I have heard that the classical Indian musical instrument, the Surbahar, makes the lowest audible note of any musical instrument. I am curious what instrument makes the lowest audible note and what that note is in relation to the lowest note on an 88-key piano.
The lower limit of human hearing is roughly 20Hz.
There are a few instruments that can play even lower notes than that, but you'll almost always hear something because you are hearing the overtones.
The lowest note on a standard grand piano is A 27.5 Hz
Some grand pianos have nine extra keys down to a low C 16.4 Hz (this is below the human hearing range, you only hear the note because you hear the overtones)
There are some large pipe organs that can produce a C one octave below that (non-audible 8.2 Hz. Notes that low are felt rather than heard)