Electric Gongs

New recording 6/20/2008 - Christopher Brown plays the Electric Gongs: listen

New video 8/06/2008 - youtube 

Electric Gongs is an interactive experimental music installation created by the de la maquina design group, and is on display at Austin Childrens Museum until Sept 2008.

The following text is from a talk I gave at the museum on April 10th, 2008 for Dorkbot 14…

The story starts kind of like this. Several years ago, I bought a 22″ wind gong just for fun. One day it was hanging on the wall and I sneezed as I walked by it. I heard the sound of my sneeze echoing inside the gong. It was a peculiar sounding echo; it seemed like certain frequencies were emphasized and others were absent. I got interested in what the sound of a gong actually consists of. It turns out that it is not really just “noise” as engineers think of it, it is more like a whole bunch of individual notes that are ringing at the same time. Like if you were to walk up to a piano, and you put your foot on the damper pedal, and played all of the keys at once. It would make a big roar. That’s what you get when you hit a gong with a mallet, a sound containing maybe 100 individual notes all ringing together. Thinking back to the way my sneeze was picked up in the gong, I realized that it might be possible to play the notes in the gong one at a time if I got rid of the mallet and used something more advanced.

tones of 36-inch electric gong

So, I did a lot of experimenting. The most recent electric gongs I have built are version four. This version uses custom electromagnetic drivers and tailored software to control the energy that makes the gongs vibrate. Version four has withstood months of continuous use with little maintenance. I have built the instruments in 20″, 22″, 28″, and 36″ diameter, and will expand the scope of my work as far as resources permit.

I mentioned that when you hit a gong with a mallet, you’re hearing a cluster of many frequencies sounding all at once. These frequencies come from the resonant modes of the gong, meaning that each frequency corresponds to a different vibrational shape in the gong. I have been greatly inspired by a book by Dr. Thomas Rossing at Northern Illinois University called Science of Percussion Instruments. Dr. Rossing studied an 18-inch crash cymbal using a technique called Electronic TV Holography. This technique allowed him to photograph the cymbal’s lines of flex as it sustained specific resonant modes. Darcy Neal and I drew from this research in our design of the tapestries that hang behind the electric gongs on exhibit at Austin Childrens Museum:

The five tapestries show us a sampling of the vibrational shapes in Dr. Rossing’s crash cymbal, and the approximate musical pitch that they produce. If you’re familiar with cymatics, you’ll recognize the nature of these patterns. The same thing is happening in the electric gongs, but we don’t have Dr. Rossing’s technology, so we can only guess what shapes these gongs are vibrating in as they produce specific notes. The motions are just too rapid and small to see with the eye.

My method involves searching for the exact resonant frequencies of the gongs and recording them. I found 20 to 30 playable notes in each gong, covering several octaves each. By putting energy back into the gong at these frequencies, it starts to sing. The notes swell up and decay slowly, much different than if you strike it with a mallet. Its more like playing it with a violin bow. I’m not going to discuss the actual mechanism in much detail, but I will tell you that it is based on electromagnetism; there is no solid coupling between the gong and the driver.

Listen

I used Google SketchUp extensively in designing the latest electric gongs; SketchUp is excellent and inspiring free software for 3D design. In this illustration, all of the components in the electric gongs are modeled to precision, and the gongs are”installed” in an accurately measured version of the actual exhibit location. I used SketchUp to generate woodworking diagrams, drawings for metal fabrication, and even color choices in the exhibit.

Visitors play the gongs by touching keys on a piano-style keyboard graphic; there is a separate color-coded keyboard for each gong. The touchscreen podium was created by David Nunez, and is based on FTIR (frustrated total internal reflection) multitouch technology. David chose to write code with Processing for visuals, and PureData (PD) for audio output.

Musically, the electric gongs are interesting to me because the notes they produce are not part of a conventional scale that we’re used to hearing. The scales are spaced somewhat randomly. Of course larger gongs produce deeper notes, but there is much overlap in the ranges that they play; the red gong is a 20″ and its lowest note is 100Hz. The green gong is 28″ in diameter and its lowest note is 63 Hz.. The blue gong is a 36″ and its lowest note is 40Hz. All of them have notes up to 1000Hz and beyond. But, the higher you go, the quieter the notes get, as you’ll see from the following recording of a 22″ electric gong running through the scales.

electric gong glissando

This is microtonal music; the pitches are not equally spaced and do not repeat at octave intervals. To help guide visitors through the experience of playing the gongs via touchscreen, David and I added an algorithm that draws lines between the note you are playing and all other notes that fit an equal-tempered scale based on the note that is currently sounding. Visually associating pitches this way guides visitors to pleasing harmonic relationships between the sound of the three gongs. (We left out the flat 5ths and minor 9ths so as not to scare the kids!).

The electric gong is a polyphonic instrument, meaning each gong can play more than one note at once. Just think of the piano analogy explained above. However, once you start asking the gong to play several pitches simultaneously the results get unpredictable. As for now though, each gong in our exhibit can receive only one note at once due to the way the software is configured.

If you’re a composer, this would be a challenging instrument to work with because not only do the scales depend on the diameter of the gong, they are specific to the individual gong. That is to say if you put two gongs of the same diameter side by side and wrote music for one, it would not sound the same on the other. Furthermore, the notes all seem to have their own character. Some swell up faster than others, some ring for a very long time, and some actually change pitch as they decay. Some notes are pure sine waves; others have harmonics that appear with them. And my favorite are the notes that begin pure but climax in a big crashing roar. I would love to work with a composer to write serious music for the electric gongs.

Gershwin’s Summertime played on 22″ electric gong

I’d love to design further refined electric gong installations in public and private spaces. I can also see the steps to build a portable “concert” version of the instrument.

You can experiment with the sound of the 36″ electric gong here.