What does the moi feel like?

[Mark Davidson]

Ed sutton wrote:

> Could I make or buy a gauge to measure this? [MOI]

A couple of things I have tried.  The first one is very simple.  Hold down
the damper pedal and place just enough weight on the key to get a sound out
of the note when you release the key.  I call this the "noise weight" or NW.
You pick up all the junk this way.  Friction, BW variations, regulation
variations, but it's interesting to play with.  If you take NW-DW then you
should get rid of a good bit ot the friction and BW variations.  A graph of
NW-DW, in theory, should be related to the MOI.

Funny thing, though.  I graphed this for my piano and instead of decreasing
nicely across the piano, it went down, then back up, then down again.  (I
have smooth SWs).  I expected a more or less decreasing curve across the
piano, albeit with some noise, and this was not what I saw.  Instead, it
appears that NW-DW and SWR are correlated (my SWR is curved in a similar
way).

The second thing is a bit more involved, but not too hard.  I tried to
imitate an arm with rigid finger dropping on the key.  So I took a piece of
2x4 about 20" long.  Put a pivot in the middle and made a "finger" on one
end - a nail, head down with a piece of felt stuck on the head to avoid
scratching.  I use a smaller block of wood on top that I can slide forward
and backward to change the balance.  I set it up so that it's level with the
finger on the key.  Lift it about 5/8" and but a block under the finger.
Pull out the block from under the finger and let it fall on the key.  Adjust
the block on top until you just get a sound, as above.  Then measure the
distance of the top block from the balance point (i.e. define the point
where it balances as zero, and measure how many mm forward you have to move
the block to get a sound - I have a scale taped on top).  Now the curve is
quite different, looks more like what you'd expect, with a nice curve from
bass to treble (still noise in it from friction, etc).  The block already
has speed and a fair amount of momentum before it comes in contact with the
key.  Somehow the fact that there is an impact and not just a constant force
(as from a weight) makes a difference in the type of curve you get. This
tool seems to be quite sensitive and numbers correlate well with the touch
of the piano.  Things like pre- and post-regulation, friction changes, and
weight changes are quite readily seen in these graphs.

-Mark