>>There are also some organs arranged in tritones so that there is NO
 >>drawing at all with any intervals.

Actually...if such organs would be in regular 1/6 comma or some of its 
near-relatives, there *would* be drawing of the tritones.  It's a pure 
interval, 45:32, which is the same as building a pure 5:4 major third 
together with a pure 9:8 whole tone.  (For example, play such a C and F# 
together, when they've been tuned within a regular 1/6 cycle, and a 
phantom pure D and/or E can sometimes be sensed in there.  And, the 
45:32 tritone itself is especially resonant whether one is hearing 
phantom extra notes in there or not.  NB: Pipes and/or strings here, 
with decent sets of upper partials; not sine wave tones!)

Details about regular 1/4, 1/5, 1/6 -- along with some of their other 
surprising features:
http://www-personal.umich.edu/~bpl/larips/meantone.html


Bradley Lehman

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