What a nice surprise - technically OT

[Newton Hunt]

The 'killer octave' is an area, usually one half to one full octave in
the top three octaves of the piano that lack power, projection or
fullness of tone.  This is a defect in soundboard design and fabrication
which causes inadequate impedance of the board or put another way the
board is not stiff enough in that immediate area.

Normal pradctice is to  harden the hammers.  An effective compensation
is to secure weights to the bottom of the board.  Or replace the board
with one properly designed and assemsbled.  Duplex scaling was an effort
to solve this problem, that never worked that well.

		Newton