When you hold a shell (or any other roughly similar shaped item) to your ear, you hear a whooshing noise which is often referred to as 'hearing the sea' inside the shell.  What causes this noise?

It's well known that we hear our own voice quite differently to how other people hear it due to bone conduction of sound.  How then do people sing in tune?  and how do some people fail to hear that they are out of tune?

(The Science and Mathematics of Sound, Frequency, and Pitch)

- by the incredible ViHart

http://www.youtube.com/watch?v=i_0DXxNeaQ0&feature=uploademail

And also, if you were to cut off the whole of your outer ear, how different would everything sound without something to direct the sound?

When i was very young i went through a stage of about a year where i would hear a high pitched noise in my ears at night time. this noise would get progressivly louder intill you could not mentally or physically take it anymore, it was the worst thing i have ever experienced. it was like the noise you hear in your ears after you have heard very loud music but this was much worse. a constant ringing in my ear that got really loud. i also got delirious at times where people seamed thurther away than what they actually was and at other times the texture on my hands felt like what i can discribe as playdough and you can feel the texture in your mouth. a really horrific sensation i dont know why, the last time i had that was about a year ago but the noises in my ears was about 10 years ago. i also remember my dad saying something to me and his noise kept repeating in my head....

i am not physically or mentally disabled in anyway, i have never encoutered something like this and have never got the answer to why this happened to me. i remember going camping and came back with a high tempreture when i was younger and i thought this started it off due to a viral infection, i could not find any other plausable reason why i suffered with this.

I  have little fantasy about space ! Can we hear sound in space?

The standard answer to this question is that our brain picks up the tiny difference between the times at which a sound arrives at each ear, and from this figures out where the sound is coming from. But simply selecting points with a particular difference in their distances will yield an entire conical surface of possible origins. Distance, I suppose, can be judged from the softness of the noise, but how do we tell which of the possible directions the sound is actually coming from?

If you played the same note, in 500 versions of exactly the same speakers (so all the same frequencies) at the same distance from the receptor (ear or decibel meter), would it be the same volume? 

If it would increase, how much by and why? 

Would it be 500 times? Or would some be cancelled out?

Thanks!

I've heard that your brain calculates the position by the time difference between the sound reaching one ear and the other. However, i'm sure this is wrong! If there's a loud bang a short distance behind you, how do you know it was behind you? The sound would reach both ears at the same time, so the source could be infront of you, or even above you!