Our organ pipe (shown below; coffee mug shown for size comparison) is roughly the same as that described on the webpage here or in this video .  We've made only a few changes in the choice of materials so that it can be fabricated very predictably.  You might notice that these references describe making a recorder, and you may wonder if you've come to the right place!  But, with the exception of the finger holes, a recorder and an organ pipe are identical! Our own video (condensed for quick presentation to a large group) for this project can be found at www.sci-experiments.com/organ_pipes/Organ_Pipes.mp4






A Review.

Pipes in a traditional large pipe organ are either "reed" pipes (in which the vibrating element that modulates the air velocity at the pipe mouth is a reed) or flue pipes (in which the vibrating element is an unstable air jet created by a flue).  We'll be making a conventional "flue" pipe which, coincidentally, is really no different from the "pipe" that is a recorder.

All flue pipes consist of an air jet or "windsheet", a "mouth" across which the air jet flows,  a "lip" against which the air jet is directed, and a pipe, which may be open or closed ("stopped") at the far end.  The "natural modes" (tones) of the pipe are mostly determined by the pipe length, with corrections for "end effects" caused by the finite width and depth of the pipe.  Which tones are produced depends in a very complicated way on the dimensions of the air jet, the pressure which drives the jet, the dimensions of the mouth and the placement of the lip.  In our pipe, we've preselected the pipe and air jet dimensions to allow the pipe to sound as both an open or closed pipe,  and to allow the fundamental, second and third harmonics to be sounded.   The size of the mouth is adjustable, and this adjustment changes the balance between the fundamental and the harmonics.

Our Pipe

The key to the fabrication of our pipe rests in the choice of the pipe inside diameter and wall thickness.  The primary consideration was to select pipe material into which can be fitted a wooden dowel of standard size.  The pipe we use has an inside diameter of almost exactly 7/8" (which matches the diameter of wooden doweling available at the local (Palo Alto, CA, USA) hardware store).  Next we need to select pipe that has a relatively thin wall.  This is partly because the wall thickness controls the air jet thickness and partly because a portion of the pipe is used as a cap over the air jet.  If the pipe is too thick, it makes the air jet too thick and it makes the air jet cap too stiff for easy installation.  Our pipe of "Nominal Pipe Size" of 3/4", has an outside diameter of 1.050" which results in a wall thickness of .087".

Conventional PVC pipe (so-called Schedule 40 and Schedule 80 as per US standards) available in the typical hardware store does not have the right wall thickness and results in an air jet that is too thick for a good organ pipe.  The author of the pipe described in http://profs.sci.univr.it/%7Egonzato/whistle/index.html
has procured his PVC pipe in Europe, where one may find thinner wall pipe in the local hardware stores.  Additionally, wood dowel in metric sizes may be a closer fit to the existing pipe.  At any rate, we used the Harvel pipe (http://www.harvel.com) listed below in the list of materials.  In Northern California, the distributor recommended by Harvel is:

Viking Supply
30996 Santana
Hayward, CA   94544
510-429-7295

The corporate website is www.vikingcorp.com and they have many distribution centers.

For our typical Noon Science group of 100+ kids, we ordered 150 feet of pipe in 15 foot lengths at $0.61 per foot.

Alternative:

The PVC pipe in our materials list is sometimes difficult to find.  An alternative is to use 1/16" wall clear acrylic plastic tubing:  it is available in 1" outside diameter.  Shops that carry this tubing also typically carry (or can obtain) 7/8" diameter solid acrylic rod.  Cutting acrylic plastic rod and tubing is a little more difficult that cutting PVC, usually requiring more specialized saws, especially if done in large classroom quantities.

Materials:

1.  NPS ¾", SDR 13.5, PVC or CPVC pipe.  One possible source is Harvel Pipe: Harvel Blazemaster 2000 3/4" SDR-13.5 CPVC 4120 Sprinkler Pipe UL Listed 2N95 175 PSI @ 150F    ASTM F442  (Listed CPVC Pipe for Underground Water Mains).   While this pipe is a nominal 3/4" pipe size, it's outside diameter is 1.050" and it's inside diameter is 7/8".
2.  7/8" diameter hardwood dowel.
3.  8 ½" x 11" Bond paper cut to 8 ½" x 6" inches
 
Tools:

1.  Hacksaw with a fine blade or Xacto hand-saw (X75300 saw set).
2.  Clamps or vise for securing the tube and dowel to your worktable while cutting.
3.  #120 to #200 grit sandpaper.
4.  Ruler or tape measure.
5.  Pencil or indelible ink felt pen.
6.  Ice cream stick


Assembly:

CAUTION!
These assembly steps are probably appropriate for 5th grade students and above.  Below these grade levels, we recommend that adults perform some of these fabrication steps in advance, especially those involving the use of sharp saws.

1.  Cut off a 25mm length of the wood dowel.  Cut off 25mm and 275mm lengths of the PVC pipe.




2.  Sand all ends flat.




3.  Draw this pattern on the end of the 11" PVC pipe (10mm wide x 38mm long).




4.  Use the hacksaw or Xacto saw to cut along the parallel lines.  Cut inside the lines so that the rough edges may be sanded smooth afterwards.  However, if you use the Xacto saw, the edges will be very clean, so you may wish to simply cut right along the lines.




5.  Gently bend the piece of plastic until it breaks off.




6.  Sand the "lip" of the pipe and the sides of the "mouth" flat and straight.  Use a square file for sanding the lip.  Note that in our video, we start with pipe into which this slot has already been cut by a machine shop.  This saves us lots of time when we're building organ pipes in mass quantities for elementary school kids.




7.  Take the short length of pipe that you cut off in Step 1 and slice out a section of this pipe by making two cuts at 90 degrees apart.  Sand the edges of the cut section smooth.  This forms the "cap".




8.  Slide the wood dowel into the end of the pipe.
.




9.  Snap the cap over the pipe.  Align the edge of the cap and dowel at the mouth.  Test your organ pipe by blowing into the end.  You should be able to make at least two different tones by blowing harder or softer.  Adjust the dowel and cap up and down along the length of the pipe to observe the effect.  Make small adjustments.




14.  Now remove the cap and dowel.  Fold a piece of the sandpaper around an ice cream stick or similar flat piece of wood, and use it to file an angle onto the lip.  Try to keep the edge of the lip straight as you sand (actually, my preferred tool for this is a square file).  Reassemble your organ pipe and test it each time you make small steps in sanding. 




15.  Practice making different "overtones" with your organ pipe.  Blowing gently will make a low-pitch "fundamental" while blowing harder will make a higher pitched overtone.  Also try putting your hand tightly over the end of the organ pipe.  You should be able to make a note that is one octave below the note that you can make with your hand removed.  You can also change the harmonic content by changing the height of the mouth (by sliding the cap and block together).  "Shorter" encourages higher overtones.
 For example,  we'll start with the "mouth" set up to it's full height.  The sound samples on the right show the sounds that can be obtained by blowing progressively harder.  The audio samples are mp3 files and a Quick Time plug-in for your browser should play them automatically when you click on the highlighted link.

Mouth at a full height of 10 mm.  The fundamental and one overtone may be produced.

Low Pressure sample 1
Medium-to-High Pressure sample 2

Mouth at a height of 7 mm.  The fundamental and two overtones may be produced.

Low Pressure sample 3
Medium Pressure sample 4
High Pressure sample 5

Mouth shortened to only 5 mm.  The fundamental is hard to excite, but the overtones are really ear-splitting. Three overtones are now possible.

Low Pressure sample 6
Medium Pressure sample 7
High Pressure sample 8
Very High Pressure sample 9


16.  Now you can make your organ pipe tunable; a sort-of trombone organ pipe.  Roll the bond paper very snugly around the organ pipe to make an 8 1/2"-long paper tube.  Tape the paper securely to itself, but allow it to slide along the outside of the pipe.    You can mark the position of the paper tube that creates notes that can be found on the piano.



Place a mark 4 cm from the top of the cap.

Place another mark at 8.5cm. Keep on going and put marks at 11.5 cm, 17 cm and 24.7 cm.


17.  Lots of useful information about the process of constructing more elaborate organ pipes can be found at

http://www.rwgiangiulio.com/