q WHY A SLIDE DIDJERIDU?
Two years ago, I made my first plastic didjeridu following Matt Newby's guide on this website. However, I found playing in only one key too restrictive for musical accompaniment, and so decided to adapt his ideas to build a tuneable, slide didjeridu; that is, one tube inside another close-fitting tube, as in the trombone. It should be noted that this didjeridu cannot be played like a trombone, to play a melody line; it's solely so you can alter the basic pitch to play in different keys.
Apart from greater musical flexibility, this arrangement also offers beginners the ideal practice instrument on which to master circular breathing, or even just learn the basic drone. This is because every pitch requires a slightly different amount and strength of breath, which is dependent on the length of the tube (very low notes require a much slower, more gentle breath, while very high ones need a good "toot"). The beginner can then alter the length of the slide didj to find the pitch that is easiest to play for him/herself.
Furthermore, the combination of the two tubes together alter the basic sound or timbre of the didjeridu in the same way that nature's randomly twisted wooden didjeridu's do, or Ron Sill's tapered (conical) didj's do, but in a slightly more controlled way.
q SOME SLIDE DIDJ THEORY
A single piece of tubing 154 cm long will produce a pitch of A (see Figure 1). However, a slide didj where (for example) the inner tube is 97 cm long (producing an F pitch on its own) combined with a fully extended outer tube, will not produce the same A pitch at 154 cm as you would expect, but at 174 cm; 20 cm longer than the single piece of tubing! (Fig. 2) This extra length means this note requires less breath, and is therefore considerably weaker and more difficult to sustain.
So for any inner tube length, as the outer tube is gradually extended, the notes become increasingly longer and weaker than if just using a single piece of tubing. This phenomenon continues until the outer tube is fully extended (when the inner and outer tube lengths are equal), where it is at its most pronounced. However, this is not necessarily a bad thing, as the timbre is also gradually altered to produce a more wooden-type quality, but only at a certain point; roughly when the slide is extended halfway. Unfortunately, you cannot have this "natural-sounding" timbre over all pitches.
Since very thick inner tubes pronounce this phenomenon even more, it is therefore relative to the thickness of the inner tube (i.e. the difference between the inside diameters of inner and outer tubes). You would think then, the thinner the inner tube, the better, as the phenomenon effectively reduces the range of the slide didj by making the lowest notes too weak to be playable. Unfortunately, while an inner tube only 1 mm thick does minimise the phenomenon, it also almost completely strips it of any "natural" timbre, and sounds too artificial for my liking (it sounds like a plastic pipe, basically). I feel that a certain amount of this "organised randomness" is necessary to give the slide didj some "life", beyond what a single piece of tubing can offer.
q RANGE OF THE SLIDE DIDJERIDU
So only a limited number of pitches are actually playable, which are determined by the length of the inner tube. A slide didj with an inner tube of D pitch can reach low G, although A is the lowest pitch reached comfortably (and actually produces the best timbre of all possibilities on this inner tube). Similarly, an E (or F) inner tube can reach low A, but B most effectively, and a C inner tube can reach low F#, but G# most effectively.
Before you build your slide didj, then, you must decide on its range; i.e. the keys in which you will most likely be playing regularly. You will not be able to build a slide didj that will cover all pitches satisfactorily (e.g. low A to high G#). The greater you try to make the range, the more the pitches at either extremity will suffer.
As I primarily accompany traditional (or some would say, not-so-traditional!) Irish music with my didj, I tend to favour the keys of D and A. Using an inner tube of D pitch, therefore, I can also play in A most comfortably, Bb and C comfortably, and can reach low G adequately. (However, it should be said that the low G pitch is so low that a single piece of tubing of the correct length (173.5 cm or 68 5/16 inches) would be more effective here.) Of the pitches I cannot reach, F is uncommon in trad music and is not missed, but the E pitch is more commonly used. I experimented with an inner tube of E pitch, but found it to be far less satisfactory overall; while I could (just about) reach all pitches common to trad music (low G to high E), many tones suffered. The low G became too long and weak to be playable, the high E on its own "tooted" too much, and the low A was far inferior to its counterpart on the D inner tube.
If you are only going to build one slide didj, I would recommend the D inner tube combination as the best overall compromise. If you really must have a wider range, it would be far better to build two slide didj's of different inner tube lengths; one for deep, rich low notes (with a D or C# inner tube), and one for the (less pleasing) high notes (with an F inner tube), and consider even using a single-piece of tubing for the low G. (To give the high notes a more natural timbre, it should be possible to build a really short didj (with a thick inner tube), which when fully extended should make the E and F pitches more pleasing, although I haven't tried this myself.)
q CHOOSING THE PIPES
The first consideration is obvious; the inner tube must fit snugly inside the outer tube. If you bring a tape measure with you to the DIY shop, you can save yourself a bit of hassle, as these tubes are typically 2 to 3 metres long. However, before you pay, make sure they do actually physically fit inside each other. If you can't find a snugly-fitting pair (which is quite possible), don't worry, there's help later.
Try to choose pipes that have completely smooth insides (for both inner and outer tubes) so moisture can run freely. The first didj I made was from a very hard, black material (possibly ABS) that had a slightly matt finish to the inside. Although it had a good loud tone, moisture used to collect so quickly that the instrument was rendered useless after five minutes playing as I just got muffled, gurgling noises! A good test is to shine a pocket torch into the pipe; if it looks totally smooth (i.e. shiny) inside then you won't have any problems with moisture. If the finish is even slightly matt however, you could have problems. Alternatively, insert a moistened finger into the pipe and draw it back out checking for any slight roughness, but it's easier to see the matt finish than to feel it.
If you have the luxury of making further choices, a wide inner tube will produce a richer sound (i.e. greater harmonic content) than a narrow one. I would recommend an inner tube of at least 4.5 cm (1 3/4 inches) inside diameter. However, avoid using very thick pipes for both the inner tube (2-3 mm (1/16th of an inch) is ideal) and outer tube (for aesthetic reasons). I used a very thin piece of drainpipe (1mm thick) for my outer tube.
Finally, if you're still stuck for choice, select pipes of the same coloured material where possible (again from an aesthetic point of view).
q CUTTING THE TUBES TO THE REQUIRED LENGTH
PITCH LENGTH(cm) LENGTH(in) F 97.4 38 5/16 E 103.1 40 5/8 D# 109.3 43 D 115.8 45 5/8 C# 122.7 48 5/16 C 130.0 51 3/16
The different inner tube lengths are given above (these lengths will vary slightly due to altitude and temperature, so if in doubt, cut slightly longer than necessary). If you're not sure what pitch you want your inner tube to be, cut it to the C length given above and test all pitches with the outer tube (you'll have to make a mouthpiece first; see next section). If they're too low for your liking, then cut the inner tube to the C#, and so on. If you reach a length that feels pretty good, but are curious to see what it's like just a little shorter, it's time to stop cutting! Remember; you can always shorten your inner tube, but you can't lengthen it.
Once you've settled on the pitch for your inner tube, it's a good idea to cut it ever so slightly shorter than necessary, so that it sounds about half a semitone sharper (higher) than required. This is so that if the other musicians or tape recorder you're accompanying are tuned slightly sharp you can hit that pitch; you can always tune flatter (lower) with the slide if necessary.
Finally, cut the outer tube about 6 or 7 cm shorter than the length of the inner tube. This is so one hand can grip the inner tube just beyond the mouthpiece, while the other can move the outer tube. When the outer tube is pushed as far as your arm will straighten, you should roughly be at the lowest pitch that can be played comfortably (the best timbre). To reach the very lowest pitch, you will have to take your mouth away from the didj to push the outer tube that little bit further (or else just use your toes!).
q MAKING A MOUTHPIECE
The basic goal for any mouthpiece is to reduce the inner diameter of the didjeridu to a size that fits your mouth more comfortably. Using beeswax seems to be the most common way, and there are pages elsewhere on the Technical Corner on how to make them. Personally, I have found beeswax mouthpieces to be too fragile and are not consistently air-tight. They also get pretty dirty after a while and are not very hygienic, as they tend to leave bits of wax stuck to your moustache/stubble and block up your pores, bringing out a rash of spots around your mouth!
Instead, I use ABS plastic to make a permanent, durable and comfortable mouthpiece. Get any spare piece of your original didjeridu material (or wider tube), and saw about 1 cm off it to create a "ring" piece. You now need to slice a segment out of this ring, so you can squeeze the ring to fit into the main didj tube. There's actually a simple formula to ensure you slice exactly the right amount out so that the ring fits snugly into the didj:
( D - d ) x PI
where D is the OUTER diameter of the ring, d is the INNER diameter of the didjeridu, and PI is 3.14
For example, if you have a didjeridu tube 4.5 cm outer diameter, and 4 cm inner diameter,
( D - d ) x PI = ( 4.5 - 4 ) x 3.14 = ( 0.5 ) x 3.14 = 1.57 cm
You therefore need to slice a segment out of the ring 1.57 cm wide (on the outer surface) and it will fit perfectly. However, when you go to mark the segment width on the ring, take off 2 mm (giving 1.37 cm in this case, or just 1.3 cm). This is because the width of the saw blade will itself add on 1 mm for each of the 2 cuts, even if you saw exactly on your marked lines. (Just to be sure, you can take off another millimetre or two if you like, resulting in a ring piece that nearly but doesn't quite fit into the didj tube; you can then file the edges down to make it fit.)
Glue this ring piece inside the main didj tube, and if you're happy with the inner diameter width, gently round the inner and outer edges of mouthpiece and didj tube with a file for comfort on the mouth.
If, however, the inner diameter of the mouthpiece is still too wide, you can do this procedure again, gluing another, even smaller, ring inside the first. Bear in mind "d" will now be the new inner diameter of the didj mouthpiece. I used two such rings on my didj, bringing the inner diameter of my mouthpiece down to 3.5 cm, from 5 cm.
q MAKING AN INNER TUBE FIT WHERE IT SHOULDN'T !
If you have problems finding two tubes that fit nicely, the above procedure can also be used to create a snugly fitting inner tube. By using the formula above, I sliced a (very!) long section out of a piece of 1 mm thick drainpipe, squeezing and re-gluing the full length to create the inner tube from the outer tube. Bear in mind that any finishing (especially sanding) you intend doing to the new inner tube should be done before the slicing, as any work on it afterwards will affect how well it fits.
To mark two parallel lines on the tube, lay it on a flat surface, and make sure it won't roll (it will probably have a slight bend which will help you here). Looking through the tube, make a mark on the tube edge where it touches the table-top. Repeat at the other end, and cut a slight notch into both marks. Knot some thread, attach through one notch, and extend it down the full length of the tube to the other notch, passing it back through the tube and out the other end so you can hold it taut. You can now make pencil marks on the tube next to the thread, every 10 cm or so. Remove the thread, and join the dots using a ruler, to ensure a perfectly straight line. To draw the second line, measure the correct width from the first line with a tape measure, and mark. Measure again 10 cm further down, and mark again, and so on.
I used a hand-saw to do the cutting, which although is very slow going, ensures 2 very straight cuts. Smooth the edges with a file and make sure this tube (when squeezed) fits into the outer tube. You can use the outer tube as a mould to clamp the inner tube while the glue dries, but you have to work quickly. Apply glue along a 10 cm section of one edge, squeeze together and attach a roll of sellotape to the inside of the tube on the glued join. Pull the tape over the edge and onto the outside of the tube over the glued section. Ram this part into the outer tube to hold it, pull the next section of the join open with one hand, apply glue, cover with tape and ram again. It's possible to glue the whole tube like this by yourself, but an extra set of hands is useful. Use normal (clear) paper sellotape (not masking or insulating tape) as it's much thinner, and keep a wet rag handy to wipe off any surplus glue that spills out from under the tape. Once it's thoroughly dried, you can remove the tape easily, but the whole join will need to be carefully sanded to remove the excess glue. All in all, quite a bit of work, but well worth it.
q FINISHING THE SLIDE DIDJERIDU
As I mentioned earlier, if your inner and outer tubes are of the same coloured material, the didj will look better. This is because apart from sanding (using long strokes down the length of the tubes) there is not much else you can do to finish the slide didj. While I haven't actually tried priming and staining the tubes, I would guess that a painted inner tube would suffer from being rubbed constantly inside the moist outer tube. (It would be a good idea to test this first on some discarded piping before you try it on the real thing.) Of course it is still possible to stain and paint just the outer tube, but I don't think it would look as effective when fully extended. Ron Sill has got some pretty amazing results from his painted didj's though, on his finishing page. Alternatively, you could mark the other pitches on the inner tube, as I have done, at the top of the outer tube, so you have visual markers to help you hit the notes spot on in a noisy environment.
q A BRIEF NOTE ON OVERTONES (HARMONICS)
Every pitch (from any instrument) is made up of a combination of many (much fainter) other pitches, which determine its overall timbre. However, it is sometimes possible to hear these other pitches, or "overtones" individually. Guitarists can do this by lightly touching a string at a certain point while plucking it, silencing the main note (the "fundamental"), and letting an overtone sound more loudly on its own.
On the didjeridu, this can be done by placing your mouth straight over the mouthpiece, blowing very hard from your lungs so that your cheeks are puffed out while keeping your lips closed, and then letting a sudden sharp burst of air out quickly. (It's easier if you extend the didj fully first.) You should get a loud "parp" which is much higher in pitch than the usual drone. In theory, this overtone should be a 12th (an octave and a 5th) above the fundamental. On a wooden didjeridu, it is usually a bit flatter, and can even be as low as a 10th (an octave and a 3rd). This is also the case with the two-tube slide didj, which is why I feel justified in saying it gives the plastic didj a more "natural" timbre.
While it will never have all the tonal nuances of a wooden didjeridu, I think the slide didj takes the plastic didjeridu as far as it will go, and is certainly a legitimate instrument in its own right. What the plastic didj perhaps lacks in sound quality, it makes up for in durability and versatility; attributes the wooden version does not have.
With utmost respect to Aboriginal Australian tradition, (like any instrument) playing the didjeridu should be first and foremost FUN! If it's not fun, you're not doing it right! J
q A NOTE ON ACCOMPANYING TRADITIONAL IRISH MUSIC ON THE DIDJERIDU
Although Stephen Cooney (Australian-born guitarist of Irish descent) has used the didjeridu extensively in numerous recordings, a didjeridu would generally be unwelcome at a typical session. That aside, it is important to realise that not all trad tunes (i.e. instrumentals) are well-suited for didjeridu accompaniment. The minor / dorian / mixolydian modes work much better than the major keys of most fast reels. As a loose guide, if the uilleann pipes can play the drone note throughout the piece, then it will work for the didjeridu just as well.
Steve Cooney studied under David Blanasi of Arnhem Land, Northern Territory, and his style of playing in Irish music is the basic tribal style he learnt. Examples of Steve's accompaniment can be found on:
( artist / album / track title / key or mode )
Séamus Begley & Stephen Cooney / Meitheal / John Brosnan's / B minor Stockton's Wing / The Stockton's Wing Collection / Skidoo / E minor Stockton's Wing / Light in the Western Sky / The Golden Stud / E dorian (1st half) & E minor (2nd half) Altan / Runaway Sunday / Gleanntáin Ghlas Ghaoth Dobhair (song) / D mixolydian
An honourable mention must also go to Liam Ó Maonlaí of the Hothouse Flowers, who also has used the didjeridu in trad. Not only is Liam a phenomenal sean-nós singer, he is a truly amazing tin whistle, piano and bodhrán player. He can be heard playing didjeridu on:
Altan / Harvest Storm / 'Sí do Mhaimeo Í (song) / A# mixolydian
It is beyond the scope of this article to fully explain modes and keys, but very briefly, here is a comparison of the different modes mentioned above in relation to the key of C major:KEY / MODE NOTES OF SCALE INTERVALS C major C D E F G A B C 1 2 3 4 5 6 7 8 C minor C D Eb F G Ab Bb C 1 2 b3 4 5 b6 b7 8 C dorian C D Eb F G A Bb C 1 2 b3 4 5 6 b7 8 C mixolydian C D E F G A Bb C 1 2 3 4 5 6 b7 8
As you can see, the common element to these three modes is the flattened seventh (b7), which is a good guide to the suitability of the tune for didj accompaniment. Finally, here is a brief list of the notes of the actual modes most commonly used in trad (i.e. those containing notes that the whistle, flute and pipes can play, based on the keys of D & G):MODE NOTES OF SCALE INTERVALS E dorian E F# G A B C# D E 1 2 b3 4 5 6 b7 8 A mixolydian A B C# D E F# G A 1 2 3 4 5 6 b7 8 B minor B C# D E F# G A B 1 2 b3 4 5 b6 b7 8 A dorian A B C D E F# G A 1 2 b3 4 5 6 b7 8 D mixolydian D E F# G A B C D 1 2 3 4 5 6 b7 8 E minor E F# G A B C D E 1 2 b3 4 5 b6 b7 8