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You can test this very easily using an iPhone's speaker pointed towards a wall. When the speaker is more than an inch or two away, it is normal volume. However, when the speaker is nearly touching the wall, the sound is much louder. Why is this?

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A rough diagram of a setup below:

setup

the blue rectangle represents an iphone. In configuration A, the speakers point towards the observer, whereas in configuration B, the speakers point towards the wall. From the many times I have tried this, configuration B is louder than configuration A.

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  • $\begingroup$ Your tags suggest that you are already in the way of the answer. Being spherical waves, sound intensity decreases inversely proportional to distance squared. The speaker facing the walls focuses waves in your position, before their intensities decrease as much as they would if they are reflected in other walls of the room. $\endgroup$ – rmhleo Sep 18 '14 at 8:53
  • $\begingroup$ @rmhleo: that should be posted as an answer $\endgroup$ – John Rennie Sep 18 '14 at 8:56
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    $\begingroup$ This works outside as well too, where there are no other walls. Why would it be louder for the sound to bounce off the wall than for it to travel directly to your ear? If you put the phone close to the wall, and then point the speakers directly towards you, it is still quieter than when you point the speakers towards the wall $\endgroup$ – woojoo666 Sep 18 '14 at 8:58
  • $\begingroup$ The actual conditions of your set up are not very clear. Still, in your case, pay attention to the possible ways the sound might reach your ears. You will find that when is louder is because an enhance of waves where you are, with respect to the case when the speaker is facing you. Notice also that when the speaker is facing you, you only receive a small portion of the ~$2\pi$ steradians coverage of the speaker. $\endgroup$ – rmhleo Sep 18 '14 at 9:08
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Your tags suggest that you are already in the way of the answer. Being spherical waves, sound intensity decreases inversely proportional to distance squared. The speaker facing the walls focuses waves in your position, before their intensities decrease as much as they would if they are reflected in other walls of the room.

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  • $\begingroup$ Please see my comment on my answer $\endgroup$ – woojoo666 Sep 18 '14 at 8:59
  • $\begingroup$ I think I understand your answer now. When the speakers are close to the wall, the observer hears both the sound directly from the speaker and the sound reflected off the wall. When the speakers are away from the wall, the observer only hears the sound waves directly from the speakers, as the waves dissipate before they can reflect off the wall. $\endgroup$ – woojoo666 Sep 18 '14 at 9:59

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