I've got a soundbar connected to a Dell U2711. If I play a piece of music on YouTube and the volume (of the YouTube player) is above 50%, the sound is distorted

I've got a soundbar connected to a Dell U2711. If I play a piece of music on YouTube and the volume (of the YouTube player) is above 50%, the sound is distorted. Since I can't control the volume in Mac OS X, and changing the volume on the soundbar itself doesn't stop the sound from distorting, I'm dependent on the volume control of the application I'm using.