Oh man, it's a normal width keyboard and it's the strings that are long. This is way cool, but I was imagining it to be the other way around, like the 500 seat piano in the fantastic and too-overlooked movie The 5000 Fingers of Dr. T.
I'm 99% sure this is the movie I've been trying to re-find for over a decade. I had this strangest memory of watching a movie while very young that involved hands and a large number but I could never find it. A 1953 musical would definitely fit what my mother would have watched on VHS in the early 90s.
I imagined this at first too and was confused because a wider piano makes no sense. The 88s keys already cover almost the entire range of human hearing. Adding just one more octave (a few keys below and above the range) would basically cover it all.
Of course, you could argue that there is merit to having low keys whose fundamental is below human hearing because the overtones would still be audible. But that seems to be of pretty limited use to me.
Bösendorfer makes some large grand pianos with 92 or 97 keys. The 92 key one has 4 extra bass keys. I don't know about the 97 key one. The extra bass keys are under a little wooden cover that you can flip up if you want to play them, but I think the real purpose of the extra strings is to vibrate sympathetically with the regular strings, giving some additional bass oomph. Maybe the long strings on the Alexander piano provide oomph enough while staying more in tune.
At the upper end it's perfectly possible to reach the end of the treble scale, so maybe the 97 key Bösendorfer has extra treble keys in addition to extra bass keys. I haven't seen one though.
They have an elaborate explanation of why they did it, and they are a commercial outfit, but the basic reason still seems to be "we wanted to see if we could".
> The 88s keys already cover almost the entire range of human hearing. Adding just one more octave (a few keys below and above the range) would basically cover it all.
This was surprising for me, I thought no way is this almost the range of hearing.
But a quick calculation showed it to be right: The range of human hearing is approximately from 20Hz to 20kHz which is ~10 octaves (20*2^10 ~= 20k). 10 octaves would need 120keys, so ~2.5 Octaves more than the 88 keys range.
In case anyone remembers, there was a company called Dr. T's music software, they developed for the Atari and Amiga. I did some work for them in the late 80s
Pic of the movie piano: http://manapop.com/wp-content/uploads/2014/09/vlcsnap-2014-0...