„The largest pipe organs in the world”, w: „The Vox Humana”, An affiliate of the American Guild of Organists, September 30, 2018.
Considering which organs are the largest leads to a major issue of their comparison: objectively, what makes one organ larger than another? The existing literature on the subject and the various classifications present the rankings of selected instruments on the basis of various criteria are often inaccurate, and there is no comprehensive approach to this subject in literature of the subject.
There are many methods of classifying organs in terms of size, and each has some degree of imperfection, because each instrument is unique in its own way. The following is a summary of the most common criteria for classification of organs in terms of size.
The most common criterion for classification of organs in terms of size is the number of stops. However, stops are extremely diverse in terms of material and construction (wood/metal, labial/reed), the amount of material used (a 2' flue stop versus the same kinds of pipes at 16ʹ), and the degree of complexity (one rank versus many ranks). In addition, some organs have stops in which each key plays only one pipe of the scale; some use combined voices — using pipes of other real stops to create an imitation (e.g. an acoustic stop Subcontrabass 32' achieved with a combination of real stops Subbass 16' + Quintbass 10 2/3'); extensions — adding a missing octave (or more or less) to the top or bottom of a rank of pipes to give a higher or lower pitch for a specific interval (e.g. adding an additional low octave to an 8’ principal could result in a 16’ principal stop in electric action instruments); and transmission — voices that use a single row of pipes to obtain a given sound in two or more sections (one rank of pipes could result in a 4’ principal and a 3’ principal).
The second criterion for comparing size is the number of pipes. This is problematic because practically, verifying the actual number of pipes in each instrument can be nearly impossible (some instruments have tens of thousands of individual pipes). In addition (though to a much lesser extent), there is the issue of the distinction of playing pipes from muted/dummy pipes (those placed in organ façades only for aesthetic reasons).