Making Your Own
			       PVC Didjeridu

			       By Matt Newby

     _________________________________________________________________

   Several months ago, I asked on rec.music.makers.builders, and in the
   didjeridu digest, what the measurements were for making your own
   didjeridu. With the leads you provided, and the help of a couple of
   physics books, I worked out the formulas for calculating the length of
   a pipe to produce a fundamental of a specific note. I then obtained
   some 2" Schedule 40 PVC piping and was able to make some decent
   sounding instruments. I borrowed a chromatic tuner to validate that my
   calculations were correct, and was pleasantly surprised to find out
   that they were right on. After a little bit of effort learning the
   instrument, I've mastered the basics enough to feel comfortable
   playing as a solo didj in our ensemble at church (raised a few
   eyebrows in the process! :-)

     * Formulae:

       Here's the measurements that I worked out for plastic pipe
       didjeridus. The formula for calculating the length of a tube,
       given that you want it to resonate at a specific frequency is as
       follows:

	 1. The speed of sound
	    V(sound) = 340 m/s at sea level (my measurements are in
	    inches, so we have to convert the speed to in/sec by
	    multiplying 340 m/s * 1/0.0254 in/m)
	    V(sound) = 13385.826 in/s

	 2. Frequency
	    The frequencies listed in the chart below are calculated by
	    this formula:
	    F(note - 1 semitone) = F(note)/(2^(1/12))
            (that's the 12th root of 2 in the denominator)
	    Where F(A) = 220 Hertz

	 3. Effective Length vs Actual Length
	    The formulas for calculating the resonant frequency of a pipe
	    were in three catagories: both ends closed, both ends open,
	    and one end closed. The didjeridu is in the last category.
	    This means that one end is where the pressure disturbance is
	    created, and is sealed to the atmosphere around it. The other
	    end is open to the atmosphere and the pressure must drop to
	    atmospheric pressure very shortly after leaving the end of
	    the tube. How far out does the pressure node go? Well, it
	    extends beyond the end of the tube at a distance roughly
	    equivalent to the interior radius of the tube. With the pipe
	    I was using, this is a little short of 2 inches.
	    L(eff) = L(actual) + DeltaL(radius of the tube)


		 Figure 1
	  Single End Closed Pipe

| ----------------Length of Pipe---------------- |
| -------------Effective Length of Pipe------------ |
				 Delta Length -- |  | --

+------------------------------------------------+
|						 :-\
  - (lip reed blows here)			 :  |
|						 :-/
+------------------------------------------------+
		 4. The Final Formula...
	    Length = (V(sound) / (2*freq)) + interior radius of the tube

     * The Chart:



 Note | Freq (Hz) | Length (in) | Made
------+-----------+-------------+------
  G   |   97.999  |    69.296	|   Y
  G#  |  103.826  |    65.463	|   N
  A   |  110.000  |    61.845	|   Y
  A#  |  116.541  |    58.430	|   N
  B   |  123.471  |    55.206	|   Y
  C   |  130.813  |    52.164	|   Y
  C#  |  138.591  |    49.292	|   N
  D   |  146.832  |    46.582	|   Y
  D#  |  155.563  |    44.024	|   Y
  E   |  164.814  |    41.609	|   Y
  F   |  174.614  |    39.330	|   Y
  F#  |  184.997  |    37.178	|   N
  G   |  195.998  |    35.148	|   Y
  G#  |  207.652  |    33.231	|   N
  A   |  220.000  |    31.422	|   Y
     * Equipment:

       I borrowed the use of my friend's Makita power mitre saw. I find
       it indispensible in cutting the PVC. It slices cleanly through the
       pipe, leaving almost glass-smooth perpendicular angles on the pipe
       and lots of coconut-like confetti all over the floor (FUN!). The
       saw plus a tape measure and a pencil and you should be in
       business. My first attempts a cutting the pipe required a hack
       saw. This works, in the sense that the pipe gets cut, but leaves a
       very imprecise edge. Precision is important in the construction of
       my set of didjs. I also checked the pitch by observing the display
       of my friend's chromatic tuner.

     * Construction:

	 1. Mouthpiece
	    I deviated from the traditional method of forming a
	    mouthpiece with wax, and chose to construct interchangeable
	    mouthpieces from two or three couplers, also made out of PVC.
            I used a coupler that dropped from an exterior diameter of 2"
            to an exterior diameter of 1.5". I then inserted another
            coupler into the 1.5" side that further tightened the
            interior diameter to 1". I find that this arrangement is
	    comfortable for playing all the didjs lower than the D#. I
            got ahold of two other inserts to go from 1" to 3/4" and from
            1" to 1/2". These allow me to play the higher pitched
	    instruments with ease. The side advantage is that they are
	    removable and interchangeable so they are extremly easy to
	    clean and convenient for sharing with other players.

			       Figure 2
			      Mouthpiece

			       +-------+
			      +-+-----+-+
			      | |     | |
			      +-+- - -+-+
			     /	+-----+  \
			    /		  \
			   +- - - - - - - -+
			   |		   |
			   +---------------+

	 2. Pipe construction
            I did not make multiple didj's of full length. I purchased
            some 2" to 2" connectors and cut the didj's as follows: I
            made two solid "base units" which produce the 220Hz A. Then I
            cut the other pipes so that, when attached to the "base unit"
	    with one of the connectors, the overall pipe length is as
	    displayed in the chart. Except for the 98Hz G didj, all the
            other pipe pieces are smaller than the A "base unit". This
	    makes for a much smaller load to carry when transporting
	    them. (Since I also play a small conga, harmonicas, melodica,
	    clave, shakers, etc., and soon will be playing a djembe,
	    portability is very important to me!)
	    This method of construction also lets me haul out the two
            "base units" along with two extensions and another player and
	    play didjchords!

	 3. Cost
            I don't think I've ever made a cheaper instrument. I can pick
            up 10' of the 2" PVC piping for $2.41 each. The couplers and
	    connectors are a little more expensive individually, but
            overall, my entire didj set probably didn't set me back more
	    than $20.

     * Conclusions and Questions:

       I've had a blast with these things so far. PVC is so inexpensive
       that even a novice like me can afford to make mistakes in
       construction, and not feel guilty about throwing away my flubs.
       I've found that Acetone does an admirable job of taking the pink
       lettering off the pipe without damaging the plastic in the
       process. I haven't had the time to explore decorations yet, so if
       any of you have any idea what kind of paint would adhere to the
       plastic, please let me know. Also, do you have any leads on where
       I can find some "appropriate" designs to paint on the tubes, as
       well as some indication of what the designs mean to the
       Aboriginals?

       I've also started constructing my didj's with some PVC traps and
       larger couplers allowing me to put a right angle bend in the pipe
       and get the "business end" of the didj pointed back at me. This is
       very nice to have when you've got an electric guitar amp on one
       side, a bass amp on the other, a drum set behind you, and a bank
       of monitor speakers in front. Let's face it, the didj isn't
       inherently as loud as the electrically amplified instruments. It
       also allows me to point my head up instead of down while playing
       so that I can see our worship leader. The larger couplers are put
       together to make a kind of bell about 4" across that slightly
       amplifies the sound produced when playing.

       While the PVC version of the Didj doesn't produce as warm or
       mellow of tones as a "genuine" Austrailian Aboriginal Didjeridu,
       its cost, and the ease of working with it make it an excellent
       choice for beginning players. For the non-discriminating ear of
       those who haven't been exposed to wooden didj's, I've found that
       many people recognize the characteristic sounds my plastic didj's
       produce, and can even cite movies and advertisements where they've
       heard the sound before.

       If you are just starting out, I recommend you get ahold of some
       instructional tapes, and invest in a little PVC to learn the
       basics. You can go a long way with plastic before you decide you
       want to spend the money for a wooden didj. I hope this article
       gives you the information you need to get started with this
       wonderful instrument.

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