In a message dated 95-12-06 00:19:01 EST, you write:

> Some of the German organs featured a rank called a
> "doppleflote" which means double flute. These were wooden with two pipes
> built into one, arranged back to back. Normally these were tuned in unison
> or sometimes slightly celeste and played simultaneously.

I fear that there may be some confusion.  And the confusion may be all mine.
IMHO, what you have here described is not a doppleflote, but a "Ludwig tone".

In contrast, a true dopplefloete is a single wooden pipe (usually stopped)
with two mouths on opposite sides.

Though the construction has passing similarity (quadrangular wooden pipe)
they are radically different.  The ludwig tone will have a septum down the
middle dividing the resonator into two distinct areas.  Tuning of a ludwig
tone is accomplished by a leaf of lead that is bent/rolled to cover the two
openings (at the top) and they are correctly tuned a celeste (one flat and
one sharp to unison pitch).  It is also possible (using a stopper) to tune
one at octaves.  Tuning them in unison would offer little improvement over a
single pipe, as the sympathy (especially with a common body) will negate much
of the second pipe's sound.

You did not solicit my comment, so I offer it only as my own, unsolicited
opinion, in hopes that it is helpful.  Please correct me if I misunderstand.

Thanks!¶
Robert