A year or two ago we had a show at the Window Gallery* featuring instrument builders who have worked with sheet metal resonators. Among the builders featured were Neil Feather, Tom Nunn, Brooks Hubbard (the builder who now carries on the Waterphones work of Richard Waters) and, represented by images and text on the wall, the late Robert Rutman.

[*The Window Gallery is a small exhibit space devoted to new instruments and sound sculpture, housed in San Francisco’s Center for New Music.]

Sheet metal resonators might seem an odd theme to build a show around. But as a starting place for  instrument-making explorations the idea turns out to be quite fertile, and several builders have fruitfully worked with it. Especially intriguing are the acoustic goings-on in large metal sheets held non-rigidly, leaving them free to carry on with their idiosyncratic resonances in response to whatever vibratory input may be given them. If the sheets are free to flex and wobble as they sound, they’ll often produce striking effects involving swelling and shifting resonances. And of course the sheets also serve as efficient sounds boards, which is to say that, having quite a lot of surface area to push the air with, they do a good job of radiating the sound out into the room.

Belatedly inspired by that show,I’ve made a set of sheet metal instruments myself recently. I’ll describe them now.

ICICLES

One is called Icicles, a name which reflects the quality of the sound. The essential idea is of very short strings under high tension attached to a hanging sheet of stainless steel (the sheet is actually suspended from the strings). The very high string frequencies excite the sizzly high resonances in the sheet, and the sheet carries on with those resonances — a heavily colored version of the string vibrations — even if you stop the string.

For this purpose, I found that the sheet doesn’t need to be very big: the size I settled on was 12”x 16” of .036” thick steel. At that size, the sizzle frequencies come through nicely. Lower frequencies, which would impart an unwanted heaviness to the sound, are not as noticeable as they would be with a larger sheet. The first version of the instrument I made has 13 strings. Each string runs through a hole near the upper edge of the sheet, loops around the outer edge, back through the hole and out to other side; thus the 13 strings under tension serve to hold the sheet, suspended. There are tuning pins at each end of each string making the string segments on both sides of the sheet tunable and playable.The idea was to have two chromatic octaves. But in practice I found that with all the various string tensions in interactive interdependence through the sheet, it was impossible to tune one string segment without throwing its opposite half and several of its near neighbors out of tune, so the instrument is scarcely tunable. It sounds wonderful, but to appreciate it you have to be happy with a lot of random pitches.

POP ICE

The reason I made the Icicle’s string segments playable on both sides of the sheet was that I expected that too many strings would rigidify the mounting of the sheet too much, inhibiting the sound and making the sizzle less sizzly. Having the segments on both sides playable allowed more notes with fewer strings. But in response to the tuning problem I followed up by making a second instrument with only the segment on one side playable, thus requiring more strings for the same number of notes, but with the hope that the resulting instrument would be more tunable. This one eventually came to be called Pop Ice, for reasons we’ll see later. Pop Ice has 25 strings — enough for two chromatically tuned octaves, in a configuration very much like that of Icicles described above, but made for playing on one side of the metal sheet only,with the unplayed string lengths opposite the playing side kept very short. But … disappointment! My concern that the increased number of strings would dampen the sizzle of the sheet proved well founded, and this version of the instrument didn’t sound as good as the other. Not only that, but it wasn’t all that much easier to tune, either! (The interaction between the strings all attached to the same somewhat flexible piece of sheet metal was still too distortable for stable tuning).

Moments like this can actually be fun. I’m speaking of the moment when one realizes that something one has been working on isn’t panning out, and that carrying on with efforts to correct the problem doesn’t look promising and may not be worthwhile. The potential fun is, this now means that there’s nothing left to lose in toying with the project in imaginative ways; one needn’t worry about messing up the whole thing since as it is the whole thing may not be worth saving anyway. With this liberated attitude, I started trying out various unlikely possibilities on the instrument to see if I could come up with something interesting, even if it was quite unlike my original intentions for the instrument. Eventually I came up with this: if you press a styrofoam sheet or cup other small styro-form directly against the strings quite close to the bridge, they produce when plucked a loud popping sound; almost no sustain but with recognizable pitch. No surprise there, really — styrofoam is always good for excellent projection; the direct string contact ensures very efficient transmission from string to styro, and the softnessof the material naturally damps out the string vibration quickly. But a very nice addition was, the stainless steel sheet picks up the vibration from the string, and in the moments following the pop of the string the sheet continues to reverberate on its own. It’s a very nice effect.

I managed to find a lightweight styrofoam tray of about 11”wide and 8½” across. That’s the right size so that it can be positioned with its edge crossing all the strings adjacent to the bridge. I added a simple system for holding it in place in the correct position. Done! The instrument is still barely tunable, but the tones, in their untuned randomness, have this unusual and very appealing pop-and-reverb sound.

SLIDE ICE

I still wanted to make something with the sizzly sheet metal sound, but which could more readily be played in a non-random tuning. I also wanted to try something with a much smaller number of strings, in the hope that that would leave the sheet more unconstrained and freer to express its own characteristic resonances.

I settled on the idea of something with longer strings that could be played either with a slide or by fingering on a fretboard. To honor the minimum-number-of-strings idea, I designed it with just two strings. Practically speaking, that’s the minimum suitable number because if the sheet were suspended from just one string it would be too much prone to swing problematically from side to side. The resulting instrument, which has come to be called Slide Ice, is much like the original Icicles in the size of the steel sheet and the way the sheet is suspended from the strings, but it has just the two strings of roughly guitar length, running over a fretboard. The player plays table-top-guitar-style, with the fretboard positioned flat in front of the player, except that the instrument is not actually on a table top but on its own stand, leaving room for the sheet hanging below.

This one worked out nicely from the start — a nice steel-sheet resonance sound, with a lower range than the original icicles (but it can go insanely high too if you want, using the slide). But it was awfully quiet! Hmm… So I figured I better put a pickup on it. I placed a piezo on the steel sheet. Piezos, you may know, are often prone to a trashy sound — wonderfully convenient for many types of instruments, and very affordable too, but frequently unflattering to the sound of the instrument. In this case, however, it immediately worked great: a nice, clear and accurate recreation of the acoustic sound, with this added bonus: placing the piezo directly on the metal sheet meant that what came out of the speaker was a purer version of the string sound as filtered through the metal sheet resonances. Since the metal sheet resonances are the main point of these instruments, that’s a welcome feature.

And while we’re on the subject … Having heard how well the pickup worked on Slide Ice, I thought to try piezos on the other instruments in the growing Icicles family — that is, on the original Icicles, on Pop Ice, and on the one I’ll be describing in a moment, called Rocking Stainless. To be clear, Pop Ice is pretty loud acoustically and doesn’t really need a pickup, while Icicles is fairly quiet and so could benefit from a bit of a boost, and Rocking Stainless is somewhere between the two. In every case the pickup worked very nicely, and the benefit of taking the sound directly from the sheet steel was consistently a plus. 

ROCKING STAINLESS

This fourth among my recent sheet metal instruments is a little different from its siblings in that the sheet does not hang from the strings, but rests upon them. This instrument, called Rocking Stainless,  has six guitar-length strings mounted on a fretted board, essentially forming a body-less stick-guitar resting on a tabletop. The stainless steel sheet for this one is 12”x20”, and it is given a slight bend to put a curve near the middle. It sits on the strings, with the curved part contacting the strings quite close to the bridge and the two ends angling up from there, extending out over the strings on one side and over the lower part of the board on the other. The bent sheet is held loosely in place near one end by an elastic cord, preventing it from tipping sideways and falling off the strings. The elastic cord doesn’t loop around the whole width of the sheet (which would cause too much damping), but passes through a pair of holes closer to the center, just wide enough to then loop around the board below, holding snug but not too tight. In this positioning, the point where the curved sheet contacts the strings acts as the bridge, and the sheet functions as the primary radiator of sound.Transmission from the strings to the sheet is efficient, since they are indirect contact.  

With this set-up the sheet can rock back and forth, adding a vibrato of both pitch and tone quality to the sound. The positioning is such that the player’s right hand as it plucks the strings can easily give the sheet a slight occasional nudge to perpetuate the rocking if desired. Anyone who has played table-top guitar will know that fretting in this position is more awkward than the usual way — or at least seems so to anyone who learned the usual way — but can still be done. The instrument also sounds great played with a slide.

Where the strings contact the curvature of the sheet, a strong jawari effect arises. (Jawari is the Indian term for the buzzing bridge found in sitar and tamboura). This combines with the metallic tone of the steel sheet, made more interesting by timbral vibrato of the rocking sheet, and all these elements together add up to a unique and exotic sound.

 

So those are the four instruments I’ve made over the last few weeks with sheet steel resonators. In addition to these, many years ago I made another sheet steel resonator instrument, Wobble Steel guitar. You can see and hear it here. Also in the realm of shifting metal resonances are a couple of instruments I’ve made borrowing the waterphone principle by which moving water causes shifting resonances in metal; you can see those here and here.

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