The Chemical Processes Behind Percussive Drums and Drum Heads

“Music is an art and a passion. It is something that can be enjoyed by almost everyone, and created by almost everyone. It affects our thoughts and affects emotions, but how does it work? What chemistry lies behind the beauty: behind the strings of a guitar and the head of a drum; behind the bell of a trumpet and the reed of a saxophone; behind the bow, gracefully gliding across the strings of a violin?” While the last post explained the processes behind guitar strings, this post will discuss the chemical processes behind percussive drums and drum heads.

Drums are probably the most important of instruments not only because they provide the beat and rhythm for music but because there are a variety of sounds that can be produced.

This is an amazing video from Thomas Lang that shows the power of the different sounds of drums and cymbals combined.

A drum is a percussion instrument. All percussion instruments produce sound by making harsh contact with the drum skin which vibrates the skin(membrane) and the air inside the drum shell to amplify the sound of the drum. The earliest drum heads were fish or reptile skins, and they were played by hand. The body of the drum was a hollowed tree trunk. These were, of course, played by cavemen. Through time, the body of the drum and the sizes were altered many times. In the 1500s, trade between Europeans and Arabs brought the exchange of different types and sizes of drums. For example, large kettledrums were copper cauldrons and calfskin stretched over it. It was used for war and ceremonial purposes. Other drum-like instruments included the tambourine and the tabor.  In 1950, manufacturers began to use plastic instead of animal skins for the head. Around this time, drums became wildly popular in bands such as the Beatles. Nowadays, the drumset is incredibly important to all types of musical genres, but are especially prominent in jazz and rock.

To make the head of the drum, a variety of chemicals are combined and heated. Polyethylene terephthalate is made by combining terephthalic acid with ethylene glycol. See below for more details. The chemicals are heated to extremely high temperatures until they are hot, liquid plastic. The liquid plastic is cooled to a solid, and then it is cut and stretched to fit the body. The edge of the plastic circle is heated and then cooled to fit the circumference of the drum, and then a steel ring is placed both within and outside the collar.

This video shows a very brief summary of drum manufacturing in Liberty Drums. Liberty Drums specialize in building plywood drums. The video does a great job of summarizing the main parts of the drum manufacturing process, such as sanding and measuring.

Polyethylene terephthalate (PET) is a chemical that is widely used for its excellent water barrier properties. Depending on how it is processed, it can be semi-rigid to rigid, and it can be strong and impact-resistant. This chemical’s most important property, viscosity, comes from the fact that it is a chain of monomers, known as polymers. Think of monomers as different, individual beads. A polymer would then be those beads strung together in a specific arrangement. The longer the polymer chains, the more viscous the overall liquid/solid would be. Viscosity refers to how fast a liquid is flowing. Higher viscosity means slower flow, and vice versa. The fact that this can be heated and cooled as needed means that the pitch and overall strength of the head can be changed. In general, PET is used in 60% of the world’s synthetic fibers. This shows how important PET is.

Terephthalic acid and ethylene glycol are the major reactants in making PET. Terephthalic acid is insoluble in water. Insoluble means that it will not dissolve when mixed with water. For example, salt is soluble. Ethylene glycol is an organic compound that is mostly used for producing PET; it is only used to help make the polyester fibers and resins that are found in PETs. In fact, most of the uses for terephthalic acid and ethylene glycol are for the fabric and plastic industry, because of how the various chemical reactions work. You can see the reaction scheme below. It also shows the elements that make up each component of the reaction.

A plastic shell of a drum is made using injection molding. Injection molding is exactly what it sounds like – material is injected into a mold and then allowed to harden to the required shape and size. Metal shells are made using casting and machining. However, most shells are made of wood. Large, thin panels make up the shell, and these panels are called veneer. Veneer is cut to proper sizes using computer-controlled saws. The pieces are glued and rolled together to form a cylinder that is about 7 to 9 layers thick. Pressure is applied, and then is is sanded with high power sanders to produce a smooth surface.

 This infographic from Pearl Drums shows the different materials and engineering methods that can be used to create different types of drums. These include types of wood, different bearing edges, and wood thickness.

 It turns out that geometry is important to various musical instruments, such as the strings of a guitar or a cymbal. Speaking of cymbals, expect to see some chemistry and cymbals in the next blog post about musical instruments!

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