iMac: Sound Output Ports Specifications

Sound Output Port

The sound output port is a 3.5 mm miniphone jack located on the I/O panel on the right side of the computer. It accepts a stereo miniplug-to-RCA cable adapter for connecting stereo equipment to the computer.

The sound output port provides line level output with the following electrical characteristics:

• output impedance: 65 Ω
• maximum level: 1.4 V nominal (root mean square), 4.0 V peak-to-peak
  

Headphone Jacks

Two headphone jacks are located on the front of the computer next to the left speaker. Each jack provides enough current to drive a pair of low-impedance headphones.

The headphone jacks have the following electrical characteristics:

• output impedance: 65 Ω
• maximum level: 1.0 V (root mean square), 2.8 V peak-to-peak

The recommended minimum headphone impedance is 32 Ω. Headphones with lower impedance can be used, but with some degradation in performance.

Sound Specifications

The frequency response of the sound circuits, not including the microphone and speakers, is within plus or minus 1 dB from 20 Hz to 20 kHz.

Total harmonic distortion plus noise (THD+N)

THD+N as a percentage of full scale are as follows:

Connector and level THD+N

• line input 0.03 percent
• line output, open circuit 0.03 percent
• headphone jack, open circuit 0.03 percent
• headphone jack, 32 Ω headphones 0.5 percent

Signal-to-noise ratios (SNR)

The signal-to-noise ratios (SNR) for various inputs and outputs are shown below. The values shown are unweighted. Values with weighting would be approximately 8 dB higher.

SNR specifications

Connector signal-to-noise ratio

• microphone 65 dB
• line output 85 dB
• headphone jacks 85 dB
• line input 85 dB
• internal CD or DVD 85 dB