Why Is There a Tiny Hole at the Top of an iPhone 4? Small Business

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The iPhone 4 model has a tiny hole at the top of the device near the earphone jack to accommodate a special microphone that is part of a sophisticated noise-canceling system. The microphone is one of two used in the iPhone, which electronically combines the sounds received from both to make phone conversations easier to understand.

Primary Mic The iPhone has a microphone located at the bottom of the phone on the left side; its primary job is to pick up the sound of your voice for phone calls. If you're in a noisy environment, however, it also unavoidably gathers extraneous, unwanted sound.

Secondary Mic The main purpose of the secondary microphone, located at the top of the iPhone 4, is to pick up ambient room noise. Because it sits at the opposite end of the phone from the primary mic, in a spot relatively isolated from your voice, it's in a near-ideal position to collect the incidental sound and noise that surrounds you -- but not your voice.

Noise-Canceling Circuit The iPhone's noise-canceling circuit works by subtracting the signal from the secondary microphone from that of the primary. The primary microphone receives both ambient noise and your voice; the secondary mic picks up just the noise. After processing, the resulting signal consists primarily of your voice and has little room noise. When you make a phone call, the person at the other end of the conversation hears your voice clearly, as the iPhone removes distracting background noises.

Speakerphone Mode Although your voice is predictably closer to the bottom microphone than the top when you use the iPhone normally, you hold the phone away from your face when you use the speakerphone mode. Although it may be tempting to hold the phone such that you're speaking to the bottom mic, this approach doesn't work well with the iPhone, as it uses only the top microphone under these circumstances.

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