Magfan you are indeed correct, the Bosendorfer mental amount of $$$ Imperial (best piano on the world by a long stretch)goes down to C (additional 9 notes) to give a full 8 octaves, so A below A1 (if there was one) would have a Hz of 13.75 add a few (can't remember the multiplyer to give a semi-tone increase (been a long time since I was at musical instrument technology college), and it is still
rather lowdown Hz wise.I've only ever played on the Bosendorfer 7'+? model daily (way back), what an instrument that was! Having only tuned piano's (back in the day also) with the Standard A1 27.5hz(that is/was hard enough to do) the big fella must be a piano tuners nightmare all those additional notes in the bass, if you have a cold, forget it pack up your tuning crank, go home, you ain't gonna hear the 'beats' that low.