Category Archives: acoustics

Barometric music

Sound is the way we perceive rapid fluctuations in air pressure. The lowest notes humans can hear are around 20 Hz — that is, when the pressure fluctuates up, down, and back to normal 20 times per second —, and the highest notes around 20,000 Hz, though the exact range varies with age, and from person to person.

One of the tools used for tracking and predicting weather is the barometer, which measures the ambient pressure of the atmosphere around it, which fluctuates. Unlike pressure associated with sound, these fluctations are very gradual; I’m no expert, but my vague impression is that each cycle — from, say, the peak of one high to the peak of the next — takes about a week, rather than a day or a month (at least here in New Zealand).

But what if we sped it up? Continue reading Barometric music

The most repetitive echo

I listened recently to a very interesting interview with Professor Trevor Cox about the longest echo ever recorded, and other acoustic topics. Near the end of the interview (around 42:44), Professor Cox mentioned that he was still looking for “the most repetitive echo” — the place where you can shout “ECHO!” and hear “Echo! Echo, echo, …” repeated the greatest number of times.

This prompted me to write an email to the radio programme about how one might generate such a repetitive echo. Then, I decided that it might be worth putting the email here, for you to read. So what follows is a slightly edited version of that email, with added pictures. Continue reading The most repetitive echo