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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;




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 |

| | | |


^ 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)


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