| Theater organs in
general, and the Organ Stop Wurlitzer in particular, require a
tremendous quantity of air to operate properly. The wind system
should be thought of in two phases. First, the blower(s), which are
responsible for generating the huge quantity of unregulated or
"static" wind required. Secondly, devices known as
"regulators" and "tremulants" stabilize and
precisely control the wind supplied to the pipes.
As stated, theater pipe organs require huge amounts of air to
operate properly. Theater organs generally run on 5 to 10 times
greater air pressure than that of church or classical organs. In
their original theater installations, the large quantity of high
pressure wind was necessary in order for the organ to be heard in
the large and sometimes cavernous auditoriums. In the case of the
Organ Stop Wurlitzer, the quantity of air required is truly
staggering.
Our blower room
contains four Spencer brand turbines. Only three of the four are
utilized at any one time. The fourth blower is on standby to ensure
no downtime in case of mechanical failure in any of the other three.
They have a combined power of 60hp. and are capable of producing air
at the rate of over 14,000 cubic feet per minute!
The turbines are
designed to produce two separate pressures of raw or
"static" wind. The main static line is 20" in
diameter and feeds the majority of the pipe organ with
"lower" pressure wind. A separate 10" diameter line
provides the "high" pressure required by some of the more
powerful pipes in the organ. Both of these lines branch throughout
the organ, like arteries, feeding the wind trunks (the wooden boxes
upon which the regulators sit).
There are other
considerations necessary for a successful blower room. Like the
saying, "children should be seen and not heard", much the
same applies to organ blowers. The concrete floor of this room is
totally separate from the foundation of the main building,
minimizing the transmission of rumble generated by this massive
machinery. The blower room walls are almost totally independent from
those of the main building, further ensuring isolation of noise.
Temperature of
the wind generated is a major consideration, especially in the
Arizona desert. Excessive heat plays havoc with the tuning stability
of the instrument. The turbines generate significant air friction,
which in turn generates heat. It is therefore necessary to pre-cool
the air going into the blowers to keep the temperature within the
pipe chambers stable. A 5 ton air conditioning unit is in operation
whenever the organ is running, even if the outside air temperature
is 20F!
One further
consideration is the source of the air for the blowers. It is
essential that an extremely clean source of air is provided,
therefore the organ's wind system is totally closed, relying
entirely on recirculated air. Make-up air is pulled from each of the
organ's chambers, and is returned to the blower room through a
36" diameter underground plenum. Many stages of air filtration
ensure grease and dust-free air, so vital to the organ's sensitive
pipework.
The numerous rectangular wooden boxes visible in the sub-chamber are
known as "regulators". The regulator takes the raw, static
wind produced by the blowers, and regulates it to a precise pressure
for the pipework it feeds. One regulator may serve one set of pipes
(known as a rank), or a "division" of several ranks.
Generally speaking, the larger regulators serve the larger
divisions, the smaller ones are quite often dedicated to a single
rank.
Tremulants, like the regulators, are located in the sub-chamber.
Patrons often compare their appearance to that of a fireplace
bellows. The tremulant is the single-most important device for
creating the heavy vibrato sound so uniquely characteristic of the
theater organ.
Each tremulant
works in conjunction with a regulator. While the regulator is always
seeking to stabilize the wind pressure, the tremulant is engaged to
quickly release air from the regulator at short, set intervals. This
creates a momentary drop in pressure. This up and down oscillation
of air pressure causes the pitch of the pipework to change, creating
a pleasant vibrato, much the way a talented vocalist controls their
voice.
Proper adjustment
of the tremulants is perhaps the most important aspect of an
excellent sounding instrument. It is also the most subjective
process involved in the tonal finishing of an instrument. There are
numerous ways of controlling the depth, shape, and speed of a
tremulated system. The end result must be well-suited to the pipes
it serves, but also must work in harmony with the other tremulated
systems in the organ. Think of it in terms of all the voices of a
choir working together to form one cohesive sound.
For more details
about The Mighty Wurlitzer, click on the links below:
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