Audibility of a compression wave

1. Jun 9, 2015

jerromyjon

In regards to another thread here, https://www.physicsforums.com/threads/sound-as-condensation-or-rarefaction-of-air.817705/ , I am convinced a compression wave would cause an oscillation as it passes your ear. This raises the question as to whether this oscillation could be audible and what factors would determine the frequency.

To begin I believe that the wave should propagate through the air at the speed of sound, but I am uncertain if that is relevant. What determines the rate at which compression followed by rarefaction occurs? My intuition tells me the temperature and pressure (ambient as well as compressed) are the important factors, but I'm coming up short on techniques to model it.

2. Jun 9, 2015

CWatters

λ
The source of the sound? For example rate of compression and rarefaction is faster for a 10kHz sine wave tone than it is for a 1kHz tone.

The equation V=fλ relates velocity, frequency and wavelength. The speed of sound varies with atmospheric conditions.

3. Jun 9, 2015

cjl

What you are describing is just a sound wave, and the frequency would just be determined by the frequency of the peaks and troughs that pass your ear. As for the propagation speed, it turns out to only depend on temperature for an ideal gas (which air is very close to).

4. Jun 9, 2015

jbriggs444

If you drive a damped harmonic oscillator with a single pulse, it will vibrate. Not nearly as much as if you drove it with a nicely tuned sine wave. But it will vibrate.

5. Jun 9, 2015

cjl

That depends on the damping - if it's overdamped, it will do a single pulse, with no oscillations or ringing.

6. Jun 9, 2015

jerromyjon

That is what I'm trying to determine. I am trying to make sure my feet are firmly planted on the ground before I contemplate a simplified scenario. I prefer to set the variables to realistic rounded figures for simplicity, such as 300K temperature (80F) and 100,000 Pa (roughly 1 atmosphere ambient pressure) but I'm not even sure what units are easiest to use.

As I didn't want to "derail" the other thread, I referred to it as a general description of what I aim to calculate. The premise is that a localized source of pressure increase in an air-tight room could create an audible oscillation as the pressure wave passes your ear. Now I am getting the impression that the magnitude of the pressure increase will contribute to the intensity (decibels) and simply the temperature will determine the frequency.