abdomen and chest to supress those particular frequencies that are likely to bounce back to us and sound ugly in a small room. That is, modern people do. And modern houses have really square corners, that can set up standing waves that confuse the ear.
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