The accompanying image is taken from Dom Bedos’ ‘ l’art du Facteur d’ Orgues’ (1776), and shows, among other things, a single organ-blower, operating one of three ‘feeders’ – or possibly, pumping two of the levers together, while an Organist, using a Manual and the Pedals, is keeping a vigilant eye on the blower. There is a square-shaped ‘Conveyance’ to take the wind towards the pipes. Not, as it appears to be, on the wall, is a figure showing how the movement of a Pedal, through a series of levers – pull-downs, trackers, backfalls – will open the ‘Pallet’ (the dark block ‘b’), a sprung, leather-covered valve, that will allow wind into the ‘Windchest’, and to the relevant pipe, but with a ‘regulator’ interposed (‘17’), to act rather like the smoothing condenser capacitor in a power-supply, Again, as far as I know (‘despite Brexit’) the pressure is normally expressed in ‘inches of wind’(as it were, the Voltage), measured by the water-level in a simple U-tube manometer. Often, in a pipe-organ, the large amount of floor-space taken up by the instrument is because the Reservoir will be a very large set of bellows, the upper surface covered with cast-iron weights (often proudly bearing the Builder’s initials), perhaps assisted by a set of steel springs.
If you look closely at the Dom Bedos illustration, you can see, near the top, a series of thin, projecting bits, like the slats of blinds, but horizontal; if you now look down and to the right, you can see a set of tubes attached to a board: this is the ‘Roller-board’, which transmits the motion initiated at the key or pedal to the pallet for that pipe, splaying out to accommodate the very different distances between pipe-feet, compared to keys or pedals, or to off-set it. Those ‘slats’ I drew your attention to, are the ‘sliders’ – slender mahogany boards, which move in grooves on the ‘wind-chest’, enabling a whole Rank of pipes to be allowed to ‘speak’, or not (hence ‘stops’, as in ‘…pull all the stops out.’). In the illustration here, only one stop is ‘Drawn’, so only one of those six ‘ranks’ (‘Stops’) will be allowed to speak. A mere six stops, given the usual ‘compass’ of 56 notes, will mean extremely carefully piercing and countersinnking 336 holes in the soundboard, with 56 corresponding ones in each slider: notice that the illustration obscures two things – that there will be far more than a mere ten pipes to each rank, and that for even weight-distribution and for others reasons (two pipes planted in close proximity and tuned a mere semitone apart, will tend to argue with one another – as well as hindering the tuner’s access and ability to tune) they will typically be arranged (‘planted’) in whole-tone order, with a ‘C side’ and a ‘C# side’ – hence the strange scale, if you’ve ever heard a tuner at work:
C [‘nex!’];D [‘nex!’];E [‘nex!’]; F# [‘nex!’]; G# [‘nex!’];A# [‘nex!’];C. In keyboard-terms, it’s: white; white; white; black; black; black; white… I’ll probably get into trouble for the under-representation of blacks.The ‘nex!’ being the muffled cry from the internals of the organ, to tell the ‘boy’ to move to the next note. Once he’s satisfied with the tuning of all the ‘C’ side of the ranks, he’ll then move to the ‘C#’ side, when the scale will be: C#;D#; E#/F; G; A; B; C#. So that’s black; black; white; white; white; white; black: I’m definitely in trouble! Well, we all know how a piano-tuner works – fitting his ‘hammer’ on to the tops of the wrest-pins, and gently yanking it to get the strings sounding as one – but how does the Organ tuner do it [scope for one of those car-stickers: Organ-tuners do it…. Well-temperedly…]. Unlike an actual Trombone, which changes the pitch by means of the slide, how can one of those many pipes – from just an inch or so up to sixteen-feet – get tuned? For ages, the tuner had a simple device – a solid cone and a hollow one conjoined; with this, he could squash the top of a pipe to make it, in effect, shorter, or open it out for the opposite. This would not be very kind to those ‘feet’, and older organs still bear the marks of generations of squishing/reaming. In any case, with unyielding zinc, this wouldn’t work at all. So, flue pipes these days are given little collars that can be tapped up or down: ⇐ comme ça. You remember ‘ears’? Some pipes are tuned by means of these: flaps of ‘metal’ on either side of the mouth can alter the pitch (+/- ¼ diameter – remember?), so the tuner gently adjusts these – knowing that his own presence (on the ‘walkway’ or ‘passage-board’) can affect the sound. Wooden pipes – flutes, often – might have a little flap of ‘metal’ at the open end, which must be folded back or unfolded to tune the pipe; then, there’s stopped pipes… Close the top of a pipe, and it thinks it’s twice as tall, so sounds an octave lower: with these, there’s a stopper, that’ll need to be pushed down or pulled up: typically, the Pedal ‘Bourdon’ that gives a soft ‘woofy’sort of sound, has just such, while, to synthesise the effect (felt, rather than heard), the lowest notes of the 32’ pedal, often are ‘acoustic’ or ‘derived’ – two pipes sounding harmonics of the note, to bamboozle the ear into ‘hearing’ the desired Fundamental tone. Similar economies of space, as much as expense, can be made with the lowest notes of other stops, where the rank with the alluring name of ‘Salicional’ (think, Salix, a Willow, so slender are the pipes) will end at ‘TC’ – Tenor C , rather than going down another octave. On its own, the Salicional is so reticent a sound, as to be inaudible to English ears (Sir Thos. Beecham, ‘…The English dont’t like music: they just like the noise it makes.’), but often, next to it, it a yet more intriguingly named one: ‘Voix Celeste’, or even ‘Unda Maris’ – ‘a Heavenly Voice’, the one, ‘a Wave of the Sea’ the other. Draw the two together, and the so-reticent Salicional wafts tremulous, wavery sounds into the furthest recesses of the largest Cathedral: traditionally, this is done by tuning the ‘Celeste’ rank slightly sharp of the Salicional, the ‘Unda Maris’ slightly flat (… or is it the other way round…?). If the sound of the Diapason is the sound we ‘hear in our heads’ when the word ‘Organ’ is used, ‘Sal. + V.C.’ is the sound we hear when on our knees – perhaps at The Consecration – or a skilful organist might employ for the words ‘Oh, still, small voice of calm’, having, no doubt, worked up to the ‘earthquake, wind, and fire’ by drawing out reeds and mixtures, one by one then using a ‘cancel’ button, or a ‘combination piston’, or, by hand, pushing in stop after stop, and closing the Swell-box – of which things, perhaps more anon.