Thu Feb 04, 2010 6:33 pm
Sorry that I haven't been able to get back before this, but the last few days have been busy!
I checked my church organ today for the mixture composition. It has two Mixtures, one on the Great, and the other on the Swell. The Great Mixture is a four rank Mixture, and is pitched at 2'. This means that the bottom pitch at the lowest C is 2', or 15, if you want to express it that way. So, for the first octave and a half, the pitches are 15, 19, 22, &26. At tenor F#, the pitches are 12, 15, 19, &22. The next octave, starting again on F# (above Middle C) is pitched at 8, 12, 15, 19. Then a half octave, from F# to soprano High C, at 5, 8 12, 15. The last octave is at 1, 5, 8, 15. This composition gives enough upper pitch to make the bass distinct. adds some power and definition in the middle range, and reinforces the regular diapason work in the upper range, which is what a good Great Mixture should do. This, by the way, is not the orginal Mixture that was on the organ, but is a reworking of that Mixture, using a new-used two rank Mixture for the bottom two pitches, and adding pipes from the original Mixture to fill out the two top pitches. The "fifths" (5, 12, 19, and 26) are softer than the "unison-octaves" (1, 8, 15, 22).
The Swell Mixture is a different story. Orginally the organ had a soft Dolce Cornet. I saw no real use for it, and the organ needed to be "brightened up". So I obtained a used Cymbale that had originally been in an Austin organ. It was pitched at 1/4', and after the first octave or two broke back in pitch every half octave, thus repeating every octave. I took some of the pipes from the Dolce Cornet and put them on the bottom end of the Cymbale, starting at 1/2', and leaving out the upper two octaves of the Cymbale, thus bring the pitch down to where, when it is coupled to the Great full Principal Chorus, it sits right on top of the Great mixture, giving a wonderfully full and bright sound. The Austin pipes are not brightly or loudly voiced, but their high pitch gives just the right amount of "top end". In the reworked Swell, I have 8', 4', and 2' Diapasons, the 8' rank being bright but somewhat softer than the 8' Great Diapason, and the 4' and 2' being voiced louder and bright, and the Cymbale works well with them.
The Choir on this organ does not currently have provision for a Mixture. I may, sometime in the future, rework a windchest to take a Mixture, moving the Cymbale to that position, and putting a lower pitched Mixture in the Swell.
I am not an organ builder, but have been studying organ registration for years. For three years I have been working on this organ, little by little bringing it up to an acceptable standard. I have listened to many other organs, and have come up with what I find acceptable for hymn-playing and Classical organ music, particularly Baroque. I do not care for G. Donald Harrison's work in this area-a lot of his mixture work was pitched too low, adding to the power of the organ, but not giving it the true classical sound. Also, he pitched the Swell Plein Jeu lower than the Great Fourniture, which might be alright for French Romantic music, but is completely wrong for either German or French Baroque, and not the best in all-round church work. A lot of newer organ builders have gone the other way, making their mixtures too high-pitched and bright. Hopefully you may find some of this worthwhile.
Michael Moore
Mike