When you bite something in two pieces, e.g. a piece of hard candy, you hear the sound through two sources: vibrations in the air, entering your ears from the outside and internal vibrations in your skull.

What I have noticed is that there is a difference in (the way I perceive*) the sound intensity when my ears are plugged with in-ear phones or earplugs, as opposed to the unplugged case. The thing that surprises me is that the sound actually seems louder (higher intensity) WITH my ears plugged. I would expect the sound to be less loud because I am blocking part of sound waves with my earplugs.

My question is whether there is a physical explanation for the higher intensity with plugged ears? Some form of resonance perhaps? Or is it really just perception?

* I mention perceived, because I can also imagine that it is some physiological effect in which the baseline of what I perceive as low and high is changed by the lack of sound coming in from the outside. If that is the case then physics.se is probably not the right place to ask this question

Psychoacoustics is a fascinating and difficult field. For a simple example: many people, myself included, perceive music thru headphones as originating somewhere in the back of our skull. Same music from stereo speakers comes from "the room."

So... your earplugs may well be providing a direct mechanical conductive path from jawbone, ear mass, etc. for some of the sound that you describe as sounding louder or clearer. It's also possible that the earplugs are effectively blocking one frequency range, thus making other frequencies appear louder in contrast.

Unplugged ears let in background noise, which is considerable and perpetual in cities. If you venture into isolated rural land, a cave, or an anechoic chamber, you can hear silence. It is a very different environment.

Here is an experiment! A dental cavity being drilled is disturbing for the high-pitched whine of the drill. Try wearing a pair of foam earplugs. They are excellent low pass filters - no whine. However, you will hear the drill grinding your tooth by bone conduction of low frequency sound. I suggest earplugs or headphones playing the fourth movement of Beethoven's Ninth Symphony.

  • So you're saying that it is basically a signal-to-noise ratio thing. The less background noise, the louder I perceive a sound? – Michiel Feb 25 '14 at 16:08
  • I tried the earplugs. Terrible idea. Signal-to-noise is a good start. Find a truly quiet place. – Uncle Al Feb 26 '14 at 23:02

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