It may surprise you to know that the iPhone has two microphones and when on a speakerphone or FaceTime call, you’re probably talking into the wrong one.
The iPhone actually has two speakers and two microphones. One set is at the top of the device and one set is at the bottom. The bottom microphone is located to the left of the dock connector. The top microphone is located next to the headphones jack.
When on a typical call the bottom microphone is active and the top microphone is used for noise cancellation.
Often when users are in a speakerphone or FaceTime call, and the person on the other end of call can’t hear them, they will move closer to the phone and speak towards the microphone at the bottom of the device. Surprisingly, that’s the wrong microphone to be talking to. Rather than using the bottom mic, Apple switches off noise cancellation and uses the top microphone to maintain a maximum distance between the bottom speaker and the voice input at the top of the iPhone.