Bongo drums are often associated with ethnic music and fun, freewheeling times. But bongos entail an application of physics that is centuries-old, based on some of the oldest instruments known to man: drums. Understanding the physics of bongo drums is the first step in learning play them and appreciate the science behind them.
Significance
Bongos are a set of two small drums connected by a bridge; they are struck with the fingers of the player's hands. The bodies of the bongos are usually made of oak or mahogany and topped with a tight "skin" on one end (an opening is left on the other). The drums that comprise a set of bongos are slightly different in size--the large one is called the "hembra," and the small one the "macho"--and produce slightly different sounds when struck. Bongos are associated with the Cuban music styles Son (pronounces "sone") and Chengii, which popularized their use.
Identification
The "heads" of the drum (also nicknamed its "skins") were once tacked to the top of the bongo, but are now controlled with an adjustable aluminum ring. Depending on how the head of the drum is tightened, different vibrational speeds can be achieved when the head is struck; looser drum heads emit a deeper (slower) sound, while tighter heads produce a higher (faster) sound. The vibrations are also controlled by how the player strikes the drum head. A dampened sound occurs when the player strikes the drum while touching it with her thumb, or by striking it on the rim, thus minimizing the vibrations of the head. Striking in the center with a full hand, however, maximizes the vibrations of the drum head, making for a louder, more energetic sound. Bongos are played using the fingertips, open palms and parts of the hand. Striking the drums causes ripples of energy along the head; if slowed down, they would resemble the rings in a pond when a stone is thrown in. The faster the rings move out, the faster the drum vibrates and the higher the pitch becomes.
Size
The size of the drums also has an effect on the sound that is generated. The smaller drum tends to produce higher notes than the larger drum. This is because the smaller head is under greater tension, and because the body of the drum is smaller, thus affecting the speed of the sound waves. Bongo sets themselves can range in size, though they generally fit between the knees of the player.
Features
Traditional (and some more expensive hand-made) bongos are crafted of wood. Mahogany and oak are the two traditional woods. The wood vibrates when the head is struck as well. The force of the impact on the head causes sound waves to bounce off the wood, altering the frequency slightly. Other, softer woods would absorb more of these sound waves and result in a "dull" or "flat" bongo sound. Oak and mahogany are harder woods, and so reflect the sound waves more clearly while altering them just slightly. Currently, most bongos purchased are made of fiberglass. Fiberglass offers a lighter weight, more durable body and lower cost than wood models, without sacrificing the acoustic value of a hard surface.
Expert Insight
Like all hand drums, the bongos create a mixture of harmonic and unharmonic resonances when they are played. In the hands of an amateur, the unharmonic resonances are more pronounced, resulting in discordant "noise" more often than music. In the hands of an expert player, the harmonic resonances of the bongos are pronounced, and unharmonic resonances are controlled or minimized (possibly even masked). Studies comparing the harmonics of similar drums (such as the Indian and Middle Eastern tabla) reveal these differences scientifically, though most listeners know intuitively the difference between a practiced player and a beginner. For more information on the harmonics of hand drums, see the Resources section.
