While the iPhone 4 and iPhone 4S does come with a 178 page instructions manual, not many of us care to read it. And even if you will take the trouble to do so, you won’t find this interesting piece of information in it.
Where to speak on your iPhone 4 & 4S for highest clarity
According to a how-to article by TidBits, Apple has two speakers and two microphones on the iPhone 4 and 4S. The two pairs swap when to be activated depending on the scenario. Given that the microphone is used for picking up your voice and the speaker doubles as a way for noise cancellation, it can get tricky sometimes. So here are a couple of tips that will tell you how to have your voice sound crystal clear on the other end of the line.
For normal operation, you just need to hold the iPhone flush to your face or at an angle depending on the size of your face to it properly envelops your ear and mouth. In this instance, the distance between the top speaker and bottom microphone ensure there is no cross feedback and noise cancellation can work like a charm. However this technique doesn’t apply to those who are left-handed. As one commenter points out in the TidBits guide:
“So the iPhone is biased towards right-handers. When a right-hander hold the phone to his/her right ear, the microphone is on top next to the mouth. When a left-hander holds the phone to his/her left ear, the microphone is on the bottom, away from the mouth. Do I need to remember to hold the phone at a slight angle to bring the mic closer to my mouth?” – David K.
Based to TB’s article, yes.
Secondly, when it comes to using the your iPhone in speaker mode, the operation is slightly different since the top microphone is now activated instead. So if you are using your iPhone 4 or 4S in speaker mode, aim your mouth to the top edges of the iPhone and not the base as you would in a normal call. Unfortunately though, the top microphone isn’t as sensitive as the bottom so clarity isn’t great. Hence why a Bluetooth headset is preferred. The same applies to FaceTime calls since it too will employ the top microphone to pick up your voice.
Hit the source for more information where to speak on your iPhone.