![]() All angles of sharp bearing edges work exactly the same way. As a result, we can negate any fluid dynamic theory or theory of compressed air pockets effecting the motion of the head, and so the angle between the bearing edge and the head and thus the distance between the shell and the head, being much, much larger that of the deflection over this edge, has no practical affect. At less than 1/128", the machining tolerances of the drum shell itself is greater than the deflection of the head at that point. Looking at the area of the head directly over the shell wall, this 1/8" deflection at the center of the head at 1.02 degrees translates to 0.0067" of actual maximal deflection only at the inner edge of the shell, tapering evenly to zero deflection at the point of contact of the bearing edge. The resulting angle between the resting position of the head and the fully deflected position would be 1.02 degrees over the 7" radius. To prove this, lets consider a shell thickness of 3/8" and a deflection of 1/8" when the head is stuck in the very center of a drum with a 14" diameter. Now, the angle of the actual bearing edge has absolutely no effect on the motion or sound of the head. Within this group of bearing edge profiles, we can include round-over profiles that are not true radii and feature a flattened "top" of the round over. This gives us the largest surface area of the head dampened by the drum shell, an area that does not change when the drum head is struck and deflected. ![]() For our discussion, we are going to examine a fully rounded edge, a sharp edge, and a flat edge.īeginning with a flat edge, or a completely squared-off shell, we can see from the diagram below that at rest, a drum head is completely contacting the entire thickness of the shell. We are going to take some liberties and make some generalizations to simplify the discussion, however the underlying theory is sound without loss of generality. The bearing edges contribute most to how that vibration eventually dampens to the point of stopping and how the energy placed in the head translates to the shell where it is dissipates as sound or resonance. There are three basic bearing edge profiles we will discuss here. These endpoints have a great deal to contribute to how each string vibrates, how each periodic wave propagates through that string, and what dampening factor can naturally be applied to each periodic wave. In other words, when you strike a drum head, it vibrates. If a drum head is imagined as a collection of strings, each running across the diameter of a shell and rotating about the shell so as to eventually cover the entire surface, then the bearing edge is the endpoints of each of those strings. ![]() the area of contact between the drum shell and the drum head. ![]() Few areas of drum construction effect the overall sound of a drum as much as the bearing edge, i.e. ![]()
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