I know the question has come up before, i've certainly asked it at least once, as to why my system audio appears "locked." it's at a set high volume and I have no control over it. Well, I figured out what the problem was and I thought i'd post the solution in case anyone else who uses iShowU (the instigator of the problem) or anyone else who has this problem can try to fix it.
When using iShowU, if you have "record system audio" selected, it changes your sound output from built-in output to "soundflower." this makes it so you cannot change your built-in output. the deceptive part is that soundflower will also give you a preview of the audio THROUGH your built-in out, making it seem as though built-in out is still running. to change this back after using iShowU, simply go to systemprefs-sound-output and change it back to built-in output.
if you've just got locked audio, look under sound output as well.... i have had other situations where i've been baffled as to my audio and found the answer here.
just in case
When using iShowU, if you have "record system audio" selected, it changes your sound output from built-in output to "soundflower." this makes it so you cannot change your built-in output. the deceptive part is that soundflower will also give you a preview of the audio THROUGH your built-in out, making it seem as though built-in out is still running. to change this back after using iShowU, simply go to systemprefs-sound-output and change it back to built-in output.
if you've just got locked audio, look under sound output as well.... i have had other situations where i've been baffled as to my audio and found the answer here.
just in case