Many years ago the artist Peter Richards created a beautiful outdoor sound work which he called the Wave Organ. As much as the Wave Organ is a sculptural piece, it is also very much a locale, a place to be. It’s situated at the end of a jetty extending into San Francisco Bay, mostly surrounded by water, with stonework benches and impressive views, at a slight remove from the bustle of the city. The main feature of the spot — the thing that people come there to see and hear — is the wave organ itself. The wave organ is a configuration of tubular hollows running through the stonework walls and surrounding rocks leading down to openings at the water’s edge positioned so that, depending on the tides, the water thrusts and gurgles around the mouths of the tubes and just inside their openings. The upper ends of the tubes are positioned in the walls where visitors can place an ear to the opening and listen.

What you hear when you listen is the random noise of the water’s action as filtered by the air column enclosed in the tube. The water sound is not exactly white noise — it varies too much from moment to moment to be described as such — but it is a broad-spectrum sound, with a wide range of frequencies appearing in roughly equal measure. Each tubular air column, meanwhile, has its own pronounced resonances, which is to say that it resonates strongly at certain frequencies while scarcely responding at all to other frequencies. Those resonant frequencies shift as varying amounts of water flow in and out at the base of the pipe and as the opening at the lower end is covered and uncovered to varying degrees, but at any given moment the pipe has its well defined frequency preferences. The result, for the person with an ear to the upper end, is that from the broad-spectrum input of water sound the air column selectively reinforces certain frequencies, producing a sound with recognizable pitch, even as it retains the gurgly feel of the water movement along with a bit of the sound of water breaking on rocks near the opening.   

So the basic principle here is of broad-spectrum input filtered by an air column with well defined resonance frequencies. This sort of arrangement has shown up in instruments by a number of builders. Before discussing some other manifestations of it, let me mention a closely related idea just to acknowledge it while not making it the focus of this writing. Said closely related idea is that of plosive aerophones. These are instruments in which the air in a chamber or tube is excited by a sudden jolt of some sort. The enclosed air responds with a resonant tone at its own natural frequency. The most familiar example is slap tubes: slap the open end of a tube with a broad, flat beater (rubber beach sandals work well), and you’ll hear a brief but satisfyingly clear, strong tone at the predominant resonance frequency of the tube. Create a tuned set of such tubes, and you’ve got a great instrument. Many other instruments based on the same principal have been made. A few years ago Experimental Musical Instruments put out an entire book about them, which you can see here.

By contrast, the instruments I’ll be talking about in this writing, like the wave organ, have an ongoing broad-spectrum input, creating a sustained tone rather than a plosive tone. I have been calling these sustained-tone instruments agitation pipes.         

To continue our agitated exploration, here’s another very cool example: the Bay Area builder and composer Krys Bobrowski has created something called the Sliding Speaker Instrument. Its initial sound source is a small speaker that is perfectly fitted to the inside of a tube of about six inches in diameter and about four feet long. The speaker can slide within the tube, and fitting snugly as it does, it acts as a stopper: as it moves it defines a stopped end point within the tube, thus varying the effective tube length and varying the air column resonance frequencies. For the listener at the open end of the tube, the sounds from the speaker are selectively reinforced by the tube resonances, and the predominant pitch as well as the general timbral quality shift as the speaker moves. You can send whatever sort of audio material you want to the speaker as it slides. Ongoing broad-spectrum sources usually are most interesting. As always, watery sounds are good. So, as you might imagine, are cocktail-party-conversation type sounds. Any number of other sounds can prove interesting as well.

My own latest entry in the field of agitation pipes is Sad Aggie. (Think Spring And Diaphragm AGitation pipe.) Sad Aggie uses as her initial sound source the spring-and-diaphragm instruments sometimes called thunder drums, spring drums or thunder tubes. These devices are commercially available in a couple of sizes from Remo Company and other manufacturers. They have a drum-like body with a narrow coil spring, typically between about 18” and 36” long, attached and hanging freely from the center of the drum head. When you agitate the spring by shaking or banging it on something, its vibration is transmitted to the drum head — a very effective sound radiator — and further augmented by the resonant chamber that is the interior of the drum. Boy, can those things roar, and the sound is the very definition of a broad-spectrum noise. I purchased a batch of these things in the smaller size. For these, the drum body is a short tube about 2.5” in diameter. To tune the individual drums clearly to specific pitches, I did two things: first, I extended the drum body tube, adding more tubing of the same diameter so that the predominant air resonance frequency of the elongated tube matched the intended pitch. To understand the second thing I did, I need to first mention that while the springs produce copiously the required broad range of frequencies, there is also one steady and recognizable tone present in the mix, albeit quiet and almost buried among the broad range of other frequencies present. The pitch of this almost-buried tone corresponds to the length of the spring. So for each drum I either shortened the spring or replaced it with a similar but longer spring, to get this spring tone in line with the intended pitch to which the air column was to be been tuned. I found that it didn’t work well to tune it to the same pitch as the air tone, because in many cases this would have left the spring too short to do its job of general agitation, so instead I set the spring tone an octave lower.

When the tuning of both air column and spring is done, the resulting sound is unusual and quite impressive, particularly when you create a tuned set of the instruments. Each such set is a Sad Aggie, in the same way that a set of tuned wooden bars is a marimba. I’ve now made two Sad Aggies. One is a set of four aggies (individual spring-and-diaphragm agitation pipes), each of which has a single large tone hole along the side. As the player holds and shakes the tube in one hand, the tone hole can be covered and uncovered with the other; also, it’s possible to cover the tone hole with the holding hand and then partially cover the open end with the other hand. The result is three available notes per aggie. The spring is tuned an octave below to the highest one of these notes, adding a quiet and unobtrusive pedal tone as the other notes thunder away. As four Aggies with tone holes produce three notes each, the set has a range of twelve notes.        

The other Sad Aggie I made has nine separate aggies, one for each note of a diatonic scale over a little more than an octave. The aggies are mounted around the sides of a single floor-standing post of about seven feet high, for which reason I call this set Tall Sad Aggie. Each aggie is spring-mounted on a short, flexible band of spring-tempered steel. You can play by pulling to one side and releasing, which creates a tuned roar as the aggie vigorously shakes back and forth on its spring-mount. You can also play by striking the springs with big, soft, very light-weight cylindrical bats of foam. (You can strike with other things as well, but most strikers make a disconcertingly clangy sound). And one more technique: you can pluck the spring coils with a fingernail, or scrape along the springs.


A few more agitation pipes:

My Waffle Gurgle Flutes look and play more like conventional flutes, being mouth-blown tubes, held in a flute-like playing position, with pitch controlled by tone holes. The broad-spectrum noise input is provided by an arrangement a bit like what is sometimes called a rubber razzer: essentially a latex tube in the form of a snipped-off balloon neck with a small mouthpiece to make it easier to blow through. With the traditional rubber razzer, when you blow through the mouthpiece it causes the balloon neck to go flapping all over the place and produce the classic razzing sound, essential to many a good vaudevillian insult. In the Waffle Gurgle Flute the balloon neck droops into the open end of a flute tube with tone holes, thus directing the razzing sound into the air column and making it pitch-controllable. 

I have also tried my hand at making water-gurgle instruments. The most successful was also the simplest in concept: a water-gurgle mouth organ. The instrument has several small chambers in the form of jars of various sizes with water in the bottoms. Through a harmonica-like mouthpiece the player sends air through one or another of several tubes, each tube leading into the water in one of the jars. When the blown air burbles up through the water, it excites the air enclosed in the portion of the jar above the water, with the resonance frequency of the enclosed air clearly dominating the resulting the tone. You can play melodies by blowing into the different holes in the mouthpiece, thus directing the air into different jars. It’s quite a nice tuned watery sound. 

Another successful water-gurgle instrument, similar in concept but different in size and form, has also been made by Tim Phillips.

One more style of agitation flute: it turns out that you can make a hollow guiro-like rasp such that the air resonance within the body is excited strongly enough by the scraping to result in recognizable pitch. This means that if the body is tubular, you can give it tone holes, making it possible to play melodically. The late Darrell DeVore did this with his bootoos. These were pairs of small bamboo stamping tubes, made to be played by percussion, stamping them end-on on a solid surface. He gave them one or two tone holes each to allow for a wider range of percussion pitches as the stamping excited the air resonance within. In this usage they fit the standard definition of stamping tubes, a form of plosive aerophone, and would not have qualified as agitation pipes as I’ve been using that phrase. However, he also filed a row of ridges into the side of each bamboo, allowing for a guiro-like scraping technique which is indeed more in keeping with the agitation pipe concept. With the air-resonance tone blending with the bambooey raspy effect, plus the melodicism of the tone holes, they make a most appealing sound.

I have made tuned rasps along similar lines, but out of plastic tubing. My thinking was that the more flexible material would allow stronger excitation of the enclosed air under the action of the scraper. (I also squashed the tubes flatter and thinned the plastic in some areas, again in hopes of making them more responsive.) I called these things scraper flutes and I made them in two forms. One is very flute-like though not mouth-blown, with up to five tone holes along the side and a way of strapping the tube into the lap to allow scraping with one hand while tone-holing with the other. The other involved a tuned set: many one-note tubes (no tone holes) tuned chromatically over a range of two-plus octaves. 


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