Voice. Most powerful and natural instrument.

Friends of my parents were opera singers. She was soprano while he was bass/baritone. I heard her practicing ones in the room and it was unbearably loud. It sounded like regular opera voice 5x louder. I've never heard him singing but when he coughed once next to me it was like an explosion.

In Indian classical music voices sound like instruments almost like imitating them. It is the other way around - instruments imitate perfection of voices.

Handel probably more than any other opera composer I've heard used the voice as an instrument, competing and complementing other instruments in their settings, especially in Julius Caesar.

Nonoise: I could not agree with you more. The current crop of singers all come from the new school of vocal nonsense.The school of vocal hysterics...

There is a legend, or truth, that one very famous Russian opera singer could break a crystal glass with his voice. In any case, he is considered to have had the most powerful voice of all singers of that time.