Speaker iPhone 4 4S just sounds next door, why?

If you have an iPhone 4 or 4S smartphone, try to set the music or whatever sounds, then try closing the speaker hole located below with your finger or thumb, then you will find only one speaker on the right that reads.



Is it with only one speaker that reads your iPhone 4 is problematic?
The answer is no problem, because although the shape and appearance the same as the speakers, which is located on the left is not a speaker, it is a Microphone. 

So do not be surprised and do not think your iPhone is problematic, because it is on iPhone 4 / 4S there is only one speaker is located on the right, while the left is Mic / microphone.