Reed pipes have actual reeds inside them which vibrate when air goes through the pipe, just like a clarinet or a bassoon. Reed pipes supply the "trumpet" and clarinet/oboe sounds on an organ, which I realize is a bit confusing, since a trumpet is not a reed instrument--but on an organ it is. Reeds have a wonderfully nasal sound, as in this french carol I played a couple of Christmases ago. If you hold your nose and say hao hao hao in an exaggerated English-imitating-French manner, you get a vague idea why the French prefer reed stops--they sound a bit like the organ holding its nose, or having a cold, or--but I'm not being very kind to the French. Let's just say they sound delightful.
Daquin: Noel VII
The remaining pipes have no such reeds, and simply make sound as the column of air moving through the pipes vibrates, and the sound escapes out of the aperture at the other end (wherever that is). These are known as "flue" pipes. The first time I saw that term I thought it was a typo. Don't you mean "flute?" I thought.
But flute pipes are something else. They are, in fact, composed of "flue" pipes, but they are only one kind of "flue" pipe. Chimney flutes, for instance, are from the "flute" family of the organ, but they, not being reeds, are composed of simple "flue" pipes.
Hmmm.....flue.....chimney.....I wonder if there's a connection.
Indeed, "chimney flute" pipes (charming name for one particular flute stop on an English organ)--chimney flute pipes do have little chimneys on top--causing the pipes to be partially capped, and forcing the air out through a small hole in the middle:
Unless I'm mistaken, I think the wooden pipes above with those little chimney extensions qualify. On the other hand, chimney flutes can be made of either metal or wood, and the chimney extensions can sometimes actually go down into the pipe instead (so says the encyclopedia of organ stops). So the pipes below may also be them. I'm not the expert, here. I'm just your friendly neighborhood organist. But I'll ask our organ people....
Actually, our organ speaks German, and so the 8 foot flute stop which the English give the rustic appellation chimney flute is instead known as the rohr flute.
It's a lovely sounding stop, although I have to say I actually prefer the "covered" flute--not half covered, but covered completely. Our organ has an 8 foot flute stop on each manual, and the one on the upper manual is a "bourdon" (from the French for "buzzing," apparently) which has a similar sound to the rohr flute, but because the pipe is capped, the air travels up the pipe and then back down---travelling 8 feet when in fact the pipe is only 4 feet tall. It has a slightly darker sound.
Both of these stops can be heard in this little piece by Pietro Yon, who is most famous for the song "Jesu, Bambino" which you hear a lot at Christmas. Mr. Yon wrote this "Toccata" for the "primitive organ" which, you'll recall from earlier installments, basically just consisted of a flute stop or two. In this piece, the only sound you hear is a simple flute stop--well, that and a truck going by near the end. Mr. Yon wrote into the score a pause big enough to drive a truck through and, well, I still have thoughts about throttling that guy for barreling down Prospect Avenue at just the wrong time.
Anyway, have a listen.
Yon, Pietro. Humoresque l'organ primitiva: Toccatina for Flute