This essay is designed to accompany a video called Membrane Reeds which can be viewed here on Youtube. In it you can see and hear a variety of membrane reed instruments, but the video doesn’t go into much detail on how to build the instruments, nor does it address the acoustics. You’ll find much more of that information in this article. An additional information source is this two-part article on membrane instruments which appeared in the late great Experimental Musical Instruments journal in 1991. I started using the term membrane reeds for these instruments back then because I knew of no pre-existing name for them in English. I’m still calling them that, since to my knowledge no other term seems to have arisen.
On a theoretical level, membrane reeds instruments function much like other reed instruments such as clarinets or oboes. But they differ in that they use a flexible membrane in place of the cane reed found in those instruments. As discussed in the video, membrane reeds can take a few different forms, but some of the most successful are based on the design of an instrument type made for sale to tourists by children in Indonesia in the 1980s and 90s. Part 1 of the two-part article referenced above explores this history.
Whether Indonesian children are making these instruments still, I don’t know. But this history as a children’s instrument tells you one of the great things about membrane reeds: They’re easy to make using commonly available materials. They’re also easy for anyone to play; no special embouchure required. And they really work, producing a strong tone. The one serious downside is that their pitch tends to be wobbly, making them difficult to play in tune.
After the EMI articles were published, a lot of experimental instrument makers outside of Indonesia started experimenting with these instruments, and for a while there was a positive fad of membrane reed making happening on this side of the Pacific. Now, thirty-odd years later, they’re still a uniquely promising area for exploration for both kids and adult instrument makers.
What is a Reed Instrument?
To understand how membrane reeds work, let’s start with a broader conception of how reed instruments in general work. Broadly speaking, in reed instruments, the steady stream of air from the player’s lungs is converted to a rapid succession of puffs of air. The reed acts as an air-gate, opening and closing over the opening in the instrument’s mouthpiece to admit the air into the main tube as a series of pulses. The pulsing activates the vibration of the air inside the tube. The tube has its own natural resonance frequencies depending primarily on tube length and the presence of any open tone holes. When things are working as they should, the tube’s resonance frequency comes to dictate the reed’s air-gating frequency. This happens as the wave fronts reflecting back and forth within the tube impinge on the reed from beneath, helping it to open and close at the air column’s natural frequency. With the air-gating system and the natural frequency of the air column thus reinforcing one another, you get a clear, strong tone.
Of course the reality is a bit more complex than that brief description suggests. For one thing, it’s not really true that the air column has its own independent frequency which it simply imposes on the air-gating system. The two elements – air column and reed – form a coupled system. The frequency preferences of the reed, as well as the rigidity and reflectiveness of the reed as the end point of the tube, both affect the resulting frequency. These frequency effects at the mouthpiece, as we’ll see later, turn out to be particularly important when we make the jump to membrane reeds.
When people think of reed instruments, they naturally think of instruments whose air-gating system uses natural reed cane – instruments like clarinets, saxophones, oboes, and many others. But the word “reed” is also commonly used, by analogy, for other reed-like air-gating systems that don’t use natural cane reeds. Think of the metal reeds used in harmonicas and various types of organs. Carrying the analogy further, some writers have described lip-buzzed brass instruments as “lip-reed instruments,” since in trumpets and such the buzzing lips serve the same air-gating function.
Membrane Reeds as Reed Instruments
And what about membrane reeds? Although membrane reeds don’t involve anything that looks remotely like natural cane reeds, they do employ an analogous air-gating system in interaction with the air column. In the above description of how traditional reed instruments work you could substitute the word “membrane” for the word “reed”, and you’d have an accurate description of membrane reeds in action.
In membrane reeds, the end of a wind instrument tube is covered with a light membrane such as a thin piece of cellophane or latex. When the player blows, the air goes into a sort of containment chamber which makes it so that the only way for the pressurized air to escape is to squeeze under the membrane and into the main instrument tube. In typical air-gate fashion, the membrane doesn’t just lift and let a stream of air through; instead, it repeatedly rises and falls, letting the air through in a rapid series of pulses. The pulsing excites the air in the tube into vibration. The resulting wave fronts within the tube, reflecting back and forth at the resonant frequency of the coupled system, impinge on the membrane from beneath, thus bringing the membrane’s pulsing frequency into agreement with the tube’s resonant frequency.
It’s important to note that even as the membrane is functioning as the air gate, it’s also acting as a stopped end to the instrument’s air column. As a stopped end, it’s not rigid like a solid end cap or plug would be – it’s light and flexible enough that the wave fronts within the tube can push it around a bit. This affects the resonant frequency of the air column: the softer the membrane, the lower the natural frequency. This effect is the main reason for the tendency of membrane reeds to be unsteady in pitch (and perhaps the greatest challenge for anyone thinking of developing membrane reeds into refined and serious musical instruments). Not only are the membranes not rigid, but they may vary in rigidity from moment to moment depending on degree of stretch, the amplitude of their pulsing, and other factors.
In discussing the resonant frequencies in wind instrument air columns, acousticians refer to something that can be called “mouthpiece equivalent length.” This is how much effective length the mouthpiece adds to the physical tube length to give rise to the resulting natural frequency of the coupled system. This effective added length is generally more than the physical length of the mouthpiece due to various effects happening within. In the case of membrane reeds, because of the non-rigidity of the membrane as a reflective end-stopper, the effective length may be surprisingly large. As a result, membrane reed instruments typically sound a good bit lower than you’d expect given the physical tube length. And if the instrument is to include tone holes, the tone hole placements tend to be out of line with what you’d expect given the tube dimensions, making them more difficult to calculate or predict.
Outer Barrel Membrane Reeds (The Indonesian Design)
A moment ago I spoke of the containment system that leaves the air no choice but to force its way under the membrane. This is a key element and it calls for more description. I’m aware of two different ways this containment system can be configured, and there may be others. Let’s start with the Indonesian system since it’s the most effective and most ingenious. We can call it the outer barrel design, reflecting its most important feature.
… But, seriously, whoever came up with this design was extraordinarily clever. Was it the work of an individual in a flash of creativity, or did the idea evolve over time through incremental improvements from many people? Was it originally the work of kids or of grownups? Answers unknown, at least to me. But the design is hard to beat: simple, clever, affordable, easy to make, and dependably functional, producing a sound that is impressively clear and loud.
As you can see in the diagrams, at the mouthpiece end of the instrument, the main tube runs through the middle of a short barrel of slightly larger diameter. The membrane covers the open top of the barrel. The barrel is positioned over the main tube so that the upper rim of the main tube presses lightly on the membrane from beneath. Through a short blow tube, the player blows into the outer barrel. The barrel is the containment chamber; from there the air has nowhere to go but to squeeze under the membrane and into the main tube. It does this in a series of pulses, as the membrane alternately lifts to let a puff of air through, then slaps back down, then lifts again, and so forth, creating the air-gating effect. The recurring pulses instigate the standing waves in the main tube. The resulting wavefronts, pushing up against the membrane from beneath at the tube’s natural frequency, bring the pulsing frequency into agreement.
In the version of the instrument commonly sold to tourists, the instrument’s main tube was a section of ½” PVC conduit, about 6″ or 8″ long. This tubing is available at hardware stores and construction sites everywhere. The nominal ½” tubing is actually a little over ½” in internal diameter, and about 7/8″ in outside diameter. If you want to make a longer, lower-pitched instrument you can extend this type of tube to as much as about 16″. If you wish to go much longer, it will be a good idea to switch to a larger tubing diameter, since with long lengths at narrow diameters it becomes difficult to sound the lowest notes (the vibrating air column will tend to jump to a higher mode of vibration).
By the way, if you don’t like plastics, you can also make successful membrane reeds of bamboo, or from metal tubing. You can see examples in the video.
Whatever you use for the main tube, it’s a good idea to ease the top edge, rounding it over slightly so that it’s less likely to cut or tear the membrane that is to go over it.
With wonderful resourcefulness, the Indonesian children’s instruments use a plastic film canister for the outer barrel. Remember, the original instruments were being made thirty or forty years ago when the litter of film canisters would have been ubiquitous wherever there were tourists. The canisters are just the right size to fit over the ½” PVC tubing of with a bit of room to spare to form the surrounding air chamber. A hole must be made in the bottom of the canister that fits airtight over the PVC tube. For the nominal ½” PVC tube, I’ve found that drilling the bottom with a 13/16″ spade bit or Forstner bit leaves a slightly undersized hole that fits quite snugly.
Nowadays you can still find the plastic canisters online. But if you can’t get hold of this type of canister, or if you’re making a larger instrument that calls for a barrel of larger diameter, you can find some other material to do the job. This could be a larger canister of some sort. Alternatively, it could be a larger diameter tubing. A short length of this larger tubing can be snug-fitted over a length of weather strip or equivalent wrapped around the main tube where the bottom of the outer barrel is to be. This provides an air-tight bottom to the barrel.
The canister also needs to be drilled to accept the short blow tube. In the tourist version of the instrument, the blow tube was usually a snippet of a sort of rigid plastic soda straw. When it comes to making a secure pressure fit for the blow tube in the canister, I’ve found soda straws a bit flimsy, so you might prefer to use a short section of some other reasonably rigid small-diameter tubing. The blow tube hole can be drilled in the side of the canister about halfway down or a little lower, at a size that allows for a snug pressure fit with whatever you’re using for the blow tube.
To hold the membrane in place, use the lid that comes with the canister. For this purpose, the middle portion of the lid must be cut away, leaving just the rim. This can be done with an X-acto knife. (For extra neatness, you may then clean up the edges of the cut with a rat tail file or small drum sander.) The membrane will be placed over the top of the canister, and the lid then pressed in place to hold the membrane in position. If you’re not using a film canister, you can just position the membrane over the top of whatever you’re using for the barrel and secure it in place with a rubber band.
Many things can be used for the membrane. The Indonesian children often used a bit of cellophane candy wrapper. Plastic bags of the sort you find in the vegetable section of a supermarket can work nicely, as can other plastic membranes of similar thickness. (My micrometer tells me that the veggie bags are less than .0001” thick.) Stretchier materials such as latex or neoprene also work well. They are quite forgiving, easily producing a tone without requiring perfect adjustment. Their downside is, they suffer more from pitch instability due to their stretchiness. Most readily available latex or neoprene membranes are thicker than the ideal, but the widely available nitrile surgical gloves aren’t bad in this regard, at less than .003″thick. Balloon rubber can work, although it’s generally thicker (typically more than .01″) and harder to blow.
Once you’ve gathered these materials, pre-drilled the canister and cut out the middle of its lid, you can put it all together. Slide the canister over the end of the main tube so that the upper end of the main tube comes up a little short of the rim of the barrel. Press-fit the blow tube into its hole in the canister, taking care not to force it in too far to where it bumps against the main tube, blocking its opening. Carefully place the membrane over the top of the barrel and press the canister lid over it so that the membrane stretches across the opening smooth but not tight. Carefully slide the barrel a bit farther down the main tube to where the rim of the main tube just touches the underside of the membrane.
And blow. Good sound? If not, adjust the position of the barrel in order to experiment with the degree of pressure between the main tube and the membrane. You want a positioning where the tone is clear and stable, but the blowing doesn’t require inordinate force. With light, stretchy membranes, it will be easy to get a good sound, but pitch will be wobbly. With a less stretchy membrane, the adjustment will be more exacting but the resulting pitch will be more stable.
Adding Tone Holes
You now have a hole-less tube, capable of one note (albeit, a bendable one). Give it more notes by adding tone holes. By the sizing and the placement of the tone holes we can create any scale we want … sort of. As we’ve noted, these instruments tend to be inconsistent in pitch, however you may place the tone holes. With some diligence, there are ways to manage this problem, as we’ll see in the course of this article. On the other hand, you may take the attitude that this is meant to be a fun, easy, non-perfectionist instrument, and be content with imperfect intonation or with whatever random, non-standard scales may emerge.
If you like the happy-go-lucky attitude (as I sometimes do myself), then you can just drill a set of tone holes at whatever locations seem suitable. A nice approach is to go for a hand-print scale. For a handprint scale, hold the tube in playing position, mark where your fingers most comfortably fall, drill the toneholes there, and enjoy whatever scale emerges. Six holes, yielding seven notes, is a comfortable number for easy playing. For the nominal ½” PVC tubing, 5/16″ is a suitable diameter for the holes. For larger diameter tubing, you can make the holes larger, up to about 3/8″. (Holes larger than 3/8″ might be hard for people with small fingers to cover completely.)
For those that want to go for a particular tuning, here, very briefly, are basics of tone hole placement. In the following, when I speak of “the first open tone hole”, I mean the open hole closest to the mouthpiece. The assumption is that all the holes beyond that will be left open (as is typical, with occasional exceptions, in wind instrument fingerings).
· The closer the first open tone hole is to the mouthpiece, the higher the resulting note.
· The larger the first open hole is, the higher the resulting note.
· The “taller” the hole (which usually means the thicker the tube wall), the lower the resulting note. In most situations this effect is small compared to the two above.
· The closer any additional open holes are to the primary open hole, and/or the larger they are, the higher the resulting note. This effect too is less pronounced, especially when the first open hole is large.
These rules apply with membrane reed instruments just as they do with other winds, but with the caveat we’ve already seen: membrane reeds tend to be inconsistent in pitch due to constantly varying conditions at the membrane, and it’s not guaranteed that you’ll get the same pitch each time you play a given configuration of open and closed holes.
With other winds, it’s possible to calculate tone hole sizes and placements in advance mathematically with good results. With membrane reeds, not so much. As noted above, the “mouthpiece equivalent length” effects are very large, and they’re prone to variation in connection with variations in membrane tension and other factors. Mouthpiece equivalent length is taken into account in tone hole calculations for other winds too of course, but with membrane reeds the effects are extreme enough and inconsistent enough to make the resulting calculations much less dependable.
So if you want to tune a membrane reed accurately to a particular scale, you’ll probably find yourself relying on a blend of intuition and educated guesswork, and on prototyping – that is, making a series of increasingly refined models. Fortunately, most types of membrane reeds are well suited to an iterative prototyping process. That’s because after you’ve made an outer barrel assembly, it’s easy to slip it onto one iteration of the main tube after another as you work your way to improved tone hole configurations. The tubing itself, if you’re working with PVC, is inexpensive, uniform, and easy to work.
Before starting the tone hole drilling process, carefully adjust the positioning of the outer barrel over the main tube for the ideal amount of pressure between the membrane and the tube rim – that is, do your best to adjust it to the point where the tone is most clear and stable, yet the blowing reasonably easy. Then, as you go through the tone hole making process, be sure to keep this positioning the same. You can do a rough check by playing the all-holes-closed note to make sure it’s consistently producing the same note when you give it the same amount of wind pressure.
Typical hole sizes for ½” PVC tubing are between ¼” and 3/8″. At ¼” the tone may be a bit choked. Holes larger than 3/8” may be difficult for smaller fingers to cover completely. In the prototyping process, it may make sense to drill holes small to begin with, and then tune up to pitch by incrementally enlarging.
A useful trick in the tone hole prototyping process: when, upon drilling a hole and testing it for pitch, you find that its pitch isn’t what you were after, you can stop it up again and redrill in a suitable nearby location. There are a few ways to re-stop a hole; here are two. The quick and dirty way is to cover it with adhesive tape. The heavier the tape the better, e.g., Gorilla tape is better than duct tape. Cellophane tape will work, but being so thin it is less than ideal, especially if you have several holes covered this way. Whatever you use, you can place two or more layers of tape to make it heavier if need be.
Adhesive tape has the disadvantage that it doesn’t work so well if you want to drill your new hole in a location that overlaps with the taped hole. The other (superior) method is to purchase a batch of 5/16″ tapered wooden plugs (typically used to cover inset screw holes in woodwork). Then drill all i”nitial holes at 5/16″. Use a plug, if need be, to backfill a misplaced hole. If you place a bit of superglue around the rim of the hole after tapping in the plug in, it’s possible to drill a new hole overlapping the old.
One you’ve gotten a good placement for a hole, it’s a good idea to use a large countersink bit to bevel the hole edges. This allows the fingers to cover the holes more leaklessly, and it creates a nice look too. Be aware that this will, in theory at least, raise the pitch very slightly.
With these techniques it’s possible to make a first tube with lots of guessed-at, misplaced hole locations that have been re-stopped, and newer hole locations holes more educatedly guessed at to arrive at better tunings. It’ll probably be pretty ugly looking, but hopefully functional and educative. This first iteration can be followed by a second tube which is both better tuned and nicer looking … and if need be, a third.
More Varieties of Membrane Reeds
In the video that accompanies this article, several types of membrane reeds appear. The membrane reed idea can take many forms! Through the remainder of this article I’ll provide more information on the various types appearing in the video. In the process we’ll touch on diverse topics in both acoustics and practical how-to, with more detail than what appears in the video.
Membrane Reed Instruments of Bamboo and Other Materials
Some people prefer to avoid the use of plastics. You can make membrane reeds of other tubular materials, such bamboo. The principals are very much the same. The biggest difference is that, unlike plastic tubings, bamboo is not uniform. This makes the construction process more painstaking. Pieces must be chosen and fitted, and the prototyping process for tonehole placement isn’t as dependable.
To make a bamboo membrane reed with the outer barrel design, you’ll first need to find one thinner and one fatter section of bamboo. The narrower one will serve as the main tube, and a short section of the larger one will serve as the barrel. The inner diameter of the larger should be between about ¼” and ½” larger than the outer diameter of the smaller. To form the bottom of the barrel, with its air-tight fit over the narrower main tube – well, there are probably various ways you could do this, but one convenient way is to use a strip of sponge rubber or weather strip of suitable thickness. This can be wrapped around and adhered to the main tube at the position where the bottom of the barrel – the short bamboo piece of larger diameter – is to be. The thickness should be such that the lower end of the barrel can slide over the sponge strip with air-tight snugness. In other respects, the construction of the bamboo membrane reed can be like that described for the PVC.
In a similar way you can make membrane reed instruments of other tubular materials, such as metals. It’ll be best if the wall of the chosen tubing material is not extremely thin, since a very thin wall may tear a thin membrane where it passes over the rim.
Longer, Lower-Pitched Membrane Reeds
Membranes can work quite well down in the lower ranges, and longer air columns have the effect of stabilizing the pitch a bit, making the longer tubes more consistent in tuning. But with longer pipes, it’s not easy to add toneholes: for any reasonable scale, the holes would have to be placed much farther apart, and no one would have fingers long enough to play them. In a moment we’ll look at the possibilities for membrane reed instruments with keys, making those long reaches possible. But first, an alternative approach which is simper and in some ways more fun, and certainly more sociable. Instead of making a single instrument that can play many notes, you can make a tuned set of many one-note instruments. They can be played by hocketing, with several players each playing one or two tubes to create interlocking melodies and rhythms.
Membrane reeds can work well with very long tubes, up to six or eight feet and more. Such lengths require larger diameters, since narrow tubes at long lengths will tend to overblow the higher overtones rather than producing the fundamental tone. With the widely available PVC tubing, you can go to the nominal ¾” size for long tubes and 1″ for very long tubes. As described above for bamboo and other alternative materials, you’ll need to use a still larger tubing for the barrel, or else find some suitable larger equivalent of the film canister. You can tune the set by cutting to different lengths, and you’ll find that the long-tube pitches are less bendy and more stable than we’ve seen with shorter tubes. The tuning is still sensitive to membrane tension though, and you will find yourself adjusting the tension occasionally in order to stay on pitch. The easier way to make the adjustment is not by resetting or tugging on the membrane to make it tighter or looser, but by fine-tuning the position of the barrel over the main tube to regulate how much the rim of the main tube pushes up on the membrane from beneath.
A Keyboard Membrane Reed
Orchestral wind instruments have elaborate keying systems to do things that would be impossible with fingers alone. They can span the distance between widely spaced holes, cover large tone holes, and cover all the holes when there are more tone holes than the player has fingers. To make such a keying system requires seriously advanced skills and tools, but here’s an alternative: with less need of advanced machine tools you can make a table-top keying system. This works for membrane reeds because, unlike some other wind instruments, membranes don’t require the player to blow directly into the mouthpiece; instead you can play through a blow tube. The instrument can lie on a table in front of the player, with something like a keyboard of spring-loaded keying levers covering the tone holes. The tone holes can be spaced as needed to get the desired scale, they can be as large as needed for good tone and tuning, and you can have as many holes needed.
You can see a tabletop membrane reed instrument in the video. It’s a fairly long, low-pitched instrument, with twelve tone holes covering a diatonic range of an octave and a fifth. The twelve lever keys have coil springs at the back which pull them down over the tone holes. The instrument’s main tube is thick-walled enough that the top surface can be flattened, providing a level surface for the seating of the key levers. The holes are surrounded by rings of sponge serving as gaskets to create a leak-proof seal when the keys come down over the holes.
So far so good. But the requirements for the keying mechanism are not quite as simple as it might seem, because of one complicating factor: it’s generally not a good idea to open a single tone hole somewhere in the middle of the tube, with the other holes both above and below it closed. That situation compromises the acoustics in a couple of ways, and the resulting sound and tuning are often disappointing. The ideal situation is one in which at least the next several tone holes after the first open one are also open. We see this in regular woodwind playing, where (with some exceptions) the player habitually leaves all the holes below the first open hole open. All of which is to say that you can’t just have a tabletop membrane reed keyboard on which you press keys one at a time anywhere along the tube, expecting to get coherent tuning and a good sound from each note. You need to fix things so that when you press any one key, the next several keys open as well.
In the tabletop membrane reed shown in the video, I did this by having a spring-steel arm extending out to one side of each key which lifts the next key, which in turn lifts the next, while the keys on the other side are unaffected. Each key may not lift its neighbor to its full height, but as long as at least a few of the following keys progressing down the tube are lifted at least a bit, you get the desired result.
The resulting instrument works well – easy to play with a strong, clear tone. As for pitch stability, well, it is harder to keep in perfect intonation than a typical orchestral wind instrument, but it’s not hopeless, and with practice the player can learn to do a good job of refining the intonation with breath control.
Another way to create a larger membrane reed instrument with pitch control is to use the ‘Moe system. You can read more about this approach to pitch control in wind instruments here and here. I’ve made wind instruments of several types using it. For details you can check the links above; in this article I’ll just say it’s a method of pitch control which can produce sliding pitch across the entire range but can also play chosen discrete pitches without glissing in between. And it works nicely in a tabletop configuration. In the video you can see a large tabletop ‘Moe Mem happily doing its thing.
Pullovers Large and Small
Until now I’ve been speaking about the outer-barrel membrane reed configuration. It’s probably safe to say that that system is the most effective we’re likely to see. Still, there are other ways to make membrane reeds. In particular, there’s an alternative approach that we can call the pullover system. The pullover type is quicker and easier to make than the outer barrel type, but also a little harder to play.
The pullover system calls for a membrane which incorporates a sort of tubular neck – which might seem an unlikely form (a membrane with a tubular neck?) until you realize that this is what you get with a latex balloon. The system does not require a barrel; no film canister or equivalent is required. Starting with a balloon of suitable size, snip off a bit of the far end to make a hole there. Place this over the end of your tube and pull down, so that the neck of the balloon ends up positioned floppily somewhere in the membrane at the top, preferably close to one side. Use rubber bands around the tube near the top to secure the balloon in place. You’re going to blow through the mouth of the balloon when you play, but to do this you need a mouthpiece of some sort. Many small tubular objects can serve this purpose, with the one special requirement that it be somehow grippable behind the teeth so that the player can pull back on it to stretch the neck. The illustration shows a typical form. Shapes like this can be found in various inexpensive small plastic pipe connectors found in hardware stores. Place the mouth of the balloon over one end of the small tubular mouthpiece tube and rubber-band it in place there. To play, you will hold the mouthpiece in your mouth while holding the main tube in such a way that balloon neck is gently stretched at a slight downward angle so that it bends just a bit over the rim of the tube. In this position, when you blow, the air will have nowhere to go but to squeeze over the rim and into the tube. It does this in pulses, and the membrane reed air-gating system is brought into effect. In its interaction with the air column the membrane behaves much as it does in the outer barrel system described earlier, and if all goes well you’ll get a clear tone.
It’s a bit of a problem that the latex in balloons is usually a bit heavier than ideal for this purpose. So while balloons can do the job, we’d do well to find a lighter membrane material. But where can we find a suitably lighter membrane which has the required tubular neck form? It turns out that we can make things work – albeit a bit awkwardly — with widely available latex or nitrile surgical gloves. (Condoms may also work.) The trick with the glove is to treat the thumb as the tubular neck, and to position things so that the glove’s fingers are positioned off to the side, mostly over the rim, held under the rubber band wrap-around and draping irrelevantly below. The thumb of the glove then serves as the tubular neck, pulling over the rim of the main tube and stretching to the mouthpiece and the player’s mouth.
As the video shows, pullovers can be made large or small. Their pitch tends to be very bendable and unstable according to the amount of stretch on the neck and its pullover angle along with other factors. You can decide to see the pitch-bendability a feature, not a bug, as it allows for an expressive sort of playing, with lots of pitch-bending and wide vibratos and intonational subtleties (if you get good at it). Adding to this is the fact that you can also modulate the pitch and tone quality with a finger directly on the vibrating membrane. Between these two methods of flexible control – neck stretch and finger on the membrane – you can have some fun.
You can especially have fun with large-diameter instruments in the lower ranges. If you make a big pullover membrane reed using, say, a section 3” plastic drain pipe several feet long, you’ll find that it can make a big, impressive tone that you can actually see (in macroscopic membrane movement) and feel (as the shaking transmitted to your teeth on the mouthpiece). Even without toneholes, using only neck-stretching and fingers on the membrane, you can get a range of a fifth or more. Compared to most instruments that’s a small range, but in an instrument with so much character and expressiveness it’s enough for some pretty colorful explorations. Not bad for an instrument that you can make in a couple of minutes.
If you do want more range, you can add tone holes. I haven’t attempted a large pullover membrane reed with many holes, but I have made several with just two holes. Coupled with the neck stretching and the finger-on-the-membrane, this allows a not-so-bad range of about an octave; possibly more.
As you can see in the video, the tone holes are quite large. On the largest of the big pullover membrane reeds I made, each of the tone holes is controlled by a big lever with a tone hole cover shaped like a curved dish at one end. Surrounding the hole on the main tube is a ring of sponge rubber which acts like a gasket when the tone hole cover is down, helping to make a leakless seal. In keeping with the nothing-fancy philosophy, the tone hole cover is held down against the sponge by a rubber band. When the lever is pressed at the opposite end, the cover lifts to open the hole, stretching the rubber band. The levers and all are configured so that the instrument can be played in a position reminiscent of a bassoonist’s posture. Things are set up so that the left hand, even as it controls its lever, can also modify tube position to control neck-stretch, as well as placing fingers on the membrane. As can be seen in the video, I also made a couple of slightly smaller instruments in this style, but with some differences in the tone hole covering systems.
Conical Membrane Reeds
Like other wind instruments, membrane reeds can be made with either cylindrical or conical tubes. I won’t go into the acoustical differences between them here except to say that both can sound quite nice. There aren’t many readily available conical tubular materials. To do some conical membrane reed experiments, I made a variety of conical forms – various lengths and cone angles — by the trick of coiling plastic laminate sheets. These are thin, adhesive-backed transparent sheets used to layer a protective coating over printed signs or whatever. It’s not hard to roll them into the desired conical form, layering multiples to thicken the walls and/or to extend the lengths as needed. You can then use the cones just as they are for preliminary experimental purposes, with the possibility of later molding plastic or ceramic over them if the results are promising and you wish to make them into something more solid and respectable.
But for the membrane reeds I did not end up going the more respectable route. Both of the two membrane reed configurations (outer barrel and pullover) sounded excellent when played through the conical bores. But the question of tone hole placement proved vexing for the conical membrane reeds. Even very widely spaced holes seemed to make surprisingly small differences in pitch, with the result that I was only able to get a very small range for any given conical tube. I don’t have a full understanding of why that should have been, although I suspect it’s related to the membrane reeds’ exaggerated mouthpiece equivalent length effect described earlier. Perhaps someone reading this will experiment further and make more progress with the idea of conical membrane reeds.
In the video you can see and hear one example of a conical membrane reed (with very limited range). The tube on this one is a natural piece of dried bull kelp seaweed (another very nice source for conical bores).
That’s All, Folks
Final words: We’ve seen that membrane reeds in their multiple forms are a wonderful avenue for exploration in wind instruments. An important question remains: does the problem of undependable pitch mean that, for all their exploratory possibilities, they can never be made suitable for music requiring accurate intonation? Let’s keep working on that.