Pipe Organ

Overview

A pipe organ produces sound by blowing pressurized air through tuned pipes, one pipe per note per timbre. A modest church instrument of 36 ranks contains about 2,100 pipes ranging from a 4.9 m open wood bass to mixture trebles shorter than a finger. The player sits at the Console, selects timbres with Stop Knobs, and plays two 61-note Manual Keyboards and a 32-note Pedalboard. Keys open valves in the Slider Windchest; stops decide which ranks of pipes those valves feed.

The organ described here uses the classic combination found in most new instruments: mechanical Tracker Key Action for touch, electric Electric Stop Action for registration, and a fan-blown Wind System in place of hand-pumped bellows.

Pipes

There are two sound generators. A Flue Pipe Rank works like a recorder: wind entering the Pipe Foot is forced through the slit between the Languid and lower lip, and the resulting air sheet flips in and out of the Pipe Mouth, locking onto the resonance of the Flue Pipe Body. Pitch follows length, an open 8-foot C pipe is about 2.4 m, and scale (diameter relative to length) sets the tone, from broad flutes to keen strings. Each pipe is tuned at its Tuning Slide and stands in a Rack Board.

A Reed Pipe Rank generates tone with a curved brass Reed Tongue beating against the slotted face of a Shallot inside the Reed Boot. The Tuning Wire clamps the tongue's vibrating length and is tapped up or down to tune. The Reed Resonator above the Reed Block filters the buzzy source spectrum into trumpet, oboe, or clarinet color. Reeds drift with temperature faster than flues, which is why they are tuned last and often.

Pipe metal is a tin-lead alloy; high-tin "spotted metal" (around 50% Sn) is standard for principal ranks, and the polished Facade Pipes in the case front run 70–90% tin. Large basses are wood.

Wind and chests

The Blower Motor, a 1.5–3 kW centrifugal fan, feeds the Reservoir Bellows, a weighted double-rise bellows that regulates delivery to a steady 70–100 mm water column. A Curtain Valve throttles the blower intake as the reservoir fills, and Concussion Bellows on the Wind Trunks absorb the pressure dip when a full chord lands. Unsteady wind is audible as pitch wobble, so regulation quality matters more than blower size.

Each division sits on a slider chest. The Chest Grid is divided into one channel per key. Pressing a key opens that channel's leather-faced Pallet Valve via its Pull-Down Wire, flooding the channel with wind. Whether a given rank speaks depends on its Slider, a perforated strip between grid and Toe Board: holes aligned, the rank is on; offset by a few millimetres, it is silent. The slider chest thus implements the key-AND-stop logic mechanically, with Coil Springs returning each pallet.

Actions

In the tracker key action, motion travels from key to pallet through Trackers, thin strips loaded only in tension, turned through corners by Action Squares and shifted sideways by Rollers on the Roller Board, since the chest is far wider than the keyboard. Tracker Regulators take up slack. The appeal is control: the player feels the pallet open and can shade attacks, something electric key actions do not transmit.

The stop action is electric. Each Stop Knob signals an Microcontroller-based combination controller on the console Bare PCB, which drives Slider Solenoids through Relays from a 24 V Power Supply; a Wire Bundle with multi-pin Connectors links console to chests. Combination Pistons recall stored registrations, moving dozens of sliders in about 50 ms.

Enclosure and case

One manual division is built inside the Swell Box, a thick-walled chamber whose front is a set of Swell Shutter louvres worked by the Expression Shoe. Closing the shutters drops the division's level by 15–20 dB, the organ's only continuous dynamic control. The Case Frame carries the full eight-to-fifteen-tonne instrument and projects the sound; tuning stability depends mainly on the room, since pipe pitch moves about 1 cent per 0.6 °C.