A few years ago, I surprised my wife by asking for a guitar for Christmas. Our budget was limited in those days, so I started at the low-cost end and remember being disappointed with the tone quality of the guitar we purchased. Even with my poorly trained ear, I could tell the difference between a $50 guitar and a $100 instrument. The jump from $100 to $200 was also easily detectable. I could even make out the difference in tone quality between a $200 and a $500 guitar. One hand-crafted instrument with a $1000 price tag had a lovely tone. However, the limitations of my ear made it difficult to detect significant improvement in tone quality beyond that stage. At any rate, I realized that an instrument manufacturer would clearly not waste precious select woods on a “cigar-box” instrument. Since then, while trying to unlock the secrets of fine tone quality, the importance of materials in crafting fine musical instruments has become apparent during my investigations of various musical instruments in the laboratory.

The extreme variations in the mechanical as well as acoustical properties of wood, not only within a given species, but even within the same tree, have plagued violin researchers for nearly 100 years and violin makers for more than 300 years. The lore of violin making tells us that a spruce tree growing on the north side of a mountain should be cut in the spring when the water is moving up in the wood cells, and that the first six or eight feet of the trunk should be discarded because the twisting and the weight of the big trunk cause increased density in the wood with a less even grain structure. The wood should then be cut into lengths, free of knots and sap cracks, and split into so-called flitches that can be used for various violin-family instruments, depending on size. When a flitch is properly cut and joined for a violin top, the annual-ring spacing, or grain, ideally should be narrow in the center of the violin top, gradually becoming wider toward the edges. Also, the grain should be vertical to the bottom surface of the top plate. The more researchers study the desirable parameters of spruce for the proper tuning of violin top and back free plates and the effects they have on the finished instrument, the more the seemingly unsupported lore of violin making makes very good sense.

Strings for musical instruments seem to be among the simplest of devices. Textbooks on acoustics commonly use them as the most elementary example of a vibrating system. However, the assumptions often made to simplify mathematics are far from the conditions that exist in real strings made of even the most suitable materials available.

Consider what a musician wants in any instrument: as wide a frequency range as practical; considerable acoustic power with a significant difference between loud and soft notes; and, if possible, the ability to play several notes at once. The last requirement dictates the presence of multiple oscillators. Long, thin strings in closely-spaced groups fit the bill, but they are inherently deficient in meeting the other criteria without help from additional devices.

Direct acoustic output from a vibrating string is negligible because it alone cannot move enough air. This deficiency has been corrected in hundreds of ingenious ways over thousands of years by mechanical coupling to a light, stiff structure large enough to radiate the lowest pitch being produced, often incorporating air-cavity resonators tuned to enhance low-frequency output. In this electronic era, unlimited power can be obtained using transducers to detect string motion as electrical voltages that can be amplified and directed to loud-speakers.

Several authors have conducted research to characterize the woods used for musical instruments. The principle of such studies is that acoustical qualities of musical instruments are linked to modal properties of the resonator, especially to the soundboard. Therefore, by knowing the mechanical parameters of materials, it is easy to deduce the frequencies of the eigen modes of a vibrating structure. Equation 1 requires only the geometrical dimension of a plate, the density, and Young's modulus to define a material:

where l is length, b is width, d is thickness, E is Young's modulus, I (= bd3/12) is inertial momentum, ρ is density, n is partial number, and fn, is frequency mode(n).

But, how do we choose the values of each parameter, since woods are variable materials with a large distribution of values-for samples coming from the same tree?

We have successfully developed an acoustic guitar (Figure 1) composed of graphite. Trademarked the RainSong® graphite guitar, this instrument uses no endangered tropical tonewoods. The instrument's sound quality is equal to that of a fine wooden guitar. At high frequencies, the clarity, sustain, and play-ability surpasses that of wooden guitars. Because of its construction, the instrument is sturdy and is impervious to humidity, heat, and water.

The development of this guitar required analysis of the theory of anisotropic sound propagation in the guitar soundboard and body, and resulted in two patents. We designed prototype guitars in collaboration with Pimentel & Sons, Guitar Makers, and used combinations of unidirectional and woven graphite and aramid fibers in an epoxy-resin matrix.

The goal of our project was to accurately duplicate—panel by panel—the acoustic properties of a fine wooden guitar. We had the resulting acoustic modes and frequencies verified in the laboratory. We then developed and constructed open-mold and resin-transfer molding tooling for a family of classical, steel-string acoustic and hollow-body electric guitars, which are now in commercial production.

Possibly the first all-composite acoustic guitar, the RainSong® represents a fundamental change in stringed-instrument construction, perhaps the first since the 17th Century Italian masters.

The RainSong® technology allows musicians to skirt the effects of climate and transport damage on their instruments. The instrument contains essentially no wood, and hence negates environmental concerns about rapid depletion of the virgin-forest woods, from which stringed instruments have traditionally been made.

Handbells have become very popular musical instruments, especially in schools and churches; about 40,000 hand-bell choirs have been reported in the United States alone. Tuned handbells are generally made of cast bronze, which has been the traditional bell material for many centuries.

Demand for handbells of lower and lower pitches has led to the development of bass bells as low as G0 (fundamental frequency of 24.5 Hz). Unfortunately, these large bass bells radiate inefficiently, especially the bells made of bronze. This is because the speed of bending waves in these bells is considerably lower than the speed of sound in air, a condition known as “being below the coincidence frequency.”

In order to obtain a higher radiation efficiency and thereby enhance the sound of bass bells, the Malmark Company has created a new bell design using aluminum rather than bronze. These bells are larger in diameter, and they have lower coincidence frequencies, both of which lead to more efficient radiation of bass notes. In addition, they are considerably lighter in weight, and thus are much more easily handled by bell ringers.

In this article, the acoustical properties of two G1 handbells, one of aluminum and one of bronze, are compared. The aluminum handbell has a diameter of 48.5 cm, a height of 34 cm, and a wall thickness from 4 to 5 mm. The bronze bell has a diameter of 38.5 cm, a height of 28.5 cm, and a wall thickness from 3 to 4 mm.

The evolution of the steel pan during the last half century represents the emergence of a truly new musical instrument. Originating in the folk culture of the Caribbean, it has become popular throughout North and South America, as well as in Europe. The haunting sounds of steel drums, generally called “steel pans” by players and tuners, are now enjoyed worldwide. Pans are usually crafted from commercial 55-gallon steel oil drums. The top with its various openings is discarded, and only the bottom, along with the side, is used for the pan. The length of the side skirt varies depending on the pitch range of the completed instrument. Thus, a bass pan will utilize almost the entire length of the original drum, whereas a lead pan, or a single tenor, will be cut to retain only a very short skirt. The pitch of each note section is primarily determined by the size and geometric shape of the section as bounded by a grooved seam. Figure 1 shows representative layouts of several pans. The note arrangement in some pans is such that several pans are required to play a melody. For example, a double-second instrument consists of two pans, while a bass includes as many as six. In addition to the section size, the mass density, stiffness, and curvature contribute significantly to the pitch of each note. The overall timbre of the tone produced depends to a great extent on the spectral content of the note. This, in turn, depends strongly on the normal modes of the excited note section, and to some lesser extent, on the normal modes of all other sections. This latter dependence is caused by the fact that all note sections are imbedded in the same solid matrix of the drumhead. Therefore, vibrations in one note section cause all note sections to vibrate. The nature of the coupling between sections has been the subject of considerable interest to researchers in the field. Inasmuch as the entire pan represents a highly nonlinear system, the tone quality also varies significantly with excitation amplitude.