Bart Roskam wrote in 080606 MMDigest:

> I tried it with a circular hole and with a D-shaped hole.  I also
> attached a sharp (aluminum) piece in the hole, to give a sharper
> edge on which the air can start to tremble.  Nothing worked though,
> and I'm now clueless as to what to try next.

These sound like the pipes I built for my calliope.  Some pictures
are at http://rpartos.org/calliope.html

The pipes are one piece, including the base.  They are made by cutting
a gap about 2/3 of the way through the PVC tubing.  I used a table saw
to do this, making repeated cuts until I achieved the correct gap width.
I used wood dowels for the fipples as I could insert and attach a dowel
plug before I cut the gap; this insured the top of the languid or fipple
was flush with the bottom of the slot.  A pipe can be made this way in
about five minutes.

Fine tuning is accomplished with a pipe cap on the end of the pipe.
The pipe is attached to the windchest using inverted PVC pipe caps,
in which a large hole has been bored.

These pipes are for 1.75-2" water gage air pressure.  If you use
a different pressure you will have to modify H, the slot height.
Two good references regarding the dimension H are

http://mmd.foxtail.com/Tech/isingform.html and
http://mmd.foxtail.com/Tech/isint.html

The working formula I came up with for the slot was

  H = 470*(P/F^2)^1/3

where

  P is the pressure in inches of water
  F is the frequency in Hertz
  H is the height of the slot in mm

Let me know if I can help further.

Dick Partos