Samsung Galaxy S4: Problem With Low-Impedance Headphones

This note provides audio measurements on the Samsung Galaxy S4 and S3 smartphones. The measurements were motivated by reports from S4 users having audio quality issues using low-impedance headphones on the order of 12 ohm. The stock headphones provided with the S3 and S4 have impedances at 1 kHz of ~ 35 ohm (measured). Based on my measurements on a single S4 (SGH-I337), there is no problem with headphones with an impedance of 16 ohm or higher.

 To check out any audio problems quantitatively, the headphone output of the S4 and S3 smartphones were connected with various pure resistive loads with values ranging from 10 to 33 ohm. Pure sine wave audio tracks with format .wav and 16bit/44.1 kHz and with -0.8 dBFS (almost full digital amplitude) were synthesized and saved as audio tracks on the smartphones. The tracks were played back using Music player and with default settings (no EQ etc.). The output on the left/right channels were monitored using a Digilent Analog Discovery dual-channel USB oscilloscope. The sound quality was also determined using a parallel connection to an Edirol MA-15D micro monitor amplifier. Various cable interchanges and substitutions verified that the results below are real and are associated with the S4. The configuration is shown below. The breakout box shows the load resistors on the left connected with banana plug binding posts, one for each audio channel:

http://www.jensign.com/S4Distortion/

http://forum.xda-developers.com/showthread.php?t=2258831