Comment by danielmittleman | Hacker News Reader

Comment by danielmittleman | Hacker News Reader

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danielmittleman

To be clear: there is NOTHING at all about sound in this article. The spectrum does not show a continuum from sound to light. It shows the electromagnetic spectrum, which does not contain any sound waves at all. One can encode acoustic information on an EM wave (that is how radios work), but the transmitted signal (from the radio tower to your radio receiver) is an EM wave, not a sound wave. The receiver converts the EM wave to the appropriate sound wave by decoding the information that was encoded into the EM wave, and using that information to drive a speaker.

Sound waves are pressure variations in the air. Thus they require air in order to propagate.

Electromagnetic waves are oscillations of an electric field (and also a magnetic field). These fields exist independent of air (or any other medium), so they can propagate in completely empty space.

These are two completely distinct phenomena. They both involve waves, but that's about all they have in common.

The diagram of the EM spectrum at the top has a very confusing section on the left where ranges of frequencies are labeled 'infrasound', 'perceptible sound' and 'ultrasound'. They have nothing to do with the ability of the corresponding radio waves to be modulated to transmit sound signals, but are literally just marking off the frequencies that correspond to those ranges in sound waves, over a diagram of EM frequencies.

Yea, that's confusing, despite not being wrong. It is a juxtaposition of two completely distinct phenomena on one graphic, which is confusing, for sure. But the whole article is about EM waves, not sound waves.

Sigh.

I didn't discuss the article. I believe I scoped my comment to the "infographic" in the first line, and closed with "But I doubt this is what the graphic is suggesting either."

I also shared the same information as your 2nd (aside: sound doesn't require air, as bone conduction headphones or scuba diving demonstrate, does require "not vacuum") and 3rd paragraph, and made the same point as in your close.

So I agree with you, which is why I objected to the graphic.

> To be clear: there is NOTHING at all about sound in this article. The spectrum does not show a continuum from sound to light.

Except that a portion of the spectrum graphic is labeled “perceptible sound.” That’s what the OP is referencing.

Perhaps the illustrator is pointing out that the frequency range of these EM waves coincides with frequency range of audible sounds? Or perhaps they’re confused. Either way, there’s no mistaking that the graphic is labeled with the words “perceptible sound.”

True, but the article is all about electromagnetism, not acoustics. I'm sure the author of the article was not the same person as the person who made the graphics. They probably ought to have communicated with each other a bit more clearly.

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