You might think you know all about the taxonomy of stringed instruments. Violins are the tiniest ones, followed by violas, cellos, and basses. But there is another, much bigger instrument, appropriately named the octobasse.

The octobasse is a string instrument that can create sounds so low that humans can’t hear them.

The octobasse was built in 1850 by the French instrument maker Jean-Baptise Vuillaume. The octobasse is quite a lot larger than a human and not very practical to transport; also, there are rumored to only be seven in existence.

But there is a playable replica at the Musical Instrument Museum in Phoenix, Arizona. The octobass is in use by exactly one (1) orchestra in the world: the Montreal Symphony Orchestra.

Playing an octobasse is different than playing other stringed instruments because it’s too big for musicians to use their hands on the strings. Instead, there’s a system of levers and pedals that create each note.

Watch some musicians experimenting with the octobasse in Phoenix.