Organ flue pipe scaling
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Scaling is the term used to describe an organ pipe's length to diameter ratio. The main pipes of an organ are flue pipes. This article describes how scaling affects their tone.
In general, the larger the diameter at a given pitch, the fuller and more fundamental the sound becomes. For example, these are representative 8' pitched stops and their diameters at middle C:
- 54.9 mm [+/-0 ht] Normalmensur
- 35.6 mm [-10 ht] thin, mordant string stop (Viole d' orchestre)
- 40.6 mm [-7 ht] broader, non-imitative string stop (Salicional)
- 46.2 mm [-4 ht] Principal stop of thinner tone quality (Violin Diapason)
- 50.4 mm [-2 ht] typical (USA) 8' Principal
- 57.4 mm [+1 ht] Principal stop of broader tone quality (Open Diapason)
- 65.4 mm [+4 ht] Flute stop of thinner tone quality (Gedeckt)
- 74.4 mm [+7 ht] Flute stop of typical tone quality (Flûte à cheminée)
- 81.1 mm [+9 ht] Flute stop of broader tone quality (Flûte ouverte)
The system most commonly used to fully document and describe scaling is Töpfer's Normalmensur, wherein the diameter of a given note is compared by means of half-tone deviations [ht] larger or smaller from a reference scale.
The reference developed by Töpfer is a rank of pipes based on:
- an internal diameter of 155.5mm at 8' C
- a mouth width which is 0.25 the circumference of such a pipe
- the diameter halves on every succeeding 17th pipe
This system can be used to produce NM Variation tables or line graphs for the analysis of existing ranks or the design of new ranks.
