Striking the drum in the center or slightly off-center seems foreign to the modern timpanist because when done on modern timpani with modern heads, the sound is very dull, non resonant, and has very little musical appeal. This happens because modern timpani have larger diameters with deeper bowls, much thinner heads and superior mechanical tolerances. For the very early instruments, the thickness and homogeneity of the heads was the primary factor influencing on the sound. The head (membrane) is in fact, the only viable source for the production of a pitched sound that can be varied or shifted to any significant degree. The other parts of the instrument, i.e. the bowl and volume of internal air simply serve as system modifiers.
Early timpani heads were produced by vellum and parchment makers. The process of treating animal skins and producing various parchment and vellum products is a millenniums old tradition. Even though the manufacturing principles remained unchanged throughout the history of parchment and vellum making, the end product varied greatly. This variance can be a consequence of things like the maker’s expertise, the quality of the skins and different raw materials used in the production processes, and the desired outcome of the end product. It could also be argued that the wealth or economy of the making process was reflected in the degree of thinness and finish. There is no doubt that various degrees of thinness and finish were produced so there is little question that the timpanists in the wealthy courts of the period could have had any thickness and finish they desired. 30
The head of choice was a less flexible, half tanned hide which was much thicker than standard “finished” vellum products. This was not because of lack of resources, but by design. Thicker heads were needed because of the impact that it had to endure from outside playing.29.1 The thickness made it less resonant so striking it slightly off-center projected the sound better and produced more of a pitch than on the edge due to the poor mechanical tolerances of the tensioning system, small diameter and shallowness of the bowl.
Other factors to be taken into consideration, of course, are the lack of pitch standards in Europe at that time, which would affect the frequency of the actual fundamental of the smaller drums with thicker natural-skin heads. This lack of pitch standards would also influence the size of the bowl needed to produce the pitch, which helps explain the varying sizes of early timpani found throughout 16th and 17th century Europe.