Ok - I might as well throw my hat in the ring. Subcontrabass Tubax (Bb). Think 8vb below a Bass Saxophone.. This one is the 9th out of 9 made by Eppelsheim for Paul Cohen who graciously let me use it a couple years ago.

 

Octocontrabass clarinet project

 

 

Glad to see Richard Bobo's subcontrabassoon being represented. I've followed his project since he started nearly 10 years ago, and the results so far are exciting.

From what I can find, Jared de Leon's octrocontrabass clarinet is taking a backseat for his other projects, many of which are just as intriguing.

Speaking of which, the saxophone family is again out of depth in the subcontrabass register. A low A subcontra only gets you down to concert G0, while both of the above attempts will eclipse it by at least a minor sixth. I would have been content with that G0, but apparently one of the Brazilian low saxophone manufacturers didn't think so and actually made an octocontrabass, one octave below the contrabass. Kudos to @Robert Glogowski for bringing this to attention in another thread.

I couldn't believe the title at first, but there are multiple concert F0's in the first clip fingered as a low D. It exists.