As with any musical instrument, modern marimbas can be built in many different ways, and there are differing opinions on how the instrument should sound. Despite this, all marimbas have a common design consisting of the frame ends, cross beam, rails, resonators, and bars.
Frame Components
The high and low frame ends of the instrument serve to support all parts (resonators, rails, and bars) and allow for wheels or castors to be attached. The size can vary, but in general they run the length of the two lowest bars on the low end (about 3.5 feet) and the two highest bars on the high end (about 1.5 feet).
There are two types of frame ends to consider. The more common design is that of metal or wooden beams connected to the wheels and the wooden end on top, which supports the rails and bars. The other design to consider is the flat panel, usually found on the Musser 250 Concert Grand. While this does not affect the sound of the bars, the distinction plays a role in frame and resonator sounds (see extended techniques) and how they can be achieved.
The crossbeam runs the length of the instrument and serves to support the instrument structurally by connecting the frame ends. It is typically made of metal or wood. When made of metal it is tubular or square shaped, and when made of wood it is plank shaped. If the sound of the cross beam is desired, it should be noted that access to it is limited to the upper two thirds of the instrument due to the low-end natural resonators obstruction.
The rails run the length of the keyboard and are attached to each frame end. The function is to suspend the bars via the string that runs through the nodal points of each bar. There are four rails per marimba (two per manual) and hooked spacers in between on which the bars are suspended. These metal spacers are typically wrapped in rubber or felt to prevent unwanted noise and sit in line with the nodal points of each bar. The rails are numbered 1-4, with 1 being on the performer’s side and 4 being on the audience side of the instrument. If frame sounds are desired, rail one is the most accessible while rail four would require the performer to be on the opposite side of the instrument. Rails two and three are essentially inaccessible unless the instrument is disassembled or the performer lies underneath the center of instrument.
Resonators
Resonators are a crucial part of the marimba sound production. They are suspended from each end directly below the bars and are typically made of brass or aluminum. The tubes create an acoustic cavity resonator each of which is tuned to the fundamental pitch of the bar directly above them. A common misconception is that the resonators are open at both ends; however, they are closed at the bottom and open at the top. If sound amplification is desired, the microphone(s) must be placed either above the instrument or underneath as close to the tops of the resonators as possible.
Resonator shapes vary on the low end of the marimba (approximately the lowest 7th) by manufacturer with the high end being tubular on virtually all models. Physicist Heather Hill in her thesis on the Acoustics of Marimba Bars states, “The resonators below the notes between C2 and C3 tend to vary in design the most between manufacturers due to the lower frequency values associated with the bars in the lower octave of the instrument.” Hill goes on to state that resonator’s purpose is to amplify only the fundamental of the bar, allowing the notated pitch of the bar being played to be the majority of what the audience hears.
On Malletech, Demorrow, Majestic, and Yamaha (6000) models, the low-end resonators are tubular throughout with joints welded together giving them a curve (on the Malletech MJB model the resonators are bent rather than sectioned in joints). The thought behind this type of design is to give a more accurate fundamental note with reduced harmonics.
On Yamaha 5100 (and lower), Adams, and Bergerault models the low-end resonators are a box shape. The rational behind this design is to produce a strong fundamental note with isolated harmonics.
The third low-end resonator type is produced by Marimba One and is commonly referred to as the oval shape design. What this amounts to is a combination of both tubular and box-shaped resonators resulting in an inverted tubular resonator. The sound, while not significantly different from other manufacturers, is generally regarded as being very warm and smooth. Currently there is a wide variety of bar widths and resonator shapes and designs available.
Bars & Tuning
The bars are the principle sound-producing parts of the instrument. In his study of the science of the marimba, Greg Merrill states, “The bars of a marimba work on the fundamental principal of a vibrating bar with two free ends: when some action, such as the impact of a mallet, sets such a bar into movement, it bends transversely...”
As with any wooden musical instrument, lower-quality wood will produce a lower quality-sound. Common materials used for marimba bars are Honduran rosewood, paduk, babinga or a synthetic material, each chosen for their density and resonance. The bars are in the shape of a rectangle with the underside of each bar shaped into an arc. This is to allow the tuning of the higher harmonics of each bar. The bars can be struck at three different points, each offering a different timbre; the center (directly above the resonators), between the center and node (or by symmetry, the edge), and directly on the nodal point.
The center will accentuate the fundamental and minimize harmonic content. When struck off-center (or the edge), the harmonics will be more prevalent. A common misconception of percussionists and composers alike is that the edge of the bars will produce the same quality sound as the center. However the edge will sound similar to the area between the center and the node producing a prevalence of the second partial. Playing on the edge of the bar is usually limited to the accidentals and only when needed, such as a very fast passage or an awkward position of the hands. When struck on the node the sound will not contain very much of the fundamental pitch of the bar. Composing with specific spots of the bar in mind should be thought of in the same way that string players play with different bow placement on the string. Different colors can be produced but specifying these will lead to less creative freedom of the performer. These subtleties will be difficult to hear in a large ensemble or chamber setting and should be limited to solo and small chamber works.
Each bar is generally tuned to the harmonic of two octaves and three and a half octaves above the fundamental pitch. For example, if C is the fundamental we also hear the harmonics of C two octaves above and E three and a half octaves above the fundamental. This is one of the principal intonation differences between marimba and a xylophone. In addition to more wood mass per bar and the part of the tree from which the wood is taken, the contemporary xylophone is tuned to the twelfth overtone. For example, when C is struck on a marimba we would hear E as the prominent overtone. On a xylophone, we would hear G as the prominent overtone. Because of this a composer should be aware of possible harmonic interference in the lower register of the marimba. If a certain interval (minor 10th, minor 17th, minor 24th, etc.) is struck, dissonance of the interval and its resultant harmonic will be very audible.
Careful consideration needs to be made when composing in the lower register of the marimba. Although every modern marimba contains bars that go from large to small, the rate of change in bar width can vary greatly from manufacturer to manufacturer. On larger models as produced by Demorrow or Malletech, the demands placed on the performer are amplified due to the greater distance between the bars. It is best to consult with a professional percussionist or marimba player to determine if there will be issues on particular brands and models.
*This article is an excerpt from "Composing for Marimba: Tools & Techniques for Composers" by Joe Millea. Please visit full version for full list of citations and examples.
