The Captive Audience, also known as Greagan's Harp is a instrument that can only be used by bards, but has a limited amount of charges, so it will destroy itself after all charges are used. The harp can be used to cast domination on a single target each time it is played, like the 5th level wizard spell Domination. The target must save vs. spell at -2 to avoid the effect. It can be bought from innkeeper at Ulgoth's Beard Inn. This area become available if the expansion pack Tales of the Sword Coast is installed, which is already included in the Enhanced Edition of Baldur's Gate.
Gregan's Harp: 'The Captive Audience.' This finely made harp is well known among the nomadic peoples of the east, though more for the infamy of its owner, Greagan of the Low Hills. He was a bard, of sorts, though less for his love of people than his hatred of hard work. He bade a mage relation construct this harp so its magic might disguise his utter lack of talent in the arts. Its power was greater than he had hoped, and he later turned to petty burglary using 'his' music to captivate his victims. Greagan ultimately dissapeared some years ago admidst rumors of a bardic college uncharacteristically moved to violence. The harp still function, though any selfrespecting-troubadour would reserve its use for the most dire of circumstances. The magic seems to be waning as well, and perhaps this one item best lost to time.