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Why do we hear a roaring or humming sound when an empty bottle is held close to our ear ?

When I hold a flask close to my ears, I hear like a sound which coming from its interior.

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The usual way that this phenomenon is described is

when you hold a sea shell up to your ear, you can hear the sea

What actually happens, according to this link, is that the vessel acts as a resonator / reflector for ambient noise - sounds that already present in the environment are amplified and stand out more.

The "you hear your blood" myth is just that - a myth. Although (healthy) human ears are exquisitely sensitive... see my answer to a recent question on the subject of just how little air movement can be perceived as noise.

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  • $\begingroup$ Testing with bottles of different wall thickness confirmed: I don't know what OP is talking about $\endgroup$ – npst Nov 22 '14 at 3:46
  • $\begingroup$ @npst - did you try just cupping your hands and holding them over your ears (without closing off the space completely)? Do that in a slightly noisy environment (some background fans, etc) and you'll hear a rushing sound, most likely. $\endgroup$ – Floris Nov 22 '14 at 4:01
  • $\begingroup$ Yes, I meant I can't find any difference between different bottles, filled or not when the ear is closed off. $\endgroup$ – npst Nov 22 '14 at 4:09

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