Loki was feeling a little too angry to be playing soothing music and so when the red lights and sirens started to go off, he is only further enraged. In need of the sheer physical release of it, he forgoes magic and favors a more brutish approach to his escape.
He wrenched the bench on which he was lying from the floor and throws it at the glass with enough force to crack it. He laughed manically at the fear in Coulson's eyes and squared the agent with a look that said 'when I get out of here, i'm coming for you'. Gathering some magical energy in his palms he launches it at the crack.
"I'm afraid we're beyond soothing music at this point agent, i'd rather like to get out now!"
The blast sends the glass into shattered and it rained down upon the floor of the observation room. And then Loki was smiling.