On Fri, 22 Mar 96 16:24:12 PST  Robbie Rhodes wrote:

[Snip]

> Now consider how lifting the hammer rest rail alters things.  The 
> Soft Pedal moves the rest rail so that the hammer travel distance is 
> reduced to one-half.  We assume that the travel of the key and action
> pneumatic is also halved, and therefore the pneumatic is working 
> between 50% open (note at rest) and 20%.  The integrated force in this 
> operating range is considerably less than half of normal, and the 
> result is that the hammer velocity is much less than it would be if 
> the force had remained constant.
>
> You questioned, John, if halving the hammer blow distance predicts a 
> 3-decibel reduction in sound intensity.  You bet it does, and the 
> equations are simple, so let's look at it.
>
[Physics discussion snipped.]

> But the above assumes that the pneumatic force is constant, yielding 
> constant acceleration.  In reality, because the pneumatic is operating 
> in the "mostly closed" region, the acceleration term "a" is also 
> reduced, and the result is that the Soft Pedal produces much more than 
> 3 db intensity reduction.
>
> I'd like very much to read the articles in AMICA Bulletin that you 
> mention.  Can someone help me obtain them?
>
> -- Robbie Rhodes
>
        OK, I think I see part of my problem here: My confusion arose 
from your first mentioning of the hammer rail pneumatic in your original 
post, but then the rest of your discussion shifted to note striker 
pneumatics, a distinction I failed to make.  I think you will agree that 
the speed/force of the hammer rail pneumatic, per se, has no effect on 
note intensity, other than from the changed blow distance it manifests, 
and I readily agree that a striker pneumatic, starting from a partially 
closed position will impart a smaller force/acceleration to the hammer, 
resulting in a softer note.  Beyond that, generalities can be a little 
dangerous as we need to discuss the design differences among the various 
manufacturers.  (Grand rather than upright actions are assumed unless 
noted otherwise, although much of this analysis applies to both.)

        I accept for the moment that a 50% blow distance DOES predict a 
nominal 3 dB reduction in intensity (I see no reason to quarrel with your
analysis, PROVIDED ALL other factors are constant.)  On the one hand 
there is the Duo-Art mechanism, none of which, in my experience, have any
means to DIRECTLY compensate for the "lost motion" resulting from the 
lifting of the hammer rail.  When the hammer rail lifts the hammer heads,
thereby removing their weight from the rest of the action chain, the key 
fronts, by gravity, fall a short distance, having no longer to support 
the hammer weight.  This of course raises the back end of the key, 
resulting in a gap ("lost motion") between the underside of the key and 
the top of the striker poppet.  BUT, the open span of the striker 
pneumatics does not change.  While it might be argued that it they will 
continue to develop the same force(s) as when the hammer rail is down, 
there are some subtle considerations.  First, the initial movement of the
pneumatic is against no resistance so that by the time the poppet reaches
the underside of the key, it is traveling faster than otherwise.  This 
and the complex dynamic of having the poppet "impact" the key (rather 
than pushing it smoothly) may affect final hammer velocity in 
non-intuitive ways.  Complicating this (as if we needed more!) are the 
purely pneumatic changes which also typically take place when the hammer 
rail rises, i.e., opening the soft pedal port also cues accompaniment 
level #2.  This would seem to be working at cross purposes (raising 
accompaniment vacuum while engaging the soft pedal) but it simply 
re-emphasizes the complex factors at work here.  Also, in those pianos 
with side-shift pneumatics (some Steinways and larger Webers), IF tubed 
according to the official charts, the softening effect is achieved by 
striking only two (of the tri-chord) strings with a normally uncompacted 
portion of the hammer felt.  The hammer lift rail only comes into play 
when the modify switch is placed in the "Soft" position.  (In a later 
discussion I will express my reasoning why I believe this is backwards.)

        On the other hand is the Ampico B mechanism (and most late A's as
well.)  Here, the keys will still visually "dip" when the hammer rail 
rises, BUT the span opening also is reduced, violating the "all other 
factors remaining constant" premise.  Here the effect will likely be MORE
than a 3 dB reduction for the reasons Robbie previously stated.  (In the 
B, an extremely ingenious mechanism facilitates the span adjustment 
procedure using the "Note Compensation Roll" which allows the extremely 
quiet sub-intensity capability of the "B", below levels that would likely
drop notes in other mechanisms.)

        So, while in the three mechanisms, properly adjusted hammer rails
will all raise the hammers halfway to the strings in response to a soft 
pedal perforation, the response of each mechanism is less consistent and 
predictable.  Happily, the roll editors seemed to be aware of these 
considerations and developed coding changes which produce pleasing and 
believable, if not 100% faithful, playback.   As Robbie originally 
noted, some empirical/experimental data would be useful here.  I really 
don't have time right now to research the tech articles for what I seem 
to remember reading.  Terry Smythe, can you help out here?  And Robbie: 
on what mechanism(s) are you making your observations?

-John Grant