Some Thoughts on Tibia Clausas
by Al Sefl ©reserved 2002
A number of posts have appeared on the Theatreorgans-L Internet forum asking
the not-so-simple questions of why there were variances in the Wurlitzer
Tibia Clausas. Ideas were put forth that some Tibia sets could not be made
to sound good and that there were inexplicable differences in the quality of
Tibia timbres from different periods of production. My commentary that
follows is an attempt to address those comments. It must also be understood
that all references to Tibias here are for the Clausa NOT the Plena. The
stoppered Tibia Clausa produces only the odd numbered harmonics whereas the
open Tibia Plena produces both odd and even numbered harmonics with a
different style of construction and voicing. My contribution to the
discourse follows:
In my humble opinion Wurlitzer was cutting corners with less voicing in the
later years. Young women were trained to curve stacks of reed tongues to
match templates provided to them and the best of the few real voicers on
staff worked only on the instruments that required a more discerning touch,
those headed for residences and churches. The peak of organ production was
in 1926 then orders started to fall off rapidly after the advent of the
talkies and this trigger economy measures in the factory. By 1929 William
Fox and his backers even tried to get Wurlitzer to cancel the contract for
the San Francisco FOX organ as it was not needed in a theatre that was
designed for sound movies. Farney Wurlitzer was the company tightwad who had
them use their own poorly made xylophone bars, glockenspiel bars, and cheap
pianos, etc., on the organs when they could have had first class Deagan
percussions like other theatre organ manufacturers. I believe Farney's penny
pinching even extended to pipe voicing where many of the ranks were never
given the touch a master voicer. Thus making a Tibia "whistle" without going
the extra mile to voice it carefully would ultimately end up as just another
cost cutting measure. This was mass production so very few of the ranks made
then put into crates ever touched the chest they ended up on until everything
arrived together at the theatre; and, very few ranks were finely voiced. As
a cost cutting measure on a shrinking sales base the later Tibias just were
not given more than rough voicing. Pipes that would speak just after their
construction kept costs down and the Tibias could be made to play as soon as
the glue and shellac hardened.
What I really find interesting is that Wurlitzer actually had two somewhat
distinct levels of voicing and quality. Since I have worked on both the
residential Wurlitzers and theatre types I have seen their fine residential
voicing versus the rough voicing done on theater bound instruments. Even the
consoles have a different level of care and finishing. But, I digress.
As stated I believe the later Tibias were given a lighter voicing treatment
to save labor costs and to support this theory I offer what many of us found
in Tibias during the 1960s when virgin instruments were still being pulled
out of theatres. In order to allow a minimum of voicing the later Tibias
were often closed at the toe so they would not overblow. This having been
done the placement of the windsheet was less critical and could be brought
into a closer position on the upper lip, what in voicing is referred to as
being made "quick." The windsheet could also be altered by filing the
windway out of the block in a different manner. This resulted in a more
thick windsheet with less ability to create the "twelfthy" harmonic timbre
most of us find desirable in a "good" Tibia. In effect the pipe was being
deliberately starved of wind so it would not show the rough voicing. I have
heard of someone who specializes in taking the later Tibias and giving them a
more proper final voicing. People who have sent ranks to be worked on give
high praise and you can hear the difference with the added treatment. The
demand for this service certainly indicates that many sets were just rapidly
produced without receiving fine voicing.
Conversely, I have run into a number of sets of Tibias where work by
"professionals" was done in the modern era that detracts rather than
enhances. I vividly recall many arguments with a well known now deceased
theatre organ luminary over his assertion that you have to "open up the
Tibias" for a better sound. This led to many sets being butchered by people
thinking they knew what they were doing to "open up" the pipes. So, there
are a great many "bad" Wurlitzer Tibias out there with dull woolly ragged
timbres that did not leave the factory that way. The worst case was a local
set that had the raised face of the languid sawed out, the slit on the block
filed deeper, and the toe opened way too much. These pipes were screaming
and unstable even with trem off. Three weeks of work were involved in
putting replacement wood back onto the languid and repairing the blocks where
the windway was filed out. An uglier set of Tibias I have never heard but
now they are quite decent after the mouths and languids were rebuilt and
recordings of them sound quite lovely.
The question remains as to what makes a good Tibia? (This is akin to asking,
"What is the meaning of life?")
Actually there should be four chapters in a book to address this, what little
is written here will not do adequate justice toward a decent answer:
Chapter One would be pipe design. It would cover scale and blowing pressures
that determine speaking power; cutup and upper lip treatments that determine
some harmonic structure; languid design including parameters such as the
height of the languid face, it's bevel angle, nicking, and the depth of the
curve cut into the top of the languid on the pipe floor for increased
"acoustical admittance"; block design; correct placement of the windsheet
onto the outer edge of the upper lip; pipe wall thickness; stopper design;
etceteras.
Chapter Two would be the windchest design. Wurlitzer pipes had a wide
latitude of operating pressures but one of the key items that made a
Wurlitzer Tibia sound good was the startup, quiescent state, and the letoff
with all three together colloquially called an envelope. Chests like the
Morton Carlsteads with superfast opening pouches develop a blast of air in a
very short instant of time. Morton Tibias were voiced "slow" with the
windsheet out more to allow for this so as to not overblow with harsh
starting transients. To the ears of many, a Tibia from one brand on the
chest of another can have strange results. A local guy has taken a perfectly
complete and good Robert Morton then slowly keeps changing out ranks. The
Wurlitzer Tibia on the Morton chest really sounds terrible because the pipe
was voiced "fast" for a different type of chest; it does however make the
best calliope imitation off trem that I have ever heard. The more complex
Wurlitzer chest with the built in concussion chamber above a pallet presents
a gradually growing wind pressure to each pipe and thus the pipe will build
up to full speech without burping, burbling, or stumbling (unwanted start up
transients). Thus the Tibia sound is very dependent on the chest action.
NOTE: For jazz nothing beats a Morton Tibia/chest to get close to that
wonderful Hammond B3 sound!
Chapter Three would be the design of the winding system. The Tibia draws air
like no other pipe in the organ with the exception of *really* large scale
Diaphonic Diapasons. The regulator must be designed to allow for a near
instantaneous large draw of wind and then to stabilize rapidly or you get
pitch bounce and sag. In most original theatre organ installations large
regulators were put in for the Tibia because even the 8' octave and sometimes
unbelievably the 16' octave were put on the one Tibia regulator. The job of
the regulator is to remain stable and when huge draws of wind by pipes drawn
at multiple pitches occurs it has to open fast enough to let in the higher
pressure static in such a fashion that no pitch change is perceived. Adding
to the complexity is that a tremulant dumping large amounts of wind from the
system is doing the opposite job of the regulator. The tremulant *is* trying
to destabilize the system. In this chapter the desired engineering
explanations would result in a regulator, windlines, chest, and tremulant
that all agree on seeing the same periodic pulse. By having this sympathetic
resonance in all parts of the system you get a stabile rate and depth without
having to use forced oscillation to drive a regulator with a huge inertial
load of pig iron on its' top. Even the blower factors into the system. Too
high a static pressure can overwhelm a regulator so that it will close too
quickly before the rest of the system has gotten wind and even break into its
own oscillation. Conversely if the static is too low the regulator cannot
achieve a stabile trem rate or provide a trem that sounds appealing and may
even stall on a big chord drawn at multiple pitches.
Chapter Four is the acoustics of the house. Houses with long echo fade times
tend to blur Tibia fast trem pulses together and houses with a dead
acoustical environment make trems sound slower. Some weird acoustics can do
odd things to trem rate perceptions. All of this gets into the study of
psychoacoustics which would be a whole book (and is) unto itself. As has
been discussed before, trem settings are highly subjective!
The bottom line is that a woolly windy Tibia is not desirable nor is one with
little harmonic structure such as the vary early Wurlitzer Tibias which were
just considered to just be "thickeners" for the large organ ensembles. The
harmonic train must have just enough content to add a bit of color without
going overboard and sounding too flutey. That harmonic train is very closely
related to the tremulant action. The well designed pipe must be able to
follow large changes in wind pressure with the trem and not fly off on the
high side or die out on the low side. How the Tibia receives the wind and
reacts to it is a complete study designed to let the harmonics change with
the wind pressure without the development of harsh inharmonic structure on
the high side of the tremulant pressure wave. It should be noted here that
Ernest M. Skinner kept the pipes and toe boards complete with valve
structures together as they moved through the factory so voicing would be
accurate (quick vs. slow). Few Wurlitzer ranks had voicing done on the chest
on which the pipes would ultimately sit. Certainly the tubular pneumatic
voicing machines seen in factory photos would in no way present wind to the
pipe the same way as the Hope-Jones electropneumatic action. To anyone who
has studied finite multivariable calculus you know that one small change
effects everything, and so it is with Tibias. The maddening part of it all
is that with everything interrelated you must walk in, listen, and start with
an understanding of the total way a system is reacting then when you change
one thing which effects everything, some items negatively. From there you
proceed to work on the next variable and the next. Luckily there is an order
to the process (1- check chest wind pressure, 2 - check static wind pressure,
3 - confirm pipe operating pressure, 4 - check tuning, 5 - etc.) that you
follow step by step to get a decent Tibia sound. There is an essential
gestalt approach where the sum of the parts are greater than the whole and
magic occurs to give you a fine Tibia at some point. Often you get there
without knowing exactly how you did it.
Were there "bad" Tibias that cannot be made good? No! But, if the windway
was originally filed out badly it falls under the same category as the
carpenter who cuts too much off a piece of lumber. That 7'11" piece will
never again be 8' exactly. However, with pipes there are fixes including
gluing new wood into the windway then revoicing depending on how much time
and work you want to put in. I have had to do this on several occasions.
For those wishing to experiment I suggest what my Grandfather had me do
during my apprenticeship, use modeling clay. With modeling clay you can add
material to see what the effect would be and have no permanent damage result.
Generally I find the languid face on poor Tibia examples to have been filed
back at too steep an angle then aggressively rounded over in a windway that
was way too open in the first place. By narrowing the slit of the windway
the harmonic development of the pipe can give the "twelfthy" tone that will
bring sweetness to a Tibia Clausa but getting there correctly can be a tricky
process. One dead giveaway that someone has screwed the pipe over is when
the top edge of the block is in any way rounded off. This tends to
delaminate the windsheet with horrible tonal results and is usually a third
rate voicer's reaction to bring the windsheet outward after excessive filing
of the languid face moved it inward. Another danger sign that someone has
"opened up the pipe" is when the flat part of the languid face is not flush
with the pipe walls upon inspection with the block removed. Sometimes just
the depth of the slit on the block was deepened with a file and a visual
inspection normally will reveal this. Many years ago when I quit regularly
dealing with damaged pipes out of total anger and frustration I wondered why
anyone would think sawing up the mouths of Tibias would make them better.
The motto should be "Kids don't do this at home!"
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
What I wouldn't give for a good graphic interface on email at this moment. I
will try to show a Tibia sideways to show the construction for more clarity
in my commentary:
~~~ upper pipe body ~~~
| | | |
| | | |
\ | | |
\\ || leathered upper lip | |
\\ || | |
\\|| | |
__ | |
face> / | _| |
___ | \ / |
| | | \_____________/ |
| / | languid |
| | | |
block
^ windway
Notes: While the languid bottom is shown flat here, in reality it is a curved
surface. Likewise, the inside of the block is a curved surface but again
this email posting cannot do that graphic curve. The languid face is shown
beveled flat on the top but is normally a slight rounded curve backward.
Nicking is usually just on the languid face on Wurlitzer but on both the
languid face and the block on some other makes. The important thing to
remember is that the windsheet is not placed by voicing as with a metal pipe
where the languid is raised or lowered. Instead Tibias require very little
rough voicing because the windsheet travels straight up to hit the upper lip
and the aim of the windsheet is very much set by pipe construction. The only
way to change the aim of the windsheet is to file the exposed face of the
languid into the slight curve. Once that curve is made there is no easy way
to move the windsheet back out if the treatment was overdone.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
However, there are two things the average organ tinkerer can do to improve a
Tibia. The first is to make sure the stopper packing is air tight. With age
the old leather shrinks and the pipe will not resonate with a solid tone it
the stopper is loose. Even a small leak at the stopper will degrade the
tone. Tight stoppers are an absolute must for a good Tibia Clausa timbre.
The second is to operate the rank on the correct pressure. Many times a poor
Tibia timbre is the result of someone just not paying attention to the wind
pressure. Too low a pressure will give a dull Tibia sound and too much will
make for harsh inharmonic generation. A good mechanical gauge regularly
calibrated against a real water column manometer is always the best first
step to take in diagnosing any Tibia problems.
Now that you have read the above tome, keep in mind that it is not gospel but
the opinions of someone who has been around organs for some 50 years and does
not consider himself an expert. Organ work is still more art than science
when you must factor in the very subjective human ear.
Two Christie Tibia pipes (ex-Granada, Willesden, London NW)