I am actually thinkung about doing the same thing here. I plan to "hang" two 100lb speakers about 10 to 12 feet behind the bar where it would be out of reach from everyone who would be smart enough to try to swing from them. I think three 3ft chains would be enough since i will make a ledge to rest the speakers as well (keeping in mind that the speakers would be between 30 to 45 degree angles. Although i cannot be at ease by thinking that they could never fall.