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.