Thomas D. Rossing- Rossing@physics.niu.edu
Physics Department
Northern Illinois University
DeKalb, IL 60115
815-753-6493
Popular version of paper 2pMU2
Presented Tuesday afternoon, June 5, 2001
141st ASA Meeting, Chicago, IL
Many new and unusual percussion instruments made of wood, metal, glass, stone, and plastic have been developed in recent years. What is often termed "contemporary sound" makes extensive use of percussion instruments.
Understanding the sounds of percussion instruments depends on determining the normal modes of vibration of these instruments, and this can be done with great accuracy by means of a technique, known as holographic interferometry, which uses a laser light source. The complex vibrations of percussion instruments can be described in terms of normal modes of vibration, which represent the ways in which an instrument can vibrate and produce sound.
Of the several techniques for observing normal modes of vibration, holographic interferometry offers by far the best spatial resolution. As in all optical holograms, laser light is split into two beams, one of which illuminates the vibrating object, and the other goes directly to the photographic film or other detector in order to create an interference pattern. In the case of a vibrating object, these interference lines give a contour map of the vibrating surface.
Bass handbells--Demand for handbells of lower and lower pitch has led to development of bass bells as low as G0 (fundamental frequency of 24.5 Hz). Unfortunately, large bass bells of conventional design radiate inefficiently, especially bells made of traditional bell bronze, because the speed of bending waves is well below the speed of sound. In order to obtain a higher radiation efficiency and thereby enhance the sound of bass bells, aluminum bells of a new design have been developed. In addition, they are considerably lighter in weight, and thus they are much more easily handled by bell ringers. Comparison of the vibrational modes of these new "enhanced bass" bells to those of traditional bronze bells, by means of holographic interferometry, reveals both similarities and significant differences.
Choirchimes--The Choirchime, developed by Malmark, Inc., is essentially a closed-end self-resonant tuning fork with a handbell clapper. Now available in chromatic sets up to 5 octaves, Choirchimes have become very popular in schools and churches, both for teaching and performing music. The vibrational modes of Choirchimes include both symmetric bending modes, parallel bending modes, and torsional modes, much as in tuning forks. The resonator tube is tuned to the lowest symmetric bending mode, while the other modes are damped out rather rapidly by the hand that holds the chime, so the sound is dominated by the fundamental.
Major third bells--For years, some carillonneurs have felt that a composition in a major key, especially if it includes chords with many notes, might sound better if played on bells with a major character, which suggests replacing the strong minor-third partial with a major-third partial. Efforts to fabricate such bells were not successful, however, because raising the minor-third partial by changing the profile also changed the frequencies of other related vibrations.
Employing a technique for structural optimization using finite element methods on a digital computer, scientists at the Technical University in Eindhoven and the Eijsbouts Bellfoundry in The Netherlands were able to design bells with the minor-third partial replaced by a major-third. The first bells had rather rapidly decaying partials, but a second design had a longer decay, more nearly that of the traditional minor-third bell.
Instruments of Harry Partch--Composer-inventor Harry Partch constructed his own musical world of microtones, elastic octaves, and percussion instruments. His tuned "cloud chamber" bowls, shown in are actually cut from acid carboys, while his mazda marimba consists of light bulbs of various sizes. His boos (for bamboo marimbas) consists of 64 pieces of bamboo tuned by cutting tongues of the right lengths, while his spoils of war consists of a variety of items: a Pernambuco (wood) block, seven brass shell casing, four "cloud chamber" bowls, two tongued pieces of bamboo with open ends, three "whang guns" (strips of spring steel controlled by pedals), and one gourd (which could be scraped to give a rasping sound).
Instruments of the Baschet brothers--Bernard and Franois Baschet have built several unusual percussion instruments using familiar sources of vibration such as strings, rods, and bars. One example is the cristal, which consists of a vertical glass rod attached to a horizontal threaded steel rod. The position of the glass road and the tuning weight are adjustable. The player excites the glass rod by stroking with wet fingers, and the glass rod sets the steel rod into vibration. The vibrations are transmitted to the sheet metal radiator through the steel gum attached to the threaded rod.
Another resonator used in the Baschets' instruments are spring steel wires, which they call "whiskers." They are generally between 60 and 100 cm in length, and a large number of whiskers of varying length are attached to the body of an instrument. In addition to vibrating sympathetically, they bend and sway and occasionally contact one another. In addition to their acoustical role, the whiskers add an intriguing visual element. Both whiskers and cone resonators are used in their aluminum piano.
Lithophones--Lithophones use vibrating stones to create sound. The ancient Chinese were fond of stone chimes, many of which have been found in ancient Chinese tombs. In a complete orchestra it was desirable to include instruments of stone, metal, silk, bamboo, wood, skin, and earth. A typical stone chime was shaped to have two arms of different lengths joined in an obtuse angle The stones were generally struck on their longer arm with a wooden mallet. A lithophone of 32 stone chimes found in the tomb of the Marquis Yi (which also contained a magnificent set of 65 bells) are scaled in size, although their dimensions do not appear to follow a strict scaling law. Sometimes the stones were richly ornamented. Icelandic lithophones generally make use of basaltic, isotropic stones which, as a result of climatic changes, have split into thin slices or slabs. They are placed on two parallel strips of wood and played with small, hard mallets.
Glass harmonicas--Glass harmonicas are basically of two types. One type employs vertical wine glasses arranged so that the performer can rub more than one glass at a time. A collection of glasses played in this manner is sometimes called a glass harp. The other type, called the armonica by its inventor Benjamin Franklin, employs glass bowls or cups turned by a horizontal axle, so the performer need only touch the rims of the bowls as they rotate to set them into vibration (Franklin's instruments can be seen in several museums, including the Franklin Museum in Philadelphia).
Ceramic instruments of Ward Hartenstein--Musical instruments of clay have been known for many centuries, but none are more attractive or sonorous than those of contemporary sculptor/musician Ward Hartenstein. One of his first instruments was a ceramic tongue drum in which cantilevered bars, carved from a solid slab, vibrate over a bowl resonator. From this developed the petal drum Another innovative instrument is the bell tree.