'Harps' in the Bible

I also heard a sound coming out of heaven like the sound of many waters and like the sound of loud thunder. Now the sound I heard was like that made by harpists playing their harps,

Then I saw something like a sea of glass mixed with fire, and those who had conquered the beast and his image and the number of his name. They were standing by the sea of glass, holding harps given to them by God.