Properties of Drum Shells and Bearing Edges

Drum shell bearing edges dictate the boundary conditions and point of contact between drum heads and drum shells. Properties of single 45o, single 45o with slight round-over, and double 45o bearing edges have been studied. It has been found that the double 45o drum allows for the best head/shell energy transfer. I. Background Tom drums are typically composed of a wooden drum shell, a head that rests of top of it, and a mechanism to apply tension to the head. A good discussion on drum physics can be found in The Physics of Musical Instruments, by Fletcher and Rossing. One important property of a drum head is its boundary conditions. The bearing edge is where the drum head comes into contact with the drum shell. There are several bearing edge shapes which are currently used in drum production. It is expected that different bearing edges will have a significant affect on the sound of drums. One possible reason for the importance of bearing edges is that the edge is the primary outlet for energy to transfer between the drum head and the drum shell. Because the sound of a drum is produced by both of these components, it would be desirable to have a higher rate of energy transfer at the bearing edge. Dennis Stauffer has supplied three 12 inch diameter, 6 inch deep single headed toms. Each has a different bearing edge design. Fig. 1. Representation of cross sections of three bearing edge designs with the outside of the shell on the left side. Single 45o, Single 45o with slight round-over, and Double 45o In figure 1, from left to right, the drums will be referred to as drum A, B, and C. I seek to determine the characteristics of these different drum shells. II. Method The three drum shells are recorded with no hardware attached and also with the lugs attached. Making these recordings requires special mounting. Because the shells cannot easily be attached to a stand, they are suspended from the ceiling using three strings. For mounting the shell only, the strings are attached to the shell using nylon screw, as seen in figure 2. For mounting the shells with the lugs, the strings are attached the screws that hold the lugs in place. A soft, heavy mallet is used to excite the drum shell. A Peavey PVM 45 microphone is positioned 5cm from the outside of the drum shell. The microphone signal goes through the line-in on a computer, and through a sound card. Cakewalk Guitar Tracks Pro is used to record the signal and to convert it to a .wav file for analysis. Fig.2 Setup for recording drum shell sounds. Using strings to support the shell only creates a small perturbation to the system. For recording the drums after all of the components have been attached, they are simply mounted on a drum stand. The mount attaches to the tension rods, rather than to the shell, allowing the drum to more fully resonate. The sound from exciting the shell is also recorded with the drum is fully mounted. Placing a hand on the drum head deadens its sound. Two PVM 22 microphones are used to record the drum sound. One is positioned over the head, and the other is very close to the shell, as shown in figure 3. The microphone windscreens are removed to get this close. A “Y” adaptor cable is used to feed the two signals into the line-in input on the computer as a stereo signal. Guitar Tracks Pro creates a stereo .wav file. Fig. 3. Two microphone setup used to record drum sounds. One microphone will record overall drum sound, while the other will focus on