Many popular designs for artificial drone reeds use plastic, wood or cane tongues which are often bent in order to have the correct "elevation" or lift at the free end. These reeds can be susceptible to catastrophic failure if excess heat or humidity relax the tongue. Suddenly the reed can become unplayable.
I am among several experimenters who have concluded that the elevation might be carved into the system so that there is no bend or distortion which can be jeoparized by humidity or aging.
When I used such a reed in my Highland pipe bass drone, I experienced no stopping, even when the tongue became dripping wet in cold, damp weather. I am now playing such a bass drone reed in my uilleann pipe, and it is proving exceptionally steady under the varying pressures of 2-octave playing even when switching from easy to medium strength chanter reeds.
My experience, and remarks from other experimenters such as uilleann pipe reedmaker Benedict Koehler in Vermont USA, suggest that the surface should have some slight curvature throughout its length, with most curvature near the fixed base of the tongue. Click here to see a 26kb diagram of these basic ideas.
I however found it difficult and time-consuming to try to create such a curved surface on plastic or metal drone reed bodies. Therfore I have switched to making the conventional flat "bed," instead putting the curvature onto the underside of the tongue. This is easy and fast to do, and if I err, it's easy enough to start again with another tongue. Once a well behaved & good-sounding tongue is found, it can be permanently glued & bound onto the body of the reed.
Click here to see a 33kb diagram of possible steps in making a "never-stop" artificial drone reed.
I have found it useful to use 2 thicknesses of stock hobby-store .015" wall-thickness tubing when using metal bodies. The inner tube is chosen to suit the drone acoustically (correct inside diameter) while the outer tube is added merely to increase the surface area onto which the tongue is mounted and against which it vibrates. I find it convenient to super-glue the tubes together, although soldering would be more permanent.
A common and easy way to make the tongue bed is to file and then sand a diagonal "flat" onto the tubing. Metal tubes can be cut rather deeply at the outer end; plastic should probably be left at least 1/2 diameter deep or else the body may tend to vibrate, which turns the reed into an odd form of double-reed and is more likely to create undesireable than desireable harmonics. (Note this is just a guess!)
I make the tongue bed surface absolutely flat. The surface is open at the outer end, where it cuts into the inner tube to form the region where air enters the vibrating reed. The upper end of the bed remains closed and is where the base of the tongue will be tied for testing, and probably super-glued once the reed is fine-tuned. The free end of the tube must be sealed; ordinary beeswax is acceptable for this, and is extremely easy to flatten in the area under the end of the tongue. Any sort of dust or powder applied to the top surface of the wax will prevent the tongue sticking to it.
Next, I also make the tongue absolutely flat. I test this by carefully tying it onto the bed and inhaling from the bottom of the reed body. Note that although the tongue needs to be extremely flat along its entire underside, an actual smooth finish is only required in the outer region over the opening into the reed body. Nicks or scratches at the base end are of no importance so long as the relaxed tongue will seal completely at the free end.
Finally, the bottom 1/2 to 2/3 of the underside of the tongue is given a tiny amount of curvature by carefully drawing it across sandpaper resting on a flat such as glass. One stroke is made at a time, and then the tongue is replaced with increasingly less length on the paper, so that the fixed base of the tonge is the most sanded after a dozen or so increasingly short strokes.
The big risk in making the curve is that more material may be sanded from one side than the other, causing the tongue to lie at a twist when bound onto the body. This points to the main advantage of putting the elevation-curve onto the tongue: if twist is created, only the tongue is affected, easily cured or replaced. If the bed acquires a twist, the much greater effort put into making the body may have to be discarded.
The base of the tongue is then temporarily bound into place. If the outer elevation is correct (a bit greater than desired for playing), the tongue can be glued into position, and an adjustable bridle fixed. If the tongue was left excessively thick, as some makers prefer, the top surface can now be thinned until the desired pitch and response are achieved. (The bridle will probably need to be removed during thinning.)
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