The sound system sends computer-generated sounds to four destinations:
- internal speaker
- Apple Speaker sound output port
- stereo headphone sound output port
- USB audio devices connected to the USB ports
The iMac computer has a single internal speaker that operates when no external speakers are connected. The internal speaker uses a monaural mix of the left and right channels.
Apple Speaker sound output port
The Apple Speaker sound output port is a 2.5 mm stereo minijack. It has a smaller diameter than the headphone sound output port so that typical headphones cannot inadvertently be plugged into it.
WARNING: Many cell phones, and some types of headphones and other audio devices, have a 2.5 mm plug. Such devices must not be plugged into the Apple sound output port. Doing so could damage the devices.
The Apple Speakers include an internal ROM that enables the computer to identify the speakers. Speakers other than the Apple Speakers should not be connected to the Apple Speaker sound output port.
Headphone sound output port
The iMac has a 3.5 mm sound output port for stereo sound output. The headphone sound output port is suitable for connecting a pair of headphones or amplified external speakers. When a plug is inserted into the headphone sound output port, the internal speaker and the Apple Speaker minijack are disconnected.
The sound output through the headphone sound output port has the following electrical characteristics:
- output level 2.0 V peak-to-peak (0.7 V RMS), open circuit
- source impedance 44 Ω
- signal-to-noise (SNR) 90 dB unweighted (typical)
- total harmonic distortion (THD) 0.03 percent or less