Here’s what I knew about the microphones in the iPhone 4 and 4S before I got the really big surprise I’m going to share with you in a moment.
The iPhone has two microphones and two speakers, one of each on the bottom and another pair on the top. The microphone on the bottom is the grille to the left of the dock connector port as you look at the front of the iPhone — the grille to the right of the port is a speaker. This makes it easy to speak into the bottom microphone during a call. When you hold the iPhone up to your ear, you’re listening through the other speaker, near the top of the front face of the iPhone; if, at the same time, you rotate the iPhone up at an angle so that the bottom left corner of the iPhone is near your mouth, your voice naturally goes into the bottom microphone. The same is true when you’re recording a voice memo, or talking to Siri.
The microphone on the top is a tiny hole next to the headphone port. When you hold the iPhone up to your ear and speak into the bottom microphone during a phone call, the top microphone is used to perform some noise cancellation trickery. Since the top microphone is much farther from your mouth than the bottom microphone, the device can assume that what it’s hearing through the top microphone is mostly background noise and that what it’s hearing through the bottom microphone is mostly your voice, and it can invert the noise input and mix that with the voice input to reduce the noise component and make your voice clearer.
And now for the surprise. When you take the iPhone away from your face during a call and put it into speakerphone mode (tap the Speaker button), the top microphone is the one that is now active. Did you know this? I sure didn’t.
This fact makes sense, when you think about it, because in speakerphone mode, the sound comes out the speaker at the bottom of the iPhone. Thus, the microphone at the bottom of the iPhone needs to be turned off; otherwise, it would pick up the sound of the remote caller emanating from that speaker and feed it back down the line. Instead, the top microphone is used, maintaining maximal distance between the sound output (the bottom of the iPhone) and the voice input (the top of the iPhone). No noise reduction is performed, because only one microphone is in use, and this makes sense as well: in speakerphone mode, the iPhone is sending the caller the sound of the entire surrounding environment. The same rule applies during a FaceTime call, because the same situation applies: a FaceTime call is, by definition, a speakerphone call. (The top microphone is also the one that’s active when recording video.)
I didn’t know all this, and so, ever since I got my iPhone 4, I had been holding the iPhone wrong during speakerphone mode: I was holding the top microphone pointed away from me, because I thought “the microphone” was the one at the bottom during a call. Now that I know about it, I hold the iPhone better, and people on the other end can hear me better. Also, I use speakerphone less, out of sympathy with my callers. When you speak into the bottom microphone, you’re using superior electronics, because the bottom microphone is a better microphone, and you’re using noise cancellation. So if you want your caller to have a good listening experience, you should hold the iPhone up to your ear or use a headset of some sort — don’t use speakerphone mode.
That’s about all I have to say on this topic. I learned something interesting and useful, and I felt many people might not be aware of it, so I’m sharing it with you. But I can’t resist also ranting briefly about why I didn’t know this simple and useful fact. I didn’t know about it because Apple didn’t tell me! It might be stated in some Knowledge Base article, but I didn’t discover it, because I didn’t know I needed to look for it (and now that I do know, I still haven’t found it). The place I looked was in that flimsy little booklet that comes with the iPhone (with the cute title “Finger Tips”), and nothing was said about it there. In fact, I stumbled upon this little nugget of knowledge by sheer accident, while I was watching, of all things, a technical developer video of a talk from WWDC 2011. If I weren’t a developer, and if I hadn’t happened to watch this particular video, I might never have found out this fact at all — though in the course of preparing this article I have found a few discussions of the same topic, based mostly on experimentation of the “Can you hear me now?” variety.
What bad thing would happen if Apple provided customers with decent instructions for using their hardware? None that I can see. But by persisting in the myth that everything about an iPhone is obvious and that no manual is needed, Apple certainly does its users a disservice. And it does itself a disservice too, because an informed public uses the device more efficiently and is happier with it.