Very low audio output to headphones on Macbook Pro Retina 13 inch I get great sound output to an external speaker with my Macbook Pro, however, when I output to headphones the sound diminishes greatly.  I have reset PRAM and the sound volume output improves, but only for a short time.  Settings all appear to be set properly.  I'm thinking there's a hardware problem.  This is why:  I have a monitor that I connect to my Macbook with an HDMI cable.  The monitor has a headphone jack.  If I plug my headphones into the monitor's headphone jack the sound output is great.  Any thoughts?  Thank you.
Could definitely be hardware related. Try testing out the headphone audio in a new "test" user account. If it continues, its most likely hardware. If its still under warranty I would take it into the Genius Bar and have them test / replace the logic board. You can check the warranty status here. https://checkcoverage.apple.com