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MMD > Archives > April 2001 > 2001.04.12 > 09Prev  Next

Duo-Art Expression Box Adjustment
By Craig Brougher

Duo-Arts that are too loud

I re-adjusted Pete Knobloch's Expression box and as he recalled,
I charted the box, and sent him a copy of the finished chart.  His
expression box regulated nicely and was properly linear.  He also was
pleased with it's balance, for awhile.  Apparently however, this did
not solve his main problem.

By checking the felt spill hole, you sometimes notice that the felt has
encroached and is almost closed.  That will prevent any decent regulation,
as also will too open a hole.  Pete -- if you want to call me, please
feel free to do so.

If a customer has a problem, he is always welcome to call and discuss
it.  I promise that if he doesn't give up, I won't.  But I didn't hear
back, and figured everything was working well.  Pete probably thought
so, too.

There are no piano problems that we can't solve, as long as I can get
answers to my questions, we will eventually pinpoint the real cause.
In this case, reverting to "the weakest springs" did not really solve
his problem either.  That should have indicated to most readers
something else is obviously the problem, and it is not still the
expression box (which I had noticed, even while adjusting it, never was
to begin with).

My regulation of his box, I felt, was to eliminate all possibility that
it could be the problem.  However, trying to make the Theme spring
about equal to the Accompaniment isn't the solution.  Unless the Theme
has more slope than the accompaniment, the Duo-Art cannot be realistic.
If the Theme is too loud, then we know what the problem is, and it's
not the spring or the zero setting.  But if both the Accompaniment and
Theme is too loud and zero is set to 5", the problem is elsewhere.

If Pete were to actually disable the Theme side of the box by
disconnecting the theme tubes and play only the accompaniment, he
might soon learn whether or not it is his Theme that's bothering him,
or something else (of course, he has to listen through the gaps).
Replacing the Theme spring with an Accompaniment Spring, and resetting
the Theme zero intensity to equal the other, makes the Duo-Art into a
"Themodist" that has only Accompaniment levels after disabling the
crash valve.  If the piano still seems too loud, I would suggest he
replace the original Theme spring and move on to other possibilities.

I have run into several Duo-Arts that could not be regulated correctly,
no matter what was done.  In each case, the reason was patent leather
valves, vinyl, or neoprene rubber valves.  Anyone rebuilding a Duo-Art
who uses these materials doesn't understand the system.  It's that

However, I have also had customers complain that their piano is "too
loud," and what they meant was, "too harsh," not that it was without
expression.  This complaint goes back to John Tuttle's article, "The
Customer Is Always Right."  If it's "too loud" by being overly bright,
then that is no longer a problem with expression but the piano itself.

I once restored a Steinway and used (Abel) hammers which were too hard.
I needled them until they could not be needled any longer -- they were
disintegrating -- and it was still awful.  So I called my supplier and
they sent me a new set.  I removed them and returned some as samples
(including one that I had driven a needle into and it could not be
removed), replaced them with the new ones, and they were the same way.
The hammers could not be voiced.  That to me means the factory, despite
their stack of Bibles, in fact DID use chemicals in their felt, because
there's no way that one can deep-needle a pure felt hammer with a
single needle (as I do it) and not eventually, over the course of
several weeks, finally bring it down and into a smooth, resonant, and
rich, clear and clean voice.

There is also the variation between pianos.  I have run into a few
(very few) bad pianos that don't sound very good with anybody's
hammers, and this is not caused by a defective soundboard or bridge, or
anything else one could point to.  It was just a poorly constructed
sound generator that amplified the noises one didn't want to hear.

Steinways are not immune, and I have seen one of those.  I have called
the Steinway factory and we have discussed the problems at length, all
to no avail.  They  admit that such is occasionally the case.  Most
people don't even notice it or don't think it's a problem, but some
people, like myself, are rankled excessively.  So I commiserate with
Pete Knobloch and know how he feels.  Pete gives me some hints as to
what his real problem may be when he said:

> About six months ago I reshaped the hammers, lubricated the regulated
> the entire action, re-pined about 25 sluggish bushings, and re-voiced
> the hammers.  This helped quite a bit.  I can now reduce the zero
> point to about 4-3/4" of vacuum but at that level a few of the keys
> still don't hit.  This is probably stack problems which I haven't
> dealt with yet.

Yeah, that's what I think, too: stack problems.  But there are still
reasons other than rubber valves why the Duo-Art mechanism can be too
loud or unable to be expressively regulated, even after the expression
box is regulated correctly.  However, they all revolve around bad
rebuilding practices and a basic lack of understanding of how the
Duo-Art works.  Remember this: Aeolian didn't give anything away in
their manual, and for the purposes of averting criticism by competitors
and critics, were obliged to make the mechanism sound pretty cut and
dried.  As we so often are realizing today, it is anything but.

If we had a new test roll that would check out the Duo-Art for this
problem, we could quickly find it and fix it.  The problem has been to
date that roll arranging and in depth rebuilding are two different arts
and so far the twain has not yet met.  The second part of this problem
is that a test roll has to be cut exactly and synched to the machinery
that punches it as a 2-to-1 master with full-sized holes, just like
Aeolian did it.  A 1-to-1 master on generic stepping that splits the
perforator divisions and compromises on hole size will not make a
legitimate test roll.

Craig Brougher

(Message sent Thu 12 Apr 2001, 16:23:20 GMT, from time zone GMT-0700.)

Key Words in Subject:  Adjustment, Box, Duo-Art, Expression

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