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It is often seen that drinking glasses are placed overturned on the walls for listening more clearly what is happening on the other side of the wall.What is the reason for this?Is the reason same for the following observation-When we speak through a paper cone our voice gets louder.My last question may not be related to this context-Why does that sound of fast wind blowing sounds when we place an overturned glass over our ears?

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  • $\begingroup$ The drinking glass enables you to hear more or less the same as what you would hear if you pressed your ear directly to the wall. But, it's hard to press your ear directly to the wall: You have to twist your neck pretty far to get your shoulder out of the way. The drinking glass just gives your shoulder some extra space so that you don't have to bend your neck as far. $\endgroup$ – Solomon Slow Jul 27 '15 at 17:33
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It doesn't have to be a drinking glass. It's the stethescope principle: by placing a rigid object against the wall, and the other end of the rigid object at your ear, the sound energy is contained within the object rather than dispersing into the air.

A drinking glass has the added advantage of a nice flat surface to push your ear against, and may possibly "collect" some of the sound energy emitted from the portion of the wall inside the rim perimeter.

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