(Michel: just saw your reply that partly answers the above question. Sorry.)
Can anyone suggest a good site with information about convolving?
(Are piano developers trying mics in various locations in the piano for recording various notes? Does the location of a bass string, given the shape of a grand piano, create a very different sequence of vibrations within the piano than an E8, say, the vibrations hitting the left side of the piano much faster than the right side, and then moving back towards the center earlier than the vibrations from the right side, etc? Or is the effect of the mic placement for the soundspace recording negligable in a place as small as a piano? Should people ask such questions?)