How low is a piano?

The Bösendorfer 290 does not extend a full octave below the standard 88 key piano. The 88 key piano goes down to A0, the 97 key Bösendorfer 290 goes down to C0, approx. 16 Hz, an additional 9 keys, a little more than half an octave extra.

http://www.boesendorfer.com/en/model-290-imperial.html

Very interesting responses folks. Thanks! Am I correct about the low bass string? I wasn't sure.

Actually it's 41Hz in standard tuning.

Grimace - You are correct (41.2Hz). There are 5 or 6 string electric bass guitars that have additional B string (31Hz) but it is made only for ease of playing. Composers would avoid writing music for 5 or 6 string instrument exclusively where most common bass has 4 strings.

I wonder why they produce instruments like Bösendorfer 290, that go below human hearing. With church organs vibration could be felt - is it the same for the piano? I though for a moment that perhaps it was designed for dogs but in spite of common "superior hearing" belief, dogs don't hear below 60Hz. It must have been for whales!!!

I believe dogs hear on the high end, not the low. High-pitched whistles and such.