Why do most owners of grand pianos have the top cover off and up of
the piano? Through a period of time the dust gets into the strings.
The copper-wound base strings accumulate dust, and through time will
help to deaden the sound to some degree. The sound "box" is below the
strings. To owners of these pianos, make sure you keep vacuuming the
copper-wound strings.

If I owned one of these pianos, I would keep the cover "down"; there is
very little difference in sound. People do not keep the front cover off
an "upright" type of piano. I have worked on and tuned grand pianos.

Stephen Bentley
North Vancouver, British Columbia, Canada