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.
Link to my main page