Drums and cymbals are instruments that are designed to project sound when they are struck with a drumstick, beater or mallet, or in the case of cymbals, each other. Understanding the physics behind drums and cymbals and the sounds they make can help you make a decision when buying a new drum kit and can help you get the best effect when playing the instrument.
Basic Vibration: Cymbals
Sound travels through vibration. Envision a pebble being dropped into a still pond, creating a circular, expanding ripple. This is how sound travels outwards from its source. Drums and cymbals both are designed to vibrate and create sound as clearly as possible. Cymbals vibrate in one of several modes, which are essentially patterns of vibration across the surface of the instrument. The different modes can occur for several different reasons, such as the thickness or shape of the cymbal and where it is struck. A glancing strike will produce a different type of vibration than a hammering blow. The bump in the centre of the cymbal reflects the vibration back into the main body of the cymbal.
Basic Vibration: Drums
The basic vibration of drums is in many ways similar to that of cymbals, except that drums have more components that could affect the vibration and therefore the sound. The drum head that is stretched over the shell receives and distributes the vibration, but this also has to pass through the drum shell and the bearing edge. The various modes of vibration occur on the drum skin, in the same way as on the surface of a cymbal, but the bearing edge and drum shell can affect the projection of the sound. Sound is transmitted through the air to your ears by the vibration of the drum compressing and separating air molecules.
The Effect of the Shell
Drum shells can be bought in either single ply or multiple ply construction. Think about the difference in how sound passes through windows. Single pane windows have a very poor resistance to sound, and you will be able to hear most sound that occurs on the other side of them. Compare this with double glazed windows, which have two panes of glass separated in the frame. Sound doesn't travel as effectively through multiple sheets of material. This situation is essentially the same with drums; single-ply drums project sound more efficiently than multiple-ply drums. Some single ply drums require a "reinforcement ring" to stabilise the structure. This ring dampens the sound of the drum, and "segment" drum shells provide the projection of single-ply shells without the dampening reinforcement ring.
The bearing edge is the section at the side of the drum where the drum head connects to the shell. The passing of vibration between these two parts is vital to projecting sound with the drum. Bearing edges can either have a single 45-degree angle, with the flat edge on the outside, or a double 45 degree angle that rises to a point like the tip of a sword. The point at which the bearing edge contacts the drum skin affects the transfer of sound between the head and the shell. The sword-like double 45 degree angle bearing edges are more effective, because the bearing edge touches the shell at a flat point, rather than on the curve, allowing a more efficient transfer of energy.