Voice. Most powerful and natural instrument.

Belting out a song is one thing "Jeniffer Hudson" singing is another. Singing a song is an art that so few know what to do? The current crop that claim to have the title singer need to go back and reevaluate what it takes to sing.

Voice can be very powerful. Check out any opera in person!
Also. i have a pretty loud voice myself. Once years ago in a Best Buy, with all the usual noise, an announcement was made for some stupid reason and it was way over the top loud. So from the back of the store i yelled back at the loudest i could manage: COULD YOU REPEAT THAT PLEASE, I COULDN'T HEAR YOU! (i was louder, and clearer than the announcement, and trust me, they heard loud and clear up front in that store.)
Funny how the whole store suddenly became ultra quiet.
LOL!
Certainly many mechanical devices can be louder than a human voice, so can a compressed air boat horn in a can!
Try a Blue Whale at 188dB or a Tiger Pistol Shrimp at 200dB
The Tiger Pistol Shrimp cheats because it uses it's claw to make the sound. Where the Blue Whale uses its vocal cords.
The human voice is the most expressive of any instrument we have. The saxophone is next along with the oboe and bassoon. After those is the violin, viol and piano, then French Horn and clarinet, various other instruments..
The least expressive IMO is the triangle, along with the drums, castanets and tuba.. (I never could understand the excitement about drummers... technical ability yes, talent yes, exciting performance yes, but musicality, Hell no!))

PS the Blue Whale sound has like 60,000 times the power of the little shrimp sound. So I guess it is not much of a contest there.

After reading Elizabeth's response I think I'll take the Blue Whale over the current crop of diva's who simply yell as loud as they can. I could only watch two minutes of the Grammys and it was so nauseating to see all of them singing together trying to out diva each other. I was waiting to hear the gong but no one hit it.

I should also clarify that when some can really belt it out that the great ones do it without apparent strain. They don't bend over like they're having a seizure, mouth agape, eyes tightly shut, doing the Joe Cocker thing.
They simply sing way better than the rest of us.