How about some opinions on the following Duo-Art questions:

What is the correct (original) material and configuration of the upright
spill valve muffler felt?  Can the material usually found there offer
the same resistance and flow limitation of  the grand spill muffler
felt?

How much does the vacuum drop for each note played (at low vacuum levels
like 5 to 10 wci), and does it recover all or in part while the notes
stay on?  Ampicos drop very little and recover very quickly.  I believe
that properly restored Duo-Arts drop 0.25 to 0.5 wci per note and
recover perhaps half of that, but stay low as long as the notes are on.
I have measured several pianos so far.  What are your values?

I remember hearing a rumor about what the editors used as a value when
coding rolls.  Does anyone know what this value is supposed to be?

Many rolls have themodist coding (snakebites) with the theme set at 0 or
some other level which is lower than the active accompaniement level.
Is this a vestige of the editing process which produces no effect and
was therefore not removed, or was this used to achieve a desired effect?
I have heard many opinions but can't recall any that made much sense.

All that opening the theme valve does (when the theme regulator is lower
than accompaniment) is connect a small volume of expression box
passageways and theme regulator pneumatic to the stack through the theme
valve.  Is this used to drop stack vacuum quickly?  Duo-Art stacks drop
very quickly anyway.  I have measured stack vacuum while these strange
codings are playing  and have not noticed anything happening.  Maybe if
I know what is supposed to happen, I can watch more closely for it.
Examples from particular rolls would be helpful.

Spencer Chase