Tinkertunes : Friction Harp

The Friction Harp

A Story of “Rediscovery”

My first introduction to the use of longitudinal waves to create music came in an article in the Detroit Free Press about the Symphonic House, a home recently built not far from where I live, constructed so that the entire structure is actually a musical instrument. The frame of the house and its spacious interior are the body and resonating chamber for a series of long strings that are played by rubbing them with rosined gloves. The friction caused by the rosin creates vibrations which bounce back and forth from one end of the wire to the other.

Longitudinal vibrations are remarkably different from the transverse vibrations which we normally associate with string instruments. The pitch of the tone is determined only by the length of the string, and not by its tension. A middle “C” for example takes about a forty foot wire.

The “long string instrument” (LSI) installation was done by Bill Close, and as I searched for more information about the LSI, I became aware of the extensive work done by Ellen Fullman. She is the preeminent developer of the LSI, having spent more than 20 years refining her instrument and playing technique. She performs on an LSI with strings as long as ninety feet.

As I researched longitudinal vibrations I discovered a number of physics demonstrations which created the vibrations with an aluminum rod rather than a wire. Intrigued, I went down to my local welding shop, and bought a six foot length of five-eighths inch aluminum rod. After coating one end of the rod with some violin bow rosin, and finding the center of the rod by balancing it on my finger, I began to rub the rosined section, squeezing it with my thumb and forefinger. It took a few tries, but soon I was able to create an ear splitting tone that made all action in the noisy steel shop cease, as the welders looked up in amazement.

My next goal became to construct an instrument from a series of rods, that could be played without having to hold each rod individually. I had the welding shop attach an aluminum bolt to the center of the rod. To my delight, the weld did not dampen the tone, nor change its pitch, and it gave me a way to mount the rods onto a post! I bought a two foot and a three foot section of the rod, to create a fifth and an octave, (thanks, Pythagorus!) and took them home to practice, and to show to my friends and family.

The folks that know me well aren’t too surprised when I show up with a “new” fascination. I’ve been creating Your Name Rings a Bell musical wire sculptures for a few years now, and these aluminum rods seemed to be a natural outgrowth of that.

I demonstrated the rods for a few dozen people, most of whom had never heard aluminum rods sing like that. My son, Miles, had learned about it a year before in Physics class, and my friend, Andy Struble at the Music House Museum, told me that he thought John Deagan had built a similar friction instrument. Like most people, I was unaware of John C. Deagan, and his incredible contributions to music and the science of sound, but he is undoubtedly one of the greatest acousticians of all time.

Andy of course, was right. Deagan had built and sold an “aluminum harp” in 1920, and as I searched the net for more information I found out about a magazine called Experimental Music and its founder, Bart Hopkins. He was very helpful in my research, and sent me a picture from a Deagan catalogue of the original “friction chimes”.

Deagan had used nickel-plated aluminum tubes with a tapered top that allowed the player to achieve a vibrato effect by waving a hand over the open end. National Music Museum at the University of South Dakota has one of Deagan’s instruments. The Circus World Museum in the Wisconsin Dells has a similar instrument called a Musical Lyre made by E.R. Street, who competed with Deagan in the early 1900’s percussion instrument manufacturing business.

In the spring of 2008, I had the great pleasure to see and play a Deagan Aluminum Harp. A very kind woman from Pennsylvania named Wren Ingram contacted me, after having been referred to this page by a curator at the Smithsonian Museum. She was going to donate her grandfather’s instrument to the museum, but offered me the opportunity to play it before she did. Once I discovered that the harp was in Buck’s County, which is also the home the the Ringing Rocks State Park, I knew I had to go.

I added a side trip to Pennsylvania on my trip to some performances in Florida, and spent a delightful evening with Wren, her mother and a family friend, and got to play the instrument her grandfather had played as part of his musical act in the resorts of the Catskills in the 1940’s.

I found that the tubes Deagan used did not continue to ring after you stopped stroking them, as the solid rods do. They required a bit more force to initiate the note as well, perhaps because the nickel coating was worn. Since it was made to be portable, it was not as stable as my instruments. The stand tended to wobble a bit, and I also prefer my horizontal mounting system, which I find much more ergonomic, even though it takes a great deal of floor space.

My first instrument looked a great deal like an antenna. I bolted the rods to a single wooden shaft, which was mounted in a triangular aluminum base. Because the bolts welded to the rods had to be of aluminum, they tended to break easily, and it was impossible to tighten them down enough to prevent the rods from pivoting when played.

I next tried fastening the rods to a frame by welding a mounting plate at the center of each rod. Like the bolts, the plates did not affect the tone or pitch of the rod, but by bolting the plates to a wooden frame, the rods became very stable, and much easier to play. After experimenting with several different positions, I decided on a horizontal mounting. This allowed me to use both hands effectively, and even to use my forearm to mute the rods.

Here is a video of the next version playing “Simple Gifts”. Recorded June 2005, with a pre-recorded piano accompaniment

This instrument has 12 tones, the lowest note is the “G” at the top of the treble clef, and that rod is nearly 12 feet long. It is very much a soprano instrument, despite its size, in the same range that most people can whistle. Because the high notes can be painfully high, I began to look for ways to lower the range of my instrument.

To get another octave lower, I would need to have an aluminum rod 24 feet long… and to support its own weight, you’d probably have to use a rod with an inch and a half diameter. That’s a custom order job from an aluminum foundry that’s going to cost a lot of money, not to mention shipping. While it may be possible to weld two 12 foot rods together, the instrument would still be too big to be practical.

Looking at other materials was the logical course. My daughter needed a project for her 8th grade science class, so we worked together to compare the pitches of longitudinal waves in a variety of metals. We obtained 3/8 inch diameter 6 foot rods made of stainless steel, copper, brass, bronze, and aluminum, and mounted them with thumb screws in a wooden board.

We’d found some information about speed of sound through various metals and knew that it’s determined by its elasticity (bulk modulus, young’s modulus) and inertia (density, molecular mass). It was clear that brass would have the slowest speed, and therefore the lowest pitch of the metals. What was surprising, however, was that foot for foot, the brass produced a note nearly an octave lower than the aluminum.

The brass also produced a tone that was more mellow or “rounder” than the aluminum. On the negative side, it costs several times more, and because it’s heavier, it takes a larger diameter rod to prevent it from drooping when suspended from the middle. I’ve cut the rods for my brass harp, and am working on a new mounting method.

My latest version uses smaller diameter rods, and a staggered bridge, so that the playing ends form a straight line. I used a recycled piano cabinet, and skewed it to support the centers.

Here is a video of “The River is Wide” on this instrument:

It has been so much fun for this old musical dog to learn a few new tricks, and I’ve been delighted to “rediscover” a new way to make music with vibrations that I didn’t even know existed. We never know where a passing fancy might take us, if we follow it. I hope that you too might find something “new” that gives you as much pleasure.