Before the advent of recorded music, speakers, and amplified music, when all music was produced acoustically, getting a full sound required large groups of musicians. Instruments and concert halls were constructed in ways that would project the music to the audience and much time went into the study of acoustics for this purpose.
To that end, luthier Jean-Baptiste Vuillaume created a monster. In 1850, he invented the Octobasse gigantic upright bass that was tuned an octave below a standard bass. This tuning, of course, is hard to confirm, because the low notes are below the range of human hearing, so I’m not sure how they worked that out, but in principle I suppose it’s possible. He built 3 of these fiddles, 2 of which survive today, along with 2 modern replicas.
It’s so big, you can’t even fret it with your hands – there’s a series of levers to fret the notes, sort of like enormous moving capos.
I recommend really cranking up your laptop speakers to get the full experience on this one. These videos are from the Musical Instrument Museum in Phoenix, AZ, a totally sweet looking place I hope to visit someday.