According to Andrew Stiller's excellent book on orchestration the contra bassoom will descend nine semi-tones below the lowest note (G zero) of its fundamental scale. I believe that is the lowest note of any acoustic instrument. BTW, most synthesizers will easily play notes below the threshold of pitch differentiation. We "feel" those notes rather than hear them. BTW, the loud pedal points on the E. Power Biggs quadrophonic SONY sacd of Bach's Toccatas/Fugues will really test any sub.

Jay